New atrial fibrillation diagnosed by 30-day rhythm monitoring.

Background: Recent studies of patients with pacemakers and implantable cardioverter/defibrillators have shown that subclinical atrial fibrillation (AF) is common and is associated with thromboembolic risk. We sought to evaluate the frequency, characteristics, and impact of new AF diagnosed by ambulatory 30-day rhythm monitoring.

Methods: The 30-day rhythm monitoring data from January 2010 to August 2015 at our institution were reviewed. Medical record review was performed on patients that had a new or preexisting diagnosis of AF.

Results: Of 2,326 patients without a previous diagnosis of AF, 78 had a new diagnosis of AF (3.4%) during 30-day monitoring. Patients with a new diagnosis of AF (mean age of 68.5 years, 56% female) had a mean CHADS-VASc score of 3.2 (±1.8). The median time to diagnosis was 6 days, and 86% were diagnosed within 14 days. In 31 patients (40%), AF was exclusively detected automatically by the monitor. Of 46 patients that had manually activated the monitor, 34 also had automatically detected AF. Each patient had a median of 7 episodes, with the median duration of the longest episode being approximately 2 hours. Following the diagnosis of AF, 37 (47%) were started on anticoagulation and 9 (12%) were prescribed aspirin.

Conclusions: A total of 3.4% of patients who underwent 30-day rhythm monitoring for any indication were found to have a new diagnosis of AF (402 per 1000 patient-years). Most of these episodes were detected automatically, corresponding to device-detected subclinical AF. The most common intervention following diagnosis of AF was initiation of oral anticoagulation.