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

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.