When five-year interim results of the Arterial Revascularization Trial (ART) were published a couple of years ago, no difference in mortality was seen between patients randomized to bilateral internal thoracic artery grafting (BITA) versus a single internal thoracic artery graft (SITA) plus a vein graft.
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Yet experienced BITA advocates like Cleveland Clinic cardiac surgeon Faisal Bakaeen, MD, were convinced it was simply too early to evaluate outcomes. “Observational studies at our institution and elsewhere have shown survival curves beginning to diverge after five years and becoming statistically significant as time passes,” he says. “In the Cleveland Clinic experience, the 20-year survival benefit for BITA over SITA is 10 percent or greater for many patient groups.”
The 10-year results of ART were expected to show BITA to be superior to SITA. But when outcomes were presented at the European Society of Cardiology meeting in August, no difference in the composite end point of death, myocardial infarction or stroke was seen between the BITA and SITA arms in the intention-to-treat analysis.
The as-treated analysis was a different story: In this analysis, BITA resulted in a statistically significant survival advantage and lower composite end point.
What accounted for this unconventional finding? “Among the different possible explanations, surgeon experience is undoubtedly a very important factor,” says Dr. Bakaeen.
Explaining the discrepancy
Interestingly, 36 percent of patients in ART received a different strategy than simply one versus multiple arterial grafts. Fourteen percent of those randomized to BITA were given a single artery graft, and 22 percent of those randomized to left ITA underwent double arterial grafting, primarily with an ITA plus a radial artery. The crossover rate from BITA to SITA ranged from 0 to 49 percent among centers and from 0 to 100 percent among individual surgeons.
A deeper dive showed that surgeons who had done fewer than 50 operations before the trial began had worse outcomes with BITA than with SITA. Conversely, more-experienced surgeons had lower crossover rates and significantly better outcomes with BITA.
“It appears some surgeons simply didn’t have enough experience with the more technically complex procedure,” Dr. Bakaeen observes.
Lack of experience with BITA may help explain why a procedure associated with superior outcomes is used in fewer than 5 percent of coronary artery bypass graft (CABG) operations in the U.S.
Why experience matters
Surgeon experience influences several factors informing decisions to use or avoid double artery grafting, including safety and proper patient selection.
“You have to tailor the operation to the patient,” says Dr. Bakaeen. “Not every patient is a candidate for double artery grafting. BITA may not be possible or will be less attractive in complex and high-risk patients and those undergoing reoperation. But for a typical patient who is young, otherwise healthy and undergoing elective CABG, we believe BITA is ideal.”
In the hands of less-experienced surgeons, BITA increased the risk of sternal wound complications in ART. But when meticulous harvesting techniques were used, the difference was no longer significant. “Meticulous use of skeletonization caused minimal damage to surrounding tissues and collateral vessels, diminishing the risk,” Dr. Bakaeen notes.
In ART, the radial artery was used for the second graft in a significant percentage of the SITA group. This also may have contributed to the trial’s negative findings, Dr. Bakaeen says, as studies have shown superior performance of radial arteries relative to vein grafts. Harvesting and handling is technically easier with radial arteries than with ITAs, but ensuring good outcomes still requires attending to some important nuances of radial arteries. Inexperienced surgeons may be unaware of the need to consider the physiological and anatomic risks to the patient, as well as target vessel selection, when choosing between a radial artery and an ITA.
“Radials are better suited to severely diseased vessels,” Dr. Bakaeen explains. “Otherwise they are vulnerable to competitive flow. The ITA is less vulnerable, and patency rates are not as significantly impacted in these cases. It’s safe to take the radial artery if collateral blood supply to the hand through the ulnar artery is appropriate. If so, the risk of impact on the hand is low.”
Convincing the unconvinced
These potential hurdles to success, compounded by lack of reimbursement for longer and more complex CABG operations, hinder widespread BITA adoption in the U.S. Reluctance is further reinforced by lack of irrefutable evidence of BITA’s superiority, say surgeons who remain on the fence. According to Dr. Bakaeen, the Cleveland Clinic experience should be convincing.
“In 1986, Dr. Floyd Loop published his landmark paper showing that use of the ITA [then called the internal mammary artery (IMA)] resulted in better patency and survival than vein grafts,” he says. “As a result, the LIMA-LAD became the gold standard for CABG. Further studies at Cleveland Clinic proved that two mammary arteries are generally better than one.”
Dr. Bakaeen hopes the Randomization of Single vs. Multiple Arterial Grafts (ROMA) study now underway at Cleveland Clinic and elsewhere will come up with conclusive, unequivocal evidence of benefit that can convince reluctant surgeons to embrace multiarterial grafting. This multicenter study, which recently completed its pilot phase, will randomize over 4,000 North American patients to CABG performed by experienced surgeons using BITA or the radial artery plus ITA.
Support for CABG subspecialization
If widespread use of multiarterial grafting is dependent on surgeon experience, how can surgeons gain the experience needed to become proficient?
“It’s up to our institutions and professional leaders to drive what’s best for patients,” says Dr. Bakaeen. “Professional societies must create training programs that enable surgeons to learn it.”
This could take years, which is why experienced surgeons are advocating for CABG to be designated a subspecialty of cardiac surgery. Dr. Bakaeen has published in support of this approach himself.
“Hospitals with subspecialty CABG programs use more arterial grafts and have better outcomes,” he says. “There’s no question that a dedicated CABG program is how patients can be assured of receiving the optimal revascularization procedure.”