A new analysis of more than 1 million Medicare beneficiaries challenges previous retrospective studies suggesting survival benefits of multi-arterial grafting over single-arterial grafting in coronary artery bypass procedures. The study, presented at The Society of Thoracic Surgeons' 61st Annual Meeting, found no difference in long-term survival when analyzing outcomes based on surgeon preference rather than traditional as-treated analyses.
The research team, led by Justin Schaffer, MD, of Baylor Scott & White Health, employed an instrumental variable approach using surgeon preference to account for unmeasured confounding factors that might influence surgical decision-making and patient outcomes.
"Traditional 'as-treated' retrospective approaches account for measurable variables that may impact survival, but these techniques are limited because they cannot account for unmeasured variables," Dr Schaffer said in a statement. "If certain assumptions hold—and we argue that they do hold in this case—analyzing data using a 'surgeon-preference' approach can account for unmeasured variables."
Initial findings from the 2001 to 2019 Medicare cohort appeared to support previous retrospective analyses showing improved survival with multi-arterial grafting (MAG). However, the data revealed significant demographic differences between MAG and single-arterial grafting (SAG) recipients, with MAG patients typically being younger, having fewer comorbidities, and coming from neighborhoods with greater community resources.
When researchers reanalyzed the data using surgeon preference as an instrumental variable, they found no significant difference in long-term survival between patients treated by surgeons who frequently performed MAG versus those who primarily used SAG. These findings align more closely with results from the Arterial Revascularization Trial (ART), which showed no significant difference in 10-year survival between MAG and SAG cohorts.
Dr Schaffer noted that the ART findings have been subject to interpretation challenges, stating, "ART is difficult to interpret in terms of MAG broadly, because a substantial number of patients, about 20% in each arm, also received radial artery conduit, and about 17% of patients randomized to bilateral internal mammary arteries received only a single mammary artery graft."
The research team identified several unmeasured variables that might influence surgeon decision-making, including conduit availability and what Dr Schaffer termed the "surgeon eyeball test." He explained, "If a surgeon 'eyeballs' a patient and does not expect them to live for many years after CABG, they may elect SAG over MAG because the purported benefits of MAG may only manifest over the long term."
Despite their findings, the researchers emphasized that their results should not discourage MAG procedures. "We do not believe our findings suggest that MAG should be performed less frequently," Dr Schaffer said. "Both surgeons who frequently perform MAG and those who rarely perform MAG can be justified in using their clinical acumen to decide on an optimal conduit strategy for each individual."
The study's authors acknowledged that their Medicare-based analysis was limited to older patients, noting that previous research using the Society of Thoracic Surgeons National Database showed greater MAG treatment effects in younger patients. They suggested that future research could apply the surgeon-preference approach to younger patient cohorts using STS data.
The field awaits results from the Randomization of Single vs Multiple Arterial Grafts (ROMA) trial, which has randomized 4300 patients to receive either MAG or SAG, potentially providing additional clarity on this clinical question.