What Does Cause Heart Attacks?

What does causeHEART ATTACKS?.

BY FREDRICK J. STARE, M.D.

THE two commonest types of heart disease — hypertensive heart disease and arteriosclerotic or coronary artery disease — are not caused by any single factor, but by many, each with varying degrees of importance in different individuals.

Hypertensive heart disease is caused by an increase in blood pressure, which is the result of constriction throughout the body of the very small blood vessels known as arterioles. They become constricted — first temporarily, later permanently — and the heart must pump harder to produce sufficient pressure to push the blood through them. This additional work for the heart will in time cause it to enlarge and to develop what is known as hypertensive heart disease. Thus a part of the chain of events which leads to hypertensive heart disease is the change that takes place in these very small blood vessels. Recent researches have suggested that these changes are due in part to the formation by the kidney of a specific substance called angiotonin.

For some unknown reason, greatly restricting the intake of sodium tends to reduce the blood pressure in a fair number of individuals with the common type of high blood pressure. Thus, the reason for the use of low sodium diets, frequently but incorrectly referred to as low salt diets. Numerous drugs have also been found in the past ten years to be helpful in reducing and controlling high blood pressure.

The most prevalent type of heart disease and the greatest killer of all is arteriosclerotic coronary artery disease, the type of heart disease which one has heard so much of since President Eisenhower had his “coronary.”Deposits, called atheroma, are formed in the inner lining of the blood vessels. They contain cholesterol and fat. When they get large enough, they impede the flow of blood, something like rust in a pipe. They interfere with the normal elasticity of the blood vessel wall. They may cause small or large hemorrhages within the wall of the blood vessel itself, and these further reduce the inside opening of the vessel. They may greatly weaken the wall of the vessel.

When this process takes place in the arteries of the brain, it is termed cerebral arteriosclerosis, the common clinical manifestation of which is a “stroke" or a “CVA" (cerebral vascular accident). Thus strokes and coronaries have much in common; in fact, they are basically the same disease: arteriosclerosis. In one, the arteries of the brain are primarily involved; in the other, the arteries of the heart; but most individuals who have had manifestations in one of these organs are apt to have a fair degree of arteriosclerosis in the other organ.

These are dangerous conditions. A blood clot (thrombus) is more likely to form in a vessel narrowed by atheroma. Should this happen so that the flow of blood is completely blocked, a portion of heart muscle (or brain tissue) just beyond this block will die because of a lack of blood to supply it with nutrients and oxygen. This dead heart tissue just beyond the blockage is called an infarct. Thus, a typical coronary involves the development, usually over a period of years, of narrowed blood vessels in the heart due to cholesterol and fat deposits, then the process of thrombosis, which is the formation of a blood clot in these narrowed vessels, and finally, the development of an area of infarction (dead heart muscle) beyond the clot. Whether death ensues from the coronary depends on its location in the heart, its size, and whether it is developed suddenly or slowly.

If the arteriosclerosis develops rather slowly, it is likely that a substitute or collateral circulation may be formed to take over the nourishment of the heart muscle in the involved area. This may be life saving when the complete stoppage of an arteriosclerotic vessel occurs by the clot.

Infarcted areas of heart muscle may be identified by means of the electrocardiograph. In fact, this is one of the chief uses of this diagnostic instrument, to determine if one has had a coronary. Further, it gives some idea of the location of the infarcted area.

WHAT does cause a heart attack? In most cases, when speaking of a heart attack, one is referring to a coronary. Heredity, diet and nutrition, fat content of the blood, body weight and changes in weight, exercise (lack of it), defects in the blood vessel wall, elevated blood pressure, smoking, and sex are factors known to be involved. Undoubtedly others will be discovered in the near future, as this is currently a very active area of research.

Heredity patterns of most diseases are not well understood, but they certainly exist, and strongly so in many diseases, especially in most of the noninfectious diseases of the heart and blood vessels. Just why these diseases have a strong hereditary background, or what is the nature of the defect in the germ plasm of the genes, remains for future research to find out. But without question heredity is a factor. A recent study mentions that coronary artery disease is four times more prevalent in the children of affected parents than in those of parents without this disease.

Diet and nutrition are significant factors in heart disease. Many investigators have noted that large groups of people throughout the world who consume diets low in fat have less coronary artery disease than those consuming diets high in fat. Such observations have come from Guatemala, southern Italy, Japan, parts of Africa, and elsewhere. Low fat content generally means a diet in which 10 to 20 per cent of the daily caloric intake is provided by fat as compared to 40 to 50 per cent in the diet with high fat content.

But in addition to the differences in the total amount of fats consumed, there are marked differences in the type of fat. The primitive and nonindustrialized societies consume what little fat they do eat largely in the form of vegetable fats — the oils of palm, coconut, corn — with smallish quantities of fish and animal fats. The high fat diets characteristic of industrialized areas are rich in animal and dairy fats as well as vegetable fats.

