Positron Emission Tomography for Assessment of Myocardial Perfusion and Viability.
The distinction between left ventricular (LV) dysfunction caused by fibrosis and that arising from viable (hibernating and/or stunned) myocardium has important implications for the management of patients with ischemic cardiomyopathy. In many of these patients, LV function can improve significantly, and even normalize, after revascularization. Positron emission tomography (PET) is the most accurate noninvasive imaging technique for detection of viable myocardium. Increased glucose uptake in dysfunctional segments with reduced blood flow at rest (PET mismatch) indicates the presence of viable myocardium, whereas a concordant reduction in blood flow and glucose uptake (PET match) indicates a myocardial scar. A PET mismatch pattern has a 79% average positive predictive value for predicting improved function after revascularization, whereas a PET match pattern has an 84% average negative predictive value for lack of such functional recovery. The greater the number of viable myocardial segments shown by PET, the greater the probability that revascularization will improve regional and global LV function and, consequently, improve heart failure symptoms and survival. In patients with PET mismatch, long-term survival is consistently poor with medical therapy but significantly improved by early referral to revascularization. This survival benefit is apparent in patients with and without angina. Conversely, long-term survival in patients without such PET mismatch is similar with medical therapy or revascularization, especially if minimal or no anginal symptoms are present. These observations suggest that noninvasive investigation of the amount of viable myocardium should be an important component of the diagnostic evaluation of patients with heart failure because of coronary artery disease. This approach will likely enhance the often difficult process of selecting patients with poor cardiac function in whom revascularization will likely improve both the quality and quantity of life.
Di Carli MF
Wayne State University School of Medicine, Detroit, Michigan.