Coronary Artery Disease

CORONARY ARTERY DISEASE

The heart, a powerful muscle that beats over 50,000 times in one day, is fed the blood and energy it needs through small tubes called coronary arteries (see Figure 1). Coronary artery disease (CAD) is the most common cause of death and disability in the United States and other industrialized countries, and it can be manifested if these arteries become narrowed by cholesterol to about half their normal diameter (see Figure 2). Cholesterol, a waxy substance, deposits slowly inside the artery. These deposits, which cause CAD, are called atherosclerotic plaques, having a central soft cholesterol core wrapped in hard fibrous tissue.

Figure 1

Plaque buildup stems from lifestyle and other coronary risk factors, including harmful diets, physical inactivity, smoking, stressful behavior patterns, elevated blood cholesterol, high blood pressure, and diabetes. The wide differences in CAD deaths among countries are largely lifestyle related. Racial differences in susceptibility tend to be minor. Diets overloaded with meat, eggs, butter, whole milk, cheese, and ice cream contain excessive cholesterol and saturated fat, which raise blood cholesterol, thus producing atherosclerosis.

Sedentary lifestyles in America are increasing. From 1991 to 1997, participation by high school students in physical education fell from 42 percent to 27 percent. Obesity increased by 60 percent in the United States in the 1990s because of decreasing physical activity and larger size and frequency of restaurant meals, especially inexpensive high-calorie fast foods. Obesity contributes to atherosclerosis in four ways. It raises blood pressure, cholesterol, and triglycerides (a type of blood fat), and it promotes diabetes, a strong and increasingly common CAD risk factor. A poor diet, and especially one containing excessive amounts of salty foods, can also increase blood pressure.

Smoking cigarettes promotes CAD by damaging the artery's inside lining and by lowering high-density lipoprotein (HDL) cholesterol, a protective fraction of the blood cholesterol. Fortunately, smoking rates have declined in the United States,

Figure 2

and ex-smokers who also exercise benefit by increasing HDL and lowering triglycerides.

In the United States in 1997, CAD caused over 1 million heart attacks and almost 500,000 deaths (one per minute), almost equally affecting men and women. Forty percent of deaths were sudden (within a few hours), usually from ventricular fibrillation, a very rapid beating of the ventricles, the heart's major muscle. A nonfatal heart attack damages the part of the ventricle deprived of blood (a myocardial infarction, or MI; see Figure3) with a 30 percent chance of recurrence within six years. Angina, less serious than an MI, is diagnosed by noting chest pain or "squeezing" after eating, exercise, emotional stress, or exposure to cold. About 350,000 new angina cases occur in the United States yearly; some of which progress to an MI, either nonfatal or fatal, especially if not treated.

The nearly 1 million new nonfatal MI or angina cases that occur yearly in the United States are treated aggressively, using relatively new surgical and nonsurgical technologies. The most common surgeries are coronary artery bypass graft surgery (CABGS) or angioplasty. About 1 million of these are performed yearly, at a cost of $3 billion. CABGS uses short lengths of veins (taken from the patient's legs) to bypass as many as five blocked or severely narrowed arteries. Angioplasty opens narrowed arteries by inflating a strong balloon, fracturing a plaque, and widening that artery segment. A metal tube (a stent) is often inserted to prevent that segment's closure. Nonsurgical approaches seek to change diet, exercise, smoking, body weight, and stress factors. Recently many new anticholesterol drugs, especially the statins, have reduced CAD extensively when used with lifestyle changes.

America's lost earnings and medical and disability payments from CAD cost about $130 billion yearly—an especially tragic burden since scientists now believe that most CAD events are preventable. Optimism regarding CAD's preventability stems from noting a 55 percent fall in CAD rates in the United States between its peak in 1967 and 1995. In turn, the peak represented a 50 percent rise from 1940.

The rise was caused by increases in smoking and rich diets associated with prosperity during and after World War II; the decline resulted from extensive health education that produced major decreases in smoking and dietary intake of saturated fat, and more recently by improved blood-pressure control from medications. CAD rates stopped declining in the United States in 1996, indicating an urgent need for more aggressive prevention. However, without the 55 percent decline since 1967, the human and financial burden would now be even greater.

The international picture has cause for great concern. Although CAD declined in developed countries from 1980 to 2000, the World Health Organization predicts that CAD will become the major cause of death in almost all countries by 2020, with over 10 million deaths per year predicted. Developing countries are repeating the earlier lifestyle mistakes of developed countries, ironically aided by aggressive promotion and export of cigarettes and unhealthy fast foods by the United States. Economists predict that rising CAD costs will greatly sap these countries' resources, delay economic growth, and cause unnecessary suffering.

Figure 3

Thus, the main lesson that the observed large fluctuations in CAD prevalence teaches is that social and environmental factors, not genetic, predominate in its cause. Therefore, CAD is an excellent example of how public health measures on lifestyle (and human behavior) can either benefit or harm our human potential.

John W. Farquhar

(see also: Atherosclerosis; Blood Lipids; Blood Pressure; Cardiovascular Diseases; Chronic Illness; Diabetes Mellitus; HDL Cholesterol; LDL Cholesterol; Lifestyle; Physical Activity; Smoking Behavior; Smoking Cessation; Tobacco Control )

Bibliography

American Heart Association (1998). 1999 Heart and Stroke Statistical Update. Dallas, TX: American Heart Association.

Farquhar, J. W., and Spiller, G. A. (2001). Diagnosis Heart Disease: Answers to Your Questions about Recovery and Lasting Health. New York: W. W. Norton.

Murray, C. J. L., and Lopez, A. D., eds. (1996). The Global Burden of Disease: A Comprehensive Assessment of Mortality and Disability from Disease, Injuries, and Risk Factors in 1990 and Projected to 2020. Cambridge, MA: Harvard University Press.

Simon, H. B. (1994). Conquering Heart Disease: New Ways to Live Well without Drugs and Surgery. Boston: Little, Brown & Co.