Coronary Artery Targets Matter in Bilateral ITA CABG

Patient survival after CABG with bilateral internal thoracic artery (ITA) grafting is partially dependent on the proportion of myocardial mass supplied by the selected target vessels, according to a new study. Because of this, operators should aim to use a bilateral ITA strategy that maximizes myocardium supplied by the internal thoracic arteries and avoids unimportant targets, researchers say.

Though contemporary US CABG practice consists mostly of a single arterial graft supplemented by vein grafts, more operators are beginning to realize the benefits of a multiarterial strategy. The ART trial failed to show a specific advantage for using two ITA grafts instead of one in terms of the composite primary endpoint of death, MI, or stroke over 10 years, but many have criticized it for a high crossover rate and for including surgeons with inconsistent experience levels.

“What I can conclusively prove is that in patients who do receive bilateral internal thoracic arteries, and all of our patients did get that in this study, if the LAD [left anterior descending artery] is not hyper dominant, then if you bypass non-LAD targets and you use the second ITA to bypass multiple important targets—and by the way, if you don't have a hyper dominant LAD, you're more likely to have multiple important non-LAD targets—then you actually improve survival,” lead author Faisal Bakaeen, MD (Cleveland Clinic, OH), told TCTMD.

As to why an operator would shy away from using the bilateral approach in the first place, he named the technical difficulty, extra time, “the small but real risk” of sternal wound complications, and lack of reimbursement for the extra time and effort associated with it. But his institution, which has pioneered this approach, uses multiarterial grafting by default in most CABG patients.

Mario Gaudino, MD (Weill Cornell Medicine, New York, NY), who was not involved in this study, told TCTMD “this paper reminds us of the importance of the surgeon in surgical trials and more in general for the outcome of surgery. This is a very important and timely reminder that there are a lot of variables that play an important role in the outcome of an operation, but one of the key variables is the experience of the operating surgeon.”

Lower Mortality With Important Targets

For the study, Bakaeen and colleagues looked at all 6,127 patients who underwent bilateral ITA CABG at their institution between January 1972 and January 2011. Of this series, 2,551 received one ITA to the LAD and had an evaluable coronary angiogram. They defined a dominant LAD as one that was wrapped around the left ventricular apex, while non-LAD targets were deemed important or less important if their terminal reach toward the apex was more than or at most 75%, respectively.

Patients with less-important additional targets used were more likely to have a dominant LAD than those with important targets (51% vs 35%; P < 0.0001). In total, 179 patients (7.0%) received a second ITA to multiple targets; 43% of those cases involved multiple important target vessels.

Over a mean follow-up period of 14 years, unadjusted survival was not affected by the importance of the second ITA target; it was about 77% at 15 years. However, multivariate analysis showed that grafting the second ITA to multiple important targets was linked with better long-term survival (P = 0.005).

Also, among patients with a nondominant LAD, operative mortality was higher in those with a second ITA grafted to a less-important artery compared with an important target (2.4% vs 0.5%; P = 0.007).

Saphenous vein grafts, regardless of target importance, did not influence long-term survival in patients who received bilateral ITAs. Neither did the severity of the coronary stenosis in the vessel bypassed by a vein graft.

Both unadjusted in-hospital mortality (0.3% vs 1.1%; P = 0.01) and deep sternal wound infection (1.2% vs 2.2%; P = 0.04) were lower in those with a second ITA grafted to an important versus less-important artery.

A Coronary Surgery Subspecialty?

In an accompanying editorial, Joanna Chikwe, MD (Cedars-Sinai Medical Center, Los Angeles, CA), and David Adams, MD (Icahn School of Medicine at Mount Sinai, New York, NY), write that the study “highlights the importance of conduit, target, and surgeon choice in the contemporary management of patients with multivessel coronary disease.”

Additionally, they say, the researchers “provide an honest insight into some of the challenges involved in adopting a multiarterial revascularization strategy across a wider platform. The use of bilateral internal thoracic artery conduits presents unique challenges, as well as long-term rewards best realized through an individualized approach to target selection by surgeons with proficiency in multiarterial revascularization.”

However, Chikwe and Adams point out the “very low numbers” of patients who received a bilateral option in the study. “In an institution that has been such a long and celebrated advocate for bilateral internal thoracic artery utilization, why did more patients not get that option?”

Some answers they suggest are the “considerable practice variation between individual surgeons” at the study institution as well as “the lack of compelling evidence, individual surgeon expertise, and risk aversion.”

As to the lack of randomized data, Bakaeen said he hopes the ongoing ROMA study will provide the “long-awaited evidence,” but pointed out that the 1986 study that originally introduced the ITA strategy was not randomized. “I think we have enough evidence . . . to actually convince the cardiovascular community that in patients who stand to benefit from the longevity of multiarterial grafting, that they should not be deprived.”

Gaudino noted that the Cleveland Clinic is a unique setting in that they typically treat the most complex cases. Because of that there may be a referral bias present in the study, he said, adding that the bilateral strategy was rarely if ever used in the 1970s and 1980s. “However, having said that, I think we should do a better job in terms of using multiple arterial grafts more frequently.”

Studies like this support the eventual establishment of coronary surgery as a subspecialty within cardiac surgery similar to how surgeons have specialized in aortic and mitral valve surgery, Gaudino said. “There is no doubt that the operation has evolved in the last decade and that the same procedure should not be applied to each individual patient. . . . I’m not saying that each surgeon should be a coronary surgeon, but I think that every team should have at least one coronary surgeon to perform more complex revascularizations in patients.”

This notion might not be met with open arms by the cardiac surgery community since CABG is the most common cardiac surgery operation in the US today, according to Gaudino; however, coronary fellowships have already began popping up. “[CABG] has been considered a little bit the bread and butter, the foundation of our specialty,” he said, which is why the notion of a coronary specialization makes some cardiovascular surgeons uncomfortable. “CABG is what they do most of the time, and so they don't want to lose patients to be referred for a coronary specialty, but I think the solution is to try to get the training and experience in more-complex procedures.”

Similarly, Bakaeen said that “not every surgeon is good at [multiarterial CABG] and that's why . . . CABG is no longer a generic operation. It is something that is now specialized and you need to be comfortable and competent when you offer a patient multiarterial grafting. I think this should be done incrementally, meaning that you may start with a radial artery because it's easier to use and then move to the bilateral internal thoracic artery, but that's a whole new topic.”