Aspirin Not Effective in Preventing Strokes in Patients With Atrial Fibrillation

• In Atrial Fibrillation, the irregular beating of the heart predisposes the patient to a risk of clot formation and stroke.
• Anticoagulants thin down the blood and prevent clot formation, making them the drug of choice for reducing stroke risk in Atrial Fibrillation.
• Despite recommendations, aspirin is still preferred over anticoagulants in a significant number of these patients, according to a recent study.

In Atrial Fibrillation, the upper chambers of the heart, known as atria, beat in an irregular fashion, leading to poor blood flow. This can lead to the formation of clots which may travel to the brain and result in a stroke. Therefore, these patients need to be prescribed blood thinners (anticoagulants) to prevent thrombus (clot) formation. Yet, many of these patients are still being treated with aspirin alone instead of anticoagulants to reduce stroke risk, according to a recent study published in the Journal of the American College of Cardiology.

The study was conducted by Jonathan Hsu, MD, at the University of California, San Diego, along with his fellow team members. They studied the National Cardiovascular Disease Registry (NCDR) Practice Innovation and Clinical Excellence (PINNACLE) for data of 327656 outpatient AF patients enrolled between January 2008 to December 2012.

They found out that in the first cohort of 210000 patients with a CHADS₂ score (risk score signifying moderate to high risk for thrombosis) equal to or higher than 2, around 61.8% were treated with anticoagulants while the remaining 38.2% were prescribed aspirin alone. In the former group, 90.9% were prescribed warfarin.

The researchers even discovered that certain characteristics predicted the type of treatment received. Patients with a deranged lipid profile, coronary artery disease and history of MI or hypertension were more likely to be treated with aspirin while male patients and those with a history of stroke, systemic embolization, congestive heart failure and higher body mass index were given anticoagulants.

Similar findings were seen on analyzing the second cohort of 294642 patients with a CHA₂DS_2-VAS_C score (a score which includes more CHD risk factors) of 2 or more.

Aspirin Offers No Stroke Protection

Aspirin is an antiplatelet drug. It prevents platelets from clumping together and forming clots, but it does not act as a blood thinner like anticoagulants. Aspirin can definitely reduce clot formation in the arterial bed but does not offer protection against thrombosis in the heart.

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“We know it is a Band-Aid", said Hsu about aspirin, "We know it's nowhere near as effective as the oral anticoagulant and some evidence suggests it's not doing anything at all."

Sanjay Deshpande, MD and Samuel Wann, MD from Columbia St. Mary’s Hospital, Milwaukee wrote in their editorial titled ‘The Clot Thickens’ published along with the study that aspirin is ineffective for prevention of thromboembolism associated with atrial fibrillation while oral anticoagulants are far superior in the same. Moreover, aspirin is associated with a risk of bleeding, though small.

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Conventionally, aspirin was used to prevent clot formation in patients with atrial fibrillation and its use, therefore, is deeply embedded in the minds of cardiologists. The change in the treatment strategy and the superiority of anticoagulants was realized quite recently after the following two trials were published:

• AVERROES (Apixaban Versus Acetylsalicylic Acid to Prevent Stroke in Atrial Fibrillation Patients who have Failed or are Unsuitable for Vitamin K Antagonist Treatment) in 2010, and
• WOEST (What is the Optimal Antiplatelet and Anticoagulant Therapy in Patients with Oral Anticoagulation and Coronary Stenting) in 2013.

Need to Educate the Physicians

Editors Deshmukh and Wann noted that while American Heart Association still slightly supports aspirin use in patients with low risk of stroke but European Society of Cardiology and NICE in England do not recommend the use of aspirin to prevent stroke in patients with atrial fibrillation at all. Therefore, it was surprising to the researchers that even the most meticulous and talented cardiologists were prescribing aspirin alone in one-third of the patients.

They speculated the reasons as under:

• Clinicians feel aspirin offers enough protection against stroke. It actually does not.
• The risk of bleeding associated with anticoagulants is a deterrent. The risk does exist but most of the times, the benefits outweigh the risk. Even aspirin is associated with a risk of bleeding.
• Patient non-compliance with regular intake of anticoagulants over a long period of time.
• Bias to follow conventional methods and resist change despite the evidence.
• Lack of awareness regarding the safer new anticoagulants that are associated with a lower risk of bleeding and offer better protection against thromboembolism.
• Resistance on the part of the patient to anticoagulants as the drugs are expensive, require following a regimen and are associated with some side effects.
• The abstractness of the benefit of stroke prevention which is hard to prove to a reluctant patient.

Thus, there is a need to address both physician-related and patient-related issues to ensure the appropriate use of anticoagulants in such patients. The researchers even discovered a wide variability across practices.

The authors therefore wrote, "Focusing on factors at the practices level, and not simply at the individual physician level, may prove important in future efforts to rectify proper prescription or (oral anticoagulation) in (A-fib) patients at risk for stroke."

References:

1. Offer anticoagulants instead of aspirin for stroke prevention
   https://www.nice.org.uk/news/article/offer-anticoagulants-instead-of-aspirin-for-stroke-prevention
2. Aspirin Often Wrongly Prescribed for Atrial Fibrillation
   https://www.nlm.nih.gov/medlineplus/news/fullstory_159459.html
3. Aspirin Instead of Oral Anticoagulant Prescription in Atrial Fibrillation Patients at Risk for Stroke
   http://content.onlinejacc.org/article.aspx?articleID=2529509

Source-Medindia