New‐onset left bundle branch block‐associated idiopathic nonischemic cardiomyopathy and time from diagnosis to cardiac resynchronization therapy: The NEOLITH II study

Abstract Background The optimal timing for cardiac resynchronization therapy (CRT) after diagnosis of new‐onset left bundle branch block (LBBB)‐associated idiopathic nonischemic cardiomyopathy (NICM) and treatment with guideline‐directed medical therapy (GDMT) is unknown. The purpose of this study was to describe relationships between time from diagnosis to CRT and outcomes in new‐onset LBBB‐associated idiopathic NICM with left ventricular ejection fraction (LVEF) ≤35%. Methods A retrospective cohort study examined associations between time from diagnosis to CRT (≤9 months vs >9 months) and clinical and echocardiographic outcomes. Results In 123 subjects with LBBB‐associated idiopathic NICM, time from diagnosis to CRT was ≤9 months in 60 (49%) subjects and 9 months in 63 (51%) subjects. Clinical outcomes were similar for those implanted ≤9 months versus >9 months for adverse clinical events (hazard ratio [HR], 0.85; 95% confidence interval [CI], 0.41–1.78; P = 0.67) and all‐cause mortality (HR, 0.57; 95% CI, 0.19–1.70; P = 0.31). Multivariable analyses demonstrated similar results. In 105 subjects with post‐CRT echocardiograms, LVEF improvement to >35% was more likely in those implanted ≤9 months when compared to >9 months (odds ratio [OR], 3.53; 95% CI, 1.32–9.46; P = 0.01). This association persisted in the final multivariable model adjusted for age at diagnosis, sex, QRS duration, post‐GDMT LVEF, and time from CRT to post‐CRT echocardiogram (OR, 5.10; 95% CI, 1.71–15.22; P = 0.004). Conclusion In LBBB‐associated idiopathic NICM, earlier CRT implantation was associated with more favorable cardiac remodeling. Delaying CRT may miss a critical period to halt and reverse progressive myocardial damage.