Risk Stratification After Myocardial Infarction: Targets and Tools

The increasing use of thrombolytic therapy and coronary revascularization, either as acute therapy or early thereafter, has ushered in the “interventional era” of management of myocardial infarction (MI). This new scenario has at least two clear cut clinical implications. First, the cardiologist can intervene earlier to change the “natural history” of MI, not only to improve the immediate inhospital prognosis but also to prevent the development of those factors affecting the clinical outcome after discharge. Second, patients currently selected for predischarge evaluation are at lower risk for subsequent cardiac events. The critical management decision is with the majority of patients who have an uncomplicated MI. Two approaches may be applied to this large cohort to assess cardiac risk before hospital discharge. One method is the initial use of noninvasive tests reserving coronary angiography for patients with abnormal test results. The second approach comprises early cardiac catheterization in virtually all survivors. The routine use of angiography after MI does not appear to lead to an improved course compared to a more selective approach. Based on observation of an excellent 1‐year outcome of patients in the conservative group of the large TIMI‐2 and SWIFT trials, one could conclude that predischarge risk stratification by stress testing and clinical assessment has been empirically, albeit not experimentally, validated. On the other hand, if a noninvasive test proved to be highly predictive of subsequent cardiac events, the need for doing routine coronary angiography would in large part be obviated. Developing or refining such a test should take into account several caveats. First, the pathophysiological mechanisms of critical cardiac events after MI are probably not identical. Obviously, no single test addresses all the potential mechanisms and accurately predicts such diverse endpoints. An additional caveat concerns the progressive improvement in sensitivity of stress testing which in turn adversely affects their prognostic value especially in patients with a low prevalence of events. This highlights the need of using a test that allows stratification of abnormal response to stress in terms of site, extension, and timing of occurrence of myocardial ischemia. Finally, the independent and incremental prognostic value of the test, compared to the other more established methods, should be assessed. Stress echocardiography is emerging as a promising tool for post‐MI risk stratification strategy. Multiple observational studies indicated that transient left ventricular dysfunction during stress has important prognostic value in predischarge risk stratification after MI. In particular, dipyridamole echocardiography (DE) has shown, in studies that used multivariate analysis, to be the best independent predictor of cardiac events of all noninvasive and invasive variables. Updated results of the subproject residual ischemia of the large scale EPIC trial indicate that, by multivariate analysis, only age and rest‐stress wall‐motion score index difference were independent and additive predictors of death. These data suggest that angiography supplies redundant information when clinical, resting echo, and DE data are considered for predicting survival after uncomplicated MI. Thus, the best “action” to take in managing the patient with uncomplicated MI is to exercise good clinical judgment, carefully monitor and test the patient for evidence of post‐MI ischemia, and act accordingly.