Heart Diseases, range of disorders of the heart. Heart diseases kill more people in developed nations than any other disease. They can arise from congenital defects, infection, narrowing of the coronary arteries, high blood pressure (hypertension), or disturbances of heart rhythm.

II CONGENITAL HEART DISEASES

Congenital heart defects include persistence of foetal connections between the arterial and venous circulations, such as the ductus arteriosus, a vessel normally connecting the pulmonary artery and the aorta only until birth. Other important developmental anomalies involve the partition separating the four cardiac cavities and the large vessels issuing from them.

In newborn “blue babies”, the pulmonary artery is narrowed and the ventricles are connected by an abnormal opening; in this cyanotic condition, the skin has a bluish tinge because the blood receives an insufficient amount of oxygen. Formerly the expectation of life for such infants was extremely limited; with the advent of early diagnosis and improved techniques of hypothermia (freezing), surgery is often possible in the first week of life and the outlook for these infants greatly improved.

III RHEUMATIC HEART DISEASE

Rheumatic heart disease was formerly one of the most serious forms of heart disease of childhood and adolescence, involving damage to the entire heart and its membranes. It usually followed attacks of rheumatic fever. Widespread use of antibiotics effective against the streptococcal bacterium that causes rheumatic fever has greatly reduced the incidence of this condition.

IV MYOCARDITIS

Myocarditis is inflammation or degeneration of the heart muscle. Although it is often caused by various diseases such as syphilis, toxic goitre, endocarditis, or hypertension, myocarditis may appear as a primary disease in adults or as a degenerative disease of old age. It may be associated with dilation (enlargement due to weakness of the heart muscle) or with hypertrophy (overgrowth of the muscle tissue).

V ATHEROSCLEROSIS

The major form of heart disease in Western countries is atherosclerosis. In this condition fatty deposits called plaque, composed of cholesterol and fats, build up on the inner wall of the coronary arteries. Gradual narrowing of the arteries throughout life restricts the blood flow to the heart muscles. Symptoms of this restricted blood flow can include shortness of breath, especially during exercise, and a tightening pain in the chest known as angina pectoris. The plaque may become large enough to completely obstruct the coronary artery, causing a sudden decrease in oxygen supply to the heart. Obstruction, also termed occlusion, can occur when part of the plaque breaks away and lodges farther along in the artery, forming a thrombosis. These events are the major causes of heart attack, or myocardial infarction, which is often fatal. People who survive a heart attack must undergo extensive rehabilitation; there is always the risk of a recurrence.

Development of fatty plaque is thought to be due partly to obesity and excessive intake of fat, chiefly animal fats, in the diet (seeNutrition, Human). A sedentary lifestyle is also thought to promote atherosclerosis, and evidence suggests that maintaining physical fitness may help prevent heart disease. Increased risk of heart attacks has also been linked to increased stress (seeStress-Related Disorders), but cigarette smoking is still the main risk factor. The occurrence of the heart attack itself is much more likely in people who have high blood pressure. The actual event precipitating the attack may involve products secreted by platelets in the blood. This has led to clinical studies testing whether people who have had a heart attack will be protected from a second one if they take drugs that block the action of platelets.

Many people with severe angina because of atherosclerotic disease can be treated with drugs such as beta blockers (for example, propranolol), which reduce the load on the heart. Those who do not obtain relief from taking drugs can often be treated by a form of surgery called coronary bypass. In this procedure, which became established in the 1970s and is now increasingly common in developed countries, a section of vein from the leg is sewn into the blocked coronary artery to form a bridge around the atherosclerotic region. In most recipients the operation relieves the pain of angina and in many people it prevents a fatal heart attack.

A second surgical procedure that was developed during the 1970s to treat atherosclerotic heart disease is balloon catheterization, technically called percutaneous transluminal coronary angioplasty. In this operation a wire with a balloon on the tip is inserted into an artery in the leg and threaded through the aorta into the coronary artery. When the balloon reaches the atherosclerotic area, it is inflated. The plaque is compressed and normal blood flow is re-established. It is estimated that about one in six coronary bypass operations can be replaced by this less intensive procedure.

