Experts and guidelines agree: Atrial fibrillation is not, by itself, a reason to prescribe aspirin.
Oral anticoagulants (OACs) are better at preventing strokes in patients with atrial fibrillation, data show. Furthermore, adding aspirin to an OAC does not benefit most patients and increases their bleeding risk, said Gregg Fonarow, MD, professor of medicine and associate chief of the division of cardiology at the University of California, Los Angeles.
But many patients with atrial fibrillation are taking aspirin anyway. In a recent study, more than a third of those on OACs were also prescribed aspirin. Fully 39% of co-treated patients had no history of atherosclerotic disease and 17% had ATRIA (Anticoagulation and Risk Factors in Atrial Fibrillation) scores indicating elevated bleeding risk. Combination treatment failed to prevent more ischemic events than OACs alone and was associated with a 50% increase in risk of major bleeding and bleeding-related hospitalizations, Dr. Fonarow and his colleagues reported in the August 13, 2013, Circulation.
Aspirin misuse in atrial fibrillation happens elsewhere, too. In a large observational study in Japan, half of afib patients were on warfarin and aspirin despite having no indication for aspirin. Dual therapy did not prevent more strokes and increased the risk of major bleeding by about 67% compared with warfarin monotherapy, researchers reported in the June 1 International Journal of Cardiology.
“Other studies and my own clinical experience support these findings,” Dr. Fonarow said. “Many patients with [afib] are receiving aspirin together with OAC, even though bleeding risk outweighs any limited potential benefits.”
Inappropriate dual therapy is so prevalent that it has triggered a new quality measure. Published by the American College of Cardiology (ACC) and the American Heart Association (AHA), it tracks the percentage of adults with atrial fibrillation who do not have coronary artery disease or vascular disease but are inappropriately prescribed both an OAC and an antiplatelet drug prior to hospital discharge.
The problem of aspirin monotherapy
On the flip side, hospitalists often encounter afib patients whose only anti-clot therapy is aspirin, even though they are clear candidates for guideline-recommended OAC treatment. In a recent large registry study, this was true of 40% of patients with CHA2DS2-VASc scores of at least 2, indicating moderate to high thromboembolic risk. More than half of these patients had no coronary heart disease or risk-equivalent condition, according to results published in the June 28 Journal of the American College of Cardiology.
Giving an afib patient aspirin “is like putting a bandage on the problem,” said study author Jonathan Hsu, MD, an assistant professor of cardiac electrophysiology at the University of California, San Diego. “It may make clinicians feel better about reducing thrombotic risk but may not be the best treatment for patients at significant embolic risk. These patients require oral anticoagulation to reduce that risk.”
Dr. Hsu and other experts said that aspirin misuse in afib seems to be multifactorial. Some patients refuse OAC treatment because they think aspirin is more effective or safer. In other cases, clinicians may believe aspirin can effectively replace or should be added to an OAC to help prevent thromboembolic events.
Clinicians might also experience “cognitive dissonance—knowing what to do, but avoiding doing it,” because they prefer to stick to the treatment practices they are used to, said Samuel Wann, MD, a cardiologist at Columbia St. Mary's in Milwaukee, Wisc. In an editorial accompanying Dr. Hsu's study, he wrote: “‘Take 2 aspirin and call me in the morning’ is not appropriate treatment for a patient with atrial fibrillation at risk for thromboembolism. The clot only thickens.”
Evidence and guidelines
Many multicenter randomized trials have shown that an OAC, not aspirin, is the treatment of choice for patients at risk for stroke related to atrial fibrillation, Dr. Wann said.
Consider the double-blind AVERROES (Apixaban Versus Acetylsalicylic Acid to Prevent Strokes) study, which included 5,599 afib patients at increased risk for ischemic events. Aspirin was associated with about twice the rate of stroke or systemic embolism as apixaban—a difference so stark that investigators stopped the trial after only 1 year.
Other atrial fibrillation trials found that aspirin resembled placebo and was inferior to warfarin for reducing thromboembolic risk. Dual antiplatelet therapy was no better—the ACTIVE (Atrial Fibrillation Clopidogrel Trial With Irbesartan for Prevention of Vascular Events)-W trial ended early after aspirin-clopidogrel proved inferior to warfarin among patients with atrial fibrillation and average CHADS2 scores of 2.
Guidelines reflect these data. Patients with afib and a CHA2DS2-VASc score of at least 2 or a history of stroke or transient ischemic attack should specifically receive an OAC, according to joint recommendations from the AHA, ACC, and Heart Rhythm Society (HRS).
