Myocardial viability: Recent developments in detection and clinical significance

The long-term prognosis of patients with ischemic cardiomyopathy is highly variable, depending on the extent of myocardial viability and the success and completeness of the revascularization techniques used. Other important factors include left ventricular function, extent of coronary artery disease (CAD), and patient age. Chronic left ventricular dysfunction in ischemic cardiomyopathy is the result of a mixture of scarred as well as hibernating myocardium. In fact, most patients have both scarring and hibernation in different regions. Transmural biopsies of dysfunctional segments reveals that recovery of function is inversely proportional to the extent of fibrosis and that endocardial fibrosis extending over 30% of the myocardial thickness precludes recovery of function. Nagueh et al. [1] evaluated the relation of contractile reserve and thallium uptake in hibernating myocardium to myocardial structure in humans. The authors found that segments with postoperative functional recovery had more wall thickening at low-dose dobutamine echocardiography (DE), higher thallium uptake, and less fibrosis (2.0 vs 28%) than those segments without recovery. Also, segments with viability on DE had less fibrosis, less vimentin and fibronectin, more glycogen, and higher thallium uptake, than those segments without viability. Importantly, segments viable by single-photon emission computed tomography (SPECT) and DE had significantly less fibrosis (1%) than those viable by only one of the two techniques. In this review, we discuss recent developments in the detection of myocardial viability, including echocardiography, nuclear cardiac imaging, magnetic resonance imaging (MRI), and other techniques.