ABC | Volume 110, Nº3, March 2018

Review Article Ket et al Practical Implications of Myocardial Viability Studies Arq Bras Cardiol. 2018; 110(3):278-288 for the measurement of myocardial viability. We included both studies showing the superiority of certain method and those comparing the efficacy of the methods from the perspective of other authors. Inclusion criteria: Types of study: as “review articles”, we included studies aimed to demonstrate the efficacy of imaging tests in measuring myocardial viability after ischemia. Population: heart disease patients with history of myocardial infarction. Exclusion criteria: Studies that did not provide a detailed description of the protocols of the diagnostic methods or of data statistical analysis, and studies that did not meet the inclusion criteria were excluded. Search on the databases The following databases were searched: • PubMed/MEDLINE: North-American database, one of the largest in health, with no limits of date. The following descriptors were used for the search on Pubmed: Myocardial viability; PET; CT; SPECT; Resonance Magnetic myocardial; Echocardiography. • LILACS: database that integrates the BIREME system and includes several scientific journals, dissertations and books. The following terms were used: Myocardial Viability ANS viability studies. • COCHRANE: database focused on systemic reviews. The terms used in this database were: Myocardial viability. Diagnostic methods Assessment of myocardial viability by dobutamine stress echocardiography The use of dobutamine stress echocardiography for detection of myocardial viability is an efficient and safe method in both acute and chronic phases of CAD, 20 with low incidence of significant events 21 (around 0,5%). 21,22 This method has favorable sensitivity (77-89%) and specificity (68-93%) not only in the post-infarction phase, 23,24 but also in the chronic phase (82% and 92%, respectively), as shown by Marzullo et al. 25 Assessment of myocardial viability using baseline-nitrate 99m Tc-Sestamibi scintigraphy Myocardial perfusion scintigraphy using nitrate- augmented 99m Tc-Sestamibi is a widely available method for assessment of myocardial viability. The use of nitrates enables the improvement of blood flow in narrowed and collateral vessels, responsible for irrigation of hypoperfused areas, which potentiates the ability of the method to detect viable tissues, especially when combined with 99m Tc‑Sestamibi. 11 This is assured by the fact that both absorption and retention of sestamibi depend on perfusion, cell membrane integrity and membrane potential (mitochondrial function), which hence constitute the markers of viable tissue. 25-27 Schinkel AF et al. 28 reported a 81% sensitivity and 69% specificity of nitrate-enhanced 99m Tc-Sestamibi scintigraphy to detect viability, which is lower than those reported with the use of PET- 18 F-FDG. 28 In Figure 1, we illustrate a case where rest perfusion defect, initially attributed to the infarction area, normalized after treatment of the coronary obstruction in the anterior descending artery, demonstrating a viable myocardium. These findings illustrate a practical limitation of imaging techniques using 99m Tc-Sestamibi in the detection of myocardial fibrosis and viability. In most studies on baseline-nitrate 99m Tc-Sestamibi scintigraphy, two patterns of images are commonly obtained: rest images and nitrate-enhanced images. Reversibility of the lesion (by filling) is indicative of viability. Sciagra et al. 29 studied 105 patients with chronic CAD and left ventricular dysfunction who underwent baseline-nitrate sestamibi perfusion imaging and showed that the most powerful prognostic predictors of events were the number of nonrevascularized dysfunctional areas with viability in sestamibi imaging 28,29 (Figure 2). Assessment of myocardial viability with 201 Tálio 201 Tálio has some limitations for routine use, due to its longer physical half-life, and relatively low photon energy and flow. This may yield images with low count-rates and possible attenuation artifacts and, consequently, suboptimal images. 4 However, 201 Tálio has the advantage of entering myocardial cells by active transportation, which increases its accuracy for detecting viable myocardium. For this purpose, two protocols are usually used – stress-redistribution-reinjection and rest- redistribution imaging. While the first is focused on data about stress-induced ischemia and viability, the second focuses only on viability 26 (Figure 3). 201 Tálio perfusion scintigraphy may show different perfusion defects that vary within a range from totally reversible to irreversible, according to the degree of improvement in the activity of late images. 7 In a meta-analysis, Schinkel et al. reported an 87% sensitivity and 54% specificity in predicting post-revascularization recovery. 28 Some studies have suggested that improvement in systolic function is not a sine qua non for clinical benefits, with a better prognosis but no improvement in the ejection fraction of some patients. 4,11,26,28 Assessment of myocardial viability using positron emission tomography with fluorine-18-deoxyglucose ( 18 F-FDG PET) Among the methods available for assessment of myocardial viability, 18 F-FDGPET is considered the gold standardmethod. 30,31 Because 18 F-FDG is a glucose analog, it is used to evaluate the metabolism of cardiac glucose, and thereby the uptake of this marker is similar to glucose utilization by myocytes. 4 280