The Current Role of Viability Imaging to Guide Revascularization and Therapy Decisions in Patients With Heart Failure and Reduced Left Ventricular Function

Abstract

This review describes the current evidence and controversies for viability imaging to direct revascularization decisions and the impact on patient outcomes. Balancing procedural risks and possible benefit from revascularization is a key question in patients with heart failure of ischemic origin (IHF). Different stages of ischemia induce adaptive changes in myocardial metabolism and function. Viable but dysfunctional myocardium has the potential to recover after restoring blood flow. Modern imaging techniques demonstrate different aspects of viable myocardium; perfusion (SPECT, PET, CMR), cell metabolism (PET), cell membrane integrity and mitochondrial function (201Tl and 99mTc-based SPECT), contractile reserve (stress echocardiography, CMR) and scar (CMR). Observational studies suggest that IHF patients with significant viable myocardium may benefit from revascularization compared to medical treatment alone but that in patients without significant viability, revascularization appears to offer no survival benefit or could even worsen the outcome. This was not supported by 2 randomized trials (STICH and PARR-2) although post-hoc analyses suggest that benefit can be achieved if decisions had been strictly based on viability imaging recommendations. Based on current evidence, viability testing should not be the routine for all patients with IHF considered for revascularization but rather integrated with clinical data to guide decisions on revascularization of high-risk patients with comorbidities. Fundamental concepts regarding viability imagingIn patients with IHF, left ventricle (LV) dysfunction can result from scar, stressinduced ischemia, resting ischemia, remodelling, stunning, hibernation or a combination of these processes. To understand the potential benefits of revascularization, knowledge of the different myocardial states in IHF is essential.(2-7) Myocardial ischemia refers to a state of inadequate oxygen delivery that cannot meet the myocardium´s metabolic demand.(8) The severity of inadequate flow will determine the intrinsic molecular adaptations of the myocardium and High Optimal medical therapy

Evolving use of PET viability imaging

“…PET 18 FDG viability imaging is frequently used to guide clinical decision-making on the role of revascularization in high-risk patients with heart failure and reduced left ventricular function, coronary artery disease (CAD) and significant comorbidities. Several observational nonrandomized studies have shown that patients with viability will likely benefit from revascularization, [1][2][3][4][5] with improvement in left ventricular function 1,5 and survival.…”

“…4 However, 4 randomized studies evaluating the value of viability imaging in patients undergoing revascularization have failed to demonstrate outcome differences. [6][7][8][9][10] The PET and Recovery Following Revascularization (PARR)-2 trial randomized 430 patients with LVEF B 35% to 18 FDG viability imaging or usual care and showed a nonsignificant trend for 1-year benefit. 6 Since the imaging recommendations were not adhered to in all the PET patients, a post hoc analysis was carried out in the PET group with management adhering to the PET recommendations and demonstrated significant benefit.…”

“…The physiological and technical aspects of PET 18 FDG viability imaging and scan interpretation have been well described in the PET imaging guidelines cosponsored by the American Society of Nuclear Cardiology and the Society of Nuclear Medicine and Molecular Imaging. 14 In a region of reduced resting perfusion, preserved 18 FDG uptake indicates viability (perfusion-metabolism mismatch or hibernation) and reduced 18 FDG uptake of similar or greater degree is consistent with nonviable tissue or scar (perfusionmetabolism match). Regions with normal perfusion are viable, even with reduced 18 FDG (perfusion-metabolism reverse mismatch), and may represent stunned myocardium.…”

“…Regions with normal perfusion are viable, even with reduced 18 FDG (perfusion-metabolism reverse mismatch), and may represent stunned myocardium. Standardized patient preparation is critical for high quality diagnostic 18 FDG images and needs to favor myocardial metabolism of glucose over fatty acids. An endogenous insulin response is achieved by oral or intravenous glucose loading after a 6 to 12 hour fast and maximizes 18 FDG uptake with less regional heterogeneity.…”

“…Standardized patient preparation is critical for high quality diagnostic 18 FDG images and needs to favor myocardial metabolism of glucose over fatty acids. An endogenous insulin response is achieved by oral or intravenous glucose loading after a 6 to 12 hour fast and maximizes 18 FDG uptake with less regional heterogeneity. Supplemental insulin may be required to maintain an optimal blood glucose.…”