The effect of left bundle branch block on left ventricular remodeling, dyssynchrony and deformation of the mitral valve apparatus: An observational cardiovascular magnetic resonance imaging study

Background: The effect of a left bundle branch block (LBBB) on cardiac function and remodeling in patients at different stages of heart failure (HF) is unknown. We used cardiac magnetic resonance imaging (CMR) to evaluate the effect of LBBB on left ventricular (LV) remodeling, mechanical dyssynchrony, functional mitral regurgitation (FMR) and deformation of the mitral valve apparatus (MVA) in LBBB patients at different stages of HF. Methods: In 12 LBBB patients with HF, 4 patients with isolated LBBB, and 4 controls, cine CMR was performed to measure LV remodeling, FMR grade and deformation of the MVA. CMR tagging was used to measure septal-to-lateral onset of shortening delay and coefficient of circumferential strain variation (CV) to quantify dyssynchrony. Results: LV end-diastolic volume (LVEDV) and end-systolic volume (LVESV) were largest in LBBB patients with HF. Patients with isolated LBBB tended to have a larger LVESV and smaller LV ejection fraction compared to controls, (56 ± 22 ml/m² versus 45 ± 9 ml/m², P = ns, 42 ± 9% versus 53 ± 4 %, P = ns). QRS duration and septal-to-lateral-onset-of-shortening delay were comparable between LBBB patients with HF and isolated LBBB patients, CV was larger (98 ± 45 versus 40 ± 4, P < 0.05). MVA tenting and FMR were present both in LBBB patients with HF and patients with isolated LBBB and were not observed in controls. Conclusion: The presence of a LBBB in asymptomatic patients is related to mechanical dyssynchrony and deformation of the MVA and may be associated with LV remodeling. If confirmed, close monitoring or even timely initiation of therapy may be warranted in patients with isolated LBBB. This advocates to conduct a longitudinal CMR follow-up study on the clinical course in patients with isolated LBBB.