IJCS | Volume 32, Nº1, January/ February 2019

DOI: 10.5935/2359-4802.20180068 70 REVIEW ARTICLE International Journal of Cardiovascular Sciences. 2019;32(1)70-83 Mailing Address: Rob S.B. Beanlands University of Ottawa Heart Institute - 40 Ruskin Street, Ottawa, Ontario, K1Y 4W7 - Canadá E-mail: rbeanlands@ottawaheart.ca Myocardial Viability: From PARR-2 to IMAGE HF - Current Evidence and Future Directions Fernanda Erthal, ChristianeWiefels, Steven Promislow, Riina Kandolin, Ellamae Stadnick, LisaMielniczuk, Terrence Ruddy, Gary Small, Rob Beanland s University of Ottawa Heart Institute, Ontário - Canadá Manuscript received July 05, 2017, revised manuscript October 03, 2017, accepted October 15, 2018. Heart Failure; Myocardial Stunning; Positron Emission Tomography Computed Tomography; Hybernating. Keywords Abstract Ischemic heart failure is a growing disease with high morbidity and mortality. Several studies suggest the benefit of viability imaging to assist revascularization decision, but there is controversy. Multiple imaging modalities can be used to accurately define hibernating myocardium; however, the best approach remains uncertain. This review will highlight current evidence and future directions of viability imaging assessment. Introduction Ischemic heart failure (HF) is the leading cause of HF and an epidemic disease worldwide with growing prevalence and high mortality rate. 1,2 In 2011, 1 in 9 death certificates in the United States listed HF. 1 In 2015 in Brazil, 27,434 deaths occurred due to HF. 3 Medical treatment, cardiac rehabilitation, revascularization and the increased understanding of its pathophysiology have improved the overall prognosis and survival of patients withHF over the last years, but, despite that, around 50% of the patients diagnosed with HF will die 5 years after the initial diagnosis. 2 Accumulated evidence of the past years has suggested that individualized-target therapywith viability imaging assessment may improve outcome. 4,14,15 This review will focus on the understanding of the viability concept and current evidence. What is viable myocardium? A simplistic way to describe viable myocardium is all tissue that is not scar/fibrosis (non-viable myocardium). Naturally, normal myocardium is viable. Dysfunctional myocardium that is viable has the potential to recover from an injury. 4,14,15 Meanwhile, two concepts under the umbrella of “viablemyocardium” can be often misunderstood. “Stunned” and “hibernating” myocardiumare conditions inwhich function is impaired but is potentially reversible. Stunned myocardium is characterized by the persistent dysfunction that follows an episode of ischemia. Hence, there is normal rest flow and impaired function. The severity and duration of the stunning (post-ischemic dysfunction) depend on duration, extent and severity of the preceding ischemic insult. So long as there is no infarction during such ischemia, full recovery is expected, the timing of which also depends on the duration, extent and severity of the preceding ischemia. If stunning occurs repeatedly, the myocardium must adapt to the repetitive injury. It does so by reducing contractile function and flow in response to these events. 15 Repetitive stunning is believed to be the precursor to hibernating myocardium, where both measured perfusion and function are reduced but restorable in whole or in part if blood flow can be adequately restored before irreversible injury occurs. This is the area of focus for viability imaging (Table 1). 4,14,15 Imaging modalities for viability assessment Several imaging modalities can be used to assess hibernating myocardium, and each has different metabolic/cellular targets and findings to detect viable and hibernating myocardium. Cardiac positron emission tomography (PET) with 18 Fluorodeoxyglucose ( 18 FDG) uses a glucose analogue to measure myocardial