A clear picture of the normal structure of and circulation through the heart is critical to understanding this lecture. Your text can provide this information.

I.               CONGENITAL DEFECTS OF THE HEART

The embryonic heart starts out as a tube-like structure that folds in upon itself and then becomes divided into its chambers by formation of septa. The truncus arteriosus divides to form the aorta and pulmonary artery.

The septa grow in from the top and bottom of the heart to form the chambers, and the developing heart folds in upon itself as well.  The ventricle is divided in two by the interventricular septum. The atrium is first divided in two by the septum primum; separation is completed by the septum secundum. The atria and ventricles are divided in the region of the atrioventricular canal, as the endocardial cushion expands. The septation of atria is more complicated than that of ventricles.

Most congenital problems arise from failure of the septa to form properly:

• Ventricular septal defect (VSD): an opening is present between the right and left ventricles. This is the most common major congenital anomaly of the heart ("hole in the heart").

A convenient way of classifying congenital anomalies is by whether they produce cyanosis ("blue-baby") as a consequence of insufficient oxygenated blood reaching the tissues. Blood in the left ventricle, which is oxygenated, is at higher pressure than blood in the right ventricle, which is not oxygenated. Therefore, with a VSD, the nonoxygenated blood in the right ventricle does not get mixed in with the oxygenated blood in the left ventricle (although the opposite certainly occurs). Therefore, oxygenated blood gets out into the tissues and there is no cyanosis.  Later in life, changes may occur that result in reverse shunting, and cyanosis may indeed develop.

VSD is relatively easy to repair surgically.

·       Atrial septal defect: An opening called the foramen ovale is present between the two atria during fetal life. In about 1 of 5 adults, this structure, which normally closes, is still open or patent. However, it is usually still functionally closed by a flap. This flap is kept shut by the relatively high pressure of the blood in the left atrium. It usually only causes a problem if the pressure in the right atrium is increased, which can happen due to a variety of reasons (e.g., cor pulmonale, which refers to right ventricular failure as a consequence of lung disease).

A true atrial septal defect, involving incomplete septation and the presence of an actual hole, may have more serious consequences. However, it does not cause cyanosis for the same reasons that a VSD does not. True atrial septal defects are not as common as VSDs.

·       Transposition of the great vessels: During development, a spiraling or helical septum forms down the length of the truncus arteriosus to divide it into the aorta and the pulmonary artery. If the septum does not spiral properly, these vessels end up attached to the heart in a reversed manner (called transposition). That is, the aorta comes off of the right rather than left ventricle, and the pulmonary artery comes off of the left ventricle. As a consequence, the aorta takes unoxygenated blood from the body and pumps it right back out, bypassing the lungs. The pulmonary artery simply sends the same blood back through the lung over and over. In other words, two closed loops are formed, and blood from the body never gets oxygenated. This, of course, produces cyanosis and is incompatible with life unless some other defect (like a VSD or a patent ductus arteriosus) allows mixing of the blood. If the diagnosis is made immediately after birth, sometimes a catheter is used to tear a hole between the atria to allow mixing of blood until further surgery can be performed.

·       Truncus arteriosus: Here the septation of the truncus arteriosus is incomplete, so that the aorta and pulmonary artery are fused into one vessel as they come off of the heart (i.e., the fetal truncus arteriosus persists as one vessel). This situation is not incompatible with life but obviously is very inefficient, since blood coming out of the heart goes randomly to the arterial or venous circulations.  This condition is often accompanied by a VSD.

• Tetralogy of Fallot: The truncus arteriosus becomes divided, but the septation is off-center so structures don't join up to the heart where they should (see page 302 in the text). Basically, the pulmonary artery is too small, and the aorta is too big. The four anomalies that constitute this condition are:

1.     Pulmonic valve stenosis: the pulmonary valve and artery are narrowed and allow insufficient blood flow to the lungs.

2.     Over-riding aorta: the too-big aorta connects to or "over-rides" both the right and left ventricles, and so receives blood from both. This means that unoxygenated blood from the right ventricle is going out to the body.

3.     Ventricular septal defect: part of the defective septation that occurs.

4.     Right ventricular hypertrophy: a consequence of the right ventricle trying to push enough blood through the narrowed pulmonary artery, compensate for the VSD, and cope with the higher than normal pressure of the left ventricle.

Because unoxygenated blood is being sent out through the aorta and because blood flow to the lungs is impaired, this condition results in a cyanotic baby. Upon X-ray, the heart often looks "boot-shaped." This is a relatively common condition that can be treated surgically.  Children with this condition often assume a squatting position, which seems to make them feel better.

