ABC | Volume 110, Nº3, March 2018

Review Article Practical Implications of Myocardial Viability Studies Wilter dos Santos Ker, 1 Thais Helena Peixoto Nunes, 1 Marcelo Souto Nacif, 2 Claudio Tinoco Mesquita 1 Setor de Medicina Nuclear - Hospital Universitário Antônio Pedro (HUAP) - Universidade Federal Fluminense (UFF), Niterói, RJ - Brazil 1 Serviço de Radiologia - Hospital Universitário Antônio Pedro (HUAP) - Universidade Federal Fluminense (UFF), Niterói, RJ – Brazil 2 Keywords TissueSurvival;DiagnosticImaging;MyocardialRevascularization / surgery; Myocardium Stunning / physiopathology. Mailing Address: Wilter dos Santos Ker • Rua Aroazes, 180, Apt 903. Postal Code 22775-060, Jacarepaguá, Rio de Janeiro, RJ – Brazil E-mail: wiltersker@hotmail.com Manuscript received August 22, 2017, revised manuscript November 16, 2017, accepted December 12, 2017 DOI: 10.5935/abc.20180051 Abstract Many non-invasive methods, such as imaging tests, have been developed aiming to add a contribution to existing studies in estimating patients’ prognosis after myocardial injury. This prognosis is proportional to myocardial viability, which is evaluated in coronary artery disease and left ventricular dysfunction patients only. While myocardial viability represents the likelihood of a dysfunctional muscle (resulting from decreased oxygen supply for coronary artery obstruction), hibernation represents post‑interventional functional recovery itself. This article proposes a review of pathophysiological basis of viability, diagnostic methods, prognosis and future perspectives of myocardial viability. An electronic bibliographic search for articles was performed in PubMed, Lilacs, Cochrane and Scielo databases, according to pre-established criteria. The studies showed the ability of many imaging techniques in detecting viable tissues in dysfunctional areas of left ventricle resulting from coronary artery injuries. These techniques can identify patients who may benefit from myocardial revascularization and indicate the most appropriate treatment. Introduction Assessment of myocardial viability using non-invasive imaging techniques has motivated several studies in search of the most promising and sensitive tests. These tests highlight the importance of a correct evaluation of this condition for an appropriate risk stratification and selection of patients considered eligible for myocardial revascularization. Since cardiac function is not a dichotomous variable, some of its aspects measured by imaging techniques may not be measurable by another method. Useful parameters to guide therapeutic strategies include ejection fraction, scar size, ischemia and remodeling extension, as well as duration of cardiac dysfunction. 1,2 Using a multimodal approach of viability, a pilot study 3 showed higher values for these variables, which were analyzed in combination, providing a more reliable characterization of myocardial function. However, due to the lack of larger studies, imaging tests based on multimodal approach are not recommended yet. It is worth pointing out that even though the presence of a viable myocardium in a large heart area is important for revascularization, the decision for this procedure should be based on patient’s clinical status, evidence of ischemia, coronary anatomy and left ventricular global and regional function. 4 Determination of myocardial viability is a common and clinically relevant challenge, that may be necessary in post‑infarction patients receiving thrombolytic therapy. Also, it may be helpful for surgeons and cardiologists in choosing the best therapy from interventionist strategy, angioplasty and myocardial revascularization. 5 This is particularly important in cases when myocardial revascularization is considered, due to highmortality rate and perioperativemorbidity in these patients. 6 In viability studies, while nuclear medicine techniques have high sensitivity, the techniques used to evaluate contractile reserve have higher specificity. Imaging methods, such as computed tomography (CT), positron-emission tomography (PET), myocardial scintigraphy, echocardiography with dobutamine and cardiac magnetic resonance (CMR) have been exhaustively investigated in attempt to establish the best method for myocardial study. 7 Pathophysiology Myocardial viability refers to myocardial cells that are alive after myocardial injury, according to cellular, metabolic and contractile functions. It describes ventricular dysfunction without tissue necrosis, which enables functional recovery after restoration of blood supply. In this context, although the definitions “stunned myocardium” and “hibernating” myocardium have distinct characteristics, the latter may represent the adaptation of repeated episodes of the former, as described by Chareonthaitawee et al. 8 (Figure 1). “Stunned myocardium” results from a rapid, severe episode of coronary occlusion followed by recovery of coronary flow. An abrupt decrease in coronary flow causes contractile dysfunction, which persists even after its restoration. Despite minimal necrosis, ventricular dysfunction may be prolonged, from hours or even weeks. A group of researchers, 9 investigating ventricular function in patients with coronary heart disease, demonstrated that repeated episodes of ischemia may lead to cumulative stunning, which contributes to the development of chronic, post-ischemic, left ventricular dysfunction. Interestingly, similar degrees of left ventricular dysfunction in distinct patients may be associated with significant differences in the degree of myocardial viability. Besides, viability is not correlated with myocardial wall thickness, since ventricular wall thinning does not necessarily mean absence of myocardial viability. 10 278