Extended Ambulatory ECG Monitoring Enhances Identification of Higher-Risk Ventricular Tachyarrhythmias in Patients with Hypertrophic Cardiomyopathy.

Background: In hypertrophic cardiomyopathy (HCM), 48-hour ambulatory monitoring has been standard practice to detect nonsustained ventricular tachycardia (NSVT), a sudden death risk marker. Extended wear ambulatory ECG devices have more recently utilized for monitoring HCM patients.

Objective: Evaluate NSVT burden identified with continuous ambulatory monitoring for up to 2 weeks compared to initial 48 hours.

Methods: 236 consecutive HCM patients (49 ± 12 years) underwent 14-day continuous ambulatory monitoring (Zio XT, iRhythm Technologies); diagnostic yield of NSVT compared for initial 48 hours vs. extended for 14 days.

Results: Of 236 patients, 114 (48%) had ≥1 runs of NSVT (median 2) over 14 days. Median length of NSVT was 7 beats (range: 3 to 67) at rates of 120 to 240 bpm (median, 167 bpm). In 42 of the 114 patients (37%), initial NSVT occurred ≤ 48 hours and in 72 (63%) only during the extended monitoring period (3 to 14 days). Diagnostic yield for detecting NSVT over 14 days was 2.7-fold greater than ≤ 48 hours (p<0.001). NSVT judged at higher risk (≥8 beats, >200 bpm, ≥2 runs in consecutive 2-day period) was identified more frequently during extended monitoring, diagnostic yield 3.0-fold greater than ≤ 48 hours (p<0.001).

Conclusion: In HCM, NSVT episodes are frequent, however, in most patients, both NSVT and higher risk NSVT were not detected during initial 48-hours and confined solely to extended monitoring period. These data support additional clinical studies to evaluate the significance of NSVT on extended monitoring on sudden death risk in HCM.