Assessing prognosis after acute myocardial infarction in the thrombolytic era.

Abstract

The use of physiologic testing for prognostication continues to be useful and widely applied in the predischarge evaluation of patients recovering from an uncomplicated acute myocardial infarction in the thrombolytic era. Because patients with abnormal exercise test results are now routinely sent for angiography, there are no randomized trials or experimental confirmation that exercise parameters are still associated with the same prognostic value in the thrombolytic era. Nevertheless, the excellent outcomes in patients treated with thrombolytic therapy and risk stratified with exercise testing provide strong empiric support for the continued use of noninvasive testing of patients without complications after thrombolytic therapy. Reviews of patient cohorts enrolled in trials of thrombolytic therapy show that these patients have a lower incidence of multivessel disease and less evidence of ischemia (ST segment depression or thallium 201 redistribution) compared with prethrombolytic cohorts. For this and other reasons, the sensitivity and specificity of exercise variables for prognosis or detection of multivessel disease are not as strong. The addition of perfusion imaging will enhance the sensitivity for detection of ischemia within or remote from the infarct zone and will provide information regarding viability. Patients who are unable to exercise or those with poor exercise tolerance, an abnormal exercise blood pressure response, inducible ischemia, or nonsustained ventricular tachycardia are candidates for further invasive evaluation and consideration for coronary revascularization. With 201Tl imaging, evidence for increased pulmonary uptake of the tracer is indicative of high risk and a high probability of an adverse outcome with medical therapy. Low-risk patients are those who achieve their target heart rate or work load without inducible angina, ST segment depression, reversible perfusion abnormalities, or increased lung 201Tl uptake. Defect size is reflective of infarct size, and patients with extensive areas of nonreversible hypoperfusion are also at high risk for future events even in the absence of ischemia. Finally, pharmacologic stress imaging with dipyridamole, adenosine, or dobutamine has been found to be safe when employed for stress testing soon after uncomplicated infarction.