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WHAT IS A HEART ATTACK AND WHY DOES IT OCCUR?

A heart attack is a sudden, local blockage of the blood circulation in the coronary artery. As a result, there is such a great lack of oxygen in the cells of the heart muscle that they die. In 95% of such cases, changes in the structure of the coronary arteries are the cause of the acute imbalance between the demand for oxygen in the heart and the blood supply of oxygen.

What is the function of these coronary vessels which originate at the base of the aorta and form a net-work throughout the heart muscle? The heart muscle which is the size of a fist and which pumps blood into the vessels by contraction (systole) must be furnished with blood through special arteries just like every organ of the body. Heart attacks develop most frequently as a result of the occlusion of a coronary artery, the function of which is to supply a certain area of the heart muscle with oxygen.

What causes such an occlusion? It is most often the result of thickening of the arterial wall and of blood clotting. However, blood clots usually develop only after a slowing down of the blood flow in the vessels. If the blood supply to any area of the myocardium (heart muscle) is blocked, then the affected area may die. Should an occlusion occur in a larger branch, then a larger area of the myocardium will die. On the other hand, the smaller the blocked branch is, the less severe the heart attack. Such minor heart attacks are, of course, much easier to overcome than major attacks. But even extensive muscle damage from severe heart attacks may heal well. In other words, heart attacks are not to be judged on an equal basis. " A heart attack rarely occurs completely unexpectedly or suddenly without any warning. Such warning signs may take the form of chest pains, that is, symptoms of angina pectoris (this chest tightness can be called stenocardia) which increase in frequency and intensity in the time period prior to the actual heart attack. An acute coronary occlusion is often preceeded by a long chronic stage of coronary heart disease (CHD) resulting in changes in the vessel walls which impede the blood flow.

The thickening and subsequent narrowing of the blood vessel walls is caused by various developments such as cholesterol deposits and inflammatory reactions. In this manner the blood supply to a particular area of the heart muscle is impaired, and this blockage eventually leads to the occlusion of a coronary vessel and the heart attack. (We are still not certain whether the formation of a blood clot comes prior to or as a consequence of the vessel occlusion. In any case, the prevention and treatment of blood clots is of great importance.)

Causes for angina pectoris and heart attacks may be found in the imbalance between oxygen demand and actual oxygen supply by the blood vessels. Such a disproportion is evident to a smaller degree in angina pectoris and to a larger degree in the case of heart attack. Impaired blood circulation may result not only when the blood vessels do not supply sufficient oxygen, but also when the heart muscle suddenly demands more oxygen (that is, oxygenated blood). Such an increased demand may be the result of physical exertion or emotional stress, as for example in a frightening situation. In this case, the adrenal glands secrete a hormone which is carried by the blood stream to the cells of the heart muscle where it causes an increase in the oxygen demand of the myocardial cells. This increased demand may in turn be one of the reasons for the occurrence of angina pectoris and heart attack in acute emotional stress. Moreover, it is suspected that cigarette • smoking can lead to the same consequences.

Since the causes of impaired circulation and increased oxygen demand are to be found not simply in the thickening of blood vessels, but instead in the interplay of the heart muscle and the coronary arteries, the term 'ischemic heart disease' (ischemic means bloodless) is frequently substituted for 'coronary disease' in current medical terminology. This differentiation is practical and is psychologically significant because in prevention, as in treatment of heart attacks, we must keep in mind all relevant factors.

Measures (such as physical exercise and emotional relaxation) which may help to improve the total blood circulation thus economize the oxygen demand and supply of the heart muscle.. In other words, the dangers of acutely impaired circulation can be avoided in this manner.

An analogy may be drawn between the distribution of coronary vessels in the myocardium and the branches of a tree. If a large branch of a tree is damaged, then the leaves which grow on this branch fall off. However, this comparison is incomplete because it does not account for the collateral blood vessels of the heart muscle. Although these collaterals do not function continually, they may be effectively enlarged by increased oxygen demand or physical exercise and may then aid in the prevention of a heart attack.

However, these collaterals which are also called anastomoses resemble a network of pathways more than branches of a tree. An analogy to a network of pathways is helpful in explaining how an acute blockage may suddenly develop as a result of a traffic jam or road repairs. (These may be comparable to the scar tissue repairs following the damage of a heart attack.) Such roadway blockages may be avoided by using detour roads, or, in this case, the collaterals. In fact, it has been shown that in man collaterals may not only be effectively used, but that previously unused collaterals then begin to function. The development of additional collaterals surrounding the area where there is scar tissue from a heart attack probably improves circulation and also leads to a diminishing or even the disappearance of the scar itself.

Two factors are important in preventing (primary prevention) and halting the progression of coronary disease. First, it is important to prevent changes in the blood vessel walls (i.e. arteriosclerosis not only in the coronary vessels, but in all organs.) Secondly, the unburdening of the myocardial work load by decreased oxygen demand is of equal importance. It is possible to attain these goals by means of medication as well as physical exercise.

The exact causes of arteriosclerosis have not been completely determined.

Nevertheless, it is certain that there is no single Cause, but that there are instead a number of interacting factors in an unhealthy life-style which cause heart attack. These are referred to as the risk factors in coronary heart disease.

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