Impact of Left and Right Bundle Branch Block on Left Ventricular Systolic Function and Myocardial Mechanics Assessed by Speckle-Tracking Echocardiography and Cardiac Magnetic Resonance Feature Tracking: A Systematic Review and Meta-Analysis.

backgroundBundle branch conduction abnormalities are associated with ventricular dyssynchrony, impaired myocardial mechanics, and progressive systolic dysfunction. Advanced deformation imaging techniques, including speckle-tracking echocardiography (STE) and cardiac magnetic resonance feature tracking (CMR-FT), may identify subclinical ventricular dysfunction beyond conventional left ventricular ejection fraction (LVEF). We performed a systematic review and meta-analysis to evaluate conventional systolic function and myocardial deformation abnormalities associated with left bundle branch block (LBBB) and right bundle branch block (RBBB).

methodsPubMed, Scopus, and EMBASE databases were systematically searched for observational studies evaluating ventricular systolic function and myocardial deformation parameters in patients with LBBB and/or RBBB using STE and/or CMR-FT. Comparative meta-analyses were performed using standardized mean differences (SMDs) with 95% confidence intervals (CIs). Separate analyses were conducted for LVEF and left ventricular global longitudinal strain (LV-GLS).

resultsSixteen studies were included in the systematic review, whereas eight were eligible for quantitative meta-analysis. Compared with healthy controls, patients with LBBB demonstrated significantly reduced LVEF (SMD -0.404, 95% CI -0.553 to -0.255; p < 0.001) and impaired LV-GLS (SMD -0.345, 95% CI -0.535 to -0.156; p < 0.001). In contrast, isolated RBBB was not associated with significant overall differences in either LVEF (SMD 0.051, 95% CI -0.146 to 0.247; p = 0.613) or LV-GLS (SMD 0.064, 95% CI -0.134 to 0.262; p = 0.527). Direct comparisons demonstrated significantly greater impairment of both LVEF (SMD -0.361, 95% CI -0.519 to -0.202; p < 0.001) and LV-GLS (SMD -0.436, 95% CI -0.595 to -0.276; p < 0.001) in LBBB than in RBBB. STE-based studies generally demonstrated larger effect sizes and greater heterogeneity than CMR-FT investigations.

conclusionsBundle branch conduction abnormalities, particularly LBBB, are closely associated with impaired left ventricular systolic performance and myocardial mechanics. LV-GLS abnormalities appeared consistently more pronounced than LVEF abnormalities across several comparisons, suggesting that myocardial deformation imaging may be more sensitive to the mechanical consequences of conduction abnormalities at a population level. Given the observational nature of the included studies, the substantial clinical and methodological heterogeneity across populations, the limited evidence available for RBBB, and the potential influence of residual confounding factors such as age and underlying structural heart disease, these findings should be considered hypothesis-generating and warrant confirmation in larger prospective studies.