Cardio System
Saturday, June 11, 2005
Introduction:
How does the body assure that oxygen and food will be delivered to all its cells? The cardiovascular system, consisting of a fluid called blood, vessels to carry the blood, and a hollow, muscular pump called the heart, transports food and oxygen to all organs and cells of the body. Blood vessels in the lungs absorb the oxygen that has been inhaled from the air, and blood vessels in the small intestine absorb food substances from the digestive tract. In addition, blood vessels carry cellular waste materials such as carbon dioxide and urea and transport these substances to the lungs and kidneys, respective, where they can be eliminated from the body.
The heart and blood vessels and the terminology related to their anatomy, physiology, and disease conditions will be explored in this chapter. The nature of blood and another body fluid called lymph will be discussed in a later chapter.
Blood Vessels and the Circulation of Blood
Blood Vessels
There are three types of blood vessels in the body. These are arteries, veins, and capillaries.
Arteries are the large blood vessels that lead away from the heart. Their walls are made of connective tissue, muscle tissue, elastic fibers, and an innermost layer of epithelial cells called endothelium. Endothelial cells, which line all blood vessels, secrete substances that affect the size of blood vessels, reduce blood clotting, and promote the growth of blood vessels. Because arteries carry blood away from the heart, they must be strong enough to withstand the high pressure of the pumping action to the heart. Their elastic walls allow them to expand as the heartbeat forces blood into the arterial system throughout the body. Smaller branches of arteries are called arterioles. Arterioles are thinner than arteries and carry the blood to the tiniest of blood vessels, the capillaries.
Capillaries have walls that are one endothelial cell thick. These delicate, microscopic vessels carry nutrient-rich, oxygenated blood from the arteries and the arterioles to the body cells. There walls are thin enough to allow passage of oxygen and nutrients out of the blood stream and into the tissue fluid surround the cells. Once inside the cells, the nutrients are burned in the presence of oxygen (catabolism) to release needed energy within the cell. At the same time, waste products such as carbon dioxide and water pass out of the cells and into the thin-walled capillaries. The waste filled blood then flows back to the heart in small veins called venules, which branch to form larger vessels called veins.
Veins are thinner walled than arteries. They conduct blood (that has given most of its oxygen) toward the heart from the tissues. Veins have little elastic tissue and less connective tissue than arteries, and blood pressure in veins is extremely low compared with pressure in arteries. In order to keep blood moving back toward the heart, veins have valves that prevent the backflow of blood and keep the blood moving in one direction. Muscular action also helps the movement of blood in veins.
Circulation of Blood
Arteries, arterioles, veins, venules, and capillaries, together with the heart, form a circulatory system for the flow of blood.
Blood deficient in oxygen flows through two large veins, the venae cavae, on its way from the tissue capillaries to the heart. The blood became oxygen-poor at the tissue capillaries when oxygen left the blood and entered the body cells.
Oxygen-poor blood enters the right side of the heart and travels through that side and into the pulmonary artery, a vessel that divides in two, one branch leading to the left lung, the other to the right lung. The arteries continue dividing and subdividing with the lungs, forming smaller and smaller vessels (arterioles) and finally reaching the lung capillaries. The pulmonary artery is unusual in that it is the only artery in the body that carries blood deficient in oxygen.
While passing through the lung (pulmonary) capillaries, blood absorbs the oxygen that entered the body during inhalation. The newly oxygenated blood next returns immediately to the heart through pulmonary veins. The pulmonary veins are unusual in that are the only veins in the body that carry oxygen-rich (oxygenated) blood. The circulation of blood through the vessels from the heart to the lungs and then back to the heart again is known as the pulmonary circulation.
Oxygen-rich blood enters the left side of the heart from the pulmonary veins. The muscles in the left side of the heart pump the blood out of the heart through the largest single artery in the body, the aorta. The aorta moves up at first (ascending aorta) but then arches over dorsally and runs downward (descending aorta) just in front of the vertebral column. The aorta divides into numerous branches called arteries that carry the oxygenated blood to all parts of the body. The names of some of these arterial branches will be familiar to you: brachial (brachi/o means arm), axillary, splenic, gastric, and renal arteries. The carotid arteries supply blood to the head and neck.
The relatively large arterial vessels branch further to form smaller arterioles. The arterioles, still containing oxygenated blood, branch into smaller tissue capillaries, which are near the body cells. Oxygen leaves the blood and passes through the thin capillary walls to enter the body cells. There, food is broken down, in the presence of oxygen, and energy is released.
One metabolic product of this chemical process is carbon dioxide (CO2). Carbon dioxide is produced in the cell but is harmful to the cell if it remains. It must thus pass out of the cells and into the capillary bloodstream at the same time that oxygen is entering the cells. As the blood makes its way back from the tissue capillaries toward the heart in venules and veins it is full of carbon dioxide and is oxygen-poor.
The circuit is thus completed when oxygen-poor blood enters the heart from the venae cavae. This circulation of blood from the body organs (except the lungs) to the heart and back again is called the systemic circulation.
Anatomy of the Heart
The human heart weighs less than a pound, is roughly the size of an adult fist, and lies in the thoracic cavity, just behind the breastbone in the mediastinum (between the lungs).
The heart is a pump, consisting of four chambers; two upper chambers called atria (singular: atrium) and two lower chambers called ventricles. It is actually a double pump, bound into one organ and synchronized very carefully. Blood passes through each pump in a definite pattern. Pump station number one, one the right side of the heart, sends oxygen-deficient blood to the lungs, where the blood picks up oxygen and releases its carbon dioxide. The newly oxygenated blood returns to the left side of the heart to pump station number two and does not mix with the oxygen-poor blood in the pump station number one. Pump station number two then forces the oxygenated blood out to all parts of the body. At the body tissues, the blood loses its oxygen and on return to the heart, to pump station number one, blood poor in oxygen (rich in carbon dioxide) is sent out to the lungs to begin the cycle anew.
Oxygen-poor blood enters the heart through the two largest veins in the body, the venae cavae. The superior vena cava drains blood from the upper part of the body, and the inferior vena cava carries blood from the lower part of the body.
The venae cavae bring oxygen-poor blood that has passed through all of the body to the right atrium, the thin walled upper right chamber of the heart. The right atrium contracts to force blood through the tricuspid valve (cusps are the flaps of the valves) into the right ventricle, which is the lower right chamber of the heart. The cusps on the tricuspid valve form a one-way passage designed to keep the blood flowing in only one direction. As the right ventricle contracts to pump oxygen-poor blood through the pulmonary valve into the pulmonary artery, the tricuspid valve stays shut, thus preventing blood from pushing back into the right atrium. The pulmonary artery then branches to carry oxygen-deficient blood to each lung.
The blood that enters the lung capillaries from the pulmonary artery soon loses its large quantity of carbon dioxide into the lung tissue, and the carbon dioxide is expelled. At the same time, oxygen enters the capillaries of the lungs and is brought back to the heart via the pulmonary veins. The newly oxygenate blood enters the left atrium of the heart from the pulmonary veins. The walls of the left atrium contract to force blood through the mitral valve into the left ventricle.
The left ventricle has the thickest walls of all four heart chambers (three times the thickness of the right ventricle). It must pump blood with great force so that the blood travels through arteries to all parts of the body. The blood is pumped out of the left ventricle through the aortic valve and into the aorta, which branches to carry blood all over the body. The aortic valve prevents the return of aortic blood to the left ventricle once it has been pumped out.
The four chambers of the heart are separated by partitions called septa (singular: septum). The interatrial septum separates the two upper chambers (atria), and the interventricular septum is a muscular wall that comes between the two lower chambers (ventricles).
The heart wall is composed of three layers. The endocardium is a smooth layer of endothelial cells that lines the interior of the heart and heart valve. The myocardium is the middle, muscular layer of the heart and its thickest layer. The pericardium is a fibrous and membranous sac surrounding the heart. It is composed of two layers, the visceral pericardium, which adheres to the heart and the parietal (parietal means wall) pericardium, which lines the outer fibrous coat. The pericardial cavity (Between the visceral and the parietal pericardia normally contains 10 – 15 ml of fluid, which lubricates the membranes as the heart beats.
Physiology of the Heart
Heartbeat and Heart Sounds
There are two phases of the heartbeat. These phases are called diastole (relaxation) and systole (contraction). Diastole occurs when the ventricle walls relax and blood flows into the heart from the venae cavae and the pulmonary veins. The tricuspid and mitral valves are open in the diastole, as blood passes from the right and left atria into the ventricles. The pulmonary and aortic valves are closed during diastole.
Systole occurs next, as the walls of the right and left ventricle contract to pump blood into the pulmonary artery and the aorta. Both the tricuspid and the mitral valves are closed during systole, thus preventing the flow of blood back into the atria.
This diastole-systole cardiac cycle occurs between 70 and 80 times per minute (100,000 times a day). The heart pumps about 3 ounces of blood with each contraction. This means that about 5 quarts of blood are pumped by the heart in 1 minute (75 gallons an hour and about 2000 gallons a day).
Closure of the heart valves is associated with audible sounds such as “lub, dub, lub, dub,” that can be heard when listening to a normal heart with a stethoscope. The “lub” is associated with closure of the tricuspid and mitral valves at the beginning of the systole and the “dub” with the closure of the aortic and pulmonary valves at the end of systole. The “lub” sound is called the first heart sound and the “dub” is the second heart sound because the normal cycle of the heartbeat starts with the beginning of the systole. An abnormal heart sound is known as a murmur.
Conduction System of the Heart
What keeps the heart at its perfect rhythm? Although the heart does have nerves that can affect its rate, they are not primarily responsible for its beat. It is known that the heart starts beating in the embryo before the heart is supplied with nerves and will continue to be in experimental animals even when nerve supply is cut.
Primary responsibility for initiating the heartbeat rests with a small region of specialized muscle tissue in the posterior portion of the right atrium, where an electrical impulse originates. This region of the right atrium is called the sinoatrial node (SA node). The SA node is called the pacemaker of the heart. The current of electricity generated by the pacemaker causes the walls of the atria to contract and force blood into the ventricle (ending diastole).
Almost like ripples in a pond of water when a stone is thrown, the wave of electricity passes from the pacemaker to another region of the myocardium. This region is at the posterior portion of the interatrial septum and is called the atrioventricular node (AV node). The AV node immediately sends the excitation wave to a bundle of specialized muscle fibers called the atrioventricular bundle or bundle of His (pronounced hiss). Within the interventricular septum, the bundle of His divides into the right and left bundle branches, which form the conduction myofibers that extend through the ventricle walls and stimulate them to contract. Thus, systole occurs and blood is pumped away from the heart. A short rest period follows, and then the pacemaker begins the wave of excitation across the heart again.
The record used to detect these electrical changes in heart muscle at the heartbeats is called an electrocardiogram (ECG or EKG, from the Greek root kardia). The normal ECG shows five waves, or deflections, the represent the electrical changes as a wave of excitation spreads through the heart. The deflections are called P, QRS and T waves. The P wave represents electrical activity in the wall of the atria (atrial depolarization). The QRS wave represents ventricular depolarization as electricity passes through the atrioventricular bundle and the ventricular wall. This is the largest wave because the ventricle contains the most muscle. The T wave represents ventricular repolarization, which is when the ventricular wall relaxes and recovers from contraction. The ECG is used to diagnose a heart attack (myocardial infarction, which causes abnormal deflections.
Normal heart rhythm (originating in the SA node and traveling through the heart) is called sinus rhythm. Sympathetic nerves speed up the heart rate during conditions of emotional stress or vigorous exercise. Parasympathetic nerves slow the heart rate when the need for extra pumping is past.
Blood Pressure
Blood pressure is the force that the blood exerts on the arterial walls. This pressure is measured by a device called a sphygmomanometer.
The sphygmomanometer consists of a rubber bag inside a cloth cuff that is wrapped around the upper arm, just above the elbow. The rubber bag is inflated with air by means of a rubber bulb. As the bag is pumped up, the pressure within it increased and is measured on a recording device attached to the cuff.
The vessels in the upper arm are compressed by the air pressure in the bag. When there is sufficient air pressure in the bag to stop the flow of blood in the artery of the arm (brachial artery), the pulse in the lower arm where the observer is listening with a stethoscope) obviously drops.
Air is then allowed to escape from the bag and the pressure is lowered slowly, allowing the blood to being to make its way through the gradually opening artery. At the point where the person listening with the stethoscope first hears the sounds of the pulse beats, the reading on the device attached to the cuff shows the higher, systolic, blood pressure (pressure in the artery when the ventricle is contracting to force the blood into the aorta and other arteries).
As air continues to escape, the sounds become progressiv3e louder. Finally, when a change in sounds from loud to soft occur, the observer makes note of the pressure on the recording device. This is called the diastolic blood pressure (pressure in the artery when the ventricles are relaxing and the heart is filling, receiving blood from the venae cavae and pulmonary veins).
Blood pressure is usually expressed as a fraction: for example, 120/80, in which the 120 represents the systolic pressure and 80 the diastolic pressure.
