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NEW ORLEANS -- For multivessel coronary artery bypass grafting (CABG), using both the left and right mammary arteries doesn't improve longer-term outcomes, the randomized ART trial showed.

Using both didn't reduce mortality at 5 years compared with using a single internal thoracic artery for the procedure (8.7% versus 8.4%, HR 1.04, 95% CI 0.81-1.32), , of the University of Oxford, England, reported here at the American Heart Association meeting and simultaneously online in the New England Journal of Medicine.

The composite rate of death from any cause, MI, or stroke in the so-called Arterial Revascularization Trial (ART) was likewise similar at 12.2% and 12.7%, respectively (HR 0.96, 95% CI 0.79-1.17).

However, as anticipated for the more complex procedure, certain adverse events were more common. Sternal wound complications occurred in 3.5% of patients getting bilateral internal thoracic artery use versus 1.9% in the single-graft group (P=0.005), and sternal reconstruction was required in 1.9% versus 0.6%, respectively (P=0.002).

But those complications appeared to be largely limited to insulin-dependent diabetes and high body mass index patients, Taggart pointed out. In other groups, the bilateral procedure is "absolutely as safe," he asserted.

Major bleeding was similar between groups in ART, which included 3,102 patients at 28 cardiac surgical centers in seven countries who were randomly assigned single or bilateral internal-thoracic-artery grafting.

"I was very surprised by the results of this study," said , of Brown University in Providence, R.I., and study discussant at a press conference for the late-breaking clinical trial session. "The conventional wisdom is that multiple arterial grafts are far superior."

Observational data has shown arterial grafts to maintain patency in more than 90% of patients out to 10 and 20 years, whereas the perfect patency rate is only 10%-15% long-term for vein grafts, Taggart noted.

As to why bilateral hasn't turned out better yet in ART, the researchers noted: "Vein-graft patency may also be improving over time, which may be related in part to better control of risk factors after CABG."

They listed out several other potential explanations:

• "First, the rate of vein-graft failure within 5 years may not be high enough to have an obvious adverse clinical effect.
• "Second, there may not be a direct association between vein-graft failure and clinical events.
• "Third, variation in surgeon experience may have reduced the effectiveness of bilateral grafting. In the ART, surgeons could adopt a variety of configurations for bilateral internal thoracic-artery grafting that could influence efficacy. In practice, several configurations, including Y graft, free graft, and in situ configuration, are all associated with excellent patency rates.
• "Fourth, there may be little difference between the effects of the two techniques on clinical outcomes, owing to better long-term vein-graft patency, asymptomatic vein-graft failure, and improved medical therapy."

But there could still be a chance for bilateral mammary artery grafts to pull ahead: The trial's primary aim and full statistical power is to compare survival rates at 10 years of follow-up.

The rate of vein graft failure is 1% to 2% per year through 5 years then accelerates, Taggart noted at the press conference. "Five years is an definitely interim point."

When asked by Sellke if he thought the 10-year results would be different than these 5-year results, Taggart replied, "Yes. I would personally, if I were going to need the operation, insist on having bilateral [internal mammary grafts] done by an experience operator because it is totally counterintuitive to believe that having more patent grafts in your heart at 10 to 20 years of follow-up is no benefit."

, of the Christiana Hospital in Newark, Del., and a past president of the AHA, agreed.

"I'm undeterred from my belief that, for patients getting CABG in their 40s, 50s, or early 60s, betting on a graft that's going to outperform vein grafts is a better strategy," he said as press conference moderator.

However, "it won't make much difference in practice just now because the reality is in North America fewer than 5% of patients get bilateral arterial grafts," Taggart said.

"It won't change practice because [there are] people who believe in arterial grafts, and [for] those who don't or aren't enthusiastic about the prospect of a slightly more technically difficult operation it will allow them to remain comfortable with not using bilateral."