Assessing myocardial viability to help select patients for revascularization to improve left ventricular dysfunction due to coronary artery disease.

Left ventricular dysfunction has become one of the most common causes of death, disability, and health care costs. Left ventricular dysfunction is usually due to coronary artery disease (CAD) and can be improved considerably by successful revascularization in many, but not all, patients. The key issue determining whether revascularization will relieve left ventricular dysfunction is whether the patient has enough viable myocardium to improve after revascularization. Viable myocardium is located anatomically in the subepicardial layers of the left ventricular wall, above the infarct in the subendocardial layers in the distribution of a stenotic coronary artery. Clinical history, physical examination, resting or exercise ECG, and imaging studies of left ventricular function often fail to distinguish patients with viable myocardium. Thallium-201 myocardial imaging at stress and rest is better if performed with reinjection of thallium-201 at rest, but this method still misses many patients with viable myocardium. Positron emission tomographic (PET) myocardial imaging to compare distributions of a perfusion tracer versus a metabolic tracer (fluorine-18-fluoro-deoxyglucose, 18FDG) has been cited as the "gold standard" method to identify viable myocardium by position papers from several professional organizations. PET imaging of rubidium-82, a potassium analogue ("washout" from "early" [first 1.5 minutes] to "late" [next 5 minutes] images) and gated magnetic resonance imaging (MRI) also show promise.