Pathological Conditions: The Heart and Blood Vessels
Heart
arrhythmias – Abnormal heart rhythms (dysrhythmias). Examples of cardiac arrhythmias:
1. Heart block (atrioventricular block) – Failure of proper conduction of impulses through the AV node to the atrioventricular bundle (bundle of His). Damage to the SA node may cause its impulses to be too weak to activate the AV node and impulses fail to reach the ventricles. If the failure occurs only occasionally, the heart will miss a beat in a rhythm at regular intervals (partial heart block). If no impulses reach the AV node from the SA node, the ventricles contract slower than the atria and are not coordinated. This is complete heart block. Implantation of a cardiac pacemaker can overcome heart block and establish a normal rhythm.
2. Flutter – Rapid but regular contractions of atria or ventricles. This condition can occur in patients with heart disease. The heart rhythm may reach up to 300 beats per minute.
3. Fibrillation – Rapid, random, ineffectual, and irregular contractions of the heart (350 beats or more per minute). In atrial fibrillation, the wave of excitation passes through the atrial myocardium even more quickly than in atrial flutter. In order to restore normal heart rhythm, an electrical device called a defibrillator is applied to the chest wall; this electric shock stops the heart and reverses its abnormal rhythm. This is also called cardioversion. Drugs, such as digoxin may also be used to convert fibrillation into regular rhythm.
A device called an automatic implantable cardioverter/defibrillator (AICD) can now be implanted in the chest to sense arrhythmias and correct them. These are pacemaker-sized devices that give shocks to change abnormal rhythms, such as ventricular fibrillation.
Radiofrequency catheter ablation (RFA) is a nonsurgical treatment used to treat arrhythmias, such as paroxysmal (sharp, sudden spasm) tachycardia. A catheter, placed in blood vessels leading up against the heart muscle, delivers a high-frequency current to burn a small portion of the muscle. This injury (ablation) to the muscle destroys the arrhythmias.
Cardiac arrest is the sudden and often unexpected stoppage of heart movement, caused by heart block or ventricular fibrillation (resulting from underlying heart disease).
Palpitations are uncomfortable sensations in the chest associated with different types of arrhythmias. Palpitations do not necessary indicate serious heart disease (smoking, caffeine, and drugs such as antidepressants can produce palpitations). Two cardiac causes of palpitations are premature ventricular contractions (PVCs) and premature atrial contractions (PACs).
Congenital heart disease – Abnormalities in the heart at birth. The following are congenital anomalies resulting from failure in the development of the fetal heart.
1. Coarctation of the aorta (CoA) – Narrowing (coarctation) of the aorta. Surgical treatment consists of removal of the constricted region and end-to-end anastomosis of the aortic segments.
2. Patent ductus arteriosus (PDA) – A small duct (ductus arteriosus between the aorta and the pulmonary artery, which normally close soon after birth, remains open (patent). This condition means that the oxygenated blood flow from the aorta to the pulmonary artery. The anomaly occurs most often in females and is commonly associated with intrauterine rubella (German measles) infection, prematurity, and infantile respiratory distress syndrome. Treatment is surgery to close the ductus arteriosus open.
3. Septal defects – Small holes in the septa between the atria (atrial septal defects [ASDs]) or the ventricle (ventricular septal defects [VSDs]). Although many septal defects will close spontaneously, others will require surgery. Septal defects can be closed while maintaining a general circulation by means of a heart-lung machine. This machine is connected to the patient’s circulatory system and relieve the heart and lungs of pumping and oxygenation functions during heart surgery.
Two recent procedures as alternatives to traditional surgery are transcatheter closure (a “clamshell” device is threaded through the blood via a catheter into the heart and into the septal defect, where it is fixed in place to block the hole) and minimally invasive heart surgery (through 3 or 4 small puncture holes in the chest; special instruments are used to repair the defect).
4. Tetralogy of Fallot – A congenital malformation of the heart involving four (tetra) distinct defects. The condition, named for Etienne Fallot, the French physician who described it in 1888. The four defects are:
A. Pulmonary artery stenosis. This means that blood is not adequately passed to the lungs for oxygenation.
B. Ventricular septal defect. The gap in the septum allows deoxygenated blood to pass into the left ventricle, and from there to the aorta.
C. Shift of the aorta to the right, so that the aorta overrides the interventricular septum. Oxygen-poor blood passes even more easily from the right ventricle to the aorta.
D. Hypertrophy of the right ventricle. The myocardium has to work harder to pump blood through a narrowed pulmonary artery.
An infant with this condition is described as a “blue baby” because of the extreme degree of cyanosis present at birth (other congenital conditions that involve a shunt of blood from the right to the left without passing through the lungs and receiving proper oxygenation can lead to cyanosis as well). Surgery is required to repair the various heart defects.
Congestive heart failure – The heart is unable to pump its required amount of blood (more blood enters the heart from the veins than leaves through the arteries). Blood accumulates in the lungs (left-sided heart failure) causing pulmonary edema (fluid seeps out of capillaries into the tiny air sacs of the lung). Damming back of blood resulting form right-sided heart failure results in accumulation of fluid in the abdominal organs (liver and spleen) and subcutaneous tissue of the legs. Congestive heart failure often develops gradually over several years, although it can be acute. Therapy includes lowering dietary intake of sodium and diuretics to promote loss of fluids.
Recent studies have shown that drugs known as angiotensin-converting enzyme (ACE) inhibitors can improve the performance of the heart and its pumping activity. These drugs also decrease pressure inside blood vessels and are used to treat hypertension (high blood pressure). If drug therapy and lifestyle changes fail to control congestive heart failure, heart transplantation may be the only treatment option. While waiting for a transplant, patients may need a device to assist the heart’s pumping. A left ventricular assist device (LVAD) is a booster pump implanted in the abdomen, with a cannula (tube) inserted into the left ventricle. It pumps blood out of the heart to all parts of the body. The LVAD is sometimes called a “bridge to transplant.”
Coronary artery disease (CAD) – Disease of the arteries surrounding the heart. The coronary arteries are three large vessels that arise from the aorta and supply oxygenated blood to the heart. It is interesting that the blood that constantly flows through the four hollow chambers of the heart does not itself nourish the myocardial tissue. Instead, after blood leaves the heart via the aorta, a portion is at once lead back over the surface of the heart through the coronary arteries, so that the heart muscle receives blood before any other organ. This seems logical because the energy requirements of the heart are greater than those of any other organ.
Coronary artery disease is usually the result of atherosclerosis. This is the deposition of fatty compounds on the inner lining of the coronary arteries (any other artery can be similarly affected). The ordinary smooth lining of the artery becomes roughened as the atherosclerotic plaque collects in the artery.
Atherosclerosis is dangerous for two important reasons. First, narrowing of the vessel due to atherosclerosis can cause inflexibility and plugging up of the vessel. Second, the roughened lining of the artery may rupture or cause abnormal clotting of blood, leading to a thrombotic occlusion (blocking of the coronary artery by a clot). In both cases, blood flow is decreased (ischemia) or stopped entirely, leading to death (necrosis) of a part of the myocardium. The area of dead myocardial tissue is known as an infarction. The infarcted area is eventually replaced by scar tissue.
The severity of a myocardial infarction (also known as a heart attack) depends on the size of the artery that is blocked and the extent of the blockage. If the blocked artery is small, the result may be death of only a small portion of the heart immediately fed by the artery. After scar tissue forms, the patient may be able to resume completely normal activity.
Angina pectoris is an episode of chest pain, often called precordial pain (precordial means in front of the chest), resulting from a temporary difference between the supply and the demand of oxygen to the heart muscle. Angina can be the result of low oxygen levels in the blood from smoking or respiratory disease), restricted blood flow to the heart (coronary artery disease), or an increase in the work of the heart beyond normal levels. For acute attacks of angina, nitroglycerine is given sublingually. This drug, one of several called nitrates, is a powerful vasodilator and muscle relaxant.
Treatment guidelines for CAD begin with controlling risk factors, such as smoking, obesity, and lack of exercise. Daily aspirin therapy (to prevent formation of clots) and drug therapy to lower cholesterol (HMGs or “statins” reduce the production of cholesterol in the liver) are also important to prevent heart disease. After the occurrence of an MI, patients may require maintenance and anti-ischemic therapy with drugs called beta-blockers, which reduce the force and speed of the heartbeat and lower blood pressure. Other drugs, such as nitrates and calcium channel blockers, cause dilatation of blood vessels, making it easier for the heart to pump blood through vessels.
Surgical treatment of CAD is an open-heart operation called coronary artery bypass grafting or CABG. Experimental keyhole (scopic) bypass grafting is being done on a very limited basis with limitations of a maximum of 3-vessel grafting being done. Cardiologist perform percutaneous transluminal coronary
angioplasty (PTCA), in which catheterizations with balloons and stents opens clogged coronary arteries.
An innovation method of treatment is transmyocardial laser revascularization (TMLR). A laser makes holes in the heart muscle to induce angiogenesis (growth of new blood vessels). Gene therapy (giving DNA or viruses containing DNA to promote expression of factors that lead to angiogenesis) is another new technique to restore damaged heart muscle.
Endocarditis – Inflammation of the inner lining of the heart caused by bacteria (bacterial endocarditis). This condition may be a complication of another infectious disease, an operation, or an injury. Damage to the heart valves produces lesions called vegetations (they resemble cauliflower) that break off into the bloodstream as emboli (material that travels through the blood). When the emboli lodge in the small vessels of the skin, multiple pinpoint hemorrhages known as petechiae (from the Italian petechio, meaning a fleabite) form. Antibiotics are effective in curing bacterial endocarditis.
Hypertensive heart disease – High blood pressure affecting the heart. This condition is caused by the contraction of arterioles leading to increased pressure in arteries. The heart itself is affected because it has to pump more vigorously to overcome the increased resistance in the arteries. Vessels lose their elasticity, become like solid pipes, and place increased burden on the heart to pump blood through the body.
Mitral valve prolapse (MVP) – Improper closure of mitral valve when the heart is pumping blood. This condition, found most frequently in otherwise healthy young women occurs because the mitral valve enlarges and prolapses into the left atrium during systole. The physician hears a midsystolic click on auscultation (listening with a stethoscope). Most people with MVP live normal lives, but because prolapsed valves can on rare occasions become infected, persons with MVP are advised to have preventive antibiotics at the time of dental procedures if the murmur is present.
Murmur – An extra heart sound, heard between normal beats. Murmurs are heard with the aid of a stethoscope and are usually caused by a valvular defect or disease that disrupts the smooth flow of blood in the heart. They are also heard in cases of interseptal defects when blood flows abnormally between chambers through holes in the septa. A functional murmur is one that is not caused by a valve or septal defect and is not a serious danger to the patient’s health. A bruit is an abnormal sound or murmur heard on auscultation. A thrill, which is a vibration felt on palpation of the chest often accompanies a murmur.
Pericarditis – Inflammation of the membranes (pericardium) surrounding the heart. In most instances, pericarditis is secondary to disease elsewhere in the body (such as pulmonary infection). Bacteria and viruses cause the condition, or the etiology may be idiopathic. Malaise, fever and chest pain occur, as well as accumulation of fluid within the pericardial cavity. Compression of the heart due to collection of fluid is called cardiac tamponade. If a considerable amount of fluid is present, pressure on the pulmonary veins may slow the return of blood from the lungs. Excess fluid is drained by pericardiocentesis.
Rheumatic heart disease – Heart disease caused by rheumatic fever. Rheumatic fever is a disease, usually occurring in childhood that can follow a few weeks after a streptococcal infection. Damage is done to the heart, particularly the heart valves, by one or more attacks of rheumatic fever. The valves, especially the mitral valve, become inflamed and scarred (with vegetations, so that they do not open and close normally. Mitral stenosis, atrial fibrillation, and congestive heart failure, due to weakening of the myocardium, are other aspects of rheumatic heart disease. Treatment consists of reduced activity, drugs to control arrhythmias, surgery to repair a damaged valve, and anticoagulant therapy to prevent emboli from forming. Mechanical or porcine (pig) valve implants are also used to replace deteriorated heart valves.
Blood vessels
Aneurysm – Local widening (ballooning out of a small area) of an artery caused by weakness in the arterial wall or breakdown of the wall owing to atherosclerosis. Aneurysm literally means to widen (eurysm) up (ana-). It may occur anywhere in the body but most commonly in the aorta. The danger of an aneurysm is that as the wall of the artery pushes outward it becomes progressively thinner and may eventually rupture. Treatment of an aneurysm depends on the particular vessel involved, the site, and the health of the patient. In aneurysms of small vessels in the brain (berry aneurysm), treatment is occlusion of the vessel with small clips. For larger arteries, such as the aorta, the aneurysm is resected and a synthetic graft is sewn within the aneurysm.
Hypertension – high blood pressure. Most high blood pressure is essential hypertension, in which the cause of the increased pressure is idiopathic. In adults, a blood pressure equal to or greater than 140/90 mmHg is considered high. Diuretics, beta-blockers, ACE inhibitors and calcium channel blockers are used as treatment for essential hypertension. Losing weight, limiting sodium (salt) intake, stopping smoking, and reducing fat in the diet are also important in therapy.
