There are also some data involving exercise testing and coronary arteriography that link persons with silent myocardial ischemia to episodes of sudden death. In a study of Norwegian workers, Erikssen and Thaulow reported a nearly 0.5 percent yearly incidence of sudden death due to coronary artery disease in an asymptomatic population. Hickman et al reported a similar number in a study of US Air Force personnel. If one makes the assumption that there are at least 250,000 unexpected sudden deaths because of coronary artery disease in the United States, and at least 25 percent (approximately 60,000) have no prior clinical history of coronary artery disease, then at least 5,000 to 10,000 of these 60,000 individuals had totally asymptomatic silent myocardial ischemia. (This figure would represent an 0.5 percent incidence of sudden death in the estimated 1-2 million asymptomatic men in this country. The derivation of this latter figure will be described subsequently.)
Sharma et al have provided direct evidence of this linkage. In their study of 19 patients who were resuscitated from out-of-hospital ventricular fibrillation, 11 had no clinical history of cardiac disease. All 19 were shown to have severe coronary artery disease and 15/19 had evidence of silent myocardial ischemia. There are also anecdotal (unpublished) reports from other centers citing similar experiences.
How Many People Have Silent Myocardial Ischemia?
Silent myocardial ischemia can be defined as transient alterations in myocardial perfusion, function, or electrical activity in the absence of chest pain or the usual anginal equivalents (arm or jaw pain, numbness, etc). The condition may occur in totally asymptomatic individuals (type 1); in asymptomatic postinfarction patients (type 2); and in patients who have angina but also have episodes of silent ischemia (type 3). One of the best prevalence studies for type 1 patients is that of Erikssen and Thaulow. In their study of 2,014 male Norwegian office workers, ages 40 to 59, they found that 50 (2.5 percent) manifested silent myocardial ischemia after exercise testing. Coronary angiography showed that a similar number of these 50 patients had single-, double-, and triple-vessel coronary artery disease. Froelicher et al, in a study involving US Air Force personnel, found significant coronary artery disease in 34 (2.5 percent) of1,390 airmen. Langou et al, in a smaller study, reported that 12 of 120 asymptomatic male industrial workers (9.3 percent) had asymptomatic coronary artery disease; silent myocardial ischemia was suspected by abnormal exercise testing, combined with fluoroscopic evidence of coronary artery calcification. Canadian Neighbor Pharmacy official website may be useful either as a source of drugs or as a way to know something new about medicine and pharmacy.
How do we estimate the prevalence of silent myocardial ischemia in post-infarction patients? We use data from the low-level exercise tests that are commonly obtained following acute myocardial infarction, plus the standard exercise tests that are often administered to patients who at some time previously have sustained an infarction. We know that about one-third of surviving patients hospitalized for acute infarction develop angina, heart failure, or serious arrhythmias. These conditions make exercise testing hazardous. Of the “uncomplicated” patients who are presumably asymptomatic at discharge, we estimate 100,000 will have a positive result of exercise test. Perhaps half of these patients, or approximately 50,000, have no symptoms despite the presence of ischemia.
In patients with angina, the prevalence of silent myocardial ischemia can be best demonstrated by ambulatory ECG (Holter) monitoring. Two important studies have shown that 60 to 100 percent of the 4 million patients with angina pectoris in the United States have frequent episodes of silent myocardial ischemia in addition to their symptomatic episodes. Thus, it is possible that about 3 million patients with angina may be affected. Because the silent episodes may occur several times more than the symptomatic episodes, painful episodes probably represent only a small portion of total ischemic episodes in patients with angina.