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INTRODUCTION

KEY POINTS

  • Following an acute or chronic ischemic injury, dysfunctional myocardium can be classified as viable (stunned or hibernating myocardium) or nonviable (necrotic and scar).

  • Hibernating myocardium is characterized by reduced perfusion at rest after repeated episodes of ischemia and/or stunning, and despite being dysfunctional, it is viable. It has the capacity for functional recovery if adequate and timely revascularization can be achieved.

  • During fasting conditions, free-fatty acids are the preferred energy substrate of the myocardium. However, ischemia can cause a shift toward glucose utilization making positron emission tomography (PET) with 18F-fluorodeoxyglucose (FDG) a highly sensitive means to evaluate the presence of hibernating myocardium.

  • While all techniques (18FDG PET, dobutamine echocardiography, 201Tl-single-photon emission computed tomography [SPECT], 99mTc-SPECT, and cardiac magnetic resonance imaging [CMR] can be used for viability assessment and guidance in decision making, some may be better in certain circumstances. Among these 18FDG PET and CMR are considered more sensitive, while dobutamine echocardiogram and CMR are considered more specific.

  • The use of viability studies is best targeted to patients at higher risk for cardiac death or other cardiac events whose benefit from cardiac revascularization may be considered less certain due to factors such as comorbidities and poor vascular targets. The revascularization benefit must outweigh the risk of a potential surgery or intervention and enable improved outcome and quality of life.

  • Several prospective outcomes trials have demonstrated clinical benefit when revascularization is guided by the presence or absence of viable tissue by 18FDG PET imaging, especially with viable myocardium over 20%.

One in every eight deaths is attributable to heart failure (HF). The prevalence of HF continues to increase. In the United States, HF has increased from 5.7 million in 2012 to 6.5 million in 2014, and it is estimated that this will be more than 8 million people by 2030. This will lead to 127% increase in healthcare costs amounting to approximately $69.7 billion.1,2 Although survival of HF patients has improved, it remains a disease with poor outcome with a 50% mortality at 5 years.3 Given the growing prevalence of ischemic heart failure (IHF) and its high mortality rate, the optimal management strategies for IHF have been the focus of research for the past several decades. Evidence, including randomized controlled trials, has accumulated and supports the notion that patients with IHF may benefit from viability imaging to guide therapy and revascularization decisions.4–12 Many studies have suggested that viability assessment using noninvasive testing is a predictor of LV function and outcome benefit with revascularization.7,8,10–13 However, the viability substudies of the recent Surgical Treatment for Ischemic Heart Failure (STICH) and STICH Extension Study (STICHES) trials called some of these observations into question (discussed in details below).14,15 The STICH(ES) trial demonstrated long-term outcome benefit for revascularization in patients with left ventricle (LV) dysfunction, angina, and suitable anatomy. The viability substudies (that used single-photon emission computed tomography ...

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