• Patent ductus arteriosus: The ductus arteriosus is a short vessel that connects the aorta to the pulmonary artery during fetal life to allow blood to bypass the lungs. This structure normally closes after birth, but it may remain open or patent. This condition does not lead to cyanosis, because pressure in the aorta is higher than pressure in the pulmonary artery. Therefore, already oxygenated blood from the aorta will be shunted into the pulmonary artery and back to the lungs. In this condition, too much blood is being sent to the lungs. It is a condition that is hard on the lungs, but it does not produce cyanosis. It can be closed off surgically with a ligation or treated with drugs.

• Coarctation of the aorta: Results from a narrowing or stenosis of the aorta. It usually lies beyond where the arteries to the head and arms branch off, so a diagnostic sign is high blood pressure in the upper extremities and low blood pressure in the lower extremities. The skin color may differ in the extremities due to the different perfusions. The body often compensates for this condition by developing a collateral circulation that helps to bypass the narrowed vessel. This condition can be treated surgically.

• Hypoplastic left heart:  refers to a condition in which the heart has little or no left ventricle.  The only hope for a cure is a heart transplant, which is problematic due to the lack of availablity of neonatal hearts.

II.             MYOCARDIAL INFARCTION (ISCHEMIC HEART DISEASE)

The coronary arteries do not have a good collateral system, so when they are occluded, a heart attack results. The symptoms of an MI include a crushing, substernal chest pain, often radiating down the left side, and faintness or lightheadedness. Risk factors are many, including heredity, age, diet, stress, smoking, hypertension, obesity, levels of LDL, diabetes, and gender. Estrogens appear to protect women from MI prior to menopause, and hormone replacement therapy after menopause may also be protective. Some of the risk factors, such as hypertension and smoking, are thought to predispose to MI by damaging the endothelial lining of the blood vessels. It is truly a multifactorial disease, with many different causes.

Atherosclerosis (meaning "lipid scarring") underlies ischemic heart disease. Atherosclerosis arises from a complex interplay between endothelial cells, macrophages, platelets, and smooth muscle cells. A late consequence of atherosclerosis is so-called "hardening of the arteries," which results from calcification of the atherosclerotic lesions.

Stages of atherosclerosis are thought to be:

1. Damage to the endothelial lining of the artery (e.g., from nicotine or hypertension)
2. Adherence of platelets to the vessel wall, with accompanying release of growth factors
3. Migration of smooth muscle cells into the intimal layer of the vessel, along with proliferation in response to the growth factors.
4. Accumulation of macrophages, deposition of connective tissue, accumulation of lipids, calcification.

The lipids that accumulate tend to be low-density lipoproteins (LDLs -- think of "L" for "lousy." The "good" lipoproteins are high-density lipoproteins, or HDLs -- think of "H" for "happy.") The atheroma or atherosclerotic plaque may, by itself, narrow the lumen of the vessel. An atherosclerotic plaque has a central core containing lipid, cholesterol, and foam cells (which are macrophages that have become filled with large amounts of lipids). It is covered by a fibrous cap. If the cap is fragile and/or calcified, it may rupture or ulcerate (perhaps as a consequence of stress, spasm, or smoking). A thrombus may then form on top, which can completely block the vessel, leading to ischemia and perhaps an MI. In large vessels such as the aorta, mural thrombi that are confined to the wall of the vessel and which do not occlude the lumen are more often seen. Some patients have apparent occlusion even though there is no recognizable thrombus; spasm of the vessel may play a role in these instances.

Increased physical demand may put increased stress on the heart. Coronary arteries fill during diastole. The faster the heart beats, the shorter diastole is, and the less perfusion there is of coronary arteries. Increased stress may also come about due to anemia, blood loss, a sudden shift to a high altitude, etc.

There are multiple possible outcomes of ischemia, including no symptoms, coronary artery disease, acute myocardial infarction (which is ischemic necrosis of heart tissue), heart failure (a loss of the ability of the heart to pump effectively), death, or angina pectoris, which is chest pain that is felt upon exertion or stress and is relieved by rest or nitroglycerin. (There are other forms of angina that can be felt even at rest.) It has been noted that many people who have collapsed due to coronary artery ischemia and have been revived have not had an MI - their heart muscle is okay; collapse may have been due to an arrhythmia brought about by ischemia. Also, heart failure may occur without a recognized MI; many small subclinical events may damage the heart muscle to the point where it is no longer able to pump effectively.

