Continuous ambulatory ECG monitoring of up to 14 days increases detection of high-risk ventricular tachyarrhythmias compared with the first 48 hours in hypertrophic cardiomyopathy

Background Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiomyopathy and a leading cause of sudden cardiac death (SCD). Nonsustained ventricular tachycardia (NSVT) identified on short-term (≤48 h) ambulatory ECG monitoring is associated with increased SCD risk. Prior prospective studies, including EXAMINE-HCM, demonstrated increased detection of NSVT with extended ambulatory cardiac monitoring (ACM) of up to 14 days, but real-world data are limited. Objective To compare diagnostic yield of NSVT and other clinically significant arrhythmias during the first 48 h of monitoring vs. the full monitoring period of up to 14 days in patients with HCM. Methods We retrospectively analyzed U.S. patients ≥18 y with HCM who underwent continuous patch-based ACM for up to 14 days from 2018-2022. Commercial fee-for-service and Medicare Advantage claims data were linked to a clinical data warehouse containing the continuous ACM results. From this linked cohort, we identified patients with HCM (ICD-10 I42.1/I42.2) who underwent 3-14 days of continuous patch-based ACM and compared arrhythmia detection during the first 48 h of monitoring to the full monitoring period (of up to 14 days). Outcomes included detection of any NSVT, high-risk NSVT (≥8 beats, >200bpm, or ≥2 runs within any 48-hour period), and other clinically actionable arrhythmias (AF, SVT, pause, AV block). Results Among 5,325 patients with HCM (median age 65 y; 50% female), median ACM wear time was 13.2 (IQR 6.9) days with 98.9% (IQR 3.5%) analyzable time. Any NSVT was detected in 1,184 (22%) and high-risk NSVT in 651 (12%) patients. Of those with NSVT, 60% had detection only after the first 48 h of monitoring (p<0.001 vs. ≤48 h monitoring). For high-risk VT, 48% had detection only after 48 h of monitoring (p<0.001 vs. ≤48 h monitoring). Clinically actionable arrhythmias were detected in 1,923 (36%) patients, with 681 (35%) detected only after the first 48 h, including 128 (20%) with AF ≥30 seconds. Conclusion Extended ambulatory ECG monitoring of up to 14 days in patients with HCM significantly increases detection of NSVT and other actionable arrhythmias vs. short-term (≤48 h) monitoring. These real-world findings align with prior prospective studies and support extended monitoring for comprehensive arrhythmia assessment and SCD risk stratification in HCM.HCM-abstract-table