ART: Bilateral IMA Bypass Grafts Miss Mark at 10 Years, or Did They?

Patrice Wendling

August 27, 2018

MUNICH — The use of bilateral vs single internal mammary artery (IMA) grafts failed to reduce the risk for death at 10 years in patients with symptomatic coronary artery disease (CAD) in the ART trial, but the devil may lie in the details.

Results of the trial showed no difference in the primary 10-year mortality outcome between patients in the bilateral- and single-graft groups in an intention-to-treat (ITT) analysis (hazard ratio [HR], 0.96; 95% confidence interval [CI], 0.82 - 1.12; P = .62).

An as-treated, nonrandomized analysis, however, suggested a strong survival benefit for those receiving more than one arterial graft (HR, 0.81; 95% CI, 0.68 - 0.95), lead author, Professor David Taggart, MD, PhD, University of Oxford, United Kingdom, reported here at the European Society of Cardiology (ESC) Congress 2018.

For the composite of death, myocardial infarction, or stroke at 10 years, bilateral grafts offered no significant benefit in the ITT analysis (HR, 0.90; 95% CI, 0.78 - 1.03; P = .12), but, once again, the as-treated analysis suggested a clear advantage over single IMA (HR, 0.80; 95% CI, 0.69 - 0.93), he said.

"I believe that the 'as-treated' is the correct result," Taggart told | Medscape Cardiology.

The 10-year results were eagerly awaited despite bilateral grafts failing to show a benefit in the composite endpoint or mortality in the interim 5-year analysis, as many surgeons felt an advantage for bilateral grafts would emerge with longer follow-up.

That optimism is supported by numerous observational studies estimating a 20% reduction in mortality with bilateral vs single IMA grafts over the long term. There is also strong angiographic evidence that IMA graft patency exceeds 90% at 20 years, while vein graft failure accelerates after 5 years, increasing overall mortality and cardiac morbidity, he said.

"Surgeons who've been doing the operation — with all that [observational] evidence and robust evidence of patency — are not going to start saying, 'Okay, we'll go back and start using vein grafts,'" Taggart said at a press briefing. "Surgeons who don't want to use arteries will look at the intention-to-treat analysis and say, "There's no benefit.'"

Jeffrey Kuvin, MD, Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire, chair of the Hotline Session where the results were formally presented, said, "the level of evidence thus far does point to arterial grafts" but that further analyses are needed, especially on body habitus and diabetes, to see where bilateral grafts may be doing more harm than good.

Nevertheless, he added, "In the hands of a very skilled surgeon and in the right type of patient, I would still advocate double mammaries."

During the press conference, Taggart advised against the use of bilateral IMAs in "patients who are severely obese, or those who have diabetes or bad lungs because patients with these conditions certainly have a higher risk of sternal wound infections."

Not Where, But by Whom

ART is the largest coronary artery bypass grafting (CABG) trial with long-term follow-up, which was available in 98.4% of the 3102 patients randomly assigned to bilateral or single grafting between June 2004 and December 2007.

Taggart said there are several possible explanations for the lack of difference in bilateral vs single IMA grafts in the ITT analysis, including the high rate of guideline-based medical therapy in more than 80% of patients, which could slow vein graft failure; the use of radial artery grafts in 22% of patients; and a high crossover rate of nearly 40%.

Also, "One of the major lessons from this trial was the number of patients who weren't experienced enough to do this operation properly," he said.

Currently, more than 90% of CABG surgeries are performed using one IMA and two saphenous vein grafts, in part because of concerns that bilateral grafts are technically more complex.

Earlier this year, the researchers reported that the conversion rate in ART was 14% from bilateral to single IMA and 4% from single to bilateral IMA. Moreover, crossover rates from bilateral to single graft IMA varied from 0% to 100% for individual surgeons and from 0% to 49% for individual centers.

In the current analysis, 10-year mortality was substantially worse with bilateral vs single IMA grafts in patients whose surgeons had performed fewer than 50 operations and favored bilateral grafts in patients whose CABG was performed by more experienced surgeons (P for interaction = .015).

To punctuate the point, Taggart highlighted an ITT analysis showing a marked survival advantage for bilateral IMA grafts at 10 years for the trial's highest-volume surgeon, who had performed 416 CABG surgeries and had a 1.2% crossover rate from bilateral to single IMA (HR, 0.69; 95% CI, 0.46 - 1.03).

"The implication of this is clearly that if your operation is done by someone who is highly experienced, the biological plausibility of the superiority of arterial grafts becomes apparent, but if the operation is done by low-volume surgeons then you don't see the benefit of it," he said in an interview.

"As in aortic surgery or mitral surgery, we increasingly recognize them as a subspecialty of adult cardiac surgery and I think this kind of data shows that this is something we need to give some consideration to in terms of coronary revascularization," he continued. "In other words, should every surgeon do it or should it be restricted to surgeons with better performance?"

Asked about the need for such a subspecialty, Kuvin said, "We do have a speciality; it's called cardiothoracic surgery, and they go through rigorous training both in general surgery and in cardiac surgery. So I'm not so sure we need a sub-sub-speciality for coronary artery bypass graft surgery."

Michael Mack, MD, Baylor Health Care System, Dallas, Texas, who was not involved in the study, told | Medscape Cardiology the ART results are not that surprising and that the reason surgeons don't use bilateral internal mammary arteries and arterial grafts is that they are not comfortable with it.

"There should be surgeons that focus just on coronary artery bypass, just like we do for mitral valve surgery, aortic valve surgery and TAVR because CABG is the most technically demanding operation that we do, yet everyone treats it as a generalist operation. Every cardiac surgeon does it," he said. "I think that's a major mistake that we — and I'm guilty of it — have made in cardiac surgery, that we have not designated it as a specialist procedure."

To that end, Mack has penned an editorial with Taggart in press with the Journal of Thoracic and Cardiovascular Surgery that will lay out the case for a new CABG subspecialty.

As to whether the 10-year ART data were persuasive, an audience survey after the presentation showed that 61% of attendees would prefer bilateral over single IMA CABG only when an experienced surgeon is available, 22% would prefer a bilateral graft in most situations, 8% would prefer full arterial revascularization with a single IMA graft, and 6% said more data are needed.

The study was funded by the UK Medical Research Council, British Heart Foundation, and UK National Institute of Health Research Efficacy and Mechanistic Evaluation and sponsored by the University of Oxford.

Taggart and Kuvin reported no relevant conflicts of interest.

European Society of Cardiology (ESC) Congress 2018 . Abstract 2320. Presented August 26, 2018.

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