New LBBB Driving LVEF Decline — EECC MCQ

Correct answer: E — New LBBB causing electrical dyssynchrony may be driving the LVEF decline — CRT should be considered (Class I for LBBB ≥150 ms with LVEF ≤35%); the development of LBBB in HFrEF accelerates disease progression and is itself an indication for CRT evaluation

New LBBB in pre-existing HFrEF is a significant development: (1) LBBB causes LV electrical dyssynchrony → mechanical dyssynchrony → further worsening of contractility and remodelling (delayed lateral wall contraction, paradoxical septal motion, functional MR worsening); (2) the LVEF decline from 32% to 22% is likely partly attributable to the dyssynchrony caused by the new LBBB; (3) CRT directly addresses this mechanism: at QRS 160 ms with LBBB and LVEF ≤35%, this patient is a Class I candidate for CRT; (4) the 2021 ESC Pacing/CRT Guidelines recommend CRT for sinus rhythm + LVEF ≤35% + LBBB ≥150 ms (strongest indication — Class I, LOE A). After CRT implantation, LVEF improvement (often back toward the pre-LBBB baseline and beyond) is expected in ~70% of LBBB patients. This scenario illustrates why regular ECG monitoring is important in HFrEF — new conduction abnormalities should trigger CRT evaluation.

Reference: ESC (2021): Pacing/CRT; ESC (2023): HF