Treatments for coronary artery disease include bypass surgery, wherein a saphenous vein from the leg or an internal mammary artery is used to circumvent the area of blockage (the artery holds up better than the vein; often the left internal mammary artery (LIMA) is used). Also used is balloon angioplasty, wherein a catheter is threaded into the artery and a balloon on its tip is inflated to literally squash the atheroma. A problem is that this procedure can also tear the plaque, which may lead to thrombosis. Sometimes a stent (plastic or metal mesh cylinder) is placed in the vessel to hold it open. This, too, may promote formation of a thrombus. Lastly, a "mini-rotorooter" can be used to shave off the plaque and capture any bits that are removed. This is called directed coronary atherectomy (DCA). These are all very common but controversial procedures.

Treatment for MI: MIs often don't occur all at once but progress over a period of hours to days. They often start at the subendocardium. Sometimes they stop there; other times they progress to a transmural infarct. This means that there is some time for early intervention. One intervention becoming widely used is infusion of anti-thrombolytic agents that dissolve clots (e.g., streptokinase or tPA; see the lecture on blood).

A subendocardial infarct involves just the inner wall of the heart; a transmural infarct involves the full thickness of the heart muscle.

Complications of myocardial infarcts include:

• Mural thrombi (mural refers to the wall of the heart): these can break off to form emboli that travel to other parts of the body (e.g., causing stroke).
• Scarring and loss of function with compensatory hypertrophy of undamaged parts of the heart. Thinning in the scarred region can lead to heart failure.
• Congestive heart failure: heart lacks sufficient muscle to pump sufficient blood.
• Damage to papillary muscles supporting heart valves: may lead to a murmur. These muscles can also rupture, which usually leads to death when rupture is complete.
• Formation of aneurysms (outpouchings of wall of heart where it is scarred and thin): These aneurysms contain tough scar tissue so they don't usually rupture, but they may cause problems as sites for formation of thrombi or in causing arrhythmias.
• Ventricular rupture: usually occurs within the first week after the MI, when the damaged tissue is still weak, is being lysed and removed by phagocytic cells, and has not yet been replaced by tougher scar tissue. Myocardial rupture is usually fatal.   Rupture usually occurs at the junction between living and dead tissue.
• Tamponade: Blood collects around heart in the pericardial space, preventing it from beating.
• Acquired VSD: may result from necrosis of tissue
• Arrhythmia: damaged muscle may lead to an irritable focus, sending out abnormal electrical impulses.
• Pericarditis (inflammation of the pericardium surrounding the heart): is due to death of underlying tissue. It can be immediate, or sometimes there is a delayed pericarditis about 2 weeks after the heart attack. This is immunologically mediated -- the body mounts an immune response to the infarcted, damaged tissue. The immune response can also damage surrounding healthy tissue, resulting in pericarditis. This same process can also occur following heart surgery.

The first tool that should be used to diagnose an MI is the EKG. Enzymes that are released from the damaged cardiac muscle cells into the blood can also be used to diagnose an MI. The MB form of creatine phosphokinase (CPK or CK) is very specific for cardiac muscle cells. It rises rapidly, but also disappears first. SGOT (also known as AST) and HBDH (also known as lactate dehydrogenase or LDH) appear later, but are less specific markers. LDH remains elevated longest but is not specific. A new test looks for the protein troponin, which is a cytoskeletal protein released from dead cardiac muscle cells. It both rises quickly and stays elevated, but it is also not specific to cardiac muscle.

The location of an MI depends on which vessel becomes occluded. The left coronary artery nourishes a large part of the heart. One of its two branches, the left anterior descending coronary artery, is the most common site for an occlusion. The symptoms may vary depending on which part of the heart is damaged.

III.           VALVULAR DISEASE

You should know the locations of the various heart valves and how they function under normal circumstances. Abnormal functioning of the valves can be assessed by echocardiograms, which look at the reflection of sound waves.

Improper closing of the valves can result from improper functioning of supporting structures (such as papillary muscles and chordae tendineae, which control the operation of the mitral and tricuspid valves) and/or from dilation of the heart. The valves are dependent on the proper narrowing of the heart with each beat to allow the flaps of the valve to meet. Digitalis, which causes the heart to contract more strongly, may help to improve valvular function. Improper functioning of the valves can be diagnosed by listening for murmurs.

Leakage through the valves is also called insufficiency or regurgitation.

