IJCS | Volume 32, Nº1, January/ February 2019

71 Table 1 - Viable and non-viable myocardium Myocardium Flow Glucose metabolism/ FDG Function Potential to recover Non-Viable Scar/Fibrosis Reduced Reduced Reduced Unlikely Viable Stunned Preserved (has suffered an intermittent ischemic insult) 65,66 Variable [can be normal, increased or reduced (reverse mismatch)] 65–69,67–71,67–71 Reduced Likely to recover if ischemic injury does not persist or become repetitive; 4,14 may benefit from revascularization Hibernation Reduced Preserved (flow-metabolism mismatch) Reduced Likely to have part or full recovery if adequate revascularization can be achieved 5,72 Ischemia Preserved at rest (impaired at stress) Normal at rest, increased at stress 67 Preserved May benefit from revascularization 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 glucose uptake. Single-photon emission computed tomography (SPECT) with thallium-201 ( 201 Tl), a potassium analogue, has the sarcolemma membrane integrity as its target (sodium/potassiumATPase pump activity). 16 SPECT with technetium-99m ( 99m Tc)-based tracers test the mitochondrial membrane integrity. 17,18 Dobutamine echocardiogram (ECHO) and dobutamine magnetic resonance imaging (MRI) measure myocardial contractile reserve. Delayed enhancement MRI and computed tomography target the amount of fibrotic tissue, and myocardial contrast ECHO targets the microvascular integrity. 19,20 In a meta-analysis by Schinkel et al. 5 reviewing 24 studies (756 patients) comparing all available imaging modalities, 18 FDGPETwas shown to be themost sensitive to predict regional function recovery, and dobutamine ECHOwas themost specific (92%, 63%, 74%and 87%and 80%, 78%, 75% and 83%of sensitivity, specificity, positive and negative predictive value for PET and ECHO, respectively). 5 CardiacMRI, whichwas underrepresented in this meta-analysis, had sensitivity, specificity, positive and negative predictive values of 74%, 82%, 78% and 78% for dobutamine stress MRI and 84%, 63%, 72% and 78% for delayed enhancement MRI. 5 In this same meta-analysis, a total of 721 patients underwent 99m Tc-tracer-based SPECT and 1,119 had 201 Tl SPECT to assess viability. 201 Tl was more sensitive and 99m Tc-tracer-based SPECT more specific to predict recovery, with sensitivity, specificity, positive and negative predictive values of 87%, 54%, 67% and 79% and 83%, 65%, 74% and 76% for 201 Tl and 99m Tc, respectively. 5 Comparisons between nuclear techniques suggest 18 FDG PET is the superior technique to detect the amount of hibernating myocardium, 21–25 except for one study directly comparing 201 Tl and 18 FDGPET, which suggested similar viability detection for both methods. 26 More recent data analyzing MRI performance in detecting viable myocardium have supported its high sensitivity. 27–30 Romero et al. 27 have conducted a meta-analysis of MRI prospective trials including 24 studies (698 patients) and found a sensitivity of 95% for predicting functional recovery for MRI with delayed enhancement. Dobutamine MRI was the most specific (91%) when compared to delayed enhancement and end-diastolic wall thickness techniques. 27 Kühl et al. 29 have studied 29 patients with chronic ischemic HF and mean ejection fraction of 32% who had both MRI and PET/SPECT ( 18 FDG for metabolism and 99m Tc SPECT for perfusion) performed at baseline and at 6-month follow-up after revascularization. 29 The group found MRI to have higher sensitivity and PET/SPECT to be more specific (97% versus 87% sensitivity and 68% versus 76% specificity for MRI and PET/SPECT, respectively). 29 Amore recent study has analyzed the feasibility of PET/ MRI scanners in evaluating segment functional recovery in 28 patients post-acute myocardial infarction (MI) and percutaneous revascularization. 30 All patients underwent PET/MRI with contrast for delayed enhancement and 18 FDG injection for uptake assessment 5-7 days after the acute event and had a follow-up MRI for contractility