Identification of individuals with nonischemic cardiomyopathy who could benefit from a cardioverter-defibrillator implant as a preventative measure. Periodic repolarization dynamics (PRD), a sign of repolarization instability linked to sympathetic activity, may be utilized to identify individuals who would benefit from prophylactic ICD implantation, researchers reasoned. Patients with nonischemic cardiomyopathy, left ventricular ejection fraction (LVEF) of ≤35%, and increased NT-proBNP (N-terminal pro-brain natriuretic peptides) were randomized to the ICD implantation/control group in the (ICD Study in Patients With Dilated Cardiomyopathy) trial. Patients with a 24-hour Holter monitor recording at baseline with technically acceptable ECG values throughout the night hours (00:00–06:00) were included in the PRD substudy. Wavelet analysis was used to measure PRD using already established methodologies. The primary outcome was death from any cause. Age, sex, NT-proBNP, estimated glomerular filtration rate, LVEF, atrial fibrillation, ventricular pacing, diabetes, cardiac resynchronization treatment, and mean heart rate were all adjusted in Cox regression models. As an experimental cut-off value for ICD implantation, we offered PRD ≥10 deg2.

About 748 out of 1,116 patients were eligible for the PRD substudy. During a median follow-up time of 5.1±2.0 years, 82 of 385 ICD patients died, whereas 85 of 363 control patients died (P=0.40). PRD was independently linked with death in Cox regression analysis (hazard ratio [HR], 1.28 [95% CI, 1.09–1.50] per SD increase; P=0.003). In the control group (HR, 1.51 [95% CI, 1.25–1.81]; P<0.001), PRD was linked with mortality, but not in the ICD group (HR, 1.04 [95% CI, 0.83–1.54]; P=0.71). There was a significant interaction between PRD and the impact of ICD installation on mortality (P=0.008), with individuals with higher PRD benefiting more from the reduction in mortality. In the 280 patients with PRD ≥10 deg2  (HR, 0.54 [95% CI, 0.34–0.84]; P=0.006; number needed to treat=6), ICD implantation was associated with a 17.5% reduction in absolute mortality, but not in the 468 patients with PRD ≥10 deg2  (HR, 1.17 [95% CI, 0.77–1.78]; P=0.46; P for interaction=0.01). Patients with nonischemic cardiomyopathy who had a higher PRD had a lower death rate after receiving a prophylactic ICD.