In secondary hypertension, there is always some associated lesion, such as glomerulonephritis, pyelonephritis or disease of the adrenal glands, that is responsible for the elevated blood pressure.
Peripheral vascular disease – Blockage of blood vessels (arteries) in the lower extremities due to atherosclerosis. When arteries in the groin or upper leg narrow or become blocked, blood flow to the lower leg and foot is reduced. Often, the femoral (thigh) artery or the popliteal (back of the knee) artery is involved. An early sign of the problem is intermittent claudication (absence of pain or discomfort in the leg at rest, but pain, tension, and weakness after walking has begun). Treatment is exercise, avoidance of nicotine, which causes vessel constriction, and control of risk factors such as hypertension, hyperlipidemia and diabetes. Surgical treatment includes endarterectomy and bypass grafting (from the normal proximal vessel around the diseased area to a normal vessel distally.
Raynaud phenomenon – Short episodes of pallor and numbness in the fingers and toes due to temporary constriction of the arterioles in the skin. This condition is usually idiopathic, but it may also be secondary to some other, more serious disorder. The episodes can be triggered by cold temperatures, emotional stress, or cigarette smoking. Protecting the body from cold and use of vasodilators are effective treatment.
Varicose veins – Abnormally swollen and twisted veins, usually occurring in the legs. This condition is due to damaged valves that fail to prevent the backflow of blood. The blood then collects in the veins, which distends to many times their normal size. Because of the slow flow of blood in the varicose veins and frequent injury to the vein, thrombosis may occur as well. Hemorrhoids (piles) are varicose veins near the anus. Surgical treatment of hemorrhoids includes injection of the sclerosing solutions, ligation with rubber bands, and cryosurgery.
Treatment of varicose veins includes wearing elastic stockings, elevation of the legs if edema occurs, and surgery to ligate (tie off) and strip (remove) the twisted, swollen veins. The surgical procedure is called vein stripping.
Laboratory Tests and Clinical Procedures
Laboratory Tests
Lipid tests – Lipids are fatty substances found in foods and in the body. Examples of lipids are cholesterol and triglycerides. Lipid tests measure the amounts of these substances in a blood sample. High levels of triglycerides and cholesterol in the blood are associated with a greater risk of atherosclerosis. A cholesterol level below 200 mg/dL in a middle-aged adult is associated with a relatively low risk for coronary artery disease (CAD). A diet high in saturated fat (solid fats of animal origin such as milk, butter, and meats) tends to increase the amount of cholesterol in the blood. Polyunsaturated fats (such as corn oil and safflower oil) do not raise blood cholesterol.
The mainstay of treatment for people with hyperlipidemia is proper diet (low fat and high fiber intake with fresh fruits and vegetables) and exercise. Niacin (a vitamin) is also helpful in reducing lipids. Drug therapy includes HMG reductase inhibitors (HMGs), which lower cholesterol by reducing its production in the liver. These are known as “statins” and examples are simvastatin, lovastatin, and pravastatin.
Lipoprotein electrophoresis – Lipoproteins are proteins that carry lipids (fats) n the bloodstream. Protein electrophoresis is the process of physically separating lipoproteins from a blood sample. High levels of low-density lipoproteins (LDL and very-low-density lipoproteins (VLDL) are associated with atherosclerosis. High levels of high-density lipoproteins (HDL), which remove cholesterol and transport it to the liver, protect adults from the development of atherosclerosis. Factors that increase HDL are estrogen, exercise and alcohol in moderation.
Serum enzyme tests – During a myocardial infarction, enzymes are released into the bloodstream from the dying heart muscle. These enzymes can be measured and are useful as evidence of an infarction. The enzymes tested for are creatine phosphokinase (CPK or CK) and lactate dehydrogenase (LDH). Other blood testes measure levels of muscle proteins, myoglobin and troponin.
Clinical Procedures
X-rays
Angiography – Dye is injected into the blood stream or heart chamber, and x-ray films are taken of the heart and large blood vessels in the chest. If dye is injected into the aorta or an artery in the groin, the procedure is called arteriography.
Digital subtraction angiography (DSA) – Video equipment and a computer are used to produce x-ray pictures of blood vessels. First, an x-ray is produced of the area to be studied, and the results are stored in a computer. Next, contrast material is injected into a vein, and a second image is produced that is also recorded in the computer. The computer then compares the two images and subtracts the first image from the second (removing parts not being studied such as bone, muscle, and fat), leaving nothing but an image of the contrast medium and vessels.
Ultrasound Tests
Doppler ultrasound – An instrument is used to focus sound waves on a blood vessel; blood flow is measured as echoes bounce off red blood cells. Velocity of blood flow increases in areas of stenosis. Arteries or veins in the arms, neck or legs are examined to detect vascular occlusion (blockage due to clots or atherosclerosis).
Echocardiography (ECHO) – Pulses of high-frequency sound waves (ultrasound) are transmitted into the chest, and echoes returning from the valves, chambers, and surfaces of the heart are electronically plotted and recorded.
Nuclear Cardiology
Positron emission tomography (PET) scan – An IV radiopharmaceutical is administered, followed by an injection of glucose. These localize in the myocardium. Uptake is proportional to the glucose metabolic activity of myocardial cells. Images showing the blood flow and functional activity of the myocardium are obtained. Indications for PET scanner use include detection of CAD, assessment of myocardial viability, and differentiation of ischemia and cardiomyopathy.
Thallium 201 scintigraphy – Thallium 201 is a radioactive isotope that is taken up by myocardial tissue. After intravenous injection, the concentration of thallium 201 is measured (by perfusion scanning). Infarcted or scarred myocardium does not extract any isotope, showing up as “cold spots.” Thallium 201 imaging can be performed before or after an exercise ECG study or as a resting study only.
Technetium 99m ventriculography (multiple-gated acquisition scan, or MUGA scan) – This radioactive test studies the motion of the left ventricular wall and measures the ventricle’s ability to eject blood. It is a test of the functioning of the heart and cardiac output.
Magnetic Resonance Imaging (MRI)
Cardiac MRI – Magnetic waves are beamed at the heart, and an image is produced. The procedure is used to obtain detailed information about congenital heart disease, cardiac masses, and lesions of large blood vessels prior to surgery.
Other Procedures
Cardiac catheterization – A thin, flexible tube (catheter) is introduced into a vein or artery and is guided into the heart for purposes of detecting pressures and patterns of blood flow. Contrast can also be injected and x-ray films made (angiography).
Cardioversion (defibrillation) – Very brief discharges of electricity are applied across the chest to stop a cardiac arrhythmia and to allow a more normal rhythm to begin.
Coronary bypass surgery (CABG) – Vessel grafts, consisting of veins taken from other parts of the body, are anastomosed (connected) to existing coronary arteries to detour around blockages in the coronary arteries and keep the myocardium supplied with oxygenated blood. Minimally invasive CABG surgery is performed with smaller incisions instead of traditional sternotomy to open the chest.
Electrocardiography (ECG, EKG) – Process of recording the electricity flowing through the heart and thus the rhythm of the heartbeat. A normal sinus rhythm begins in the SA nodes and is between 60 and 100 beats per minute, with normal intervals and no ectopic beats.
Endarterectomy – This procedure involves surgical removal of the innermost (end-) lining of an artery when it is thickened by fatty deposits (atheromas) and thromboses.
Extracorporeal circulation (ECC) – A heart-lung machine (pump oxygenator) is used as a bypass to divert blood from the heart and lungs while the heart is being repaired. Blood leaves the body, enters the heart-lung machine, where it is oxygenated, and then returns to a blood vessel (artery) to circulate through the bloodstream. Extracorporeal means outside (extra-) the body (corpor/o).
Holter monitoring – A compact version (about the size of a portable tape player) of an electrocardiograph (instrument to measure the electricity flowing through the heart) is worn during a 24-hour period to detect cardiac arrhythmias.
Percutaneous transluminal coronary angioplasty (PTCA) – In this procedure, also called balloon angioplasty, a balloon-tipped catheter is inserted via the femoral (thigh) artery and threaded up the aorta into a coronary artery. The balloon is inflated, compressing fatty deposits or plaque against the side of the artery and opening the artery to allow for passage of blood. Balloon valvuloplasty is used to open narrowed cardiac valves and is seen as a possible alternative to surgery for valvular stenosis. Stents (expandable slotted tubes are now used instead of PTCA to create wider lumens and make restenosis less likely.
In previous chapters we have discussed the diverse and important function of many organs of the body. These functions include conduction of nerve impulses, production of hormones and reproductive cells, excretion of waste materials, and digestion and absorption of food substances into the bloodstream. In order to perform these functions reliably and efficiently, the body organs are powered by a unique energy source. The cells of each organ receive energy from the food substance that reaches them after being taken into the body. Food contains stored energy that can be converted into the energy of movement and work. This conversion of stored energy into the activity energy of work occurs when food and oxygen combine in cells during the chemical process of catabolism. It is obvious, then, which each cell of each organ is dependent on a constant supply of food and oxygen in order to receive sufficient energy to work well.
How does the body assure that oxygen and food will be delivered to all its cells? The cardiovascular system, consisting of a fluid called blood, vessels to carry the blood, and a hollow, muscular pump called the heart, transports food and oxygen to all organs and cells of the body. Blood vessels in the lungs absorb the oxygen that has been inhaled from the air, and blood vessels in the small intestine absorb food substances from the digestive tract. In addition, blood vessels carry cellular waste materials such as carbon dioxide and urea and transport these substances to the lungs and kidneys, respective, where they can be eliminated from the body.
The heart and blood vessels and the terminology related to their anatomy, physiology, and disease conditions will be explored in this chapter. The nature of blood and another body fluid called lymph will be discussed in a later chapter.
Blood Vessels and the Circulation of Blood
Blood Vessels
There are three types of blood vessels in the body. These are arteries, veins, and capillaries.
Arteries are the large blood vessels that lead away from the heart. Their walls are made of connective tissue, muscle tissue, elastic fibers, and an innermost layer of epithelial cells called endothelium. Endothelial cells, which line all blood vessels, secrete substances that affect the size of blood vessels, reduce blood clotting, and promote the growth of blood vessels. Because arteries carry blood away from the heart, they must be strong enough to withstand the high pressure of the pumping action to the heart. Their elastic walls allow them to expand as the heartbeat forces blood into the arterial system throughout the body. Smaller branches of arteries are called arterioles. Arterioles are thinner than arteries and carry the blood to the tiniest of blood vessels, the capillaries.
Capillaries have walls that are one endothelial cell thick. These delicate, microscopic vessels carry nutrient-rich, oxygenated blood from the arteries and the arterioles to the body cells. There walls are thin enough to allow passage of oxygen and nutrients out of the blood stream and into the tissue fluid surround the cells. Once inside the cells, the nutrients are burned in the presence of oxygen (catabolism) to release needed energy within the cell. At the same time, waste products such as carbon dioxide and water pass out of the cells and into the thin-walled capillaries. The waste filled blood then flows back to the heart in small veins called venules, which branch to form larger vessels called veins.
Veins are thinner walled than arteries. They conduct blood (that has given most of its oxygen) toward the heart from the tissues. Veins have little elastic tissue and less connective tissue than arteries, and blood pressure in veins is extremely low compared with pressure in arteries. In order to keep blood moving back toward the heart, veins have valves that prevent the backflow of blood and keep the blood moving in one direction. Muscular action also helps the movement of blood in veins.
Circulation of Blood
Arteries, arterioles, veins, venules, and capillaries, together with the heart, form a circulatory system for the flow of blood.
Blood deficient in oxygen flows through two large veins, the venae cavae, on its way from the tissue capillaries to the heart. The blood became oxygen-poor at the tissue capillaries when oxygen left the blood and entered the body cells.
Oxygen-poor blood enters the right side of the heart and travels through that side and into the pulmonary artery, a vessel that divides in two, one branch leading to the left lung, the other to the right lung. The arteries continue dividing and subdividing with the lungs, forming smaller and smaller vessels (arterioles) and finally reaching the lung capillaries. The pulmonary artery is unusual in that it is the only artery in the body that carries blood deficient in oxygen.
While passing through the lung (pulmonary) capillaries, blood absorbs the oxygen that entered the body during inhalation. The newly oxygenated blood next returns immediately to the heart through pulmonary veins. The pulmonary veins are unusual in that are the only veins in the body that carry oxygen-rich (oxygenated) blood. The circulation of blood through the vessels from the heart to the lungs and then back to the heart again is known as the pulmonary circulation.
Oxygen-rich blood enters the left side of the heart from the pulmonary veins. The muscles in the left side of the heart pump the blood out of the heart through the largest single artery in the body, the aorta. The aorta moves up at first (ascending aorta) but then arches over dorsally and runs downward (descending aorta) just in front of the vertebral column. The aorta divides into numerous branches called arteries that carry the oxygenated blood to all parts of the body. The names of some of these arterial branches will be familiar to you: brachial (brachi/o means arm), axillary, splenic, gastric, and renal arteries. The carotid arteries supply blood to the head and neck.
