MRI assessment of myocardial viability

In the presence of coronary artery disease, global left ventricular (LV) systolic function is a critical prognostic indicator. Because of enhanced therapy for myocardial infarction, more patients survive but are left with residual myocardial damage that predisposes them to developing CHF in the future. Although treatments for CHF are evolving, preventing and minimizing further deteriorations in LV function are paramount in this population. Distinguishing severe LV dysfunction caused by thinned, infarcted myocardium with fibrosis and scarring from that due to viable but dysfunctional myocardium from chronic hypoperfusion has significant implications for clinical management. In patients in whom noninvasive testing identifies viability, undergoing revascularization improves outcomes. Noninvasive imaging techniques used to assess viable myocardium are based on demonstrating the presence of one or more of the following features: (1) contractile reserve; (2) sufficient perfusion for the delivery of substrates and removal of metabolic byproducts; (3) intact myocyte membranes to maintain ionic/electrochemical gradients; and (4) preserved metabolism with generation of high-energy phosphates. While nuclear and dobutamine echocardiography have been widely used for viability assessment, cardiac magnetic resonance imaging (CMR) is increasingly becoming an accepted clinical tool, particularly in light of its high spatial resolution, intrinsic ability to image 3-dimensionally, and greater soft tissue differentiation. Moreover, the versatility of the technique potentially allows for the simultaneous assessment of regional wall motion, perfusion, and metabolism. An overview of the CMR techniques is presented.