Different Roads to the Assessment of Myocardial Viability

Abstract

The assessment of myocardial viability remains clinically important, yet diagnostically challenging. Tamaki et al1 probe various approaches with positron emission tomography (PET). Since myocardial viability refers to a state of reversible impairment of contractile function, the authors correctly measure the accuracy of each approach against the postrevascularization outcome in systolic segmental wall motion as a yardstick of myocardial viability. The investigators conclude that (1) severe flow reductions accurately define myocardium as nonviable. In contrast, mild to modest reductions discriminate only poorly between viable and nonviable tissue. (2) The addition of stress-induced defects incrementally improves the identification of viable myocardium, even though the reasons for such improvement remain uncertain. (3) The combined evaluation of rest blood flow and 18F-deoxyglucose uptake as a tracer of exogenous glucose utilization distinguishes most reliably between viable and nonviable myocardium. As the authors acknowledge, the latter observation on the high predictive accuracy of blood flow metabolism patterns represents an extension of their earlier work.2 3 Together with other previous investigations,4 5 6 7 the present data further strengthen the case of flow metabolism patterns as accurate indexes of the myocardial state. Yet, the study does not answer clinically or therapeutically critical questions. It would have been important to know the effects of revascularization on global left ventricular function, clinical symptoms, or both and how such changes might relate to mismatches …