The relatively large arterial vessels branch further to form smaller arterioles. The arterioles, still containing oxygenated blood, branch into smaller tissue capillaries, which are near the body cells. Oxygen leaves the blood and passes through the thin capillary walls to enter the body cells. There, food is broken down, in the presence of oxygen, and energy is released.
One metabolic product of this chemical process is carbon dioxide (CO2). Carbon dioxide is produced in the cell but is harmful to the cell if it remains. It must thus pass out of the cells and into the capillary bloodstream at the same time that oxygen is entering the cells. As the blood makes its way back from the tissue capillaries toward the heart in venules and veins it is full of carbon dioxide and is oxygen-poor.
The circuit is thus completed when oxygen-poor blood enters the heart from the venae cavae. This circulation of blood from the body organs (except the lungs) to the heart and back again is called the systemic circulation.
Anatomy of the Heart
The human heart weighs less than a pound, is roughly the size of an adult fist, and lies in the thoracic cavity, just behind the breastbone in the mediastinum (between the lungs).
The heart is a pump, consisting of four chambers; two upper chambers called atria (singular: atrium) and two lower chambers called ventricles. It is actually a double pump, bound into one organ and synchronized very carefully. Blood passes through each pump in a definite pattern. Pump station number one, one the right side of the heart, sends oxygen-deficient blood to the lungs, where the blood picks up oxygen and releases its carbon dioxide. The newly oxygenated blood returns to the left side of the heart to pump station number two and does not mix with the oxygen-poor blood in the pump station number one. Pump station number two then forces the oxygenated blood out to all parts of the body. At the body tissues, the blood loses its oxygen and on return to the heart, to pump station number one, blood poor in oxygen (rich in carbon dioxide) is sent out to the lungs to begin the cycle anew.
Oxygen-poor blood enters the heart through the two largest veins in the body, the venae cavae. The superior vena cava drains blood from the upper part of the body, and the inferior vena cava carries blood from the lower part of the body.
The venae cavae bring oxygen-poor blood that has passed through all of the body to the right atrium, the thin walled upper right chamber of the heart. The right atrium contracts to force blood through the tricuspid valve (cusps are the flaps of the valves) into the right ventricle, which is the lower right chamber of the heart. The cusps on the tricuspid valve form a one-way passage designed to keep the blood flowing in only one direction. As the right ventricle contracts to pump oxygen-poor blood through the pulmonary valve into the pulmonary artery, the tricuspid valve stays shut, thus preventing blood from pushing back into the right atrium. The pulmonary artery then branches to carry oxygen-deficient blood to each lung.
The blood that enters the lung capillaries from the pulmonary artery soon loses its large quantity of carbon dioxide into the lung tissue, and the carbon dioxide is expelled. At the same time, oxygen enters the capillaries of the lungs and is brought back to the heart via the pulmonary veins. The newly oxygenate blood enters the left atrium of the heart from the pulmonary veins. The walls of the left atrium contract to force blood through the mitral valve into the left ventricle.
The left ventricle has the thickest walls of all four heart chambers (three times the thickness of the right ventricle). It must pump blood with great force so that the blood travels through arteries to all parts of the body. The blood is pumped out of the left ventricle through the aortic valve and into the aorta, which branches to carry blood all over the body. The aortic valve prevents the return of aortic blood to the left ventricle once it has been pumped out.
The four chambers of the heart are separated by partitions called septa (singular: septum). The interatrial septum separates the two upper chambers (atria), and the interventricular septum is a muscular wall that comes between the two lower chambers (ventricles).
The heart wall is composed of three layers. The endocardium is a smooth layer of endothelial cells that lines the interior of the heart and heart valve. The myocardium is the middle, muscular layer of the heart and its thickest layer. The pericardium is a fibrous and membranous sac surrounding the heart. It is composed of two layers, the visceral pericardium, which adheres to the heart and the parietal (parietal means wall) pericardium, which lines the outer fibrous coat. The pericardial cavity (Between the visceral and the parietal pericardia normally contains 10 – 15 ml of fluid, which lubricates the membranes as the heart beats.
Physiology of the Heart
Heartbeat and Heart Sounds
There are two phases of the heartbeat. These phases are called diastole (relaxation) and systole (contraction). Diastole occurs when the ventricle walls relax and blood flows into the heart from the venae cavae and the pulmonary veins. The tricuspid and mitral valves are open in the diastole, as blood passes from the right and left atria into the ventricles. The pulmonary and aortic valves are closed during diastole.
Systole occurs next, as the walls of the right and left ventricle contract to pump blood into the pulmonary artery and the aorta. Both the tricuspid and the mitral valves are closed during systole, thus preventing the flow of blood back into the atria.
This diastole-systole cardiac cycle occurs between 70 and 80 times per minute (100,000 times a day). The heart pumps about 3 ounces of blood with each contraction. This means that about 5 quarts of blood are pumped by the heart in 1 minute (75 gallons an hour and about 2000 gallons a day).
Closure of the heart valves is associated with audible sounds such as “lub, dub, lub, dub,” that can be heard when listening to a normal heart with a stethoscope. The “lub” is associated with closure of the tricuspid and mitral valves at the beginning of the systole and the “dub” with the closure of the aortic and pulmonary valves at the end of systole. The “lub” sound is called the first heart sound and the “dub” is the second heart sound because the normal cycle of the heartbeat starts with the beginning of the systole. An abnormal heart sound is known as a murmur.
Conduction System of the Heart
What keeps the heart at its perfect rhythm? Although the heart does have nerves that can affect its rate, they are not primarily responsible for its beat. It is known that the heart starts beating in the embryo before the heart is supplied with nerves and will continue to be in experimental animals even when nerve supply is cut.
Primary responsibility for initiating the heartbeat rests with a small region of specialized muscle tissue in the posterior portion of the right atrium, where an electrical impulse originates. This region of the right atrium is called the sinoatrial node (SA node). The SA node is called the pacemaker of the heart. The current of electricity generated by the pacemaker causes the walls of the atria to contract and force blood into the ventricle (ending diastole).
Almost like ripples in a pond of water when a stone is thrown, the wave of electricity passes from the pacemaker to another region of the myocardium. This region is at the posterior portion of the interatrial septum and is called the atrioventricular node (AV node). The AV node immediately sends the excitation wave to a bundle of specialized muscle fibers called the atrioventricular bundle or bundle of His (pronounced hiss). Within the interventricular septum, the bundle of His divides into the right and left bundle branches, which form the conduction myofibers that extend through the ventricle walls and stimulate them to contract. Thus, systole occurs and blood is pumped away from the heart. A short rest period follows, and then the pacemaker begins the wave of excitation across the heart again.
The record used to detect these electrical changes in heart muscle at the heartbeats is called an electrocardiogram (ECG or EKG, from the Greek root kardia). The normal ECG shows five waves, or deflections, the represent the electrical changes as a wave of excitation spreads through the heart. The deflections are called P, QRS and T waves. The P wave represents electrical activity in the wall of the atria (atrial depolarization). The QRS wave represents ventricular depolarization as electricity passes through the atrioventricular bundle and the ventricular wall. This is the largest wave because the ventricle contains the most muscle. The T wave represents ventricular repolarization, which is when the ventricular wall relaxes and recovers from contraction. The ECG is used to diagnose a heart attack (myocardial infarction, which causes abnormal deflections.
Normal heart rhythm (originating in the SA node and traveling through the heart) is called sinus rhythm. Sympathetic nerves speed up the heart rate during conditions of emotional stress or vigorous exercise. Parasympathetic nerves slow the heart rate when the need for extra pumping is past.
Blood Pressure
Blood pressure is the force that the blood exerts on the arterial walls. This pressure is measured by a device called a sphygmomanometer.
The sphygmomanometer consists of a rubber bag inside a cloth cuff that is wrapped around the upper arm, just above the elbow. The rubber bag is inflated with air by means of a rubber bulb. As the bag is pumped up, the pressure within it increased and is measured on a recording device attached to the cuff.
The vessels in the upper arm are compressed by the air pressure in the bag. When there is sufficient air pressure in the bag to stop the flow of blood in the artery of the arm (brachial artery), the pulse in the lower arm where the observer is listening with a stethoscope) obviously drops.
Air is then allowed to escape from the bag and the pressure is lowered slowly, allowing the blood to being to make its way through the gradually opening artery. At the point where the person listening with the stethoscope first hears the sounds of the pulse beats, the reading on the device attached to the cuff shows the higher, systolic, blood pressure (pressure in the artery when the ventricle is contracting to force the blood into the aorta and other arteries).
As air continues to escape, the sounds become progressiv3e louder. Finally, when a change in sounds from loud to soft occur, the observer makes note of the pressure on the recording device. This is called the diastolic blood pressure (pressure in the artery when the ventricles are relaxing and the heart is filling, receiving blood from the venae cavae and pulmonary veins).
Blood pressure is usually expressed as a fraction: for example, 120/80, in which the 120 represents the systolic pressure and 80 the diastolic pressure.
Pathological Conditions: The Heart and Blood Vessels
Heart
arrhythmias – Abnormal heart rhythms (dysrhythmias). Examples of cardiac arrhythmias:
1. Heart block (atrioventricular block) – Failure of proper conduction of impulses through the AV node to the atrioventricular bundle (bundle of His). Damage to the SA node may cause its impulses to be too weak to activate the AV node and impulses fail to reach the ventricles. If the failure occurs only occasionally, the heart will miss a beat in a rhythm at regular intervals (partial heart block). If no impulses reach the AV node from the SA node, the ventricles contract slower than the atria and are not coordinated. This is complete heart block. Implantation of a cardiac pacemaker can overcome heart block and establish a normal rhythm.
2. Flutter – Rapid but regular contractions of atria or ventricles. This condition can occur in patients with heart disease. The heart rhythm may reach up to 300 beats per minute.
3. Fibrillation – Rapid, random, ineffectual, and irregular contractions of the heart (350 beats or more per minute). In atrial fibrillation, the wave of excitation passes through the atrial myocardium even more quickly than in atrial flutter. In order to restore normal heart rhythm, an electrical device called a defibrillator is applied to the chest wall; this electric shock stops the heart and reverses its abnormal rhythm. This is also called cardioversion. Drugs, such as digoxin may also be used to convert fibrillation into regular rhythm.
A device called an automatic implantable cardioverter/defibrillator (AICD) can now be implanted in the chest to sense arrhythmias and correct them. These are pacemaker-sized devices that give shocks to change abnormal rhythms, such as ventricular fibrillation.
Radiofrequency catheter ablation (RFA) is a nonsurgical treatment used to treat arrhythmias, such as paroxysmal (sharp, sudden spasm) tachycardia. A catheter, placed in blood vessels leading up against the heart muscle, delivers a high-frequency current to burn a small portion of the muscle. This injury (ablation) to the muscle destroys the arrhythmias.
Cardiac arrest is the sudden and often unexpected stoppage of heart movement, caused by heart block or ventricular fibrillation (resulting from underlying heart disease).
Palpitations are uncomfortable sensations in the chest associated with different types of arrhythmias. Palpitations do not necessary indicate serious heart disease (smoking, caffeine, and drugs such as antidepressants can produce palpitations). Two cardiac causes of palpitations are premature ventricular contractions (PVCs) and premature atrial contractions (PACs).
Congenital heart disease – Abnormalities in the heart at birth. The following are congenital anomalies resulting from failure in the development of the fetal heart.
1. Coarctation of the aorta (CoA) – Narrowing (coarctation) of the aorta. Surgical treatment consists of removal of the constricted region and end-to-end anastomosis of the aortic segments.
2. Patent ductus arteriosus (PDA) – A small duct (ductus arteriosus between the aorta and the pulmonary artery, which normally close soon after birth, remains open (patent). This condition means that the oxygenated blood flow from the aorta to the pulmonary artery. The anomaly occurs most often in females and is commonly associated with intrauterine rubella (German measles) infection, prematurity, and infantile respiratory distress syndrome. Treatment is surgery to close the ductus arteriosus open.
3. Septal defects – Small holes in the septa between the atria (atrial septal defects [ASDs]) or the ventricle (ventricular septal defects [VSDs]). Although many septal defects will close spontaneously, others will require surgery. Septal defects can be closed while maintaining a general circulation by means of a heart-lung machine. This machine is connected to the patient’s circulatory system and relieve the heart and lungs of pumping and oxygenation functions during heart surgery.
Two recent procedures as alternatives to traditional surgery are transcatheter closure (a “clamshell” device is threaded through the blood via a catheter into the heart and into the septal defect, where it is fixed in place to block the hole) and minimally invasive heart surgery (through 3 or 4 small puncture holes in the chest; special instruments are used to repair the defect).
