MYOCARDIAL VIABILITY: WHY, WHEN OR EVER?

There is currently a general consensus that survival after revascularization in patients with chronic CAD and left ventricular dysfunction (defined as LVED < 30-40%), is improved in patients with detected viability on noninvasive testing. Absence of viability is associated with no survival benefit of the mechanical (surgical or percutaneous) therapies compared to the medical strategies.
Available data is based on observational, retrospective and/or single center studies and meta-analysis.  Large, prospective, multi-center, randomized trials are not available.
The presence of “viability” is most often defined as recovery of contractile function after revascularization as opposed to a more appropriate, but a much harder end-point, of survival benefit.
The available non-invasive techniques include 1) dobutamine echocardiography (testing myocardial contractile reserve), 2) nuclear methods (Tl-201, Tc99m based perfusion imaging testing membrane integrity and F18 FDG PET metabolic imaging for detection of ischemic myocyte glucose metabolism) and lately 3) contrast enhanced MRI.  MRI’s unique spatial resolution, which allows visualization of subendocardial necrosis, is becoming a leading candidate for a “gold standard” in viability imaging.  However, accumulated data and availability are still far behind echo and nuclear experience. Renewed interest in myocardial neuro imaging (using I 123 MIBG), currently being tested in a large global trial, may have therapeutic implications (e.g. effect of beta blockade, indications for AICD implantation) for ischemic as well as non-ischemic cardiomyopathies.
Detection of “viability” is of importance in properly selected patients in the era of ever increasing prevalence of congestive heart failure (5 million patients in the US) and in the era of ever increasing complexity and cost of available therapies.