This pathogenesis may manifest as the chest pain of angina. Occasionally myocardial ischemia may occur without causing a sensation of chest pain; this condition is called silent ischemia.
When angina is present in an individual, it is certain that at least one coronary artery will show a greater than 70% obstruction or stenosis if a balloon angiogram is done to visualize the coronary arteries. The obstructive plaque of atheroma is often focal and usually occurs in the proximal portion of the coronary artery and not too distant from the origin of the aorta. Because the lesions are focal and proximal, they are easily reached with the balloon, which dictates the success of angioplasty and bypass surgery. In some individuals and in many diabetics, lesions are multifocal and longer with irregularities that produce a diffuse disease that is more difficult to treat with angio-plasty, stents, or bypass surgery. A 25% decrease in the outer radius of a normal coronary artery results in about a 60% decrease in a cross-sectional area. In an artery with 75% stenosis, a 10% decrease in the outer radius would produce a complete occlusion.
During periods of exercise or exertion, catecholamine release causes an increase in heart rate, and an increase in the velocity and force of myocardial contraction produces an elevation in blood pressure and an increase in myocar-dial oxygen demand. In the presence of significant coro¬nary artery stenosis, an oxygen deficit occurs. Myocardial ischemia increases catecholamine release, resulting in an additional increase in heart rate and blood pressure with further oxygen lack, and the vicious circle ensues (Fig. 2). In addition the coronary arteries fill during the diastolic period, which is shortened during an increase in heart rate.

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