4. Tetralogy of Fallot – A congenital malformation of the heart involving four (tetra) distinct defects. The condition, named for Etienne Fallot, the French physician who described it in 1888. The four defects are:
A. Pulmonary artery stenosis. This means that blood is not adequately passed to the lungs for oxygenation.
B. Ventricular septal defect. The gap in the septum allows deoxygenated blood to pass into the left ventricle, and from there to the aorta.
C. Shift of the aorta to the right, so that the aorta overrides the interventricular septum. Oxygen-poor blood passes even more easily from the right ventricle to the aorta.
D. Hypertrophy of the right ventricle. The myocardium has to work harder to pump blood through a narrowed pulmonary artery.
An infant with this condition is described as a “blue baby” because of the extreme degree of cyanosis present at birth (other congenital conditions that involve a shunt of blood from the right to the left without passing through the lungs and receiving proper oxygenation can lead to cyanosis as well). Surgery is required to repair the various heart defects.
Congestive heart failure – The heart is unable to pump its required amount of blood (more blood enters the heart from the veins than leaves through the arteries). Blood accumulates in the lungs (left-sided heart failure) causing pulmonary edema (fluid seeps out of capillaries into the tiny air sacs of the lung). Damming back of blood resulting form right-sided heart failure results in accumulation of fluid in the abdominal organs (liver and spleen) and subcutaneous tissue of the legs. Congestive heart failure often develops gradually over several years, although it can be acute. Therapy includes lowering dietary intake of sodium and diuretics to promote loss of fluids.
Recent studies have shown that drugs known as angiotensin-converting enzyme (ACE) inhibitors can improve the performance of the heart and its pumping activity. These drugs also decrease pressure inside blood vessels and are used to treat hypertension (high blood pressure). If drug therapy and lifestyle changes fail to control congestive heart failure, heart transplantation may be the only treatment option. While waiting for a transplant, patients may need a device to assist the heart’s pumping. A left ventricular assist device (LVAD) is a booster pump implanted in the abdomen, with a cannula (tube) inserted into the left ventricle. It pumps blood out of the heart to all parts of the body. The LVAD is sometimes called a “bridge to transplant.”
Coronary artery disease (CAD) – Disease of the arteries surrounding the heart. The coronary arteries are three large vessels that arise from the aorta and supply oxygenated blood to the heart. It is interesting that the blood that constantly flows through the four hollow chambers of the heart does not itself nourish the myocardial tissue. Instead, after blood leaves the heart via the aorta, a portion is at once lead back over the surface of the heart through the coronary arteries, so that the heart muscle receives blood before any other organ. This seems logical because the energy requirements of the heart are greater than those of any other organ.
Coronary artery disease is usually the result of atherosclerosis. This is the deposition of fatty compounds on the inner lining of the coronary arteries (any other artery can be similarly affected). The ordinary smooth lining of the artery becomes roughened as the atherosclerotic plaque collects in the artery.
Atherosclerosis is dangerous for two important reasons. First, narrowing of the vessel due to atherosclerosis can cause inflexibility and plugging up of the vessel. Second, the roughened lining of the artery may rupture or cause abnormal clotting of blood, leading to a thrombotic occlusion (blocking of the coronary artery by a clot). In both cases, blood flow is decreased (ischemia) or stopped entirely, leading to death (necrosis) of a part of the myocardium. The area of dead myocardial tissue is known as an infarction. The infarcted area is eventually replaced by scar tissue.
The severity of a myocardial infarction (also known as a heart attack) depends on the size of the artery that is blocked and the extent of the blockage. If the blocked artery is small, the result may be death of only a small portion of the heart immediately fed by the artery. After scar tissue forms, the patient may be able to resume completely normal activity.
Angina pectoris is an episode of chest pain, often called precordial pain (precordial means in front of the chest), resulting from a temporary difference between the supply and the demand of oxygen to the heart muscle. Angina can be the result of low oxygen levels in the blood from smoking or respiratory disease), restricted blood flow to the heart (coronary artery disease), or an increase in the work of the heart beyond normal levels. For acute attacks of angina, nitroglycerine is given sublingually. This drug, one of several called nitrates, is a powerful vasodilator and muscle relaxant.
Treatment guidelines for CAD begin with controlling risk factors, such as smoking, obesity, and lack of exercise. Daily aspirin therapy (to prevent formation of clots) and drug therapy to lower cholesterol (HMGs or “statins” reduce the production of cholesterol in the liver) are also important to prevent heart disease. After the occurrence of an MI, patients may require maintenance and anti-ischemic therapy with drugs called beta-blockers, which reduce the force and speed of the heartbeat and lower blood pressure. Other drugs, such as nitrates and calcium channel blockers, cause dilatation of blood vessels, making it easier for the heart to pump blood through vessels.
Surgical treatment of CAD is an open-heart operation called coronary artery bypass grafting or CABG. Experimental keyhole (scopic) bypass grafting is being done on a very limited basis with limitations of a maximum of 3-vessel grafting being done. Cardiologist perform percutaneous transluminal coronary
angioplasty (PTCA), in which catheterizations with balloons and stents opens clogged coronary arteries.
An innovation method of treatment is transmyocardial laser revascularization (TMLR). A laser makes holes in the heart muscle to induce angiogenesis (growth of new blood vessels). Gene therapy (giving DNA or viruses containing DNA to promote expression of factors that lead to angiogenesis) is another new technique to restore damaged heart muscle.
Endocarditis – Inflammation of the inner lining of the heart caused by bacteria (bacterial endocarditis). This condition may be a complication of another infectious disease, an operation, or an injury. Damage to the heart valves produces lesions called vegetations (they resemble cauliflower) that break off into the bloodstream as emboli (material that travels through the blood). When the emboli lodge in the small vessels of the skin, multiple pinpoint hemorrhages known as petechiae (from the Italian petechio, meaning a fleabite) form. Antibiotics are effective in curing bacterial endocarditis.
Hypertensive heart disease – High blood pressure affecting the heart. This condition is caused by the contraction of arterioles leading to increased pressure in arteries. The heart itself is affected because it has to pump more vigorously to overcome the increased resistance in the arteries. Vessels lose their elasticity, become like solid pipes, and place increased burden on the heart to pump blood through the body.
Mitral valve prolapse (MVP) – Improper closure of mitral valve when the heart is pumping blood. This condition, found most frequently in otherwise healthy young women occurs because the mitral valve enlarges and prolapses into the left atrium during systole. The physician hears a midsystolic click on auscultation (listening with a stethoscope). Most people with MVP live normal lives, but because prolapsed valves can on rare occasions become infected, persons with MVP are advised to have preventive antibiotics at the time of dental procedures if the murmur is present.
Murmur – An extra heart sound, heard between normal beats. Murmurs are heard with the aid of a stethoscope and are usually caused by a valvular defect or disease that disrupts the smooth flow of blood in the heart. They are also heard in cases of interseptal defects when blood flows abnormally between chambers through holes in the septa. A functional murmur is one that is not caused by a valve or septal defect and is not a serious danger to the patient’s health. A bruit is an abnormal sound or murmur heard on auscultation. A thrill, which is a vibration felt on palpation of the chest often accompanies a murmur.
Pericarditis – Inflammation of the membranes (pericardium) surrounding the heart. In most instances, pericarditis is secondary to disease elsewhere in the body (such as pulmonary infection). Bacteria and viruses cause the condition, or the etiology may be idiopathic. Malaise, fever and chest pain occur, as well as accumulation of fluid within the pericardial cavity. Compression of the heart due to collection of fluid is called cardiac tamponade. If a considerable amount of fluid is present, pressure on the pulmonary veins may slow the return of blood from the lungs. Excess fluid is drained by pericardiocentesis.
Rheumatic heart disease – Heart disease caused by rheumatic fever. Rheumatic fever is a disease, usually occurring in childhood that can follow a few weeks after a streptococcal infection. Damage is done to the heart, particularly the heart valves, by one or more attacks of rheumatic fever. The valves, especially the mitral valve, become inflamed and scarred (with vegetations, so that they do not open and close normally. Mitral stenosis, atrial fibrillation, and congestive heart failure, due to weakening of the myocardium, are other aspects of rheumatic heart disease. Treatment consists of reduced activity, drugs to control arrhythmias, surgery to repair a damaged valve, and anticoagulant therapy to prevent emboli from forming. Mechanical or porcine (pig) valve implants are also used to replace deteriorated heart valves.
Blood vessels
Aneurysm – Local widening (ballooning out of a small area) of an artery caused by weakness in the arterial wall or breakdown of the wall owing to atherosclerosis. Aneurysm literally means to widen (eurysm) up (ana-). It may occur anywhere in the body but most commonly in the aorta. The danger of an aneurysm is that as the wall of the artery pushes outward it becomes progressively thinner and may eventually rupture. Treatment of an aneurysm depends on the particular vessel involved, the site, and the health of the patient. In aneurysms of small vessels in the brain (berry aneurysm), treatment is occlusion of the vessel with small clips. For larger arteries, such as the aorta, the aneurysm is resected and a synthetic graft is sewn within the aneurysm.
Hypertension – high blood pressure. Most high blood pressure is essential hypertension, in which the cause of the increased pressure is idiopathic. In adults, a blood pressure equal to or greater than 140/90 mmHg is considered high. Diuretics, beta-blockers, ACE inhibitors and calcium channel blockers are used as treatment for essential hypertension. Losing weight, limiting sodium (salt) intake, stopping smoking, and reducing fat in the diet are also important in therapy.
In secondary hypertension, there is always some associated lesion, such as glomerulonephritis, pyelonephritis or disease of the adrenal glands, that is responsible for the elevated blood pressure.
Peripheral vascular disease – Blockage of blood vessels (arteries) in the lower extremities due to atherosclerosis. When arteries in the groin or upper leg narrow or become blocked, blood flow to the lower leg and foot is reduced. Often, the femoral (thigh) artery or the popliteal (back of the knee) artery is involved. An early sign of the problem is intermittent claudication (absence of pain or discomfort in the leg at rest, but pain, tension, and weakness after walking has begun). Treatment is exercise, avoidance of nicotine, which causes vessel constriction, and control of risk factors such as hypertension, hyperlipidemia and diabetes. Surgical treatment includes endarterectomy and bypass grafting (from the normal proximal vessel around the diseased area to a normal vessel distally.
Raynaud phenomenon – Short episodes of pallor and numbness in the fingers and toes due to temporary constriction of the arterioles in the skin. This condition is usually idiopathic, but it may also be secondary to some other, more serious disorder. The episodes can be triggered by cold temperatures, emotional stress, or cigarette smoking. Protecting the body from cold and use of vasodilators are effective treatment.
Varicose veins – Abnormally swollen and twisted veins, usually occurring in the legs. This condition is due to damaged valves that fail to prevent the backflow of blood. The blood then collects in the veins, which distends to many times their normal size. Because of the slow flow of blood in the varicose veins and frequent injury to the vein, thrombosis may occur as well. Hemorrhoids (piles) are varicose veins near the anus. Surgical treatment of hemorrhoids includes injection of the sclerosing solutions, ligation with rubber bands, and cryosurgery.
Treatment of varicose veins includes wearing elastic stockings, elevation of the legs if edema occurs, and surgery to ligate (tie off) and strip (remove) the twisted, swollen veins. The surgical procedure is called vein stripping.
Laboratory Tests and Clinical Procedures
Laboratory Tests
Lipid tests – Lipids are fatty substances found in foods and in the body. Examples of lipids are cholesterol and triglycerides. Lipid tests measure the amounts of these substances in a blood sample. High levels of triglycerides and cholesterol in the blood are associated with a greater risk of atherosclerosis. A cholesterol level below 200 mg/dL in a middle-aged adult is associated with a relatively low risk for coronary artery disease (CAD). A diet high in saturated fat (solid fats of animal origin such as milk, butter, and meats) tends to increase the amount of cholesterol in the blood. Polyunsaturated fats (such as corn oil and safflower oil) do not raise blood cholesterol.
The mainstay of treatment for people with hyperlipidemia is proper diet (low fat and high fiber intake with fresh fruits and vegetables) and exercise. Niacin (a vitamin) is also helpful in reducing lipids. Drug therapy includes HMG reductase inhibitors (HMGs), which lower cholesterol by reducing its production in the liver. These are known as “statins” and examples are simvastatin, lovastatin, and pravastatin.
Lipoprotein electrophoresis – Lipoproteins are proteins that carry lipids (fats) n the bloodstream. Protein electrophoresis is the process of physically separating lipoproteins from a blood sample. High levels of low-density lipoproteins (LDL and very-low-density lipoproteins (VLDL) are associated with atherosclerosis. High levels of high-density lipoproteins (HDL), which remove cholesterol and transport it to the liver, protect adults from the development of atherosclerosis. Factors that increase HDL are estrogen, exercise and alcohol in moderation.
Serum enzyme tests – During a myocardial infarction, enzymes are released into the bloodstream from the dying heart muscle. These enzymes can be measured and are useful as evidence of an infarction. The enzymes tested for are creatine phosphokinase (CPK or CK) and lactate dehydrogenase (LDH). Other blood testes measure levels of muscle proteins, myoglobin and troponin.
