Aspirin for AF Fading Away

SNOWMASS, COLO.– The sun may be setting on the use of aspirin for thromboprophylaxis in patients with nonvalvular atrial fibrillation. The 2014 American College of Cardiology/American Heart Association/Heart Rhythm Society guidelines are unique among the major international guidelines in giving a modest IIb, Level of Evidence C endorsement to the option of aspirin or no treatment in patients with atrial fibrillation (AF) and a CHA₂DS₂-VASc score of 1. In contrast, the 2014 U.K. NICE (National Institute for Health and Care Excellence) guidelines, the 2013 Asian Pacific Heart Rhythm Society guidelines, and the 2012 European Society of Cardiology guidelines all recommend consideration of oral anticoagulation – eschewing aspirin – in patients with a CHA₂DS₂-VASc score of 1 or more, Dr. Bernard J. Gersh noted at the Annual Cardiovascular Conference at Snowmass.

Dr. Bernard Gersh

The NICE guidelines put the matter succinctly, stating, “The main departure from prior guidelines is that aspirin should not be used in AF simply to reduce the risk of stroke, as it is not as effective as NOACs [novel oral anticoagulants] ... and can cause more bleeding side effects.”

Dr. Gersh was coauthor of a recently published think piece that argued that exaggerated misperceptions of aspirin’s efficacy and safety have led to its inappropriate status as “the easy option” for stroke prevention in AF (Eur. Heart J. 2015;36:653-6).

“By giving physicians a soft option of aspirin in CHA₂DS₂-VASc 1 patients, we’re allowing them an excuse not to use an oral anticoagulant, which is what they should be using,” Dr. Gersh explained at the conference.

He noted that an analysis of more than 41,000 Medicare beneficiaries with AF in 2007-2008 showed that only 66.8% were on warfarin.

“There’s no doubt that warfarin, and for that matter the NOACs, are underutilized, and it’s possible that the misperception that aspirin is effective may contribute to that underutilization,” asserted Dr. Gersh, professor of medicine at the Mayo Clinic, Rochester, Minn.

The cardiologist added that the widely held belief that aspirin reduces stroke risk by roughly 20%, compared with placebo, in patients with AF is based upon seriously flawed data. True, a meta-analysis of six placebo-controlled randomized trials done in an earlier era concluded that aspirin reduced the relative risk of stroke by 19%, but what’s often overlooked is that aspirin significantly outperformed placebo in only one of those six studies – the SPAF 1 trial – where in one arm aspirin achieved an “almost implausible” 94% relative risk reduction.

“Nothing reduces risk by 94%,” Dr. Gersh observed, adding that the SPAF 1 methodology was, upon careful examination, “completely unacceptable” by contemporary standards.

He was a coinvestigator in a study of 7,347 AF patients on oral anticoagulation therapy in 176 U.S. practices participating in the ORBIT-AF registry (Outcomes Registry for Better Informed Treatment of Atrial Fibrillation). The analysis showed that concomitant use of aspirin and an oral anticoagulant in patients with AF is common in everyday clinical practice, being employed in 35% of the study population. Of note, 39% of these patients had no history of CAD and therefore weren’t on aspirin for secondary cardiovascular prevention, and 17% of them were at elevated bleeding risk because of an ATRIA (Anticoagulation and Risk Factors in Atrial Fibrillation) bleeding risk score of 5 or more.

The key, disturbing finding was this: The adjusted risks of major bleeding and hospitalization for bleeding were 53% and 52% greater, respectively, in patients on an oral anticoagulant plus aspirin than with an oral anticoagulant alone (Circulation 2013;128:721-8).

On the basis of this study and other evidence, Dr. Gersh believes the use of aspirin in patients with AF should be considered only in those with CAD, where a case can be made for its use in secondary prevention alongside an oral anticoagulant to reduce stroke risk. But even then, aspirin’s use is reasonable only in those at low risk of bleeding, and extra vigilance and prophylaxis with a proton pump inhibitor are called for.

“If a patient is at high risk of bleeding, I personally would not give aspirin,” the cardiologist added.

The big remaining question – and an area of current controversy – concerns the safety of halting aspirin in AF patients on an oral anticoagulant who’ve undergone coronary stenting. Ongoing studies are looking at this issue, and answers are expected within a year or 2.

Dr. Gersh reported serving as a consultant to Merck and Ortho-McNeil-Janssen and on data safety monitoring boards for Baxter, Medtronic, and Teva.