During World War II, and during various famines, a rough correlation has been observed between the fat intake and incidence of heart disease. As the fat intake decreased, so did the incidence of heart disease, and when fats became plentiful, the heart disease rate increased.

However, fats are not the only dietary differences between those regions with a low and a high incidence of coronary artery disease. The former are usually low in sugar and animal protein and high in starch and fiber. The vitamin and mineral content may also differ appreciably from that in American diets.

Probably the strongest evidence linking diet and nutrition to arteriosclerosis has come from animal experimentation. In the past decade it has been possible to produce this disease experimentally in a number of different species, ranging from rabbits and chicks to dogs and monkeys. The last — being primates, as is man — may have special significance. With animal experimentation, it is usually possible to plan the study so that a single change in diet is the major variable. This is seldom possible in observations on man. While there are major dietary differences between the South African Bantu and the urban citizen of Johannesburg or Boston, so too are there a hundred other environmental differences.

Animal experimentation has emphasized the importance of the cholesterol and fat content of the blood in the production of arteriosclerosis, including coronary arteriosclerosis. Usually it is only when the cholesterol level of the blood is elevated that this disease can be produced experimentally. The amount of fat and type of fat in the animals’ diets are important in this respect. Other nutrients have also been shown to be involved under certain experimental conditions. These include protein, sugar, two or three of the B-vitamins, and recently even the mineral magnesium.

Because of the interest in cholesterol, it might be well to comment further about it. Cholesterol is a normal constituent of all animal tissues. One of its functions is to serve as a building block for some of the hormones. It is present in almost all foods of animal origin, but more so in some than in others. Egg yolk and milk fat are rich sources in common foods. But in addition to ingesting cholesterol, our bodies make cholesterol, mainly in the liver. Fats in the diet seem to be the food component from which the body prefers to make cholesterol. Actually it has been shown repeatedly that the cholesterol content of the diet has very little to do with the cholesterol content of the blood. It is the level of cholesterol in the blood that is of concern in coronary artery disease and not the cholesterol content of the diet.

Some researchers claim to have shown that blood clots more quickly when the fat content is elevated. This may explain why a fair number of coronary heart attacks take place late at night, four to five hours after a large meal rich in fat. Were it possible to change our food habits appreciably. many workers in this field think it would be desirable to have the large meal of the day in the morning or at noon and have the evening meal be a light snack or supper. On the other hand, there are competent hematologists who dispute the belief that high blood-fat levels favor blood clotting. This is an important aspect of the problem, on which research is continuing.

EXTRA body weight means extra work for the heart and extra body tissue to be nourished, but these are probably unimportant as far as coronary artery disease is concerned. Frequently during periods of rapid gain in weight the cholesterol and fat level of the blood is increased. It is during such periods that cholesterol deposits may be laid down in the walls of the blood vessels and thus form atheroma. When the weight reaches a plateau, the cholesterol in the blood may decrease somewhat, but the damage in the form of cholesterol deposits has already occurred. The hazards of overweight may not be the extra pounds, but the chemical changes in the blood which accompany the gain in weight! Thus, those who reduce should certainly make up their minds to stay reduced.

Can cholesterol once deposited in blood vessel walls be removed? This is another problem currently under investigation. There is some evidence to suggest that if the deposits are not too extensive and have not been present for too long, they may be reduced in size, possibly removed. This may be accomplished if one is successful in appreciably lowering blood cholesterol and keeping it down. Weight reduction and then keeping one’s weight down are about the most useful procedure in this respect for the average person.

Exercise is important in its effect on body weight. There is only one way to use up extra calories, and that is to burn them up by exercise. The beginning of obesity in adolescence is frequently due to lack of exercise rather than excessive caloric intake. The same applies to weight gain experienced in the forties. Exercise is also important in keeping the muscles of the blood vessel wall in good tone. It is thought that a heart well exercised is better able to develop a substitute or collateral circulation should this become necessary because of the formation of a thrombus.

The important thing about exercise is that it be daily and moderate in degree. Exercise has often been ridiculed as a means of helping to control weight. This is based on two misconceptions, that most common types of exercise require only a little energy, and that increase in exercise always gives rise to an increase in appetite. The first misconception can be avoided if one will take the trouble to look at any table of energy expenditures of various activities: walking for a man of 150 pounds uses up 200 to 400 calories per hour depending on speed, running 800 to 1000 calories. Further, the calories used up are proportional to body weight; thus a person of 200 pounds uses more calories in exercise than one of 150 pounds.

