Identification of viable myocardium.

Abstract

In recent years, diagnostic testing to evaluate the presence and extent of viable but dysfunctional myocardium has become an important component of the clinical assessment of patients with chronic CAD and LV dysfunction. It is well established that impaired LV function in such patients is not always an irreversible process related to previous myocardial infarction, because LV function may improve considerably after myocardial revascularization procedures.1 2 3 4 5 6 The mechanism for this improvement in systolic function remains a matter of uncertainty and debate because the underlying processes responsible for reversible contractile dysfunction are often difficult to ascertain in patients, and the development of animal models of chronic reversible dysfunction has been disappointing to date. Restoration of blood flow to chronically underperfused myocardium may lead to the functional recovery of hibernating myocardium,1 3 5 whereas revascularization of myocardium with adequate perfusion at rest but with recurrent ischemic episodes during stress may successfully reverse persistent contractile dysfunction caused by repetitive stunning.7 8 9 10 Although the terms “hibernation” and “stunning” represent uniquely different pathophysiological processes with distinct definitions, in clinical circumstances the boundaries between stunning and hibernation are often indistinct. It is likely that both hibernation and repetitive stunning do occur clinically and contribute to ischemic LV dysfunction. Moreover, both processes may occur in the same patient and even coexist in the same myocardial region. Given the critical balance between reduced perfusion, reduced function, and reduced coronary flow reserve in the hibernating myocardium, some myocardial regions that are hibernating at rest may develop ischemia during exercise with a subsequent process of postischemic stunning superimposed on the baseline hibernating state. Thus, the clarity with which chronic LV dysfunction can be defined as hibernation, repetitive stunning, or a combination of the two processes is limited. On the other hand, …