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SAN DIEGO -- Continuing an antiplatelet agent beyond 1 year after stenting may be safer for anticoagulated atrial fibrillation patients, a small randomized trial suggested.

Among patients receiving oral anticoagulation alone, combined risk of death, MI, stroke, or systemic embolism past the first year post-stenting was significantly higher than in patients continuing a single antiplatelet agent -- aspirin or clopidogrel (Plavix) -- plus oral anticoagulant treatment.

That composite primary endpoint rate was 15.7% in the 54-patient oral anticoagulation alone group versus 13.6% in the 47 combined therapy group patients, which did not meet criteria for noninferiority (HR 1.16, P=0.20 for noninferiority), reported Yukiko Matsumura-Nakano, MD, of Kyoto University Graduate School of Medicine in Japan, at the Transcatheter Cardiovascular Therapeutics meeting here.

Net clinical effect -- pooling the efficacy findings and major bleeding -- did meet noninferiority, due to a trend for more major bleeding in the combined therapy group (by TIMI criteria 8.4% vs 4.9%, P=0.07). Clinically significant minor bleeding wasn't assessed.

However, the trial was "underpowered and inconclusive" due to prematurely terminated enrollment far short of the planned 2,000 patients, the researchers cautioned in a paper Circulation. "Future larger studies are required to establish the optimal antithrombotic regimen in this population."

The open-label OAC-ALONE trial initially intended to enroll 2,000 patients with atrial fibrillation and stable coronary artery disease in Japan, but recruitment was too slow -- only 696 ended up enrolled, with 680 completing follow-up to a median 2.5 years.

The mentality of "leave well enough alone" for patients who haven't had bleeding problems means it's difficult to recruit for trials like this, commented press conference moderator C. Michael Gibson, MD, of Beth Israel Deaconess Medical Center in Boston. "Cardiologists think they know the answer, and they don't want to expose their patient to some of this."

While there have been some trials in atrial fibrillation populations specifically within the first year after stenting, such as RE-DUAL and PIONEER, and some ongoing, "even when you look at all the trials that will be enrolled, it's still short of, say, the thirty or forty thousand patients you would need to really look at things like ischemic stroke," Gibson noted. "The trials will be done but they will still be underpowered."

Among patients randomized to oral anticoagulation alone after 1 year post-stenting, 75% took warfarin and 25% were on a newer oral anticoagulant (NOAC). In the group randomized to continue their single platelet agent beyond that point, aspirin was that agent for 86% and clopidogrel in 14%. By Japanese criteria, the time in therapeutic range with warfarin was high, at 70%. By global criteria, it was around 50%.

"This study suggests that we probably can stop one of the two [antiplatelet agents] and get by with a single agent," commented Morton Kern, MD, of the University of California Irvine and a panelist at a press conference for the late-breaking clinical trial session at which the results were discussed.

"I don't think anybody is quite comfortable yet to not give either aspirin or aspirin and clopidogrel," he added, "but we do want to reduce the triple drug [use]."

Guidelines and expert consensus recommend oral anticoagulation alone as the default, based on observational data, to limit the risk of bleeding in afib patients, Gilles Lemesle, MD, PhD, of Centre Hospitalier Universitaire de Lille, France, wrote in an .

"These tantalizing observations do not settle the issue of which strategy should be considered as default in clinical practice (and for which patients) but will be useful in planning future trials," Lemesle concluded.

Duration of antiplatelet therapy after drug-eluting stenting in the broader population has gone back and forth, with many investigators pushing for ever-shorter regimens within the first year whereas the landmark DAPT Trial suggested a net benefit to continuing a thienopyridine plus aspirin well beyond 1 year even with the higher bleeding risk.

"We see at this meeting, everywhere, many trials coming out saying shorter, shorter, shorter," said Gibson.

"The focus of interventional cardiologists is to minimize the duration treating the stent but there is a patient attached to the stent and there is the issue of secondary prevention -- not the stent but those nonculprit events."

Atrial fibrillation patients in particular are a challenge, noted press conference discussant Mark Reisman, MD, of the University of Washington Medical Center in Seattle.

"We obviously maintain patients on oral anticoagulation. We, if possible, continue a single platelet inhibitor," he said. "A number of these patients now, frankly are being driven somewhat toward consideration of Watchman left atrial appendage occlusion devices because of concern about bleeding, which is not insignificant."

OAC-ALONE is a good start, but well-powered studies looking beyond 1 year in atrial fibrillation are needed, Gibson said. Meta-analyses so far have suggested less bleeding but no less effectiveness with two versus three antithrombotic agents, he noted.