No Survival Benefit with Myocardial Viability After CABG: STICH

Batya Swift Yasgur, MA, LSW

August 22, 2019

Myocardial viability (MV) does not appear to confer greater long-term survival benefit of coronary artery bypass grafting (CABG) in patients with ischemic cardiomyopathy, a follow-up of the STICH trial suggests.

Researchers studied 601 patients who had coronary artery disease (CAD) amenable to CABG and a left ventricular ejection fraction (LVEF) of 35% or lower.

They were randomly assigned to undergo CABG and receive medical therapy or to receive medical therapy alone, with LVEF measured at baseline and then 4 months after follow-up period (median 10.4 years).

In the 318 surviving patients, the presence of viable myocardium was associated with improvement in left ventricular systolic function, regardless of treatment; however, this improvement was not related to long-term survival.

"This is a very high-risk population of patients and bypass surgery is a high-risk proposition, so ideally, if you had a test to identify what patients would benefit from the surgery, that would be great," lead author Julio Panza, MD, chief of cardiology at Westchester Medical Center in Valhalla, New York, told theheart.org | Medscape Cardiology.

"For years, based on results of retro studies, we have believed test of [myocardial] viability can be a differentiator of patients who do vs those who don't benefit from that surgery, but our results do not prove that hypothesis," he said.

The study was published online today in the New England Journal of Medicine.

Growing Population

"The study relates to a very important and growing population — those with ischemic cardiomyopathy," Panza commented.

Ventricular dysfunction caused by ischemic heart disease is "amenable to the benefit of surgical revascularization," the authors write.

The Surgical Treatment for Ischemic Heart Failure (STICH) trial and its extension trial (STICHES) showed that, after a follow-up of 10.4 years, patients with ischemic cardiomyopathy who underwent CABG had better outcomes than those who received medical therapy alone, the authors reported.

"The STICH trial showed that bypass surgery can indeed help patients in the long term, despite initial high risk of doing vs not doing the operation," Panza said.

However, a further study conducted between 2002 and 2007 (median follow-up of 5.1 years) found that the presence of MV was not associated with a survival benefit from CABG — findings that were inconsistent with previous assumptions.

"This particular study was performed to more definitely assess whether a test for myocardial viability will identify patients who will benefit the most from surgery," Panza said.

The study also looked at the relationship between the presence of MV and changes in LVEF during early stages of follow-up and the effect of MV on subsequent long-term prognosis.

No Long-Term Survival Benefit

MV was evaluated using single-photon-emission computed tomography (SPECT), dobutamine echocardiography, or both.

In patients who had undergone SPECT, patients with 11 or more viable segments on the basis of relative tracer activity were classified as having MV.

For dobutamine echocardiography, patients with MV were defined as those with 5 or more segments with abnormal resting systolic function, but continuing to manifest contractile reserve during dobutamine administration.

The original STICH trial included 1212 patients with CAD and LVEF of 35% or lower.

Patients who underwent SPECT, dobutamine echocardiography, or both within 90 days before or after randomization and before initiation of therapy were included in the MV substudy (N = 601, mean [SD] age 60.7 [± 9.4, 87% male). Of these, 81% were considered to have MV.

During a median follow-up of 10.4 years, a total of 391 patients (65%) died; however, the overall incidence of death did not differ significantly between those with (313 [64%] of 487 patients) and those without (78 [68%] of 114 patients) a viable myocardium (hazard ratio [HR], 0.81; 95% confidence interval [CI], 0.63 - 1.03; P = .09).

These findings did not change, even after adjustment for other relevant prognostic variables (P = .64).

For the current study, patients (n = 487) were divided into 4 subgroups. Among the patients with MV, 244 had been assigned to the CABG group and 243 to the medical-therapy group.

Among the patients without MV, 54 had been assigned to the CABG group and 60 to the medical-therapy group.

CABG plus medical therapy was associated with a lower incidence of death from any cause, vs medical therapy alone; however, the interaction between the presence or absence of MV and the beneficial effect of CABG + medical therapy over medical therapy alone was not significant (P = .34).

The researchers obtained similar findings regarding the secondary endpoints of death from cardiovascular causes and the composite of death from any cause or hospitalization for cardiovascular causes.

"Modest" LVEF Improvement

During the first 4 months of follow-up, 34 of the 601 patients died. Of the remaining 567 patients, 318 (56%) underwent paired imaging at baseline and at 4 months for measurement of LVEF.

Of these, neither the incidence of death from any cause nor the incidence of death from cardiovascular causes differed significantly between patients who showed improvement in LVEF and those without LVEF improvement.

When changes in LVEF were analyzed according to MV status, regardless of treatment assignment, patients with viable myocardium (n = 248) had a modest increase in LVEF from baseline to month 4 (least-squares mean [± SE] change, 2.29 [±0.56).

In contrast, among patients without a viable myocardium (n = 70), there was no significant change in LVEF (least-squares mean change, −1.08 [±1.07).

Analysis of all four subgroups showed similar magnitude of improvements in LVEF in the CABG group as well as the medical-therapy group with viable myocardium.

By contrast, among patients without MV, neither group showed improvement in LVEF.

Moreover, no strong correlation was found in LVEF change and the amount of viable myocardium.

Similarly, the change in LVEF was not related to the degree of left ventricular remodeling in patients with or without MV.

"Our findings confirm the results of the main trial, which is that bypass surgery improves long-term prognosis of the patients, but there was no interaction in the presence or absence of myocardial viability, and testing did not necessarily identify patients who would benefit the most," Panza commented.

"Additionally, the study looked at recovery of ventricular systolic function, which can improve after surgery, and to some extent with medical treatment as well, but it was not found to be related to subsequent survival," he said.

"One limitation of this study," Panza noted, "is that because it was conducted between 2002 and 2007 and was a long-term follow-up study, the test now considered the most accurate for myocardial viability — the MRI — was not available widely at the time."

Do Not Rely on a Single Test

Commenting on the study for theheart.org | Medscape Cardiology, Jeroen J. Bax, MD, PhD, director of Noninvasive Imaging, Department of Cardiology, Leiden University Medical Center, the Netherlands, called the STICH trial "the only large randomized controlled trial in this field."

Bax, who is also the immediate past president of the European Society of Cardiology, noted that "dysfunctional but viable myocardium is important in the recovery of function after revascularization [and] the current data from the STICH trial (with very long follow-up) confirm that."

However, cautioned Bax, who was not involved with the study, "the recovery of function does not translate into improved long-term prognosis in this study."

Therefore, he added, "The remaining questions are: Will stress-inducible ischemia be reduced? Will quality of life improve? What will be the effect on left ventricular reverse remodeling? And many patients will have mitral regurgitation; will concomitant valve repair during surgery alter outcome?"

Panza added, "These findings suggest that the decision on whether to send a patient to surgery or not should not depend on results of a single test, but should be a consequence of tailoring the decision to individual patients, based on multiple factors."

The STICH trial was supported by cooperative agreements with the  National Heart, Lung, and Blood Institute. The STICHES trial was supported by a separate grant from the National Institutes of Health. Panza reports no relevant financial relationships. The other authors' disclosures can be found here. Bax has disclosed no relevant financial relationships.

N Engl J Med. Published online August 22, 2019. Abstract

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