An approach to myocardial viability based on perfusion, function and metabolic substrates.

In the clinical assessment of myocardial viability, the concept of down-regulation of contractile function is important in understanding the interaction between coronary flow and ventricular function. In this state, the myocardium remains viable, although lacking overt contractile function, and may be totally reversible with complete revascularization. This abnormality is also associated with altered cellular metabolism, and individual substrate determinations are not necessarily as predictive of myocardial viability as are evaluations of overall oxidative metabolism. Nuclear cardiology imaging techniques can monitor oxidative phosphorylation and predict the overall viability of cardiac tissue. In addressing the clinical challenge of identifying those patients who would receive the most benefit from coronary revascularization, it is clear that a diagnostic test which combines blood flow and an evaluation of left ventricular wall motion would be of great potential value. One can make a strong case for the use of thallium imaging as an acceptable and readily available method, but the use of positron emission tomography (PET) tracers has been a strong gold standard. Recent work suggests that PET data do have a clinical impact in patient management, treatment, and the prediction of long-term morbidity and mortality. Patients with known coronary artery disease and significant left ventricular dysfunction need a functional evaluation of myocardial viability. Given this type of evaluation, patients should not be condemned to end-stage heart disease without performing at least one test for potential reversibility.