Atrial signal amplitude predicts atrial high-rate episodes in implantable cardioverter defibrillator patients: Insights from a large database of remote monitoring transmissions

Background: Parameters measured during implantable cardioverter defibrillator (ICD) implant also depend on bioelectrical properties of the myocardium. We aimed to explore their potential association with clinical outcomes in patients with single/dual-chamber ICD and cardiac resynchronization therapy defibrillator (CRT-D). Methods: In the framework of the Home Monitoring Expert Alliance, baseline electrical parameters for all implanted leads were compared by the occurrence of all-cause mortality, adjudicated ventricular arrhythmia (VA), and atrial high-rate episode lasting ≥24 hours (24 h AHRE). Results: In a cohort of 2976 patients (58.1% ICD) with a median follow-up of 25 months, event rates were 3.1/100 patient-years for all-cause mortality, 18.1/100 patient-years for VA, and 9.3/100 patient-years for 24 h AHRE. At univariate analysis, baseline shock impedance was consistently lower in groups with events than without, with a 40 Ω cutoff that better identified high-risk patients. However, at multivariable analysis, the adjusted-hazard ratios (HRs) lost statistical significance for any endpoint. Baseline atrial sensing amplitude during sinus rhythm was lower in patients with 24 h AHRE than in those without (2.45 [IQR: 1.65-3.85] vs 3.51 [IQR: 2.37-4.67] mV, P <.01). The adjusted HR for 24 h AHRE in patients with atrial sensing >1.5 mV vs those with values ≤1.5 mV was 0.52 (95% CI: 0.33-0.83), P =.006. Conclusions: Although lower baseline shock impedance was observed in patients with events, the association lost statistical significance at multivariable analysis. Conversely, low sinus rhythm atrial sensing (≤1.5 mV) measured with standard transvenous leads could identify subjects at high risk of atrial arrhythmia.