CAD is caused by atherosclerosis. Atherosclerosis is a chronic, progressive disorder of the arteries in which deposits of cholesterol, calcium, and abnormal cells (that is, plaques) build up on the inner lining of the arteries.
Photo 1 (above) - Atherosclerosis The top artery shows a normal lumen, or opening ("L"). The bottom artery illustrates what happens to the lumen when plaques form in the arterial wall.
These plaques can cause a gradual but progressive narrowing of the artery, and as a result, blood flow through the artery becomes more difficult. When the obstruction becomes large enough, the patient may experience angina.
"Angina" refers to the symptoms a patient experiences any time the heart muscle is not getting enough blood flow through the coronary arteries. Angina is usually felt as a discomfort (often a pressure-like pain) in or around the chest, shoulders, neck or arms.
"Stable angina" is angina that occurs in a nearly predictable fashion, for instance, with exertion or after a big meal. Stable angina generally means that a plaque has become large enough to produce a partial obstruction of a coronary artery.
When a person with stable angina is at rest, the partially blocked artery is able to meet the needs of the heart muscle. But when that person exercises, (or has some other stress that makes the heart work harder), the obstruction prevents an adequate increse in blood flow to the heart muscle, and angina occurs. So stable angina usually means there that there is a significant plaque in a coronary artery that is partially obstructing the flow of blood.
In addition to causing obstruction by a gradual increase in their size, plaques are also subject to sudden rupture, which can produce a very sudden obstruction. The medical conditions caused by the rupture of a plaque are referred to as Acute Coronary Syndrome (ACS). ACS is always a medical emergency.
“Unstable angina” is one type of ACS. Unstable angina occurs when a plaque has partially ruptured, causing a sudden worsening of the blockage in the artery. In contrast to stable angina, symptoms in unstable angina occur unpredictably, (that is, they are not particularly related to exertion or stress), and notably, tend to occur at rest. (Another name for unstable angina is "rest angina.") Patients with unstable angina are at high risk of developing a total occlusion of the coronary artery, leading to a myocardial infarction.
Myocardial infarction, or heart attack, is a more dire form of ACS. Here, the ruptured plaque causes a total (or near total) occlusion of the coronary artery, so that the heart muscle supplied by that artery dies. A heart attack, therefore, is death of heart muscle. The seriousness of a myocardial infarction depend largely on how much heart muscle has died. A small heart attack is one in which only a small portion of the heart muscle dies. A large heart attack is one in which a large portion of heart muscle dies.
Photo 2 - Blockages in the coronary arteries In this figure, arterial narrowings threaten to cause a heart attack with substantial muscle loss.
If a patient receives medical attention within a few hours of the onset of a heart attack, the size of the heart attack can be greatly reduced by administering “clot-busting drugs," or by performing an immediate angioplasty (and most often, stenting) to open up the blocked artery.
After surviving a heart attack, the patient is still at risk. Further heart attacks are possible if more plaques are present in the coronary arteries. Also, depending on the amount of heart muscle that has been damaged, the patient can develop heart failure. Furthermore, damaged heart muscle can cause a permanent instability in the heart's electrical system, which can lead to sudden cardiac arrest. So after a heart attack, all of these risks need to be carefully evaluated, and steps need to be taken to reduce each of these risks to the greatest extent possible. Here is more information on reducing risk after surviving a heart attack.
The best way to deal with coronary artery disease, of course, is to prevent it. All of us should do everything we can to reduce our CAD risk factors.
For those who already have CAD, reducing these same risk factors becomes even more important, in order to slow the progression of the disease. In addition, several avenues are available for treating CAD, including drug therapy, surgical therapy, and angioplasty and stenting. The treatment of CAD always needs to be individualized, and optimal therapy depends on careful consideration of all the options, by both the doctor and the patient.
McGovern, PG, Pankow, JS, Shahar, E, et al. Recent trends in acute coronary heart disease--mortality, morbidity, medical care, and risk factors. The Minnesota Heart Survey Investigators. N Engl J Med 1996; 334:884.
Rosamond, WD, Chambless, LE, Folsom, AR, et al. Trends in the incidence of myocardial infarction and in mortality due to coronary heart disease, 1987 to 1994. N Engl J Med 1998; 339:861.