ABC | Volume 110, Nº3, March 2018

Review Article Ket et al Practical Implications of Myocardial Viability Studies Arq Bras Cardiol. 2018; 110(3):278-288 Figure 1 – Main feature of the physiopathology of stunned myocardium and hibernating myocardium [adapted from Chareonthaitawee et al. 8 ]. Stunned myocardium and hibernating myocardium in the pathophysiology of reversible left ventricular dysfunction Different mechanisms and similarities Stunned myocardium • Adverse effect of ischemic injury • Without histopathological changes Hibernating myocardium • According to researches, protection against adaptative reduction of blood flow or ischemia Viability preserved Progressive, dynamic histopathological changes Repeated stunning • May lead to transition from stunned to hibernating myocardium in response to severe coronary flow reduction • Progressive, dynamic histopathological changes. “Hibernating myocardium” has been defined as the presence of severe systolic dysfunction with evidence of hypoperfusion at rest; 3 it refers to a myocardium with preserved cellularity, but reduced blood flow, leading to depressed ventricular function, even at rest. 11 The first theory of hibernating myocardium characterized it as an adaptation to chronic hypoperfusion whose intensity was not sufficiently significant to cause infarction. 12 This was supported by CMR and PET studies on dysfunctional myocardial areas with reduced blood flow. 13,14 However, pathogenesis of hibernating myocardium is still subject of studies and has not been elucidated yet,; it is believed, however, to be conditioned to a functional dysregulation related to mitochondrial impairment, in attempt to protect cardiac muscle cells from ischemia. 11,15 Hibernating is also known to have intrinsic cellular and extracellular changes, that may be associated with the time required for reversibility of the process, 12 which may vary from days to 14 months. 16,17 Clinical implications Assessment of viability may significantly contribute to the identification of patients who would benefit from revascularization, particularly by the improvement in ventricular function and survival. To demonstrate the clinical usefulness of viability, a meta-analysis was performed with 24 studies on different techniques on viability detection in patients with chronic coronary artery disease (CAD) and myocardial dysfunction. Annual mortality rate in the group of patients with myocardial viability and in drug treatment was 16%, in contrast with 3.2% in the group that underwent revascularization. 18,19 In CAD patients, left ventricular dysfunction may be caused by areas of viable myocardium and fibrotic areas combined. Assessment of cardiac muscle using imaging methods enables the localization, quantification of viability in dysfunctional myocardium and possibility of anatomical revascularization, which is essential for treatment planning of these patients. 11 This article proposes a review of pathophysiological bases of myocardial viability, diagnostic methods available, prognosis and risk for this condition. A bibliographic search was performed on the electronic databases PubMed, Lilacs, Cochrane and Scielo, based on pre-established criteria. Methods To achieve the objectives and results proposed, a descriptive review of scientific literature was conducted of studies on diagnostic accuracy of imaging tests used 279