Whether exercise increases appetite depends on the extent of the exercise and whether one is usually active or sedentary. If the exercise is mild to moderate and is done by a sedentary individual, it will not increase appetite.

Most people gradually become overweight because they consume a few more calories each day. If each day they would take a little more exercise they would burn up the extra calories. One does not become overweight between Christmas and New Year’s, rather between New Year’s and Christmas. Hence, the practical importance of daily minimum to moderate extra physical activity. Walking still remains the most available and inexpensive type of exercise.

Coronary artery disease in this country is usually more common and severe in patients who have elevated blood pressure or hypertension, and smoking usually elevates the blood pressure. Increased pressure within the blood vessels favors development of coronary heart disease in a number of ways, one of them, for example, being the occurrence of small hemorrhages within the blood vessel wall itself with further narrowing of the vessel. A sustained or a sudden increase in blood pressure may also cause an aneurysm (weak spot) to “blow out” with sudden loss of blood into the brain (cerebral hemorrhage or stroke); or if the aneurysm is in the abdominal aorta, as is common in severe arteriosclerosis, into the abdominal cavity.

It is well established that coronary artery disease is more prevalent among cigarette smokers than nonsmokers and that it occurs at an earlier age in smokers. This does not “prove” that smoking causes coronary artery disease, but it’s not much of an inducement to smoke!

What does sex have to do with heart attacks — that is, real heart attacks? It has long been known that coronary artery disease is four to five times more prevalent in the male than in the female. But this discrepancy begins to disappear after the menopause, and by the middle fifties to sixties the disease is of equal prevalence in both sexes. Attempts have been made to treat the disease in men by giving them some of the female sex hormones. But so far these studies are purely in the research stage and have little practical application.

Experimentally, a sex difference in the susceptibility to the development of arteriosclerosis has also been found in a number of different types of animals. But for some unknown reason it is frequently in the opposite direction to that found in man. Thus, female rabbits and chickens are more susceptible to arteriosclerosis than males, and their susceptibility can be lessened by giving them large doses of the male sex hormones. Likewise the susceptibility of the male rabbit or chick can be increased by giving it female hormones.

A most interesting finding in sex as it relates to coronary artery disease is the observation from a group of pathologists from Washington University School of Medicine and Barnes Hospital in St. Louis that since the 1940s there has been a marked shift in the distribution of fatal coronary artery disease. They claim that the disease is now almost as prevalent in women as in men, even as early as the forties. No real explanation is available for this startling finding, though numerous speculations are possible: increased smoking of women, less exercise because of pushbutton housekeeping, gain in weight; but let me emphasize, these are all speculations.

No mention has been made so far of “stress and strain.” Are they involved in heart attacks? Stress and strain are difficult to measure and evaluate. Most of us are apt to think that many Americans, particularly ourselves, are under considerable stress and strain. Stress and strain certainly exist among those people in other parts of the world where coronary artery disease is rare, though it is most likely caused by different events. Primitive Africans, highly superstitious and in frequent fear of their lives, are under stress — yet coronary artery disease among them is rare.

The war dances, chants, and witch doctors of primitive societies may all serve a useful purpose in exteriorizing stress — getting rid of it. Too many of us keep our stress within us.

Stress and strain are likely to be highly individualized. What may be stress and strain for one person are not for another. It is entirely possible that the stress and strain of today’s civilization are in certain individuals important in bringing about, along with other factors, the changes that result in a heart attack. While there is today no objective evidence to support this idea, it should be pointed out that few serious attempts have been made to study it.

Now what does cause heart attacks? Certainly a number of factors are involved, as has been mentioned. Undoubtedly they work together, and some are of more importance in certain individuals than in others. There is nothing one can do about one’s heredity. But if you have parents or grandparents who died early from coronary or cerebral arteriosclerosis, it is most important that you minimize the other factors that contribute to these diseases. Thus, you should really keep your weight within bounds, get regular exercise, eat a wellbalanced diet and not too much of it, and eliminate smoking. If, in addition, your doctor finds that you consistently have an elevated blood cholesterol, there are certain things he can suggest which may lower it.

The factors which cause heart attacks are additive. This was pointed out in a recent study of the United States Public Health Service, where it was shown that men who were overweight and also had an elevated blood cholesterol and an elevated blood pressure suffered a higher incidence of heart attack than those who had any two of these findings. Those with any two findings had a higher rate than those who had only one. Our heredity and sex we can do nothing to change; we can do something to minimize the other factors if we really want to.

Arteriosclerosis is a serious condition, the main cause of death in Western civilization. Your doctor is the one who should handle this problem for you, an individual patient. Do not depend on a magazine article, like this or any other one, to solve your personal medical problems. At best it can only point out current concepts and trends in generalities, but to apply these findings to you as an individual requires the skill and knowledge of a trained physician.