Inflammation of Heart Tissues

Endocarditis is inflammation of the endocardium. It affects the valves more severely than other areas of the heart and can lead to deposition of scar tissue, causing valves to become stenosed or incompetent.

Myocarditis is inflammation of the myocardium and can lead to heart failure.

Pericarditis is inflammation of the pericardium. Pericarditis can result from bacterial or viral infections and can be extremely painful.

Rheumatic heart disease can result from streptococcal infection in young people. Toxin produced by the bacteria can cause an immune reaction called rheumatic fever about 2 to 4 weeks after the infection. The immune reaction can cause inflammation of the endocardium, called rheumatic endocarditis. The inflamed valves, especially the bicuspid valve, can become stenosed or incompetent. The effective treatment of streptococcal infections with antibiotics has reduced the frequency of rheumatic heart disease.

Reduced Blood Flow to Cardiac Muscle

Coronary heart disease reduces the amount of blood that the coronary arteries are able to deliver to the myocardium. The reduction in blood flow damages the myocardium. The degree of damage depends on the size of the arteries involved, whether occlucion (blockage) is partial or complete, and whether occlusion is gradual or sudden. As the walls of the arteries thicken and harden with age, the volume of blood they can supply to the heart muscle declines, and the ability of the heart to pump blood decreases. Inadequate blood flow to the heart muscle can result in angina pectoris, which is a poorly localized sensation of pain in the region of the chest, left arm, and left shoulder.

Degenerative changes in the artery wall can cause the inside surface of the artery to become roughened. The chance of platelet aggregation increases at the rough surface, which increases the chance of coronary thrombosis (formation of a blood clot in a coronary vessel). Inadequate blood flow can cause an infarct, and area of damaged cardiac tissue. A heart attack is often referred to as a coronary thrombosis or a myocardial infarct. The outcome of coronary thrombosis depends on the extent of the damage to heart muscle caused by inadequate blood flow and whether other blood vessels can supply enough blood to maintain the heart's function. Death can occur swiftly if the infarct is large; if the infarct is small, the heart can continue to function, in some cases, the infarct weakens the wall of the heart, and the wall ruptures; but, in most cases, scar tissue replaces damaged cardiac muscle in the area of the infarct.

People who survive infarctions often lead fairly normal lives if they take precautions. Most cases call for moderate exercise, adequate rest, a disciplined diet, and reduced stress.

Congenital Conditions Affecting the Heart

Congenital heart disease is the result of abnormal development of the heart. The following conditions are common congenital defects:

Septal defect is a hole in a septum between the left and right sides of the heart. The hole may be in the interatrial or interventricular septum. These defects allow blood to flow from one side of the heart to the other and as a consequence, greatly reduce the pumping effectiveness of the heart.

Patent ductus arteriosus results when a blood vessel called the ductus arteriosus, which is present in the fetus, fails to close after birth. The ductus arteriosus extends between the pulmonary trunk and the aorta. It allows blood to pass from the pulmonary trunk to the aorta, thus bypassing the lungs. This is normal before birth because the lungs are not functioning. If the ductus arteriosus fails to close after birth, blood flows in the opposite direction, from the aorta to the pulmonary trunk. As a consequence, blood flows through the lungs under a higher pressure and damages them. In addition, the amount of work required of the left ventricle to maintain an adequate systemic blood pressure is increased. Stenosis of a heart valve is a narrowed opening through one of the heart valves. In aortic or pulmonary valve stenosis, the workload of the heart is increased because the ventricles must contract with a much greater force to pump blood from the ventricles. Stenosis of the bicuspid valve prevents the flow of blood into the left ventricle, causing blood to back up in the left atrium and in the lungs, resulting in congestion of the lungs. Stenosis of the tricuspid valve causes blood to back up in the right atrium and systemic veins, causing swelling in the periphery.

An incompetent heart valve is a heart valve that leaks. Therefore, blood flows through the valve when it is closed. The workload of the heart is increased because incompetent valves reduce the pumping efficiency of the heart. For example, an incompetent aortic semilunar valve allows blood to flow from the aorta into the left ventricle during diastole. Thus, the left ventricle fills with blood to a greater degree than normal. The increased filling of the left ventricle results in a greater stoke volume because of Starling's law of the heart. The pressure produced by the contracting ventricle and the pressure in the aorta is greater than normal during ventricular systole. However, the pressure in the aorta decreases very rapidly as blood leaks into the left ventricle during diastole.

An incompetent bicuspid valve allows blood to flow back into the left atrium from the left ventricle during ventricular systole. This increases the pressure in the left atrium and pulmonary veins which results in pulmonary edema. Also, the stroke volume of the left ventricle is reduced, which causes a decrease in systemic blood pressure. Similarly, an incompetent tricuspid valve allows blood to flow back into the right atrium and systemic veins causing edema in the periphery.

Cyanosis is a symptom of inadequate heart function of babies suffering from congenital heart disease. The term "blue baby" is sometimes used to refer to infants with cyanosis. The blueness of the skin is caused by low oxygen levels in the blood in peripheral blood vessels.

Conditions Associated with Aging

Several heart diseases develop as people age, and they gradual become more severe as people grow older. The following conditions are common in elderly people.

Heart failure is the result of progressive weakening of the heart muscle and the failure of the heart to pump blood effectively. Hypertension (high blood pressure) increases the afterload on the heart, can produce significant enlargement of the heart, and can finally result in heart failure. Advanced age, malnutrition, chronic infections, toxins, severe anemias, or hyperthyroidism can cause degeneration of the heart muscle resulting in heart failure. Heredity factors can also be responsible for increased susceptibility to heart failure.

