Role of Cardiac Magnetic Resonance Imaging in the Assessment of Myocardial Viability

D ysfunctional myocardium that remains viable has the potential for contractile recovery after reperfusion. 1 Dysfunctional but viable myocardium has been broadly divided into 2 closely linked pathophysiological states, myocardial hibernation and stunning.Stunned myocardium is the result of an ischemic insult leading to contractile dysfunction despite adequate reperfusion.Hibernating myocardium describes downregulation of myocyte metabolism as a result of prolonged reduction in perfusion, or, in some cases, repetitive episodes of myocardial stunning. 2The exact nature of structural changes in hibernating myocardium remains controversial. 3However, a spectrum of histological alterations has been noted, ranging from cellular dedifferentiation (fetal phenotype) to cellular degeneration (with more extensive fibrosis) with loss of contractile and cytoskeletal proteins.Worsening histological perturbations correlate with increasing duration of chronically low perfusion.Thus, accurate and early detection of viable myocardium has become an increasingly important guide to prognosis and therapy.Until recently, scintigraphic techniques and stress echocardiography were the mainstay of diagnosis. 4,5The focus of the present article is on the rapidly emerging clinical role of cardiovascular MRI (CMR) in the detection of viable myocardium.