Clinical Procedures
X-rays
Angiography – Dye is injected into the blood stream or heart chamber, and x-ray films are taken of the heart and large blood vessels in the chest. If dye is injected into the aorta or an artery in the groin, the procedure is called arteriography.
Digital subtraction angiography (DSA) – Video equipment and a computer are used to produce x-ray pictures of blood vessels. First, an x-ray is produced of the area to be studied, and the results are stored in a computer. Next, contrast material is injected into a vein, and a second image is produced that is also recorded in the computer. The computer then compares the two images and subtracts the first image from the second (removing parts not being studied such as bone, muscle, and fat), leaving nothing but an image of the contrast medium and vessels.
Ultrasound Tests
Doppler ultrasound – An instrument is used to focus sound waves on a blood vessel; blood flow is measured as echoes bounce off red blood cells. Velocity of blood flow increases in areas of stenosis. Arteries or veins in the arms, neck or legs are examined to detect vascular occlusion (blockage due to clots or atherosclerosis).
Echocardiography (ECHO) – Pulses of high-frequency sound waves (ultrasound) are transmitted into the chest, and echoes returning from the valves, chambers, and surfaces of the heart are electronically plotted and recorded.
Nuclear Cardiology
Positron emission tomography (PET) scan – An IV radiopharmaceutical is administered, followed by an injection of glucose. These localize in the myocardium. Uptake is proportional to the glucose metabolic activity of myocardial cells. Images showing the blood flow and functional activity of the myocardium are obtained. Indications for PET scanner use include detection of CAD, assessment of myocardial viability, and differentiation of ischemia and cardiomyopathy.
Thallium 201 scintigraphy – Thallium 201 is a radioactive isotope that is taken up by myocardial tissue. After intravenous injection, the concentration of thallium 201 is measured (by perfusion scanning). Infarcted or scarred myocardium does not extract any isotope, showing up as “cold spots.” Thallium 201 imaging can be performed before or after an exercise ECG study or as a resting study only.
Technetium 99m ventriculography (multiple-gated acquisition scan, or MUGA scan) – This radioactive test studies the motion of the left ventricular wall and measures the ventricle’s ability to eject blood. It is a test of the functioning of the heart and cardiac output.
Magnetic Resonance Imaging (MRI)
Cardiac MRI – Magnetic waves are beamed at the heart, and an image is produced. The procedure is used to obtain detailed information about congenital heart disease, cardiac masses, and lesions of large blood vessels prior to surgery.
Other Procedures
Cardiac catheterization – A thin, flexible tube (catheter) is introduced into a vein or artery and is guided into the heart for purposes of detecting pressures and patterns of blood flow. Contrast can also be injected and x-ray films made (angiography).
Cardioversion (defibrillation) – Very brief discharges of electricity are applied across the chest to stop a cardiac arrhythmia and to allow a more normal rhythm to begin.
Coronary bypass surgery (CABG) – Vessel grafts, consisting of veins taken from other parts of the body, are anastomosed (connected) to existing coronary arteries to detour around blockages in the coronary arteries and keep the myocardium supplied with oxygenated blood. Minimally invasive CABG surgery is performed with smaller incisions instead of traditional sternotomy to open the chest.
Electrocardiography (ECG, EKG) – Process of recording the electricity flowing through the heart and thus the rhythm of the heartbeat. A normal sinus rhythm begins in the SA nodes and is between 60 and 100 beats per minute, with normal intervals and no ectopic beats.
Endarterectomy – This procedure involves surgical removal of the innermost (end-) lining of an artery when it is thickened by fatty deposits (atheromas) and thromboses.
Extracorporeal circulation (ECC) – A heart-lung machine (pump oxygenator) is used as a bypass to divert blood from the heart and lungs while the heart is being repaired. Blood leaves the body, enters the heart-lung machine, where it is oxygenated, and then returns to a blood vessel (artery) to circulate through the bloodstream. Extracorporeal means outside (extra-) the body (corpor/o).
Holter monitoring – A compact version (about the size of a portable tape player) of an electrocardiograph (instrument to measure the electricity flowing through the heart) is worn during a 24-hour period to detect cardiac arrhythmias.
Percutaneous transluminal coronary angioplasty (PTCA) – In this procedure, also called balloon angioplasty, a balloon-tipped catheter is inserted via the femoral (thigh) artery and threaded up the aorta into a coronary artery. The balloon is inflated, compressing fatty deposits or plaque against the side of the artery and opening the artery to allow for passage of blood. Balloon valvuloplasty is used to open narrowed cardiac valves and is seen as a possible alternative to surgery for valvular stenosis. Stents (expandable slotted tubes are now used instead of PTCA to create wider lumens and make restenosis less likely.
How does the body assure that oxygen and food will be delivered to all its cells? The cardiovascular system, consisting of a fluid called blood, vessels to carry the blood, and a hollow, muscular pump called the heart, transports food and oxygen to all organs and cells of the body. Blood vessels in the lungs absorb the oxygen that has been inhaled from the air, and blood vessels in the small intestine absorb food substances from the digestive tract. In addition, blood vessels carry cellular waste materials such as carbon dioxide and urea and transport these substances to the lungs and kidneys, respective, where they can be eliminated from the body.
The heart and blood vessels and the terminology related to their anatomy, physiology, and disease conditions will be explored in this chapter. The nature of blood and another body fluid called lymph will be discussed in a later chapter.
Blood Vessels and the Circulation of Blood
Blood Vessels
There are three types of blood vessels in the body. These are arteries, veins, and capillaries.
Arteries are the large blood vessels that lead away from the heart. Their walls are made of connective tissue, muscle tissue, elastic fibers, and an innermost layer of epithelial cells called endothelium. Endothelial cells, which line all blood vessels, secrete substances that affect the size of blood vessels, reduce blood clotting, and promote the growth of blood vessels. Because arteries carry blood away from the heart, they must be strong enough to withstand the high pressure of the pumping action to the heart. Their elastic walls allow them to expand as the heartbeat forces blood into the arterial system throughout the body. Smaller branches of arteries are called arterioles. Arterioles are thinner than arteries and carry the blood to the tiniest of blood vessels, the capillaries.
Capillaries have walls that are one endothelial cell thick. These delicate, microscopic vessels carry nutrient-rich, oxygenated blood from the arteries and the arterioles to the body cells. There walls are thin enough to allow passage of oxygen and nutrients out of the blood stream and into the tissue fluid surround the cells. Once inside the cells, the nutrients are burned in the presence of oxygen (catabolism) to release needed energy within the cell. At the same time, waste products such as carbon dioxide and water pass out of the cells and into the thin-walled capillaries. The waste filled blood then flows back to the heart in small veins called venules, which branch to form larger vessels called veins.
Veins are thinner walled than arteries. They conduct blood (that has given most of its oxygen) toward the heart from the tissues. Veins have little elastic tissue and less connective tissue than arteries, and blood pressure in veins is extremely low compared with pressure in arteries. In order to keep blood moving back toward the heart, veins have valves that prevent the backflow of blood and keep the blood moving in one direction. Muscular action also helps the movement of blood in veins.
Circulation of Blood
Arteries, arterioles, veins, venules, and capillaries, together with the heart, form a circulatory system for the flow of blood.
Blood deficient in oxygen flows through two large veins, the venae cavae, on its way from the tissue capillaries to the heart. The blood became oxygen-poor at the tissue capillaries when oxygen left the blood and entered the body cells.
Oxygen-poor blood enters the right side of the heart and travels through that side and into the pulmonary artery, a vessel that divides in two, one branch leading to the left lung, the other to the right lung. The arteries continue dividing and subdividing with the lungs, forming smaller and smaller vessels (arterioles) and finally reaching the lung capillaries. The pulmonary artery is unusual in that it is the only artery in the body that carries blood deficient in oxygen.
While passing through the lung (pulmonary) capillaries, blood absorbs the oxygen that entered the body during inhalation. The newly oxygenated blood next returns immediately to the heart through pulmonary veins. The pulmonary veins are unusual in that are the only veins in the body that carry oxygen-rich (oxygenated) blood. The circulation of blood through the vessels from the heart to the lungs and then back to the heart again is known as the pulmonary circulation.
Oxygen-rich blood enters the left side of the heart from the pulmonary veins. The muscles in the left side of the heart pump the blood out of the heart through the largest single artery in the body, the aorta. The aorta moves up at first (ascending aorta) but then arches over dorsally and runs downward (descending aorta) just in front of the vertebral column. The aorta divides into numerous branches called arteries that carry the oxygenated blood to all parts of the body. The names of some of these arterial branches will be familiar to you: brachial (brachi/o means arm), axillary, splenic, gastric, and renal arteries. The carotid arteries supply blood to the head and neck.
The relatively large arterial vessels branch further to form smaller arterioles. The arterioles, still containing oxygenated blood, branch into smaller tissue capillaries, which are near the body cells. Oxygen leaves the blood and passes through the thin capillary walls to enter the body cells. There, food is broken down, in the presence of oxygen, and energy is released.
One metabolic product of this chemical process is carbon dioxide (CO2). Carbon dioxide is produced in the cell but is harmful to the cell if it remains. It must thus pass out of the cells and into the capillary bloodstream at the same time that oxygen is entering the cells. As the blood makes its way back from the tissue capillaries toward the heart in venules and veins it is full of carbon dioxide and is oxygen-poor.
The circuit is thus completed when oxygen-poor blood enters the heart from the venae cavae. This circulation of blood from the body organs (except the lungs) to the heart and back again is called the systemic circulation.
Anatomy of the Heart
The human heart weighs less than a pound, is roughly the size of an adult fist, and lies in the thoracic cavity, just behind the breastbone in the mediastinum (between the lungs).
The heart is a pump, consisting of four chambers; two upper chambers called atria (singular: atrium) and two lower chambers called ventricles. It is actually a double pump, bound into one organ and synchronized very carefully. Blood passes through each pump in a definite pattern. Pump station number one, one the right side of the heart, sends oxygen-deficient blood to the lungs, where the blood picks up oxygen and releases its carbon dioxide. The newly oxygenated blood returns to the left side of the heart to pump station number two and does not mix with the oxygen-poor blood in the pump station number one. Pump station number two then forces the oxygenated blood out to all parts of the body. At the body tissues, the blood loses its oxygen and on return to the heart, to pump station number one, blood poor in oxygen (rich in carbon dioxide) is sent out to the lungs to begin the cycle anew.
Oxygen-poor blood enters the heart through the two largest veins in the body, the venae cavae. The superior vena cava drains blood from the upper part of the body, and the inferior vena cava carries blood from the lower part of the body.
The venae cavae bring oxygen-poor blood that has passed through all of the body to the right atrium, the thin walled upper right chamber of the heart. The right atrium contracts to force blood through the tricuspid valve (cusps are the flaps of the valves) into the right ventricle, which is the lower right chamber of the heart. The cusps on the tricuspid valve form a one-way passage designed to keep the blood flowing in only one direction. As the right ventricle contracts to pump oxygen-poor blood through the pulmonary valve into the pulmonary artery, the tricuspid valve stays shut, thus preventing blood from pushing back into the right atrium. The pulmonary artery then branches to carry oxygen-deficient blood to each lung.
The blood that enters the lung capillaries from the pulmonary artery soon loses its large quantity of carbon dioxide into the lung tissue, and the carbon dioxide is expelled. At the same time, oxygen enters the capillaries of the lungs and is brought back to the heart via the pulmonary veins. The newly oxygenate blood enters the left atrium of the heart from the pulmonary veins. The walls of the left atrium contract to force blood through the mitral valve into the left ventricle.
The left ventricle has the thickest walls of all four heart chambers (three times the thickness of the right ventricle). It must pump blood with great force so that the blood travels through arteries to all parts of the body. The blood is pumped out of the left ventricle through the aortic valve and into the aorta, which branches to carry blood all over the body. The aortic valve prevents the return of aortic blood to the left ventricle once it has been pumped out.
The four chambers of the heart are separated by partitions called septa (singular: septum). The interatrial septum separates the two upper chambers (atria), and the interventricular septum is a muscular wall that comes between the two lower chambers (ventricles).
The heart wall is composed of three layers. The endocardium is a smooth layer of endothelial cells that lines the interior of the heart and heart valve. The myocardium is the middle, muscular layer of the heart and its thickest layer. The pericardium is a fibrous and membranous sac surrounding the heart. It is composed of two layers, the visceral pericardium, which adheres to the heart and the parietal (parietal means wall) pericardium, which lines the outer fibrous coat. The pericardial cavity (Between the visceral and the parietal pericardia normally contains 10 – 15 ml of fluid, which lubricates the membranes as the heart beats.
Physiology of the Heart
Heartbeat and Heart Sounds
There are two phases of the heartbeat. These phases are called diastole (relaxation) and systole (contraction). Diastole occurs when the ventricle walls relax and blood flows into the heart from the venae cavae and the pulmonary veins. The tricuspid and mitral valves are open in the diastole, as blood passes from the right and left atria into the ventricles. The pulmonary and aortic valves are closed during diastole.
