September 12, 2003

Advances
Adequate anticoagulation level reduces stroke impact for patients with atrial fibrillation

A research team from the MGH and Kaiser Permanente of Northern California has shown that patients with atrial fibrillation who receive an appropriate level of anticoagulation therapy not only reduce their risk of having a stroke, they also cut the risk that any stroke they have will result in death or serious disability. The study in the Sept. 11 issue of The New England Journal of Medicine is the first to examine the effect of anticoagulation intensity on stroke outcome in patients with atrial fibrillation.

"It is very unusual to have a stroke when on anticoagulation therapy, but this study shows that it is possible to reduce the severity and complications for patients who do experience that uncommon event," says Elaine Hylek, MD, of the MGH General Medicine Division, the study's lead author.

Atrial fibrillation, a type of irregular heartbeat, is the strongest common risk factor for stroke. Many patients with atrial fibrillation are treated with blood-thinning medications - most frequently aspirin or the prescription drug warfarin - and previous studies have confirmed that achieving adequate levels of anticoagulation - as reflected by levels of 2.0 to 3.0 on a blood test called INR - can significantly reduce the risk that a stroke will occur.

The current report analyzed data on more than 13,000 Kaiser patients with atrial fibrillation, 600 of whom experienced ischemic (caused by a blood clot) stroke in the three-year period studied. Among patients who had a stroke while taking warfarin, those with an INR less than 2.0 had a risk of a severe stroke or dying in the hospital that was three times greater than patients with an INR greater than 2.0. For patients who had been taking aspirin, the risks were similar to those of patients with low INR, and those taking no anticoagulants had an even higher risk. Achieving adequate INR levels also reduced the risk of dying within 30 days of the stroke.

"All anticoagulation therapy has risks, including hemorrhage, and balancing those risks against the possibility that insufficient therapy will lead to a severe stroke is a serious concern," Hylek says. "Our results show that the risk of hemorrhage does not increase until INR levels reach 4.0, which should assure patients and physicians that the currently advocated INR target of 2.5 is most likely the right balance point." Other MGH authors of this study are Daniel Singer, MD, senior author; Yuchiao Chang, PhD, and Lori Henault, MPH.