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Value of Myocardial Viability Testing in STICH
Abstract & Commentary
By Michael H. Crawford, MD, Editor
Sources: Bonow RO, et al. Myocardial viability and survival in ischemic left ventricular dysfunction. N Engl J Med 2011;364:1617-1625; Fang JC. Underestimating medical therapy for coronary disease...again. N Engl J Med 2011;364:1671-1673.
It is believed that returning blood flow to chronically ischemic but viable myocardium in patients with heart failure due to coronary artery disease will improve symptoms and reduce mortality. However, the data supporting this belief is flawed. Thus, the surgical treatment for ischemic heart failure (STICH) investigators conducted a sub-study of the 601 patients who had viability studies performed. Initially this was required in the protocol, but later it was made optional to improve enrollment. The STICH objective was the comparative efficacy of optimal medical therapy vs medical therapy plus coronary bypass surgery. This sub-study tested the hypothesis that those with demonstrable myocardial viability randomized to bypass surgery would do better than those without viability. The primary endpoint was all-cause mortality. Secondary endpoints included death from cardiovascular cause and a combined endpoint of death from any cause and hospitalization for cardiovascular causes. Intention-to-treat and actual treatment analyses were performed.
Among the 601 out of 1212 patients enrolled in STICH who had viability testing, 487 had viable myocardium. Of the latter, 244 were assigned to surgery. Of the 114 without viable myocardium, 54 were assigned to surgery. Overall those with viable myocardium had a lower death rate than those without (37% vs 51%, hazard ratio [HR] 0.64; 95% confidence interval [CI], 0.48-0.86, P = 0.003). After adjustment for baseline variables, this association with survival was no longer significant (P = 0.21). The combined endpoint after adjustment was significant (P = 0.003), but not other secondary endpoints. No interaction was observed based upon treatment groups in any endpoint analyzed by intention to treat or actual treatment. The authors concluded that the identification of viable myocardium did not predict a better survival from bypass surgery compared to optimal medical therapy alone.
Patients with left ventricular (LV) dysfunction or heart failure due to ischemic heart disease often have 2 or 3 vessel disease and are considered for surgical revascularization. Since they are higher risk for surgery, the surgeons are often reluctant to operate. They are especially reluctant if the LAD cannot be bypassed or if the patient has no angina. At this point, viability testing is often suggested. In my experience, viability testing is only useful if it shows viability, because then the surgeons are more likely to operate. This study is of interest because it shows that even in these patients medical therapy reduces mortality and rehospitalization as well as surgery. This begs the question of why do expensive viability testing?
Unfortunately, we do not really know what care strategy was being tested here since viability testing was not randomized, but rather was at the discretion of the caring physician at each site. The demonstrated significant differences between the patient characteristics who did and did not have viability studies suggests considerable selection bias. Another problem is that SPECT and dobutamine stress echo were employed, which may have affected the results. Also, PET and contrast enhanced MRI were not used, which many believe are more accurate. In addition, only 19% of the patients tested had nonvariable myocardium which reduces the power of the study for detecting an impact of revascularization in these patients. Finally, the death rate was low in the medical group with viability (7%/year) making it difficult to show a benefit from surgery. Surgery has an upfront mortality cost that would have been avoided if percutaneous revascularization was used. Many of these patients would now be treated by percutaneous techniques.
In the univariate model, viability did predict the endpoint of the study but not in the multivariate model. This suggests that other clinical factors, such as ejection fraction and heart failure class, reflected the viability status and provided other prognostic information. Most (61%) of the patients had angina pectoris; perhaps this is enough evidence of viability. The study excluded those with left main disease and those with severe angina. Perhaps any angina or objective evidence of ischemia (positive stress test with imaging) should favor revascularization. This strategy would leave those with low EF and heart failure symptoms as candidates for further evaluation for revascularization. The results of this study suggest that such patients may do as well with optimal medical therapy. One strategy would be to try medical therapy first and refer only those with persistent heart failure symptoms and low EF to revascularization. In this group viability testing my play a role, but this remains to be validated.