Assessment of myocardial viability in patients before revascularization

Information on myocardial viability can be useful to decide when coronary artery revascularization is indicated for patients with acute myocardial infarction (AMI) and left regional or global ventricular dysfunction. Difficulties in assessing viability arise because the same part of the ventricular wall can have a mixture of necrotic tissue and viable myocardium. Diagnostic markers of myocardial viability are: the preservation of wall thickness, the presence of contractility reserve, the presence of blood perfusion reserve, integrity of the wall cells, and preservation of cellular metabolism. Echocardiography and thallium or technetium imaging are methods currently used to assess myocardial viability because of their availability and relatively low cost. Although positron emission tomography (PET) has been considered the gold standard, its unavailability may limit its clinical use. Recent publications have demonstrated the accuracy of cardiac magnetic resonance imaging (cardiac MRI) in assessing myocardial viability, together with noninvasive procedures to study the markers of viability noted above. Late contrast enhancement with gadolinium is the most accurate and simplest method. The late open artery hypothesis recommends, on the basis of scant evidence, systematic revascularization of the culprit artery. Although no large randomized studies focused on prognosis are available yet, several small studies provide sufficient evidence of functional recovery of viable myocardium after coronary artery revascularization of the culprit artery in patients with global or regional ventricular dysfunction. The assessment of myocardial viability to decide whether culprit artery revascularization is indicated is a strategy currently based on more evidence than the more indiscriminate recommendations based on the late open artery hypothesis.