Incidence and timing of potentially high-risk arrhythmias detected through long term continuous ambulatory electrocardiographic monitoring

BACKGROUND: Ambulatory electrocardiographic (ECG) monitoring is the standard to screen for high-risk arrhythmias. We evaluated the clinical utility of a novel, leadless electrode, single-patient-use ECG monitor that stores up to 14 days of a continuous recording to measure the burden and timing of potentially high-risk arrhythmias. METHODS: We examined data from 122,815 long term continuous ambulatory monitors (iRhythm ZIO® Service, San Francisco) prescribed from 2011 to 2013 and categorized potentially high-risk arrhythmias into two types: (1) ventricular arrhythmias including non-sustained and sustained ventricular tachycardia and (2) bradyarrhythmias including sinus pauses >3 s, atrial fibrillation pauses >5 s, and high-grade heart block (Mobitz Type II or third-degree heart block). RESULTS: Of 122,815 ZIO® recordings, median wear time was 9.9 (IQR 6.8-13.8) days and median analyzable time was 9.1 (IQR 6.4-13.1) days. There were 22,443 (18.3%) with at least one episode of non-sustained ventricular tachycardia (NSVT), 238 (0.2%) with sustained VT, 1766 (1.4%) with a sinus pause >3 s (SP), 520 (0.4%) with a pause during atrial fibrillation >5 s (AFP), and 1486 (1.2%) with high-grade heart block (HGHB). Median time to first arrhythmia was 74 h (IQR 26-149 h) for NSVT, 22 h (IQR 5-73 h) for sustained VT, 22 h (IQR 7-64 h) for SP, 31 h (IQR 11-82 h) for AFP, and 40 h (SD 10-118 h) for HGHB. CONCLUSIONS: A significant percentage of potentially high-risk arrhythmias are not identified within 48-h of ambulatory ECG monitoring. Longer-term continuous ambulatory ECG monitoring provides incremental detection of these potentially clinically relevant arrhythmic events.