Heart function in the he elderly gradually becomes less efficient. Although the age at which the heart becomes less efficient varies considerably and depends on many factors, by the age of 70 there is often a decease in cardiac output of about one third. Because of the decrease in reserve strength of the heart, many elderly people are often limited in their ability to respond to emergencies, infections, blood loss, or stress.

Heart Medications

Digitalis: Slows and strengthens contractions of the heart muscle. This drug is frequently given to people who suffer from heart failure, although it also can be used to treat atrial tachycardia.

Nitroglycerin: Causes dilation of veins and arteries throughout the body, resulting in a deceased venous return to the heart and a reduced preload. During exercise when the heart rate and stroke volume are increased, vasodilation of blood vessels in the exercising skeletal muscles and vasoconstriction in most other blood vessels results in an increased venous return to the heart and an increased preload. Nitroglycerin causes dilation of all of the veins and arteries without an increase in heart rate or stroke volume. When all blood vessels dilate, a greater volume of blood pools in the dilated blood vessels, causing a decrease in the venous return to the heart. The reduced preload causes cardiac output to decease, resulting in a decreased amount of work performed by the heart. Nitroglycerin is frequently given to people who suffer from coronary artery disease, which restricts coronary blood flow. The decreased work performed by the heart reduces the amount of oxygen required by the cardiac muscle. Consequently, the heart does not suffer from a lack of oxygen, and agina pectoris does not develop.

Beta-adrenergic blocking agents: Reduce the rate and strength of cardiac muscle contractions, thus reducing the heart's demand for oxygen. Beta-adrenergic blocking agents bind to receptors for norepinephrine and epinephrine and prevent these substances from having their normal effects. Beta-adrenergic blocking agents are often used to treat people who suffer from rapid heart rates, certain types of arthythmias, and hypertension.

Calcium channel blockers: Reduce the rate at which calcium ions diffuse into cardiac muscle cells and smooth muscle cells. Because the action potentials that produce cardiac muscle contractions depend in part on the flow of calcium ions into the cardiac muscle cells, the calcium channel blockers can be used to control the force of heart contractions and reduce arrhythmia, tachycardia, and hypertension. Because entry of calcium inot smooth muscle cells causes contraction, calcium channel blockers cause dilation of blood vessels. Calcium channel blockers dilate coronary blood vessels and increase blood flow to cardiac muscle. Consequently, calcium channel blockers can be used to treat angina pectoris.

Antihypertensive agents: Several drugs are used specifically to treat hypertension. These drugs reduce blood pressure and therefore reduce the work required by the heart to pump blood. In addition, the reduction of blood pressure reduces the risk of heart attacks and strokes. Drugs used to treat hypertension include drugs that reduce the activity of the sympathetic nervous system, drugs that dilate arteries and veins, drugs that increase urine production (diuretics), and drugs that block the conversion of angiotensinogen to angiotensin 1.

Anticoagulants: Prevent clot formation in persons with damage to heart valves or blood vessels or in persons who have had a myocardial infarction. Aspirin functions as a weak anticoagulant. One aspirin each day may benefit those who are likely to experience a coronary thrombosis.

Instruments and Selected Procedures

Artificial pacemaker: An instrument placed beneath the skin, equipped with an electode that extends to the heart. An artificial pacemaker provides an electrical stimulus to the heart at a set frequency. Artificial pacemakers are used in patients in whom the natural pacemaker of the heart does not produce a heart rate high enough to sustain normal physical activity. Modern electronics has made it possible to design artificial pacemakers that can increase the heart rate as increases in physical activity occur. It is likely that rapid development of electronics for artificial pacemakers will increase the degree to which the pacemakers can regulate the heart.

Heart lung machine: A machine that serves as a temporary substitute for the patient's heart and lungs. It pumps blood throughout the body and oxygenates and removes carbon dioxide from the blood. It has made possible many surgeries on the heart and lungs.

Heart valve replacement or repair: A surgical procedure performed on those who have diseased valves that are so deformed and scarred from conditions such as endocarditis that the valves are severely incompetent or stenosed. Substitute valves made of synthetic materials such as plastic or Dacron are effective; valves transplanted from pigs are also used.

Heart transplants: Heart transplants are possible when the immune characteristics of a donor and the recipient are closely matched. The heart of a recently decreased donor is transplanted to the recipient, and the diseased heart of the recipient is removed. People who have received heart transplants must remain on drugs that suppress their immune responses for the rest of their lives. Unless they do so, their immune system rejects the transplanted heart.

Prevention of Heart Disease

Proper nutrition is important in reducing the risk of heart disease. A recommended diet is low in fats, especially saturated fats and cholesterol, and low in refined sugar. Diets should be high in fiber, whole grains, fruits, and vegetables. Total food intake should be limited to avoid obesity, and sodium chloride intake should be reduced.

Tobacco and excessive use of alcohol should be avoided. Smoking increases the risk of heart disease by at least tenfold, and excessive use of alcohol also substantially increases the risk of heart disease.

Chronic stress, frequent emotional upsets, and a lack of physical exercise can increase the risk of cardiovascular disease. Remedies include relaxation techniques and aerobic exercise programs involving gradual increases in duration and difficulty in activities such as swimming, jogging, or aerobic dancing.

Hypertension is abnormally high systemic blood pressure. Hypertension affects about one fifth of the population. Regular blood pressure measurements are important because hypertension does not produce obvious symptoms. If hypertension cannot be controlled by diet and exercise, it is important to treat the condition with prescribed drugs. The cause of hypertension in the majority of cases is unknown.

Some data suggest that taking a small dose of aspirin regularly will reduce the chance of a heart attack. Most of the research has involved males, but data indicate that aspirin may also reduce the chance of heart attacks in females. Aspirin inhibits the synthesis of prostaglandins in platelets, which in turn can help prevent clot formation.