Cardiology · Medical Literature
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.
Abstract
Bundle 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). PubMed, 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). Sixteen 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. Bundle 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.
Clinical relevance
Bundle branch block (BBB)-related ventricular dyssynchrony is a common clinical finding, yet conventional LVEF may underestimate the true degree of mechanical impairment, particularly in patients with preserved or borderline ejection fraction. This systematic review and meta-analysis addresses the diagnostic gap by quantifying the additive value of advanced deformation imaging—speckle-tracking echocardiography (STE) and CMR feature tracking (CMR-FT)—in detecting subclinical LV dysfunction in LBBB and RBBB populations. Clinicians managing patients with conduction abnormalities for device therapy candidacy, risk stratification, or surveillance should be aware that LVEF alone may be insufficient to capture the full burden of myocardial mechanical dysfunction.
Key findings
1. LBBB was associated with significantly reduced LVEF compared with healthy controls (SMD -0.404, 95% CI -0.553 to -0.255; p < 0.001), confirming a moderate but statistically robust effect on conventional systolic function. 2. LBBB was independently associated with impaired LV global longitudinal strain (LV-GLS) vs. controls (SMD -0.345, 95% CI -0.535 to -0.156; p < 0.001), indicating subclinical myocardial deformation abnormalities beyond LVEF. 3. Isolated RBBB demonstrated no significant difference in LVEF relative to controls (SMD 0.051, 95% CI -0.146 to 0.247; p = 0.613), suggesting preserved global systolic function in this subgroup. 4. Isolated RBBB similarly showed no significant impairment of LV-GLS vs. controls (SMD 0.064, 95% CI -0.134 to 0.262; p = 0.527), indicating that isolated RBBB may not produce meaningful LV mechanical dysfunction at a population level. 5. Direct head-to-head comparisons confirmed significantly greater impairment of 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 versus RBBB, with LV-GLS showing the larger effect size differential. 6. Across multiple comparisons, LV-GLS abnormalities appeared consistently more pronounced than LVEF abnormalities, suggesting superior sensitivity of myocardial deformation imaging to the mechanical consequences of conduction disease; STE-based analyses yielded larger effect sizes but greater heterogeneity than CMR-FT investigations.
Practice implications
In patients with LBBB—particularly those being evaluated for cardiac resynchronization therapy (CRT) eligibility or monitored for LBBB-induced cardiomyopathy—LV-GLS by STE should be incorporated into routine echocardiographic assessment, as it appears more sensitive than LVEF alone in detecting early or subclinical LV mechanical dysfunction. Isolated RBBB, in the absence of structural heart disease or other comorbidities, does not appear to impose significant LV systolic or deformation burden at a population level, and aggressive intervention based solely on conduction morphology is not supported by this evidence. Given the observational nature of included studies, residual confounding from age and structural disease, and limited RBBB-specific data, these findings should be considered hypothesis-generating; prospective, confounder-adjusted studies are needed before definitive changes to device therapy or surveillance protocols are adopted.