Aortic valve: Senile calcific aortic stenosis is a disease that is most common in elderly men. It is due to wear and tear on the valve. The valve becomes calcified and stiff, so it doesn't move well. Blood doesn't flow well in either direction. Most aortic valve problems are more common in men, mitral valve problems in women.

Bicuspid aortic valve: One in a hundred people is born with an aortic valve that has only two leaflets, rather than the usual three; indeed, this is the most common cardiovascular abnormality. In their youth, people usually tolerate this condition well. But as they reach their 50's, the valve may become calcified, stenotic, and prone to infection (as are all abnormal heart valves -- with the possible exception of a prolapsed mitral valve without murmur). This stenosis tends to occur at an earlier age than in people with the normal tricuspid aortic valve, since damage due to wear and tear is accelerated.

Mitral valve: The leaflets of the mitral valve are attached to the papillary muscles by chordae tendineae. Six to eight percent of women have some degree of a mitral valve problem. The cause is unknown. In most, but not all, women, it is asymptomatic or minimally symptomatic. In instances where there is leakage of the valve, women may need to take prophylactic antibiotics for dental work and other procedures that risk introducing bacteria into the bloodstream. Mitral valve problems are much rarer in men, but tend to be more serious when they do occur. Current surgical therapy tries to take a "tuck" to tighten up the valve, which is also supported with a prosthetic ring.  Changes related to mitral valve prolapse, listed in order of increasing severity, can be classified as follows:

1. Billowing: valve extends backwards like a parachute, but there is no leakage. May hear a mid-systolic click, but no murmur.
2. Prolapse: billowing along with leakage (regurgitation). May hear a murmur or mid-systolic click.
3. Floppy valve
4. Floppy and flail: chordae tendineae are ruptured; must be treated surgically.

Rheumatic fever: This disease seems to be confined to certain communities, but it is on the uprise, perhaps due to a change in the strain of Streptococcus that is involved. It is not the same as scarlet fever, although both diseases are due to strep infections. Scarlet fever is caused by a toxin released from strep bacteria that are infected with a bacterial virus (bacteriophage). Scarlet fever has no direct effects on the heart. Rheumatic fever is caused by Group A b -hemolytic strains of strep.

Rheumatic fever arises only from strep throats and not from strep infections elsewhere in the body, for unknown reasons. Strep throats are usually diagnosed by culture or by the Q (for quick) test, which detects streptococcal antigens (not antibodies, which would take weeks to develop). Q tests are reliable if performed properly, but often they are not. A negative Q-test should probably be backed up with a traditional throat culture.

Rheumatic fever involves an immunological process called molecular mimicry, wherein antibodies that the body produces against molecules on the strep bacterium cross-react with similar-looking molecules in the heart, nervous system, skin, and joints. That is, antigens on the strep mimic the body's own antigens. Action of these antibodies against the nervous system and joints usually lead to only temporary problems, but an attack against the heart valves can lead to permanent damage. The valves may become stenotic or hardened. When this happens to the mitral valve, it takes on a "fish-mouth" appearance with only a slit-like opening. Damage may occur to any of the valves. Damage to and subsequent scarring of valves in rheumatic fever occurs at the corners or commissures of the valves, which become stenotic. The valve cannot close in the center. The effect is similar to what would happen if you sewed just the corners of your mouth shut. Along with the stenosis, there is insufficiency (regurgitation) of the affected valve. The damage becomes worse with each round of infection. Fortunately, the incidence of this disease is decreasing in the US, and it is now a relatively rare condition.   It is important to continue antibiotic therapy for strep throat long enough to eliminate all organisms to prevent rheumatic fever.

Marfan's Syndrome: This is a hereditary disease marked by abnormal, weakened connective tissue. As a consequence, the aorta may dilate, leading to insufficiency of the aortic valve. This process is called annuloaortic ectasia. Aneurysms due to tertiary syphilis may also lead to aortic valve insufficiency.

Endocarditis is infection of the heart valves and may be bacterial or fungal. Any significant abnormalities of the valves, heart, and vessels predispose to endocarditis, with the exception of atrial septal defect. Damaged heart valves may first be covered with a deposit of platelets, a condition called nonbacterial thrombotic endocarditis (NBTE). There is no infection at this point, and NBTE by itself does not lead to damage. However, the stage is set if bacteria are introduced into the blood. Such introduction can occur during dental work, for example, and people with known valve abnormalities may be advised to take antibiotics prophylactically before such procedures. Recently, the diet drug combination "Phen-Fen" has been associated with damage to valves.

