People with pacemakers or defibrillators who experience only short episodes of an abnormal heart rhythm known as atrial fibrillation have a very low risk of stroke, according to a study released Monday.

After analyzing 37,000 ECGs of 5,379 patients over two years, researchers found that long episodes of atrial fibrillation were associated with increased risk of stroke, heart failure, ER visit or hospitalization for an abnormal heart rhythm, or death. In contrast, patients experiencing only short episodes of atrial fibrillation — less than 20 seconds —were at no more risk of stroke or other cardiovascular complications than people without atrial fibrillation.

During the study:

  • more than 15,000 episodes of atrial fibrillation occurred
  • 94 patients were hospitalized for atrial fibrillation
  • 265 patients were hospitalized for heart failure
  • 47 patients were hospitalized for stroke
  • 359 patients died

The results suggest the risks of bleeding associated with taking blood thinners called anticoagulants outweighs the risk of stroke in patients who only experience short episodes of atrial fibrillation.

Physicians should continue to monitor patients to see if prolonged episodes of atrial fibrillation develop, said Steven Swiryn, M.D., clinical professor of cardiology at the Feinberg School of Medicine at Northwestern University in Chicago, Illinois.

The study is published in the American Heart Association journal Circulation.