Patients with atrial fibrillation are often prescribed warfarin to reduce the risk of stroke. But a new study has found that patients who undergo a surgical procedure to correct arrhythmia are more likely to stop taking the drug.

As part of the Michigan Anticoagulation Quality Improvement Initiative, researchers at the University of Michigan analyzed the warfarin usage of 734 patients across the state between 2011 and 2013.

The study, published in JAMA Cardiology, found that 36.8 percent of the patient population were off warfarin within one year of starting it. However, the numbers varied greatly when researchers limited their range to patients who had undergone electrical cardioversion or radiofrequency ablation during that period. In that group, 54.1 percent of patients were not on warfarin a year after their procedure.

"This may or may not be good news, because when someone's had a recent procedure, there may be good reason to interrupt anticoagulant therapy," said James Froehlich, MD, a researcher with the collaborative and a University of Michigan Frankel Cardiovascular Center cardiologist.

Only 29.5 percent of patients who didn’t undergo a procedure discontinued warfarin treatment during the study.

“We need to understand why they are stopping warfarin and figure out what other medications might be better adhered to in order to prevent strokes," Froehlich said.

The problem for many cardiologists is that there is no specific stop date for anticoagulation therapy. Cardiologists make recommendations, but there is no industry standard.

"We need more data to help us understand what the risk of stroke is after cardioversion or ablation, to inform physician decision-making and guidelines," said Geoffrey Barnes, MD, a cardiologist at the University of Michigan Frankel Cardiovascular Center.

It is currently typical for cardiologists to stop anticoagulants after a patient undergoes cardioversion, but more data is needed. There is currently no standard for ablation.