Is viability testing now unnecessary for CAD patients with low LVEF?
Viable myocardium doesn't boost long-term benefit from coronary artery bypass grafting (CABG) in patients with ischemic cardiomyopathy and coronary artery disease (CAD), a STICH trial analysis found.
All-cause mortality was less likely over a median 10.4 years when the subset of patients who underwent myocardial viability testing were randomized to CABG over medical therapy alone (62% vs 69%; adjusted HR 0.73, 95% CI 0.60-0.90), in line with the main extension trial results released in 2016.
However, myocardial viability did not influence the beneficial survival effect of CABG (P=0.34 for interaction), reported the investigators led by Julio Panza, MD, of Westchester Medical Center in Valhalla, New York, in the New England Journal of Medicine.
Similar findings were reported for the secondary endpoints of death from cardiovascular causes and combined all-cause mortality and cardiovascular hospitalization.
Viability had been assessed in roughly half of the 1,212-person STICH cohort before initiation of therapy. It was measured using single-photon-emission CT (SPECT) and/or dobutamine echocardiography -- universally mandated per protocol at first but then no longer required after enrollment problems.
The lack of a relationship between myocardial viability and CABG benefit is a "very significant finding" and has the potential to change clinical practice by having practitioners forgo viability as a criterion when making decisions regarding revascularization or not in ischemic cardiomyopathy, commented James Fang, MD, of the University of Utah, Salt Lake City.
"However, the use of viability has become so ingrained in clinical practice (in large part due to the intuitive nature of the concept and prior studies) that it is unclear if this study will be enough to change the mind of clinicians," he nevertheless told MedPage Today in an email.
"This is a very interesting study that is important for both surgeons and PCI [percutaneous coronary intervention] operators. Basically, it states that viability testing is not necessary, that one should use their clinical judgment and extent of coronary disease to determine who will benefit from revascularization," commented Cindy Grines, MD, of Northside Cardiovascular Institute in Atlanta.
It has been argued that the tests used for viability in this study are not accurate, she said, adding that the results might have been different if PET scanning was performed. Then again, "I would argue that most physicians do not have access to cardiac PET, thus these results are relevant to their practice," she continued.
In the study, 81% of those tested were found to have viable myocardium, the presence of which was associated with a roughly 2% improvement in left ventricular ejection fraction (LVEF) at 4 months, regardless of treatment. However, there was no relationship between LVEF improvement at that point and subsequent death.
"Since this slight EF improvement was not predictive of survival, one may question whether EF is a useful surrogate endpoint for ischemic patients," Grines said.
Panza's team concluded that their findings overall were "consistent with previous observations and deemphasize the relevance of changes in LVEF as a determinant of long-term prognosis in patients with ischemic cardiomyopathy. Thus, our results suggest that abatement or reversal of left ventricular systolic dysfunction is not a critical mechanism involved in mediating the beneficial effect of CABG in these patients."
The myocardial viability substudy of STICH included 601 CAD patients enrolled with LVEFs of 35% or lower. Individuals were randomized to medical therapy with or without CABG.
A previous report had already shown no link between myocardial viability and survival benefit from CABG at 5-year follow-up.
The investigators pointed to the fact that they had a relatively small sample with viability assessment as a limitation of the study. Moreover, there was only one LVEF measurement taken (at 4 months) during the whole follow-up period.
These limitations to the report may make practitioners less enthusiastic in changing their practice, Fang said.
"I must say I would have expected that presence of ischemia/viability would have an important implication for outcomes," commented Roxana Mehran, MD, of Mount Sinai School of Medicine in New York City, who cited the COURAGE trial showing this to be an important predictor.
One wonders whether if there were more patients with viability in that trial, an important survival benefit to PCI over optimal medical therapy in stable angina might have turned up, Mehran suggested. She said that viability may now have important implications in ISCHEMIA.
ISCHEMIA is a trial of patients with stable angina (showing moderate or severe ischemia on stress testing) who were assigned randomly to revascularization plus optimal medical therapy or a conservative strategy alone. Results are expected to be presented by the end of the year.
Grines pointed out that 55% of the patients in the STICH substudy didn't have significant angina -- either no angina or Canadian Cardiovascular Society Class I angina -- and they still benefited from CABG.
The study was funded by the NIH.
Panza, Fang, Grines, and Mehran disclosed no conflicts.
New England Journal of Medicine
Source Reference: Panza JA, et al "Myocardial viability and long-term outcomes in ischemic cardiomyopathy" New Engl J Med 2019; DOI: 10.1056/NEJMoa1807365.
Read the original article on Medpage Today: STICH: CABG Survival Benefit Doesn't Hinge on Myocardial Viability