Systole occurs next, as the walls of the right and left ventricle contract to pump blood into the pulmonary artery and the aorta. Both the tricuspid and the mitral valves are closed during systole, thus preventing the flow of blood back into the atria.
This diastole-systole cardiac cycle occurs between 70 and 80 times per minute (100,000 times a day). The heart pumps about 3 ounces of blood with each contraction. This means that about 5 quarts of blood are pumped by the heart in 1 minute (75 gallons an hour and about 2000 gallons a day).
Closure of the heart valves is associated with audible sounds such as “lub, dub, lub, dub,” that can be heard when listening to a normal heart with a stethoscope. The “lub” is associated with closure of the tricuspid and mitral valves at the beginning of the systole and the “dub” with the closure of the aortic and pulmonary valves at the end of systole. The “lub” sound is called the first heart sound and the “dub” is the second heart sound because the normal cycle of the heartbeat starts with the beginning of the systole. An abnormal heart sound is known as a murmur.
Conduction System of the Heart
What keeps the heart at its perfect rhythm? Although the heart does have nerves that can affect its rate, they are not primarily responsible for its beat. It is known that the heart starts beating in the embryo before the heart is supplied with nerves and will continue to be in experimental animals even when nerve supply is cut.
Primary responsibility for initiating the heartbeat rests with a small region of specialized muscle tissue in the posterior portion of the right atrium, where an electrical impulse originates. This region of the right atrium is called the sinoatrial node (SA node). The SA node is called the pacemaker of the heart. The current of electricity generated by the pacemaker causes the walls of the atria to contract and force blood into the ventricle (ending diastole).
Almost like ripples in a pond of water when a stone is thrown, the wave of electricity passes from the pacemaker to another region of the myocardium. This region is at the posterior portion of the interatrial septum and is called the atrioventricular node (AV node). The AV node immediately sends the excitation wave to a bundle of specialized muscle fibers called the atrioventricular bundle or bundle of His (pronounced hiss). Within the interventricular septum, the bundle of His divides into the right and left bundle branches, which form the conduction myofibers that extend through the ventricle walls and stimulate them to contract. Thus, systole occurs and blood is pumped away from the heart. A short rest period follows, and then the pacemaker begins the wave of excitation across the heart again.
The record used to detect these electrical changes in heart muscle at the heartbeats is called an electrocardiogram (ECG or EKG, from the Greek root kardia). The normal ECG shows five waves, or deflections, the represent the electrical changes as a wave of excitation spreads through the heart. The deflections are called P, QRS and T waves. The P wave represents electrical activity in the wall of the atria (atrial depolarization). The QRS wave represents ventricular depolarization as electricity passes through the atrioventricular bundle and the ventricular wall. This is the largest wave because the ventricle contains the most muscle. The T wave represents ventricular repolarization, which is when the ventricular wall relaxes and recovers from contraction. The ECG is used to diagnose a heart attack (myocardial infarction, which causes abnormal deflections.
Normal heart rhythm (originating in the SA node and traveling through the heart) is called sinus rhythm. Sympathetic nerves speed up the heart rate during conditions of emotional stress or vigorous exercise. Parasympathetic nerves slow the heart rate when the need for extra pumping is past.
Blood Pressure
Blood pressure is the force that the blood exerts on the arterial walls. This pressure is measured by a device called a sphygmomanometer.
The sphygmomanometer consists of a rubber bag inside a cloth cuff that is wrapped around the upper arm, just above the elbow. The rubber bag is inflated with air by means of a rubber bulb. As the bag is pumped up, the pressure within it increased and is measured on a recording device attached to the cuff.
The vessels in the upper arm are compressed by the air pressure in the bag. When there is sufficient air pressure in the bag to stop the flow of blood in the artery of the arm (brachial artery), the pulse in the lower arm where the observer is listening with a stethoscope) obviously drops.
Air is then allowed to escape from the bag and the pressure is lowered slowly, allowing the blood to being to make its way through the gradually opening artery. At the point where the person listening with the stethoscope first hears the sounds of the pulse beats, the reading on the device attached to the cuff shows the higher, systolic, blood pressure (pressure in the artery when the ventricle is contracting to force the blood into the aorta and other arteries).
As air continues to escape, the sounds become progressiv3e louder. Finally, when a change in sounds from loud to soft occur, the observer makes note of the pressure on the recording device. This is called the diastolic blood pressure (pressure in the artery when the ventricles are relaxing and the heart is filling, receiving blood from the venae cavae and pulmonary veins).
Blood pressure is usually expressed as a fraction: for example, 120/80, in which the 120 represents the systolic pressure and 80 the diastolic pressure.
Pathological Conditions: The Heart and Blood Vessels
Heart
arrhythmias – Abnormal heart rhythms (dysrhythmias). Examples of cardiac arrhythmias:
1. Heart block (atrioventricular block) – Failure of proper conduction of impulses through the AV node to the atrioventricular bundle (bundle of His). Damage to the SA node may cause its impulses to be too weak to activate the AV node and impulses fail to reach the ventricles. If the failure occurs only occasionally, the heart will miss a beat in a rhythm at regular intervals (partial heart block). If no impulses reach the AV node from the SA node, the ventricles contract slower than the atria and are not coordinated. This is complete heart block. Implantation of a cardiac pacemaker can overcome heart block and establish a normal rhythm.
2. Flutter – Rapid but regular contractions of atria or ventricles. This condition can occur in patients with heart disease. The heart rhythm may reach up to 300 beats per minute.
3. Fibrillation – Rapid, random, ineffectual, and irregular contractions of the heart (350 beats or more per minute). In atrial fibrillation, the wave of excitation passes through the atrial myocardium even more quickly than in atrial flutter. In order to restore normal heart rhythm, an electrical device called a defibrillator is applied to the chest wall; this electric shock stops the heart and reverses its abnormal rhythm. This is also called cardioversion. Drugs, such as digoxin may also be used to convert fibrillation into regular rhythm.
A device called an automatic implantable cardioverter/defibrillator (AICD) can now be implanted in the chest to sense arrhythmias and correct them. These are pacemaker-sized devices that give shocks to change abnormal rhythms, such as ventricular fibrillation.
Radiofrequency catheter ablation (RFA) is a nonsurgical treatment used to treat arrhythmias, such as paroxysmal (sharp, sudden spasm) tachycardia. A catheter, placed in blood vessels leading up against the heart muscle, delivers a high-frequency current to burn a small portion of the muscle. This injury (ablation) to the muscle destroys the arrhythmias.
Cardiac arrest is the sudden and often unexpected stoppage of heart movement, caused by heart block or ventricular fibrillation (resulting from underlying heart disease).
Palpitations are uncomfortable sensations in the chest associated with different types of arrhythmias. Palpitations do not necessary indicate serious heart disease (smoking, caffeine, and drugs such as antidepressants can produce palpitations). Two cardiac causes of palpitations are premature ventricular contractions (PVCs) and premature atrial contractions (PACs).
Congenital heart disease – Abnormalities in the heart at birth. The following are congenital anomalies resulting from failure in the development of the fetal heart.
1. Coarctation of the aorta (CoA) – Narrowing (coarctation) of the aorta. Surgical treatment consists of removal of the constricted region and end-to-end anastomosis of the aortic segments.
2. Patent ductus arteriosus (PDA) – A small duct (ductus arteriosus between the aorta and the pulmonary artery, which normally close soon after birth, remains open (patent). This condition means that the oxygenated blood flow from the aorta to the pulmonary artery. The anomaly occurs most often in females and is commonly associated with intrauterine rubella (German measles) infection, prematurity, and infantile respiratory distress syndrome. Treatment is surgery to close the ductus arteriosus open.
3. Septal defects – Small holes in the septa between the atria (atrial septal defects [ASDs]) or the ventricle (ventricular septal defects [VSDs]). Although many septal defects will close spontaneously, others will require surgery. Septal defects can be closed while maintaining a general circulation by means of a heart-lung machine. This machine is connected to the patient’s circulatory system and relieve the heart and lungs of pumping and oxygenation functions during heart surgery.
Two recent procedures as alternatives to traditional surgery are transcatheter closure (a “clamshell” device is threaded through the blood via a catheter into the heart and into the septal defect, where it is fixed in place to block the hole) and minimally invasive heart surgery (through 3 or 4 small puncture holes in the chest; special instruments are used to repair the defect).
4. Tetralogy of Fallot – A congenital malformation of the heart involving four (tetra) distinct defects. The condition, named for Etienne Fallot, the French physician who described it in 1888. The four defects are:
A. Pulmonary artery stenosis. This means that blood is not adequately passed to the lungs for oxygenation.
B. Ventricular septal defect. The gap in the septum allows deoxygenated blood to pass into the left ventricle, and from there to the aorta.
C. Shift of the aorta to the right, so that the aorta overrides the interventricular septum. Oxygen-poor blood passes even more easily from the right ventricle to the aorta.
D. Hypertrophy of the right ventricle. The myocardium has to work harder to pump blood through a narrowed pulmonary artery.
An infant with this condition is described as a “blue baby” because of the extreme degree of cyanosis present at birth (other congenital conditions that involve a shunt of blood from the right to the left without passing through the lungs and receiving proper oxygenation can lead to cyanosis as well). Surgery is required to repair the various heart defects.
Congestive heart failure – The heart is unable to pump its required amount of blood (more blood enters the heart from the veins than leaves through the arteries). Blood accumulates in the lungs (left-sided heart failure) causing pulmonary edema (fluid seeps out of capillaries into the tiny air sacs of the lung). Damming back of blood resulting form right-sided heart failure results in accumulation of fluid in the abdominal organs (liver and spleen) and subcutaneous tissue of the legs. Congestive heart failure often develops gradually over several years, although it can be acute. Therapy includes lowering dietary intake of sodium and diuretics to promote loss of fluids.
Recent studies have shown that drugs known as angiotensin-converting enzyme (ACE) inhibitors can improve the performance of the heart and its pumping activity. These drugs also decrease pressure inside blood vessels and are used to treat hypertension (high blood pressure). If drug therapy and lifestyle changes fail to control congestive heart failure, heart transplantation may be the only treatment option. While waiting for a transplant, patients may need a device to assist the heart’s pumping. A left ventricular assist device (LVAD) is a booster pump implanted in the abdomen, with a cannula (tube) inserted into the left ventricle. It pumps blood out of the heart to all parts of the body. The LVAD is sometimes called a “bridge to transplant.”
Coronary artery disease (CAD) – Disease of the arteries surrounding the heart. The coronary arteries are three large vessels that arise from the aorta and supply oxygenated blood to the heart. It is interesting that the blood that constantly flows through the four hollow chambers of the heart does not itself nourish the myocardial tissue. Instead, after blood leaves the heart via the aorta, a portion is at once lead back over the surface of the heart through the coronary arteries, so that the heart muscle receives blood before any other organ. This seems logical because the energy requirements of the heart are greater than those of any other organ.
Coronary artery disease is usually the result of atherosclerosis. This is the deposition of fatty compounds on the inner lining of the coronary arteries (any other artery can be similarly affected). The ordinary smooth lining of the artery becomes roughened as the atherosclerotic plaque collects in the artery.
Atherosclerosis is dangerous for two important reasons. First, narrowing of the vessel due to atherosclerosis can cause inflexibility and plugging up of the vessel. Second, the roughened lining of the artery may rupture or cause abnormal clotting of blood, leading to a thrombotic occlusion (blocking of the coronary artery by a clot). In both cases, blood flow is decreased (ischemia) or stopped entirely, leading to death (necrosis) of a part of the myocardium. The area of dead myocardial tissue is known as an infarction. The infarcted area is eventually replaced by scar tissue.
The severity of a myocardial infarction (also known as a heart attack) depends on the size of the artery that is blocked and the extent of the blockage. If the blocked artery is small, the result may be death of only a small portion of the heart immediately fed by the artery. After scar tissue forms, the patient may be able to resume completely normal activity.
Angina pectoris is an episode of chest pain, often called precordial pain (precordial means in front of the chest), resulting from a temporary difference between the supply and the demand of oxygen to the heart muscle. Angina can be the result of low oxygen levels in the blood from smoking or respiratory disease), restricted blood flow to the heart (coronary artery disease), or an increase in the work of the heart beyond normal levels. For acute attacks of angina, nitroglycerine is given sublingually. This drug, one of several called nitrates, is a powerful vasodilator and muscle relaxant.
Treatment guidelines for CAD begin with controlling risk factors, such as smoking, obesity, and lack of exercise. Daily aspirin therapy (to prevent formation of clots) and drug therapy to lower cholesterol (HMGs or “statins” reduce the production of cholesterol in the liver) are also important to prevent heart disease. After the occurrence of an MI, patients may require maintenance and anti-ischemic therapy with drugs called beta-blockers, which reduce the force and speed of the heartbeat and lower blood pressure. Other drugs, such as nitrates and calcium channel blockers, cause dilatation of blood vessels, making it easier for the heart to pump blood through vessels.
