Risk stratification soon after acute infarction.

Two decades ago, exercise testing “soon after acute myocardial infarction” meant that stress testing was performed 3 weeks after the acute event.1 It was conventional wisdom that patients recovering from acute myocardial infarction should avoid physical activities exceeding a workload of 3 METs for some time.2 Formal physical rehabilitation was not commenced before 10 weeks after infarction. In 1979, Theroux et al3 challenged this concept by submitting patients with recent and uncomplicated acute infarction to submaximal exercise electrocardiography at the time of hospital discharge, which at that time was '11 days after infarction. Not only was submaximal exercise testing shown to be safe in such patients, it also provided important prognostic information concerning the occurrence of future cardiac events. Although this landmark study set the stage for the use of exercise testing to evaluate patients with recent myocardial infarction, the prognostic power of exercise electrocardiography in later studies was found to be limited.4 This was probably due to difficulties in interpreting exercise ECGs in patients with abnormal resting ST-T segments. A few years later, Gibson et al5 showed that the addition of Tl myocardial perfusion imaging to submaximal predischarge exercise electrocardiography significantly enhanced the power of the test for predicting future cardiac events compared with that of exercise electrocardiography alone. More recently, Mahmarian et al6,7 demonstrated that quantitative single photon emission computed tomography (SPECT) myocardial perfusion imaging with either exercise or pharmacological vasodilation in patients with recent myocardial infarction allowed patients to be stratified into low-, intermediate-, or high-risk groups. Cardiac events after infarction have been noted to occur predominantly during the 4 to 6 weeks after the acute event, after which time the cardiac event rate is considerably lower.8 Thus, risk stratification by stress testing should be performed before the patient is discharged from the hospital. When exercise testing is postponed until several weeks after infarction to achieve maximal exercise effort, there is substantial risk that some patients will already have suffered the cardiac events about which one wished to prognosticate. The 1996 “Guidelines for Management of Patients with Acute Myocardial Infarction” recommend submaximal exercise testing at 4 to 6 days after infarction and symptom-limited exercise at 10 to 14 days after infarction.9