New-onset left bundle branch block–associated idiopathic nonischemic cardiomyopathy and left ventricular ejection fraction response to guideline-directed therapies: The NEOLITH study

Background Left ventricular ejection fraction (LVEF) response to guideline-directed medical therapy (GDMT) and to early cardiac resynchronization therapy (CRT) in new-onset idiopathic nonischemic cardiomyopathy (NICM) and left bundle branch block (LBBB) is not well described. CRT is recommended if LVEF remains ≤35% after at least 3 months of GDMT. Objective The purpose of this study was to describe LVEF response to GDMT at 3 months and to early CRT in new-onset LBBB–associated idiopathic NICM. Methods A retrospective cohort study was performed in subjects with new-onset idiopathic NICM, LVEF ≤35%, and LBBB or narrow ( Results In 102 subjects (70 with narrow QRS complex and 32 with LBBB), post-GDMT LVEF was >35% in 39 narrow QRS complex subjects (56%) and 2 LBBB subjects (6%) (P 35% (relative risk 10.30; 95% confidence interval 2.63–40.27; P = .0008) and absolute difference between post-GDMT LVEF and initial LVEF (β = 16.296; standard error=2.977; P Conclusion GDMT did not significantly improve LVEF in new-onset LBBB–associated idiopathic NICM at 3 months. Most remained candidates for CRT, and a high percentage were super-responders. Optimal timing for CRT implantation requires further investigation.