The most frequent risk factor for endocarditis is mitral valve prolapse (MVP), but only because MVP is so common in the population. The risk of any individual woman with MVP developing endocarditis is actually quite low. IV drug abuse is also a big risk factor. For unknown reasons, IV drug users tend to get infections in the right side of the heart; others usually get left-side infections. Infections of IV drug users are more often caused by staph than strep. Infections can eat holes through the valves or destroy the chordae tendineae.  Note that even normal valves are subject to developing endocarditis; in fact, patients with normal valves are the second most frequent group to suffer from endocarditis (with patients with MVP being first).  Third most frequently involved are valves affected by degenerative changes, and fourth are congenitally defective valves.

Subacute bacterial endocarditis may be hard to diagnose, and it results from organisms that are not too virulent (e.g., Streptococcus viridans) and thus usually infect only damaged valves. Acute bacterial endocarditis is produced by more virulent organisms (such as Staphylococcus) and is easier to diagnose, but can be a very bad disease. Gram-negative bacteria seldom cause endocarditis, since they appear to lack the proper adhesion factors to allow them to stick to the heart valves.

Valve replacements are a common means of therapy for damaged valves. Most often, a cow or pig valve that is specially treated to render it non-antigenic is used, although mechanical valves (e.g., the St. Jude's valve) are employed as well. The replacement pig valve may become calcified, but it takes 10 years on average for this to occur. The pig valves are therefore good for older people. Thrombosis can be a problem, requiring recipients to take anticoagulants.

IV. COMPENSATORY MECHANISMS OF THE HEART

The heart may try to compensate for damage or injury in one of several ways:

Normal ventricle

Concentric hypertrophy: the whole ventricle wall becomes evenly thickened in response to a pressure overload (e.g., systemic hypertension, aortic stenosis).

Eccentric hypertrophy: The wall is of normal thickness, but the chamber is enlarged due to a volume overload (e.g., a leaky valve).

Compensatory hypertrophy: Part of the muscle wall becomes hypertrophied to try to compensate for an area that is damaged, for example due to an infarct.

V. CARDIOMYOPATHY

Cardiomyopathy refers to conditions in which the primary problem is in the heart muscle (myocardium) itself. There are three categories of cardiomyopathies: 1) dilated cardiomyopathy; 2) hypertrophic cardiomyopathy (with or without obstruction to outflow); and 3) restrictive cardiomyopathy (where diastolic filling is impaired, e.g., when amyloid protein infiltrates the heart muscle so it cannot expand properly).

• Dilated cardiomyopathy: All four chambers of the heart become enlarged, weak, and floppy, although it is usually the ventricles that are most affected.  Often, the cause is idiopathic (unknown). Alcohol can directly damage the heart muscle and may lead to this condition, but not all alcoholics develop it. Also, it is thought (but not proven) that this condition may result from viral infections of the heart (myocarditis) due to organisms such as Coxsackie B virus and echovirus. Sometimes, for unknown reasons, dilated cardiomyopathy occurs peripartum or postpartum.  This condition is the most common reason for a heart transplant.

• Hypertrophic cardiomyopathy (HCM): The heart becomes overly thick and muscular; it overcontracts and has trouble relaxing. The thickening is often (but not always) most pronounced between the ventricles, a condition called asymmetric septal hypertrophy (ASH). HCM is also called idiopathic hypertrophic subaortic stenosis (IHSS). IHSS can be associated with outflow problems, due to the stenosis. Despite its name, subaortic stenosis does not have to be part of the disease. However, as the name implies, the cause is unknown. One theory proposes that the disease is caused by an initial viral infection, which then sets off a self-perpetuating cycle of immune-mediated damage. It is fairly common, tends to run in families, and, microscopically, the muscle fibers of the heart appear disarrayed. A significant percentage of people under 35 who die during athletic competition of cardiac events suffer from HCM. If people with this condition survive their childhood and teen years, the risk of sudden death diminishes.

• Restrictive cardiomyopathy:  The heart is rigid and cannot expand (i.e., diastole is impaired).  There are many causes, including radiation fibrosis and amyloidosis. Endomyocardial fibrosis is an example of a restrictive cardiomyopathy of unknown cause.  It is a disease principally of young adults and children in Africa and other tropical areas.

Cocaine can also cause sudden death from heart problems. It does so by causing vascular spasms, neural effects, and necrosis of heart muscle.

Arrhythmias: Those that occur in young people often run in families and are due to fatty replacement of parts of the heart muscle. This condition is called arrhythmogenic right ventricular dysplasia.

