STICH: Viability Testing Didn't Affect Treatment Outcomes

April 04, 2011

April 4, 2011 (New Orleans, Louisiana) — A substudy [1] of a randomized comparison of medical therapy with or without bypass surgery for ischemic heart disease in patients with LV systolic dysfunction [2] found that: overall, substantial viable myocardium evident at baseline imaging studies had no independent bearing on all-cause mortality over five years; and such viability didn't influence the relative effectiveness of the two treatment strategies, either for all-cause mortality or the secondary end points of CV mortality and CV hospitalization.

The findings, from the Surgical Treatment for Ischemic Heart Failure (STICH) trial, based on a selected cohort of about half the total trial population, don't necessarily mean myocardial viability doesn't have functional implications, observe the substudy authors, led by Dr Robert O Bonow (Northwestern University, Chicago, IL). Viability, they note, is probably directly related to, for example, LV ejection fraction and chamber volumes. But the substudy does suggest that "assessment of myocardial viability alone should not be the deciding factor in selecting the best therapy" for patients with ischemic heart disease and LV dysfunction.

The substudy also questions the value of the decades-old practice of assessing myocardial viability by perfusion scans or other functional imaging methods to predict benefit from coronary revascularization--at least in the kind of patients STICH included: considered amenable to CABG, with LVEF <35% and no significant left-main coronary disease.

The substudy of the STICH revascularization trial and, separately, its primary results, are published online today in the New England Journal of Medicine to coincide with their presentation here at the American College of Cardiology (ACC) 2011 Scientific Sessions/i2 Summit.

While the viability substudy included only the 601 patients who underwent viability assessment, at the discretion of the recruiting investigators--the method could be either single photon-emission computed tomography (SPECT) perfusion imaging or dobutamine echocardiography--the primary analysis included the trial's entire cohort of 1212 patients. The latter found no significant difference in the primary end point of all-cause mortality between the medical-therapy-only and medication-plus-CABG groups, as also reported today by heartwire . The addition of CABG to meds did significantly lower the composite rate of death from any cause or CV hospitalization (p<0.001), a secondary end point.

After pointing out the abundant and longstanding but primarily observational support for revascularization guided by viability testing, Dr James C Fang (University Hospitals and Case Medical Center, Cleveland, OH) writes in an accompanying editorial that it was "perhaps surprising" that viability didn't predict a survival benefit from revascularization [3]. The findings, however, "should be interpreted cautiously," given the substudy's limitations; for example, patients were selected for viability testing individually at the physicians' discretion.

"However, the substudy's findings do raise reasonable questions about the most appropriate method to assess myocardial viability," Fang writes. "The analysis is a strong reminder that in this era of cost-effectiveness, the role of expensive technologies should be accountable to a rigorous study of incremental benefit."

STICH also had a separate arm for patients who went on to receive ventricular reduction surgery; as published in 2009 and reported at the time by heartwire , such surgery made no significant impact on symptoms, functional outcomes, or clinical outcomes.

In the current substudy analysis, the patients underwent viability testing by either method and were classified "as either having or not having substantial myocardial viability" based on prespecified criteria for either SPECT imaging or dobutamine echo, according to the authors; the blinded assessments were done at independent core laboratories.

Overall, 39% of the patients died over a median follow-up of 5.1 years; 37% of the 487 patients classified as having substantial viability at baseline died, compared with 51% of the 114 remaining patients. The 36% reduction in the unadjusted hazard ratio was significant, at p=0.003; the significance deteriorated to p=0.21 after adjustment for baseline prognostic features, including LVEF, LV end-systolic and end-diastolic volume indexes, and a risk score derived from age, renal function, presence or absence of cerebrovascular disease, and other variables.

Viability was similarly associated with a significant 39% drop in CV death (p=0.003) in an unadjusted analysis that became nonsignificant (p=0.34) after adjustment for baseline risk markers. On the other hand, a significant 41% fall in the composite of death or CV hospitalization (p<0.001) remained significant (p=0.003) after adjustment.

There was no significant interaction between substantial viability at baseline and whether the patient had been randomized to medical therapy only or meds plus CABG for the end point of death from any cause (p=0.53), CV death (p=0.70), or death/CV hospitalization (p=0.39).

The authors acknowledge other limitations of the study, including the highly selected nature of the subgroup that underwent viability studies, the small proportion of patients judged not to have substantial viability (which limited statistical power), and the use of two different imaging methods for assessing myocardial viability.

This story will be updated with comments.

Disclosures for the authors are listed in the report; the primary STICH revascularization study received funding support from Abbott Laboratories.


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