About Coronary Artery Disease

Also known as coronary heart disease, CAD is caused by atherosclerosis ("hardening of the arteries"), the gradual buildup of fatty deposits in the arteries circling the heart, which provide it with the oxygen and nutrients it needs to pump blood throughout the body.

Over time, these fatty deposits can grow large enough to restrict blood flow to the heart muscle. The diminished blood flow can cause chest pain, or angina. When the blood flow in one or more coronary arteries is completely cut off, the result is a heart attack, or injury to the heart muscle. The widespread use of cholesterol-lowering drugs has helped reduce the number of heart attacks. And for those who do have them, clotbusters and other medications, improved technologies, and physician awareness of such lifesaving measures as providing a beta blocker to heart attack patients as they leave the hospital have helped more people survive heart attacks and go on to live many more years.

Causes

Like all arteries, the coronary arteries are muscular tubes with a smooth lining, allowing blood to flow freely. Yet atherosclerosis begins early in life. Even before the teen years, the blood vessel walls begin to show streaks of fat and cholesterol. As you get older, this fatty matter builds up, slightly injuring the blood vessel walls. The cells inside the walls react by releasing chemicals that make the walls stickier. Other substances floating through your bloodstream, such as platelets (disk-shaped particles that aid clotting), inflammatory cells, proteins, and calcium, adhere to the walls. The fat and other substances combine to form larger deposits, called plaques. Over time, these plaques can build up, narrowing the channel through which blood flows. If the narrowing is severe, the heart muscle becomes oxygen-starved, a condition called ischemia.

As the size of a blockage increases, sometimes a narrowed artery develops "collateral circulation," growing small, capillary-like branches that reroute blood around the narrowed area. During increased exertion, however, these "collaterals" might be unable to meet the heart muscle's demand for oxygen.

The fatty plaques may develop a hard, fibrous "cap" over the soft, mushy contents. If the hard surface cracks or tears, the fatty insides will leak or gush out. Clot-forming cells called platelets come to the area and create a blood clot around the material ejected from the plaque. The clot might subsequently break apart on its own, restoring blood flow. More commonly, however, it lodges in the vessel, narrowing it further or blocking it entirely.

A blood clot that completely occludes the artery is called a coronary thrombus or coronary occlusion, and it will cause one of three types of problems, all of which are life-threatening emergencies:

Unstable angina: This may be a new symptom or a change from stable angina. The angina may occur more frequently, occur more easily at rest, feel more severe, or last longer. Although this angina can often be relieved with oral medications, it is unstable and may progress to a heart attack. Usually more intense medical treatment or a procedure is required. Unstable angina is an acute coronary syndrome and should be treated as a medical emergency.

Non-ST segment elevation myocardial infarction (NSTEMI): This heart attack, or MI, does not cause changes on an electrocardiogram (ECG). However, chemical markers in the blood indicate that damage has occurred to the heart muscle. In NSTEMI, the blockage may be partial or temporary, and so the extent of the damage relatively minimal.

ST segment elevation myocardial infarction (STEMI): This heart attack, or MI, is caused by a prolonged period of blocked blood supply. It affects a large area of the heart muscle, and so causes changes on the ECG as well as in blood levels of key chemical markers.

Risk Factors

Some risk factors for heart disease, such as advancing age, obviously cannot be changed. For more on these, see below.

Age. The older you get, the more likely you are to develop heart disease. Approximately 85 percent of people who die of coronary artery disease are older than 65.

Gender. Men have a greater risk than women of having a heart attack, particularly at a younger age, but more women than men die from them. The rate of male CAD has remained flat while the incidence of female CAD has risen dramatically.

Menopause. Prior to menopause, the hormone estrogen helps protect against CAD. Afterward, changes in the walls of the blood vessels make it more likely for plaque and blood clots to form. Changes occur in the level of lipids (fats) in the blood. There is an increase in fibrinogen (a substance in the blood that helps the blood to clot). Increased levels of blood fibrinogen are related to heart disease and stroke. After menopause, a woman's risk increases until at age 70, women and men have equal chances of dying from heart disease. Post-menopausal women have a higher rate of complications and death than men after bypass surgery and angioplasty. But this may be related in part to the fact that women's symptoms of coronary artery disease are not as typical, so they may not get treatment until their disease is more advanced.

Family history. If a first-degree relative—either of your parents, your brothers or sisters, or your children—has had heart disease, your own risk of CAD is higher. If that relative is a male younger than 55 or a female younger than 65, the risk is much higher.

A note about hormone replacement therapy and heart disease risk

For many years, research based on observation showed that hormone replacement therapy (HRT) might reduce the risk of heart disease in women. It now appears that these findings were likely due to the lifestyles of women who take HRT and not the medical benefits of HRT itself.

More recent studies of women, such as the Heart and Estrogen/progestin Replacement Study (HERS) and the Women's Health Initiative (WHI) concluded that overall health risks exceed the benefits provided by HRT. Women who participated in the WHI showed an increased risk for breast cancer, CAD (including nonfatal heart attacks), stroke, blood clots, and gall bladder disease. Based on the results of these studies, women who already have heart disease should not take HRT.

There are other risks and benefits from HRT. It is important to discuss the risks and benefits of HRT with your own doctor before making a decision.