IJCS | Volume 32, Nº1, January/ February 2019

76 Table 2 - Comparison of the STICH Viability Substudy with PARR-2 - Adapted with permission from Mielniczuk et al., JACC Cardiovasc Imaging 43 STICH substudy PARR-2 Patient population Randomized? Not the substudy Yes Mean age, years 60.7 63 Male sex 85 84 Previous CABG 3 19 Diabetes mellitus 39 39 Estimated GFR < 60 mL/min/1.73m 2 7.5 34 Mean serum creatinine 108 µmol/L Viability testing SPECT or dobutamine echocardiography PET Prevalence of viability 81 22 Values are % unless otherwise indicated. CABG: coronary artery bypass grafting; GFR: glomerular filtration rate; SPECT: single- photon emission computed tomography. Erthal et al. Myocardial viability: from PARR-2 to IMAGE HF - current evidence and future directions Int J Cardiovasc Sci. 2019;32(1)70-83 Review Article Beyond clinical events, there is evidence that patients undergoing FDGPET have improved quality of life versus standardcare (notundergoingFDGPET) at least intheshort term. 40 Other studies have also reported revascularization directed by FDGPET improves HF symptoms and quality of life. 10,41 There is also evidence to support that viability imaging with PET is cost-effective when hibernation data are used to guide revascularization. 42 Comparing PARR2 and STICH It is important to understand the differences between PARR-2 and STICH in order to appreciate their respective significance. 6,35,40,43 First, in STICH, patients had to be acceptable for revascularization. While patients were randomized to coronary artery bypass graft surgery versus optimal medical therapy, imaging was not randomized nor did it direct the therapy decision. Conversely, in PARR-2, patients in whom decisions regarding revascularization was uncertain were randomized to FDG PET viability imaging versus standard care with no FDG PET imaging. The tests for viability assessment were also different: 18 FDG PET in PARR-2 and SPECT or dobutamine ECHO in STICH. Compared to the STICH population, PARR-2 patients hadmore renal dysfunction (7.5% versus 34%), had more prior coronary artery bypass graft surgery (3% versus 19%), more multivessel coronary artery disease (75% versus 90%) and less viable myocardium (81% versus 22%), suggesting these patient cohorts were not the same (Table 2). 40,43 From those studies, it is safe to conclude that viability imaging is not needed in all patients with ischemic heart disease and left ventricular dysfunction who are being considered for revascularization. However, there may be high-risk patients whose decisions are particularly difficult where viability imaging has a role. 40,43 Viability tests: when should we use it? Current evidence and guidelines support the use of viability imaging to assist decision-making in patients with ischemic HF (Table 3). 44–50 The imaging modality of choice for viability assessment needs to be individualized according to each clinical scenario, technology availability and institution expertise. 14,40,41,49–52 In our experience, viability imaging is appropriate in patients with known or strongly suspected ischemic HF, New York Heart Association (NYHA) ≥ II, moderate to severe left ventricular dysfunction (left ventricular ejection fraction< 40%), moderate to large perfusiondefects andno significant ischemia, significant comorbities and/or poor vessel targets (Figure 5). 49,51,52 On the other hand, viability is not (or less) useful in patients with predominantly angina CCS > II, thosewith normal or mild left ventricular dysfunction, critical left main coronary artery disease, patients with good revascularization targets, those with already-demonstrated moderate to severe ischemia and those with minimal or no comorbidities. 51,52 Figure 6 illustrates two examples of viability imaging. When viability imaging is needed, the choice of which test depends on specific advantages of the different modalities, availability and local expertise. Until comparative evidence is available (see “FutureDirections”), the following is an approach to selectwhich test for viability in which circumstance as suggested by the authors: 51,52 1. Normal or mild left ventricular dysfunction – viability imaging is rarely needed. 2. Moderate left ventricular dysfunction – any method can be considered depending on availability and local expertise. 3. Very severe left ventricular dysfunction - consider nuclear methods (SPECT, FDG PET) or late