HIV can directly damage the myocardium and predisposes to carditis.

II.             ANEURYSMS

These are outpouchings or weakenings that occur rarely in the heart and more commonly in the abdominal or thoracic aorta.  These vessels are too big to get occluded by atherosclerosis, but the atherosclerotic plaques may weaken the vessel wall and lead to aneurysms. For unknown reasons, atherosclerosis (and consequently aneurysms) occur in the aorta most commonly below the diaphragm, but atherosclerosis is still the most common cause of aneurysms in the thoracic aorta. Rupture of an aneurysm may be rapidly fatal.   Aneurysms in the heart usually do not rupture.

Aneurysms can also occur as a result of infection. These are called mycotic aneurysms. Despite the fungal-sounding name, these infections are usually bacterial. Aneurysms are only rarely seen in the coronary arteries, but may occur in children who have Kawasaki's disease (which is rare in the US and more common in Japan). Syphilis infections can lead to aneurysms, which usually occur only in the ascending thoracic aorta. The aortic valve may also be damaged by syphilis. Surgical treatment involves implanting cloth supports, etc.

A dissecting aneurysm is one in which blood collects in the internal layers (media) of the vessel wall. Risk factors for a dissecting aneurysm include Marfan's syndrome (in which there is a hereditary weakening of connective tissue), hypertension, pregnancy (which weakens the aortic wall and connective tissue in general), and tears that may occur during medical procedures. These most commonly occur in the thoracic aorta, not the abdominal. The blood that leaks into the wall of the vessel creates a "false lumen."

A common mode of death in auto accidents is a severing or transection of the aorta as the chest wall stops (for example, by hitting the steering column), but the aorta keeps on going.

III.           VASCULITIS

Inflammation of the vessels can be classified according to the size of the vessel involved. In some types of vasculitis, the patient has anti-neutrophil cytoplasmic antibodies (ANCA). How these antibodies are involved in producing the disease is unclear, but they serve as a good marker. The diseases associated with ANCA include Wegener's granulomatosis, which affects vessels in the lung and kidney, and polyarteritis nodosa (PAN), which can affect small arteries throughout the body.

Other types of vasculitis include giant cell arteritis, which affects the vessels supplying the brain and eyes, especially the temporal artery. This disease can lead to blindness. Takayasu's arteritis particularly affects the aorta and is most common in women.

IV.           KAPOSI’S SARCOMA

This is a malignant tumor of blood vessels that is particularly prevalent in AIDS patients.

V.             THE PERICARDIUM

Pericarditis is an inflammation of the membranous lining around the heart, giving it a rough appearance. Clinically, one can hear a "pericardial rub" resulting from the friction of the roughened membrane against the heart. This can result from several conditions, including rheumatic fever, therapeutic radiation, myocarditis due to viral infection, collagen diseases (e.g., lupus), or spread of TB, pneumonias, or cancers from lungs or other organs. It may resolve with no consequences, or it can cause scarring that restricts the heart from expanding (called restrictive pericarditis). Rheumatic fever, MIs, surgery, etc. may also lead to accumulation of fluid around the heart, called a pericardial effusion.

Cardiac tamponade may occur when fluid fills the space between the pericardium and the heart rapidly (e.g., blood from a stab wound or from a rupture following an MI). The heart may as well be encased in cement, as it can no longer expand after contracting. If the pericardium fills with fluid very quickly, this condition may prove fatal. If scar tissue forms, it may lead to chronic restrictive pericarditis.

VI.           TUMORS OF THE HEART

The only primary tumor worth mentioning is atrial myxoma, a benign tumor that usually forms in the left atrium. It can flop into the valve when the patient assumes certain positions, leading to "positional faintness". Tumors are rare because the cells of the heart do not divide. Lung or breast cancers or melanomas may spread to the heart.  Sometimes a benign tumor called rhabdomyoma develops in the hearts of children.

VII.         HEART FAILURE

Heart failure is the end result of a variety of processes. Forward failure occurs when the pumping function of the heart is lost. There is decreased output, increased retention, and too little blood flow to the tissues. There is retention of salt and water because the kidneys perceive insufficient blood volume, which unfortunately only makes the situation worse. There may be peripheral or pulmonary edema, cardiogenic shock, etc.

Backward failure occurs when the heart cannot accept venous return adequately. Pulmonary edema results as the blood backs up. The patient may cough up fluid. There is distension of the neck veins (jugular venous distension), peripheral edema, and paroxysmal nocturnal dyspnea (waking up with shortness of breath).