During the 1970s and early 1980s it became apparent that a dramatic drop was occurring in mortality from atherosclerotic heart disease in several developed countries. Although no definitive explanation for this decline has been given, public health officials have attributed it to widespread detection and treatment of high blood pressure and a decrease in the amount of animal fat in the average Western diet. However, coronary heart disease remains the leading cause of mortality in Britain.

Some people who die of apparent heart attack exhibit no evidence of severe atherosclerosis. Research has shown that a decrease in blood flow to the heart can also be from the spontaneous contraction of an apparently healthy coronary artery (vasospasm). This may also contribute to heart attacks brought on by atherosclerosis.

VI ARRHYTHMIAS

The immediate cause of death in many heart attacks, whether atherosclerosis is present or not, is ventricular fibrillation—cardiac arrest. This is a rapid ineffective beating of the ventricles. Normal heart rhythm can often be restored by a massive electric shock to the chest, a finding that has led to emergency rescue teams in many cities being trained in this technique.

Minor variations in the heart rhythm usually have little pathological significance. The heart rate responds to the demands of the body over such a wide range that variations are generally within normal limits. Severe defects, however, in the sinoatrial node or in the fibres that transmit impulses to the heart muscle can cause dizziness, faintness, and eventually death. The most serious of these conditions is called complete heart block. It can be corrected by insertion of an artificial pacemaker, a device that gives timed electric shocks to make the heart muscle contract in a regular pattern. Most other arrhythmias are not dangerous except in people with underlying heart disease. In these patients, especially those who have already had a heart attack, arrhythmias are treated with propranolol, lidocaine, and disopyramide.

VII OTHER MAJOR AILMENTS

Often found among older people is pulmonary heart disease, which is usually the result of a lung ailment such as emphysema, or a disease affecting circulation to the lungs, such as atherosclerosis of the pulmonary artery. Another condition found in older people is congestive heart failure, in which the ventricles pump far less efficiently. The muscular walls of the ventricles enlarge with the effort to propel more of the blood into the circulation, giving rise to the large, floppy hearts characteristic of this syndrome. People with this ailment have a reduced capacity for exercise. Their condition can often be improved with one of the derivatives of digitalis, which increases the pumping efficiency of the heart.

VIII DIAGNOSIS

The electrocardiograph, an instrument for recording the electrical currents produced by the heart muscle during various phases of contraction, is an important diagnostic tool. The efficiency of the heart as a pump may be measured accurately by the use of cardiac catheterization. In this technique a tube is introduced, through a vein or an artery or both, into the right, left, or both heart cavities, the pulmonary artery, and the aorta. This process allows determination of the rate of blood flow and recording of blood pressure in intracardiac and large vessels. The technique makes it possible to detect abnormal communications between right and left heart cavities.

In another diagnostic technique, angiocardiography (or cinefluoroscopy), photographic recordings are obtained of the heart cavities and of the pathways and contours of the pulmonary vessels and aorta, with its branches; the technique involves injecting a substance opaque to X-rays into a vein.

Even more accurate delineation of areas of reduced blood flow in the heart is provided by a new technique that visualizes the flow of a radioactive isotope of the element thallium into heart muscle. A computerized camera records the extent of thallium penetration during the systole-diastole cycle of the heart, precisely showing small areas of tissue damage. Yet another technique that is now being used is ultrasound (ultrasonic imaging).

IX HEART TRANSPLANTS

In 1967 a human heart from one person was transplanted into the body of another by the South African surgeon Christiaan Barnard. Many surgeons have since adopted the procedure. The major problem at first was the body’s natural tendency to reject tissues from another individual (seeImmunity; Transplantation, Medical). By the early 1980s, however, due to the use of immunosuppressive drugs, particularly cyclosporin, many more cardiac transplant recipients were living beyond one year. By the 1990s the operation had become more commonplace in developed nations, such as the US and Britain, with many patients living for five to ten years following a heart transplant.