Trials of anticoagulants for stroke prevention generally involve patients with frequent and symptomatic atrial fibrillation (AF); however, the growing population of patients with implanted cardiac devices has enabled the detection of subclinical AF. The manufacturer-sponsored ASSERT trial in patients with a dual-chamber pacemaker or implantable cardioverter-defibrillator was designed to evaluate whether a special pacing algorithm would prevent AF and whether subclinical AF is associated with clinical events. All 2580 participants had hypertension and no history of AF.
Three months after enrollment, device detection algorithms had recorded subclinical atrial tachycardia (defined as an atrial rate >190 beats/minute for >6 minutes) in 10% of patients. At this point, participants with pacemakers were randomized to receive or not to receive continuous overdrive atrial suppression.
During a mean of 2.5 years of follow-up, use of the special pacing algorithm did not significantly reduce AF. Clinically documented AF occurred in only 16% of patients with device-documented atrial tachycardia in the first 3 months. Subclinical atrial tachycardia in the first 3 months was significantly associated with both clinically documented AF and stroke or systemic embolism. However, the association with stroke or systemic embolism was no longer significant when patients with atrial tachycardia detected after the first 3 months (an additional 24.5%) were included in the analysis.
Comment: Clinical atrial fibrillation is not only associated with stroke but is almost certainly causative; moreover, no evidence suggests that symptomatic AF is more prothrombotic than asymptomatic AF. Although the current findings are by no means definitive for guiding anticoagulation decisions, they do support taking device-documented subclinical AF seriously. If an asymptomatic patient's CHADS2 score is high and subclinical episodes are frequent or prolonged, I would consider anticoagulation. These findings also support aggressively screening patients with cryptogenic stroke for occult AF and initiating anticoagulation if any AF is detected.
— Mark S. Link, MD
Published in Journal Watch Cardiology January 18, 2012
