Total ischemic burden: pathophysiology and prognosis.

Myocardial ischemia is caused by decreased supply (primary ischemia), increased demand (secondary ischemia) or a combination of the two (mixed ischemia). The sum of all episodes--with or without pain--constitutes the total ischemic burden. During out-of-hospital activities, many episodes occur at lower than expected heart rates, suggesting that a vasoconstrictive component is involved in the genesis of such episodes. These silent attacks may be even more important clinically than painful attacks. It has been suggested that silent myocardial ischemia has an adverse impact on prognosis in patients with totally asymptomatic ischemia or asymptomatic postinfarction ischemia. Further, it has been shown that there is a direct relation between the duration and frequency of silent myocardial ischemia and subsequent cardiac events in patients with unstable angina. Therefore, aggressive therapy may be warranted in certain groups of patients in whom silent myocardial ischemia constitutes a significant part of the total ischemic burden.