Subclinical atrial fibrillation significantly increases stroke risk

Approximately 25% of all strokes are of unknown cause, and it has long been hypothesised that short subclinical episodes of atrial fibrillation (AF) may be an important common aetiological factor. While several studies have attempted to detect episodes of subclinical AF, most have been hampered by the infrequency of such episodes and the unlikelihood of picking them up even with monitoring over a period of days or weeks. In the USA around 400 000 pacemakers are inserted each year, many of which are able to detect and record episodes of rapid atrial rate, which correlate with electrocardiographically documented AF. In this study Healy et al evaluated whether subclinical episodes of AF detected by these devices were associated with an increased risk of ischaemic stroke.

Recruiting 2580 individuals, 65 years of age or older, with hypertension and no history of AF, in whom a pacemaker or defibrillator had recently been implanted, patients were monitored for 3 months to detect subclinical AF (episodes of atrial rate >190 bpm for more than 6 min) and were followed for a mean period of 2.5 years for the primary outcome of ischaemic stroke or systemic embolism. Within 3 months, subclinical AF had been detected in 261 patients (10.1%). Subclinical AF was associated with an increased risk of clinical AF (HR, 5.56; 95% CI 3.78 …