Corresponding guidelines from the European Society of Cardiology call the evidence for aspirin in atrial fibrillation “weak, with a potential for harm.” And the U.K.'s National Institute for Health and Care Excellence directs clinicians not to prescribe aspirin “solely for stroke prevention” in afib. Aspirin “is no longer considered a cost effective alternative” to OACs for atrial fibrillation, those guidelines state.
A gap in the guidelines
But current guidelines leave questions about whether and how to use aspirin in patients with atrial fibrillation plus coronary artery disease or risk-equivalent conditions, Dr. Hsu said. Data on these patients are lacking, and there seem to be no studies underway to clarify the issue, he added.
Two factors are especially important for guiding aspirin-related decisions in this subgroup of patients: whether vascular disease is stable or acute, and the patient's individual bleeding risk.
“In the setting of acute myocardial infarction or after percutaneous coronary intervention, aspirin may be required,” Dr. Hsu added. “In stable coronary artery disease, however, aspirin may be unnecessary.”
The European Society of Cardiology guidelines concur, recommending an OAC instead of aspirin in patients with afib and stable vascular disease, that is, no acute event or revascularization for either coronary or peripheral artery disease in the past 12 months.
For patients with afib and CHA2DS2-VASc scores of at least 2 who have just undergone coronary revascularization, the AHA/ACC/HRS guidelines suggest an OAC with clopidogrel, but without aspirin. Here, the European Society of Cardiology differs slightly, recommending an undefined “period” of triple therapy with an OAC, aspirin, and clopidogrel, followed by an OAC plus a single antiplatelet drug, followed by an OAC alone after 1 year in stable patients. But the European guidelines also note an absence of robust data supporting those recommendations.
The take-home message? “There may be select patients for whom aspirin therapy may be indicated after an acute coronary syndrome or after stenting,” Dr. Fonarow said. To evaluate bleeding risk, clinicians can use automated scoring systems, including ATRIA, HAS-BLED, and ORBIT-AF, he noted.
When to intervene
Misuse of aspirin in atrial fibrillation “is important enough that hospitalists should consider changing prescriptions when they encounter it and should actively change prescriptions when dual prescribing has led to a bad outcome,” said Anthony Breu, MD, a hospitalist who is director of medical resident education at VA Boston Healthcare System and an instructor at Harvard Medical School.
If Dr. Breu is caring for a patient with afib who is on both aspirin and warfarin, he will “investigate a bit why they are on both,” he said. “Do they also have a mechanical mitral valve? Was a coronary stent recently placed?” If the answer is no, he might stop the aspirin but will first contact the prescribing clinician to ask why the patient is on dual therapy.
“If I don't hear back, I don't always discontinue aspirin,” he said. But he will do so if the patient was admitted with a gastrointestinal bleed. “In this situation, I still think it is important to reach out to the prescribing physician, whether it be a primary care doctor or a cardiologist. But if I am unable to reach them for clarification or confirmation, I still make this change.”
What about atrial fibrillation patients on aspirin monotherapy—should hospitalists switch them to an OAC? “Patients are frequently not prescribed anticoagulants because of prior falls or a perceived risk of falling,” said Dr. Breu. “There are situations where I don't question this and may be missing an opportunity to intervene and optimize a patient's treatment regimen.” His hesitation stems from knowing that the prescriber typically has more insight into the patient's fall risk and might just switch the patient back to aspirin, he said. “Regardless of my hesitation, it is surely the case that I don't open a dialogue with the prescriber often enough.”
Hospitalists play a vital role in reducing thromboembolic risk associated with afib, Dr. Hsu noted. “Because hospitalists often see patients with atrial fibrillation and are important in controlling which medications patients will take after hospitalization, it is imperative that hospitalists take charge of changing these prescription medications if necessary,” he said.
That means understanding guideline-based therapies, assessing thromboembolic risk, deciding whether patients are candidates for OACs, and alerting primary care physicians and cardiologists about medication changes, Dr. Hsu added.
Dr. Fonarow agreed. “In every setting where patients with [afib] are being cared for, it is worth reassessing their anticoagulation regimen, and if they are receiving antiplatelet therapy, whether this is appropriate or not,” he said. “Hospitalists can play a very important role in this regard, identifying [afib] patients where aspirin would be best discontinued, and discussing this with the patient and the patient's continuity-of-care physicians.”