A study presented this week at The Society of Thoracic Surgeons’ 61st Annual Meeting explores findings in more than a million U.S. Medicare beneficiaries who underwent CABG from 2001 to 2019. The researchers found that patients who received multi-arterial grafting (MAG) had improved survival over those who received single-arterial grafting (SAG), supporting findings from prior retrospective studies.
Importantly, they also found that MAG recipients tended to be younger, were from neighborhoods with more community resources, and had fewer comorbidities than SAG recipients at the time of surgery. However, when they re-analyzed the data, substituting surgeon preference for MAG or SAG as an instrumental variable to account for unmeasured confounding variables, they noted no difference in long-term survival.
“Our analysis provides new insights on an important clinical question—whether CABG with multiple arteries used as a conduit, rather than one artery and veins from the leg, may benefit patients by improving their long-term survival,” said lead study author Justin Schaffer, MD, a cardiothoracic surgeon at Baylor Scott & White Health in Plano, Texas.
Several important retrospective studies, including a landmark study published last year that employed the STS National Database, have suggested that MAG may improve long-term survival over SAG. However, the Arterial Revascularization Trial (ART), a randomized controlled trial by Taggart and colleagues, found no significant difference in 10-year survival among the two patient cohorts.
“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,” Dr. Schaffer explained. “These factors have led to controversy in its interpretation, but ART remains the highest level of evidence regarding MAG that is currently available.”
In their study presented this week at STS 2025, Dr. Schaffer’s team used surgeons' preference for performing MAG or SAG as an instrumental variable instead of a traditional as-treated analysis comparing patients who received MAG or SAG:
“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. “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.”
The team’s application of surgeon-preference as an instrumental variable requires several assumptions:
Certain surgeons prefer MAG, while others prefer SAG. Patient-to-surgeon assignment is unrelated to the surgeon’s treatment preference. A surgeon’s use of MAG or SAG is independent of additional treatments that may affect outcomes—for example, a surgeon may prefer coronary endarterectomy during CABG. Several variables may influence a surgeon’s decision, said Dr. Schaffer, but those variables aren’t or can’t be measured in clinical or administrative databases. One broad category includes conduit availability—for example, a patient may have had a prior amputation, a diminutive radial artery that fails an “Allen’s test,” or previous lower-extremity vein stripping procedures—unmeasured factors that may bias surgeons for or against MAG.
“Another important variable is what is termed the ‘surgeon eyeball test,’” Dr. Schaffer added. “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.”
Although their traditional “as-treated” analysis supported the findings of the STS National Database analysis published last year by Saadat and colleagues in The Annals of Thoracic Surgery, the research team’s “surgeon-preference” analysis noted no difference in outcomes between patients who underwent CABG by frequent MAG compared to frequent SAG surgeons. Dr. Schaffer’s team was “somewhat surprised by the results of our surgeon-preference analysis.” However, they added, the results “perhaps explain the discordance between current ‘as-treated’ retrospective analyses and data from the ART trial.”
The researchers emphasized that understanding the survival benefit of MAG over SAG requires randomized data, and it remains an important and open clinical question. They also noted that the Randomization of Single vs Multiple Arterial Grafts (ROMA) trial randomized 4,300 patients to receive either MAG or SAG, and the results from this trial (when available) will perhaps help answer this important clinical question.
They noted that because their analysis was focused on the Medicare population, the cohort was limited to older patients. “In the recent STS National Database analysis, the treatment effect of MAG was greatest in younger patients,” Dr. Schaffer noted. “We would be interested to see a surgeon-preference approach using STS data to assess whether undergoing CABG by a frequent MAG surgeon be associated with improved survival in a younger cohort of patients.”
“We do not believe our findings suggest that MAG should be performed less frequently,” he 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 STS National Database, one of the largest and most comprehensive clinical registries with nearly 10 million cardiothoracic procedures performed by 4,300+ surgeons. With over 95% of adult and congenital cardiac surgery procedures and a majority of lung cancer and esophageal cancer surgery in the U.S., the data and outcomes from the STS Database specialty registries provide true national benchmarks for clinical outcomes of cardiothoracic surgery.
# # #
About STS
Founded in 1964, The Society of Thoracic Surgeons is a not-for-profit organization representing more than 7,800 cardiothoracic surgeons, researchers, and allied healthcare professionals worldwide who are dedicated to ensuring the best possible outcomes for surgeries of the heart, lung, and esophagus, as well as other surgical procedures within the chest. The Society’s mission is to improve the lives of patients with cardiothoracic diseases.
END