Surgical treatment of CAD is an open-heart operation called coronary artery bypass grafting or CABG. Experimental keyhole (scopic) bypass grafting is being done on a very limited basis with limitations of a maximum of 3-vessel grafting being done. Cardiologist perform percutaneous transluminal coronary
angioplasty (PTCA), in which catheterizations with balloons and stents opens clogged coronary arteries.
An innovation method of treatment is transmyocardial laser revascularization (TMLR). A laser makes holes in the heart muscle to induce angiogenesis (growth of new blood vessels). Gene therapy (giving DNA or viruses containing DNA to promote expression of factors that lead to angiogenesis) is another new technique to restore damaged heart muscle.
Endocarditis – Inflammation of the inner lining of the heart caused by bacteria (bacterial endocarditis). This condition may be a complication of another infectious disease, an operation, or an injury. Damage to the heart valves produces lesions called vegetations (they resemble cauliflower) that break off into the bloodstream as emboli (material that travels through the blood). When the emboli lodge in the small vessels of the skin, multiple pinpoint hemorrhages known as petechiae (from the Italian petechio, meaning a fleabite) form. Antibiotics are effective in curing bacterial endocarditis.
Hypertensive heart disease – High blood pressure affecting the heart. This condition is caused by the contraction of arterioles leading to increased pressure in arteries. The heart itself is affected because it has to pump more vigorously to overcome the increased resistance in the arteries. Vessels lose their elasticity, become like solid pipes, and place increased burden on the heart to pump blood through the body.
Mitral valve prolapse (MVP) – Improper closure of mitral valve when the heart is pumping blood. This condition, found most frequently in otherwise healthy young women occurs because the mitral valve enlarges and prolapses into the left atrium during systole. The physician hears a midsystolic click on auscultation (listening with a stethoscope). Most people with MVP live normal lives, but because prolapsed valves can on rare occasions become infected, persons with MVP are advised to have preventive antibiotics at the time of dental procedures if the murmur is present.
Murmur – An extra heart sound, heard between normal beats. Murmurs are heard with the aid of a stethoscope and are usually caused by a valvular defect or disease that disrupts the smooth flow of blood in the heart. They are also heard in cases of interseptal defects when blood flows abnormally between chambers through holes in the septa. A functional murmur is one that is not caused by a valve or septal defect and is not a serious danger to the patient’s health. A bruit is an abnormal sound or murmur heard on auscultation. A thrill, which is a vibration felt on palpation of the chest often accompanies a murmur.
Pericarditis – Inflammation of the membranes (pericardium) surrounding the heart. In most instances, pericarditis is secondary to disease elsewhere in the body (such as pulmonary infection). Bacteria and viruses cause the condition, or the etiology may be idiopathic. Malaise, fever and chest pain occur, as well as accumulation of fluid within the pericardial cavity. Compression of the heart due to collection of fluid is called cardiac tamponade. If a considerable amount of fluid is present, pressure on the pulmonary veins may slow the return of blood from the lungs. Excess fluid is drained by pericardiocentesis.
Rheumatic heart disease – Heart disease caused by rheumatic fever. Rheumatic fever is a disease, usually occurring in childhood that can follow a few weeks after a streptococcal infection. Damage is done to the heart, particularly the heart valves, by one or more attacks of rheumatic fever. The valves, especially the mitral valve, become inflamed and scarred (with vegetations, so that they do not open and close normally. Mitral stenosis, atrial fibrillation, and congestive heart failure, due to weakening of the myocardium, are other aspects of rheumatic heart disease. Treatment consists of reduced activity, drugs to control arrhythmias, surgery to repair a damaged valve, and anticoagulant therapy to prevent emboli from forming. Mechanical or porcine (pig) valve implants are also used to replace deteriorated heart valves.
Blood vessels
Aneurysm – Local widening (ballooning out of a small area) of an artery caused by weakness in the arterial wall or breakdown of the wall owing to atherosclerosis. Aneurysm literally means to widen (eurysm) up (ana-). It may occur anywhere in the body but most commonly in the aorta. The danger of an aneurysm is that as the wall of the artery pushes outward it becomes progressively thinner and may eventually rupture. Treatment of an aneurysm depends on the particular vessel involved, the site, and the health of the patient. In aneurysms of small vessels in the brain (berry aneurysm), treatment is occlusion of the vessel with small clips. For larger arteries, such as the aorta, the aneurysm is resected and a synthetic graft is sewn within the aneurysm.
Hypertension – high blood pressure. Most high blood pressure is essential hypertension, in which the cause of the increased pressure is idiopathic. In adults, a blood pressure equal to or greater than 140/90 mmHg is considered high. Diuretics, beta-blockers, ACE inhibitors and calcium channel blockers are used as treatment for essential hypertension. Losing weight, limiting sodium (salt) intake, stopping smoking, and reducing fat in the diet are also important in therapy.
In secondary hypertension, there is always some associated lesion, such as glomerulonephritis, pyelonephritis or disease of the adrenal glands, that is responsible for the elevated blood pressure.
Peripheral vascular disease – Blockage of blood vessels (arteries) in the lower extremities due to atherosclerosis. When arteries in the groin or upper leg narrow or become blocked, blood flow to the lower leg and foot is reduced. Often, the femoral (thigh) artery or the popliteal (back of the knee) artery is involved. An early sign of the problem is intermittent claudication (absence of pain or discomfort in the leg at rest, but pain, tension, and weakness after walking has begun). Treatment is exercise, avoidance of nicotine, which causes vessel constriction, and control of risk factors such as hypertension, hyperlipidemia and diabetes. Surgical treatment includes endarterectomy and bypass grafting (from the normal proximal vessel around the diseased area to a normal vessel distally.
Raynaud phenomenon – Short episodes of pallor and numbness in the fingers and toes due to temporary constriction of the arterioles in the skin. This condition is usually idiopathic, but it may also be secondary to some other, more serious disorder. The episodes can be triggered by cold temperatures, emotional stress, or cigarette smoking. Protecting the body from cold and use of vasodilators are effective treatment.
Varicose veins – Abnormally swollen and twisted veins, usually occurring in the legs. This condition is due to damaged valves that fail to prevent the backflow of blood. The blood then collects in the veins, which distends to many times their normal size. Because of the slow flow of blood in the varicose veins and frequent injury to the vein, thrombosis may occur as well. Hemorrhoids (piles) are varicose veins near the anus. Surgical treatment of hemorrhoids includes injection of the sclerosing solutions, ligation with rubber bands, and cryosurgery.
Treatment of varicose veins includes wearing elastic stockings, elevation of the legs if edema occurs, and surgery to ligate (tie off) and strip (remove) the twisted, swollen veins. The surgical procedure is called vein stripping.
Laboratory Tests and Clinical Procedures
Laboratory Tests
Lipid tests – Lipids are fatty substances found in foods and in the body. Examples of lipids are cholesterol and triglycerides. Lipid tests measure the amounts of these substances in a blood sample. High levels of triglycerides and cholesterol in the blood are associated with a greater risk of atherosclerosis. A cholesterol level below 200 mg/dL in a middle-aged adult is associated with a relatively low risk for coronary artery disease (CAD). A diet high in saturated fat (solid fats of animal origin such as milk, butter, and meats) tends to increase the amount of cholesterol in the blood. Polyunsaturated fats (such as corn oil and safflower oil) do not raise blood cholesterol.
The mainstay of treatment for people with hyperlipidemia is proper diet (low fat and high fiber intake with fresh fruits and vegetables) and exercise. Niacin (a vitamin) is also helpful in reducing lipids. Drug therapy includes HMG reductase inhibitors (HMGs), which lower cholesterol by reducing its production in the liver. These are known as “statins” and examples are simvastatin, lovastatin, and pravastatin.
Lipoprotein electrophoresis – Lipoproteins are proteins that carry lipids (fats) n the bloodstream. Protein electrophoresis is the process of physically separating lipoproteins from a blood sample. High levels of low-density lipoproteins (LDL and very-low-density lipoproteins (VLDL) are associated with atherosclerosis. High levels of high-density lipoproteins (HDL), which remove cholesterol and transport it to the liver, protect adults from the development of atherosclerosis. Factors that increase HDL are estrogen, exercise and alcohol in moderation.
Serum enzyme tests – During a myocardial infarction, enzymes are released into the bloodstream from the dying heart muscle. These enzymes can be measured and are useful as evidence of an infarction. The enzymes tested for are creatine phosphokinase (CPK or CK) and lactate dehydrogenase (LDH). Other blood testes measure levels of muscle proteins, myoglobin and troponin.
Clinical Procedures
X-rays
Angiography – Dye is injected into the blood stream or heart chamber, and x-ray films are taken of the heart and large blood vessels in the chest. If dye is injected into the aorta or an artery in the groin, the procedure is called arteriography.
Digital subtraction angiography (DSA) – Video equipment and a computer are used to produce x-ray pictures of blood vessels. First, an x-ray is produced of the area to be studied, and the results are stored in a computer. Next, contrast material is injected into a vein, and a second image is produced that is also recorded in the computer. The computer then compares the two images and subtracts the first image from the second (removing parts not being studied such as bone, muscle, and fat), leaving nothing but an image of the contrast medium and vessels.
Ultrasound Tests
Doppler ultrasound – An instrument is used to focus sound waves on a blood vessel; blood flow is measured as echoes bounce off red blood cells. Velocity of blood flow increases in areas of stenosis. Arteries or veins in the arms, neck or legs are examined to detect vascular occlusion (blockage due to clots or atherosclerosis).
Echocardiography (ECHO) – Pulses of high-frequency sound waves (ultrasound) are transmitted into the chest, and echoes returning from the valves, chambers, and surfaces of the heart are electronically plotted and recorded.
Nuclear Cardiology
Positron emission tomography (PET) scan – An IV radiopharmaceutical is administered, followed by an injection of glucose. These localize in the myocardium. Uptake is proportional to the glucose metabolic activity of myocardial cells. Images showing the blood flow and functional activity of the myocardium are obtained. Indications for PET scanner use include detection of CAD, assessment of myocardial viability, and differentiation of ischemia and cardiomyopathy.
Thallium 201 scintigraphy – Thallium 201 is a radioactive isotope that is taken up by myocardial tissue. After intravenous injection, the concentration of thallium 201 is measured (by perfusion scanning). Infarcted or scarred myocardium does not extract any isotope, showing up as “cold spots.” Thallium 201 imaging can be performed before or after an exercise ECG study or as a resting study only.
Technetium 99m ventriculography (multiple-gated acquisition scan, or MUGA scan) – This radioactive test studies the motion of the left ventricular wall and measures the ventricle’s ability to eject blood. It is a test of the functioning of the heart and cardiac output.
Magnetic Resonance Imaging (MRI)
Cardiac MRI – Magnetic waves are beamed at the heart, and an image is produced. The procedure is used to obtain detailed information about congenital heart disease, cardiac masses, and lesions of large blood vessels prior to surgery.
Other Procedures
Cardiac catheterization – A thin, flexible tube (catheter) is introduced into a vein or artery and is guided into the heart for purposes of detecting pressures and patterns of blood flow. Contrast can also be injected and x-ray films made (angiography).
Cardioversion (defibrillation) – Very brief discharges of electricity are applied across the chest to stop a cardiac arrhythmia and to allow a more normal rhythm to begin.
Coronary bypass surgery (CABG) – Vessel grafts, consisting of veins taken from other parts of the body, are anastomosed (connected) to existing coronary arteries to detour around blockages in the coronary arteries and keep the myocardium supplied with oxygenated blood. Minimally invasive CABG surgery is performed with smaller incisions instead of traditional sternotomy to open the chest.
Electrocardiography (ECG, EKG) – Process of recording the electricity flowing through the heart and thus the rhythm of the heartbeat. A normal sinus rhythm begins in the SA nodes and is between 60 and 100 beats per minute, with normal intervals and no ectopic beats.
Endarterectomy – This procedure involves surgical removal of the innermost (end-) lining of an artery when it is thickened by fatty deposits (atheromas) and thromboses.
Extracorporeal circulation (ECC) – A heart-lung machine (pump oxygenator) is used as a bypass to divert blood from the heart and lungs while the heart is being repaired. Blood leaves the body, enters the heart-lung machine, where it is oxygenated, and then returns to a blood vessel (artery) to circulate through the bloodstream. Extracorporeal means outside (extra-) the body (corpor/o).
Holter monitoring – A compact version (about the size of a portable tape player) of an electrocardiograph (instrument to measure the electricity flowing through the heart) is worn during a 24-hour period to detect cardiac arrhythmias.
Percutaneous transluminal coronary angioplasty (PTCA) – In this procedure, also called balloon angioplasty, a balloon-tipped catheter is inserted via the femoral (thigh) artery and threaded up the aorta into a coronary artery. The balloon is inflated, compressing fatty deposits or plaque against the side of the artery and opening the artery to allow for passage of blood. Balloon valvuloplasty is used to open narrowed cardiac valves and is seen as a possible alternative to surgery for valvular stenosis. Stents (expandable slotted tubes are now used instead of PTCA to create wider lumens and make restenosis less likely.
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