Subclinical Atrial Fibrillation May Increase Risk of Stroke

Patients with pacemakers or implantable cardioverter-defibrillators (ICD) who experience episodes of subclinical atrial fibrillation are at higher risk for stroke and systemic embolism, a study by Stuart Connoly, MD, and colleagues of McMaster University in Ontario found.

Published in the Jan. 12 issue of the New England Journal of Medicine, the study showed that within 3 months of receiving an implantable device, 10.1% of patients with hypertension but no history of atrial fibrillation had a subclinical atrial tachyarrhythmia.  Those who experienced an atrial tachyarrhythmia were twice as likely to have an ischemic stroke or systemic embolism over the next 2 and a half years of follow-up. 

The study included 2580 patients, 65 years of age and older with either a pacemaker or ICD recently placed.  All patients had hypertension and no history of atrial fibrillation. 

For three months researchers used the implanted devices to monitor for episodes involving an atrial rate of 190 beats per minute or greater for over 6 minutes.  Higher rates of clinical atrial fibrillation and either ischemic stroke or systemic embolism were found in patients who experienced a subclinical atrial tachyarrhythmia within the first three months.  

Among the 51 patients who had an ischemic stroke or systemic embolism, 11 had a subclinical atrial tachyarrhythmia and none had clinical atrial fibrillation in the first 3 months. The population attributable risk of stroke or systemic embolism related to subclinical atrial fibrillation was 13%, researchers found. 

-Michael Potts