Viability Studies Before Selecting Revascularization?
Abstract & Commentary
By Michael H. Crawford, MD
Source: Sawada SG, et al. Effect of revascularization on long-term survival in patients with ischemic left ventricular dysfunction and a wide range of viability. Am J Cardiol. 2010;106:187-192.
Although ischemic left ventricular (LV) dysfunction is an indication for revascularization, little is known about the long-term benefits of revascularization and the value of viability studies. Thus, these investigators from Indiana University performed a retrospective, observational study of their database of 14 years of dobutamine stress echocardiography (DSE) for viability. In 274 patients with reduced left ventricular ejection fraction (LVEF), those who had revascularization therapy were compared to those who had medical therapy. Viable myocardium by DSE was present in 32% of the 274 patients. Other baseline characteristics of the two groups were similar, except that revascularized patients had more non-viable myocardium. Revascularization was performed in 47% (93% had bypass surgery). Over the mean 4.5-year follow-up, 35% of the revascularized patients died vs. 48% of the medically treated patients. After adjustment for propensity score showed that revascularized patients had a better survival (5.9 years) vs. medically treated patients (3.3 years, HR 0.42, 95% CI 0.27-0.65, p <.0001). This difference was apparent early in the first year and increased with time. Cardiac mortality showed the same results. The authors concluded that revascularization increases long-term survival in patients with ischemic cardiomyopathy and variable viability.
Commentary
This study supports my practice of revascularizing patients with reduced LV function and good target vessels for revascularization. This study is not randomized, but rather they used propensity matching to compensate for this weakness. Whether this approach is reliable is debatable, but only three of 27 important clinical features of the patients were not equivalent at baseline: percent with hyperlipidemia, multivessel CAD, and viable myocardium. All three were higher in the revascularized patients. However, some key features that you expect to be different between the groups were not. The presence of nonviable myocardium was seen in 27% of the medical therapy patients and 22% of the revascularization patients (p = NS). Viability in > 25% of the LV myocardium in 29% vs. 35% (p = NS) and myocardial ischemia in 75% vs. 80% (p = NS). Both groups had a mean ejection fraction of 32%. Also, the follow-up results were adjusted for the use of beta blockers, which could affect mortality.
The results showed improved total mortality over five years of follow-up in the revascularization group and a 55% reduction in cardiac mortality after adjustment for beta-blocker use (higher usage in the revascularization group). These results are similar to previous studies that used the results of viability studies to segregate the treatment of the patients. One caveat to this study is that it is almost exclusively a coronary bypass surgery study (93%). Whether similar results would be obtained with percutaneous (PCI) interventions needs further study, but it is hard to imagine that mortality would not be lower with PCI, despite an expected need for repeat PCI in some. Thus, I believe the practice of referring patients with good target vessels and a moderately low EF to revascularization is reasonable. However, the role of viability studies is unclear. In this study not everyone had a viability study and in those that did the results between the two groups was either not different or was adjusted by the propensity score. Consequently any effect of viability testing was removed or diminished in value. Prior viability based studies using improved myocardial segmental contractility as the gold standard, have shown about an 80% sensitivity, which means that 20% of patients who have viable myocardium would be falsely labeled as non-viable. Unfortunately a similar analysis was not done in this study. A large randomized trial of viability directed medical vs. surgical therapy in heart failure patients (HEART) is underway. Hopefully, we will have results soon. Until further data is available, I use viability studies to aid the decision to revascularize, but do not rely on them exclusively because of their limited accuracy.
Although ischemic left ventricular (LV) dysfunction is an indication for revascularization, little is known about the long-term benefits of revascularization and the value of viability studies.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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