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Study Finds Wide Variations in Projected Heart Benefits of Anti-Blood-Clotting Medications for People with Atrial Fibrillation

The reported rates of ischemic stroke in four large studies vary substantially, creating uncertainty about the predicted benefits of anticoagulation medication, according to new findings by Kaiser Permanente researchers and colleagues.

Although taking anti-blood-clotting medications has been shown in clinical trials to dramatically reduce the risk of ischemic stroke in people with atrial fibrillation, wide variations in how the initial risk of stroke is estimated may mean that some people do not necessarily experience an overall benefit.

Alan S. Go, MD, study co-author

“While people with atrial fibrillation taking these medications have fewer strokes, their risk of having a serious brain hemorrhage is also higher, so it would be ideal to identify the subset of patients who are at high enough risk for ischemic stroke to warrant these drugs,” said Alan S. Go, MD, of the Kaiser Permanente Division of Research, co-author of a new study published today in Annals of Internal Medicine.

In the study, “Effect of Variation in Published Stroke Rates on the Net Clinical Benefit of Anticoagulation for Atrial Fibrillation,” researchers analyzed data from more than 33,000 members of Kaiser Permanente in northern and southern California who were diagnosed with atrial fibrillation between 2006 and 2009.

They used computer simulations to estimate the benefits of several anti-blood-clotting treatments for patients before starting anticoagulation treatment, based on the stroke rates published from four different populations with atrial fibrillation.

“We found that the estimated clinical benefit of anticoagulation with warfarin varied four-fold when based non the stroke rates in four major, published, atrial fibrillation studies,” said lead author Sachin Shah, MD, MPH, of the University of California, San Francisco.

The researchers noted that treatment thresholds may need to be revised in favor of more accurate individualized assessments of stroke and bleeding risks in people with atrial fibrillation.

“Clinical practice guidelines need to acknowledge the uncertainty in current estimates of individual atrial fibrillation in patients’ risk of stroke,” said senior author Daniel E. Singer, MD, professor at Harvard Medical School.

“Most of the variation in stroke risk we describe resulted from different ways the studies were conducted. Our analysis highlights the need for more accurate, precise, and contemporary data on both ischemic stroke and brain hemorrhage rates in representative patients with atrial fibrillation.”

Additional study co-authors were Mark H. Eckman, MD, University of Cincinnati College of Medicine; and Sara Aspberg, MD, PhD, Danderyd Hospital, Stockholm, Sweden.

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