Nearly 85 percent of patients with a history of atrial fibrillation who had an acute ischemic stroke did not receive guideline-recommended anticoagulation or had anticoagulation levels that did not fall in the therapeutic range, according to a registry analysis.

Lead researcher Ying Xian, MD, PhD, of the Duke Clinical Research Institute and Duke University Medical Center, and colleagues published their results online in JAMA on March 14.

The researchers noted that atrial fibrillation increases the risk of strike by a factor of 4 to 5 and accounts for 10 percent to 15 percent of ischemic strokes.

In this trial, known as PROSPER (Patient-Centered Research Into Outcomes Stroke Patients Prefer and Effectiveness Research), the researchers analyzed 94,474 patients with a known history of atrial fibrillation or atrial flutter who had experienced an acute ischemic stroke. All of the patients were admitted from October 2012 through March 2015 to 1,622 hospitals participating in the American Heart Association/American Stroke Association Get With the Guidelines–Stroke Registry program.

The mean age of patients was 79.9 years old, and 57 percent were women. Before their strokes, 83.6 percent were not receiving therapeutic anticoagulation, 7.6 percent were receiving therapeutic warfarin and 8.8 percent were receiving novel oral anticoagulants. At the time of their stroke, 13.5 percent had a subtherapeutic warfarin with an INR of less than 2, while 39.9 percent were receiving only antiplatelet therapy and 30.3 percent were not receiving any antithrombotic treatment.

“While some of these patients may have had reasons for not being anticoagulated, such as high bleeding or fall risk, more than two-thirds had no documented reason for receiving inadequate stroke prevention therapy,” Xian said in a news release.

Of the 91,155 patients considered high-risk, 83.5 percent were not receiving therapeutic warfarin or novel oral anticoagulants before suffering their strokes.

The unadjusted rates of moderate or severe strokes were 15.8 percent for patients receiving therapeutic warfarin, 17.5 percent for patients receiving no antithrombotic therapy 27.1 percent for patients receiving no antithrombotic therapy, 24.8 percent for patients receiving antiplatelet therapy only and 25.8 percent for patients receiving subtherapeutic warfarin.

The unadjusted rates of in-hospital mortality were 6.4 percent for patients receiving therapeutic warfarin, 6.3 percent for patients receiving novel oral anticoagulants, 9.3 percent for patients receiving no antithrombotic therapy, 8.1 percent for patients receiving only antiplatelet therapy and 8.8 percent for patients receiving subtherapeutic warfarin.

When compared with no antithrombotic treatment, therapeutic warfarin, novel oral anticoagulants and antiplatelet therapy only were associated with lower odds of moderate or severe stroke, according to the researchers. They also found that after adjusting for multiple variables, therapeutic warfarin, novel oral anticoagulants and antiplatelet therapy only were associated with lower odds of in-hospital mortality compared with no antithrombotic treatment.

The researchers acknowledged the study had a few limitations, including its retrospective, observational design, which meant treatment selection and unmeasured confounding could affect the results. The registry also only included patients who had a stroke and excluded patients with atrial fibrillation who were treated with different antithrombotic regimens and did not have a stroke. In addition, the findings might not be generalizable to patients treated at hospitals not participating in the registry or patients in other countries.

“These findings highlight the human costs of atrial fibrillation and the importance of appropriate anticoagulation,” Xian said in a news release. “Broader adherence to these atrial fibrillation treatment guidelines could substantially reduce both the number and severity of strokes in the U.S. We estimate that between 58,000 to 88,000 strokes might be preventable per year if the treatment guidelines are followed appropriately.”