RISK FACTORS



Several risk factors for the development of cor­onary artery disease have been identified by ep­idemiological studies. The more risk factors pres­ent in any individual patient, the greater the likelihood that he will develop coronary artery disease. However, there is no absolute correlation between risk factors and incidence of coronary disease. Age, sex, and family history are strong risk factors for coronary artery disease that cannot be altered in any particular patient. Regardless of sex, the risk of developing symptomatic coronary artery disease increases with age. Mortality in males from coronary artery disease is much higher than in females, and females lag behind males in coronary artery disease deaths by approximately 10 years. Coronary disease mortality tends to equalize in men and women at age 50, possibly related to higher risk in women after menopause or the elimination of higher-risk males at an ear­lier age. The existence of coronary artery disease in a parent or sibling is a strong risk factor. Dis­tinct differences, some of which may be due to genetic and environmental factors, are found in the high incidence of coronary disease in white Western males and low incidence in Japanese males living in Japan.

Hypertension, hyperlipidemia, smoking, and glucose intolerance are potentially amenable risk factors that are independently associated with coronary risk. Hypertension is clearly associated with an increased risk of coronary and cerebral vascular disease. Treatment of even mild hyper­tension (diastolic pressure 90 to 104 mm Hg) re­duces mortality from both stroke and myocardial infarction, implying not only an association but a causative role for hypertension. Both systolic and diastolic blood pressure elevation are associated with an increased risk. There is no distinct blood pressure value under which risk suddenly be­comes low; that is, over a wide range of blood pressures, the higher the blood pressure, the higher the risk.

A strong relationship exists between total serum cholesterol and the development of coro­nary artery disease. The higher the serum choles­terol, the higher the risk of coronary disease, even within the usually accepted “normal” cholesterol values of Americans. The low density lipoprotein (LDL) fraction of total cholesterol is directly as­sociated with the risk of atherosclerosis, and the high density lipoprotein (HDL) fraction appears to be inversely related to the incidence of ather­osclerosis. HDL levels are higher in women than in men at all age levels. They are increased by regular exercise and are reduced in diabetes mel-litus. The serum triglyceride level is a weaker risk factor and may not be independent when adjusted for obesity or glucose intolerance. It is possible to lower serum cholesterol a small amount with diet and/or medications. Recent evidence implies that modifications in serum cholesterol may lead to a small improvement in risk. Many patients already have developed a manifestation of coronary artery disease when they consult a doctor, and “second­ary prevention” (that is, prevention of more com­plications once one coronary event has already occurred) has been disappointing. However, di­etary modification to lower serum cholesterol seems prudent in both asymptomatic patients with an elevated or high normal cholesterol (greater than 200 mg/dl) and in patients with known coronary artery disease. Drug treatment to effect marked reduction in serum cholesterol should probably be reserved for patients with well-defined hypercholesterolemia.

Cigarette smoking is a major independent risk for coronary artery disease that is proportional to the number of cigarettes smoked daily and applies equally to men and women. Those who stop smoking develop a lesser risk within a year or two of discontinuation, but the risk remains slightly higher than that of patients who never smoked. The risk of sudden death is sharply reduced after smoking is stopped.

Glucose intolerance is an independent risk fac­tor for coronary artery disease that in women vir­tually eliminates the lower risk conferred by the female sex. Diabetes affects small as well as me­dium-sized vessels. There is currently no con­vincing evidence that rigid control of diabetes ap­preciably decreases the incidence of coronary atherosclerosis.

A variety of other risk factors have been de­scribed, but none of these factors has been shown to contribute independently to the development of atherosclerosis. Patients who are 20 per cent or more above ideal body weight have an increased risk of atherosclerosis, but this risk appears to be associated with the increased incidence of dia­betes, hypertension, and hyperlipidemia. How­ever, control of body weight is reasonable for both primary and secondary prevention. Likewise, the benefit of physical activity is controversial, and any protective aspect of physical activity may be secondary to the absence of other risk factors. “Type A” personality (aggressive, ambitious, and associated with a stressful environment) has been associated with coronary disease, but this person­ality is often associated with other adverse risk factors. There is little convincing evidence that modification of the type A personality is possible or alters risk.

The risk of atherosclerosis in women who use oral contraceptives and have other adverse factors (e.g., smoking) is elevated. Oral contraceptives may alter blood pressure, lipoproteins, and clot­ting mechanisms.