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 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.
Some of the electrical parameters routinely measured at ICD/CRT‐D implant differed according to long‐term clinical outcome. Shock impedance values were lower in patients who experienced death and both atrial and ventricular arrhythmias during follow‐up. Subjects with atrial signal amplitude below 1.5 mV showed a significant higher risk of atrial arrhythmias as compared to those with >1.5 mV, potentially revealing the presence of a more impaired atrial tissue.