Old habits die hard in medicine. For decades the skeptical cardiologist and his cardiology brethren and sistren have prescribed aspirin to prevent stroke in patients with atrial fibrillation.
For those patients with atrial fibrillation (AF) who were considered low risk it was felt that aspirin provided some benefit in preventing the clots that fly out of the heart (and land in arteries elsewhere in the body) at an acceptably low risk of bleeding. For higher risk patients more powerful and effective agents (oral anticoagulants) are usually recommended.
The American guidelines on AF (2014) gave a IIB recommendation to aspirin. IIB is not a ringing endorsement having been described as “this is our suggestion, but you may want to think about it.”
- For patients with nonvalvular AF and a CHA2DS2-VASc score of 1, no antithrombotic therapy or treatment with an oral anticoagulant (OAC) or aspirin may be considered. (Level of Evidence: C)*
However, in the last 5 years the significant bleeding risks associated with taking low dose aspirin have become more widely appreciated.
Thus, in the 2016 European guidelines on the management of AF the authors state that “the evidence supporting antiplatelet mono therapy (e.g. aspirin or clopidogrel) for stroke prevention in AF is very limited” and the bleeding rate” is similar to OAC”:
Aspirin and other antiplatelets have no role in stroke prevention (III A). The combination of anticoagulation with antiplatelets increases bleeding risk and is only justified in selected patients for a short period of time; for example, in patients with an acute coronary syndrome or stent, balancing the risk of bleeding, stroke and myocardial ischaemia (IIa B/C).
Stroke risk evaluation is based on the CHADS-VASc score. With a score ≥2 in male and ≥3 in female patients, anticoagulation for stroke prevention is clearly recommended, while in a score of 1 in males and 2 in females, anticoagulation should be considered. No antithrombotic therapy of any kind should be prescribed in patients with a CHADS-VASc score of 0 (males) or 1 (females).
Antiplatelet therapy increases bleeding risk, especially dual antiplatelet therapy (2.0% vs. 1.3% with antiplatelet monotherapy; P < 0.001), with bleeding rates that are similar to those on OAC. Thus, antiplatelet therapy cannot be recommended for stroke prevention in AF patients.
The focused update (2019) on AF from America said nothing about aspirin alone for AF.
It’s not just European experts who feel this way. At a 2016 Cardiovascular CME conference, American experts in the field were unanimous in their condemnation of aspirin use
“The European guidelines have done away with aspirin for stroke prevention in atrial fibrillation. It barely made it into our current US guidelines. I don’t think aspirin should be in there and I don’t think it will be there in the next guidelines. The role of aspirin will fall away,” said Bernard J. Gersh, MB, ChB, DPhil, Professor of Medicine at the Mayo Clinic in Rochester, Minnesota. “It’s not that aspirin is less effective than the oral anticoagulants, it’s that there’s no role for it. There are no good data to support aspirin in the prevention of stroke in atrial fibrillation.”
“The use of aspirin has probably been misguided, based upon a single trial which showed a profound effect and was probably just an anomaly,” said N.A. Mark Estes III, MD, Professor of Medicine and Director of the New England Cardiac Arrhythmia Center at Tufts University in Boston, and a past president of the Heart Rhythm Society
I would just take it off of your clinical armamentarium because the best available data indicate that it doesn’t prevent strokes. I’m certainly not using it in my patients. Increasingly in my patients with a CHA2DS2-VASc of 1, I’m discussing the risks and benefits of a novel oral anticoagulant,” said Dr. Estes.
Those are amazingly definitive statements. But, as I’ve learned we can’t just except what the “experts” and the guidelines tell us we have to look at the original studies informing these decisions.
In 1991 the seminal study proving the benefits of warfarin in preventing stroke (Stroke Prevention in Atrial Fibrillation (SPAF) trial) was published.
It compared warfarin (measured by PT ratio) to placebo and aspirin 325 mg to placebo in preventing stroke in AF patients. Warfarin reduced stroke by 67% and aspirin by 42%. The risk of significant bleeding was similar at around 1.5% per year for all three arms.
Based on this and other AF trials (AFASAK, CAFA, SPINAF, EAFT, et al. ) when I gave talks or taught cardiology fellows in the 1990s my message (similar to this presentation) emphasized the superior benefits of warfarin compared to aspirin (especially when monitored by INR in a 2.0 to 3.0 range) in higher risk AF patients. Overall it was felt that aspirin (dosing varying from 100 to 325 mg) reduced stroke/embolism by 20-30% compared to placebo and would offer benefit to those patients at low risk or who could not tolerate warfarin.
Based on the 2014 American guidelines (and a focused update in 2019 which did not address this issue) I had not been actively taking my low risk patients off baby aspirin.
I was prompted to re-research this question and write this post because a 58 year old woman with paroxysmal AF and hypertension called the office today asking if I wanted her to take a baby aspirin daily. She has a CHADS2VASC score of 2 (woman and hypertension) and falls into the category where we should have an in depth conversation about the risks and benefits of anticoagulant therapy.
I have that discussion with her each visit and thus far we’ve decided to hold off on starting an anticoagulant drug like Eliquis. She has promised to record her ECG daily (using her Kardia Mobile ECG device) and report any onset of AF. If AF recurs we will have another discussion about Eliquis.
I spent several hours pouring over the original studies and more recent studies, reviews and meta-analyses and reached the following conclusions:
With the advent of the newer oral anticoagulants (NOACs) in the last decade which offer better stroke reduction and less bleeding than warfarin patient-physician discussions should be about taking a NOAC or not. Aspirin should not be considered as a lower risk/effective alternative as its benefits are minimal and bleeding risks similar to NOACs.
I told my patient no on the daily baby aspirin and from now on I will recommend stopping aspirin (assuming no other reason to be on it) to all my low risk AF patients.
The components of the stroke risk score- CHA2DS2-VASc = Congestive Heart failure, hypertension, Age ≥75 (doubled), Diabetes, Stroke (doubled), Vascular disease, Age 65–74, and Sex (female);
For those interested in a discussion on why females get a point in the risk score but a different cut-off for OAC therapy this is from the ESC guidelines:
Many risk factors contribute to the increased risk of stroke in patients with AF as expressed in the CHA2DS2-VASc score. The evidence for female sex as a risk factor has been assessed in many studies. Most studies support the finding that females with AF are at increased risk of stroke. One meta-analysis found a 1.31-fold (95% CI: 1.18–1.46) elevated risk of stroke in females with AF, with the risk appearing greatest for females ≥75 years of age (S4.1.1-35). Recent studies have suggested that female sex, in the absence of other AF risk factors (CHA2DS2-VASc score of 0 in males and 1 in females), carries a low stroke risk that is similar to males. The excess risk for females was especially evident among those with ≥2 non–sex-related stroke risk factors; thus, female sex is a risk modifier and is age dependent (S4.1.1-49). Adding female sex to the CHA2DS2-VASc score matters for age >65 years or ≥2 non–sex-related stroke risk factors
If you’re curious what constitutes a IIB recommendation it is described in the yellow box below My best summary is still “not a ringing endorsement”.
If you want to see the ESC guideline recommendations in detail