Myocardial viability in ischemic heart disease: New directions and perspectives

In patients with ischemic heart disease detection of myocardial viability is of major clinical and prognostic importance and may significantly affect therapeutic decisions. Reversible left ventricular dysfunction may be due to different pathophysiological mechanisms, including myocardial hibernation and stunning, structural and ultrastructural myocardial changes and alterations in gene expression leading to myocardial cell dedifferentiation. Each of these mechanisms may have different importance related to the clinical history of the patient and severity and duration of left ventricular dysfunction and may significantly influence the extent and time course of functional recovery after myocardial revascularization. In the clinical arena detection of myocardial viability is currently based on the use of nuclear techniques, which show preserved tracer uptake and metabolism in viable myocardium and echocardiographic methods, which detect residual contractile reserve. Both techniques show a similar sensitivity in predicting functional recovery after revascularization, but dobutamine echocardiography has a higher specificity and therefore may be clinically more useful. Due to the limitations of current nuclear and echocardiographic methods in detecting myocardial viability, new developments are directed towards better quantification of viable myocardium and simultaneous assessment of myocardial metabolism, perfusion and function. Doppler tissue imaging, intravenous contrast echocardiography and ECG-gated SPECT with combined evaluation of metabolism and perfusion seem to be the most promising and cost-effective methods for a comprehensive assessment of myocardial viability. The major prognostic importance of myocardial viability in patients with severe left ventricular dysfunction is demonstrated by the fact that patients with a significant amount of viable myocardium have a marked survival benefit from revascularization and an improvement in left ventricular function and NYHA functional class compared with those without or only marginal viability. Thus, in patients with severe dysfunction preoperative quantification of viable myocardium is of utmost importance to identify patients who can benefit from revascularization. In patients with lesser amount of viable myocardium the possible beneficial effect of revascularization on survival, even in the absence of significant improvement in ventricular function, is yet to be demonstrated and should be assessed in future prospective clinical trials.