Current Diagnostic Techniques of Assessing Myocardial Viabilit in Patients With Hibernating and Stunned Myocardium

T he differentiation of viable from nonviable myocardium in patients with coronary artery disease and left ventricular dysfunction is an issue of increasing clinical relevance in the current era of myocardial revascularization. It is now well established that impaired left ventricular function does not always represent an irreversible process. However, until recently, determining whether impaired regional or global left ventricular function at rest was a potentially reversible process could be made only retrospectively, after the patient had undergone coronary artery angioplasty or bypass surgery.1-6 Because enhanced left ventricular function after revascularization is associated with improved survival,7-9 diagnostic procedures that identify reversible asynergy prospectively may provide significant prognostic information. Thus, the accurate distinction between viable and scarred or necrotic myocardium has important clinical implications, especially in patients who are being considered for interventional therapy. In the past, coronary artery patency and preserved regional contractile function were used to identify viable myocardium. However, the inadequacy of an occluded epicardial coronary artery to predict nonviable myocardium was realized when coronary collateral circulation was shown to be capable of sustaining myocardial function at rest10-12 and even during exercise.12-14 Conversely, a patent coronary artery after thrombolytic therapy is insufficient evidence that the dysfunctional myocardium perfused by this artery is viable.15 Electrocardiographic criteria for viability are also imprecise. Although left ventricular function after revascularization is more likely to improve in patients with non-Q wave rather than Q wave infarctions,16 electrocardiographic Q wave criteria are not specific for determining the extent of scarred or viable myocardium after myocardial infarction.3,17-19 Similarly, both animal and clinical studies have also demonstrated that regional myocardial contractile function does not reliably distinguish viable myocardium from nonviable myocardium.20-24 It has been shown that under certain conditions, when viable myocytes are subjected to ischemia, prolonged alterations in myocyte