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A-Fib & Risk of Stroke

A-Fib & Risk of Stroke

ATRIA Findings: Anticoagulants for Stroke Prevention Versus Risk of Intracranial Hemorrhage

By Steve S. Ryan, PhD

Anticoagulants are prescribed for Atrial Fibrillation patients to reduce the risk of clots and stroke. But anticoagulants can also increase the risk of intracranial hemorrhage. So, who benefits and who may be harmed?

The “AnTicoagulation and Risk Factors in Atrial Fibrillation” Study (ATRIA) has contributed significantly to better understanding which A-Fib patients will benefit most from anticoagulant therapy.

A-Fib and Stroke Risk

As a consequence of atrial fibrillation, the pooling of blood in the atrial chambers of the heart significantly increases the risk of formation of blood clots. If a piece of a blood clot breaks off and travels to the brain it can occlude (block) a blood vessel and prevent blood from reaching the affected area of the brain. This condition is known as an ischemic stroke and can cause severe disability including the inability to walk or talk.

Ischemic Stroke Versus Intracranial Hemorrhage

In order to reduce the risk of ischemic stroke in people with atrial fibrillation, anticoagulant (blood thinner) medications are often prescribed. The most commonly used blood thinner is warfarin (Coumadin) although aspirin may also sometimes be used. While blood thinners can prevent ischemic stroke in people with atrial fibrillation, paradoxically, they can also cause bleeding into the brain, a condition known as intracranial hemorrhage.

Unfortunately, doctors don’t have a fool-proof method of determining which patients with atrial fibrillation will benefit from blood thinners (prevention of ischemic stroke) and which patients may be harmed by blood thinners (cause an intracranial hemorrhage).

Clearly, more research is necessary to more accurately identify those patients who would benefit the most from taking blood thinners as opposed to those who are more likely to be harmed by taking blood thinners.

The “AnTicoagulation and Risk Factors in Atrial Fibrillation” Study (ATRIA)

The “AnTicoagulation and Risk Factors in Atrial Fibrillation” Study (ATRIA) published in 2009, by a collaborative group of researchers from the Massachusetts General Hospital, the University of California at San Francisco, and Kaiser Permanente of Northern California, has contributed significantly to better understanding which patients with atrial fibrillation would benefit most from receiving anticoagulants for stroke prevention.

The study population consisted of 13,559 people with atrial fibrillation with a median age of 73 years. Twenty (20) percent of the subjects had no major risk factors for ischemic stroke. The major risk factors for ischemic stroke include older age (75 years or older), previous history of stroke, diabetes, hypertension, and congestive heart failure. This stroke-risk classification system is known as the CHADS2 grading system and is used by doctors as a basis for classifying patients with atrial fibrillation into stroke risk categories (low, intermediate, or high).

The researchers followed the clinical course of these 13,559 patients for a median of 6 years. At the time of enrollment into the study, 53% of the subjects were receiving warfarin (Coumadin) as prophylaxis for stroke prevention. During the follow-up period, the researchers identified a total of 1,092 thromboembolic events (occlusion of a blood vessel by a blood clot) among the study subjects, the overwhelming majority of which (1,017 cases or 93%) were ischemic strokes. Of the patients who experienced a thromboembolic event, 37% were receiving warfarin and 63% were not receiving warfarin.

The researchers also identified 299 patients among the study cohort who experienced an intracranial hemorrhage, of which 193 patients (65%) were receiving warfarin.

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ATRIA Study Key Findings

The major findings of the study can be summarized as follows:

• The greatest benefit of anticoagulation therapy for the prevention of ischemic stroke was observed among patients with a history of ischemic stroke and those in the highest stroke risk category as determined by the CHADS2 stroke-risk grading system.

• In general, the net benefit of receiving warfarin anticoagulation therapy increased with advancing age. Patients with atrial fibrillation in the oldest age group (85 years of age or older) derived more benefit from warfarin prophylaxis than patients in the 75 to 84 year age group, although the benefits of warfarin prophylaxis was apparent in this age group as well.

• This finding strongly suggests that elderly people with atrial fibrillation who are not taking warfarin are at increased risk for ischemic stroke, however, adding warfarin for prevention of ischemic stroke in elderly people does not significantly increase the risk of intracranial hemorrhage.

• Younger people with atrial fibrillation (64 years or younger) who are considered at low risk for developing an ischemic stoke as measured by the CHADS2 stroke-risk grading system, appear to derive little benefit from warfarin prophylaxis and, indeed, adding warfarin may do more harm (intracranial hemorrhage) than good (prevention of ischemic stroke).

Who Will Benefit, Who May Be Harmed

In summary, this study has contributed significantly to more clearly identifying which patients with atrial fibrillation will derive the most benefit from warfarin anticoagulation therapy and which patients may be harmed by this treatment.

If you have atrial fibrillation, talk to your doctor about the risks and benefits of taking blood thinner medications. In general, older people and those at highest risk for ischemic stroke as determined by the CHADS2 stroke-risk grading system will gain the most from anticoagulation therapy.

Blood thinners, however, may not be advantageous and may cause more harm than good in younger patients with atrial fibrillation who are considered to be at low risk for developing an ischemic stroke.

Reference for this Article
Singer, DE, et al. The Net Clinical Benefit of Warfarin Anticoagulation in Atrial Fibrillation, Annals of Internal Medicine, 2009 Vol 151, 5 pp297-305. Last accessed Jan 10, 2013 URL:

Posted January 2013

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Return to Index of Articles: Drug Therapies (Medicines)

Last updated: Wednesday, August 26, 2020

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