Mechanisms of left ventricular dyssynchrony: A multinational SPECT study of patients with bundle branch block
Saara Sillanmäki1,2, Alessia Gimelli3, Shahzad Ahmad4
1Institute of Clinical Medicine, University of Eastern Finland, Joensuu, Finland.
Insights
Left ventricular mechanical dysfunction, not QRS duration, significantly contributes to left ventricular mechanical dyssynchrony (LVMD) in LBBB and RBBB patients. Ejection fraction is a key predictor of LVMD.
Area of Science:
- Cardiology
- Cardiac Imaging
- Electrophysiology
Background:
- Left ventricular mechanical dyssynchrony (LVMD) is a critical factor in heart failure.
- Understanding the underlying mechanisms of LVMD is essential for effective treatment strategies.
- Conduction abnormalities like left bundle branch block (LBBB) and right bundle branch block (RBBB) are associated with LVMD.
Purpose of the Study:
- To investigate the relative contributions of QRS duration (QRSd), left ventricular ejection fraction (EF), volumes, and myocardial scar to LVMD.
- To compare these factors in patients with LBBB and RBBB against a control group.
- To identify key predictors of LVMD.
Main Methods:
- Analysis of myocardial perfusion imaging studies from 275 LBBB patients, 83 RBBB patients, and 172 controls.
- LVMD was quantified using phase bandwidth and phase standard deviation from gated single-photon emission tomography.
- Statistical analysis included variance explained and receiver operating characteristic (ROC) analysis.
Main Results:
- Prevalence of LVMD was 85% in LBBB and 40% in RBBB.
- Ejection fraction, scar severity, and LBBB morphology explained 70% of the variance in PhaseBW.
- Ejection fraction showed high predictive value (AUC 0.918) for LVMD, with an optimal cutoff of 47%; QRSd was not predictive.
Conclusions:
- Left ventricular mechanical dysfunction, particularly reduced ejection fraction, is a more significant driver of LVMD than conduction abnormalities like QRS duration.
- These findings challenge the current emphasis on QRSd as the primary predictor for cardiac resynchronization therapy (CRT) response.
- Further research is needed to refine predictors of CRT response and optimize patient selection.
Background:
To better understand the mechanisms of left ventricular (LV) mechanical dyssynchrony (LVMD), we explored the relative contributions of QRS duration (QRSd), LV ejection fraction (EF), volumes and scar to LVMD measured by gated single-photon emission tomography in a population of consecutive patients with left bundle branch block (LBBB) and right bundle branch block (RBBB) compared to controls.
Methods:
Myocardial perfusion imaging studies of 275 LBBB and 83 RBBB patients from three centers were analyzed. LVMD was defined as an abnormal phase bandwidth or phase standard deviation. Hospital and gender-specific normal values were obtained from 172 controls.
Results:
The prevalence of LVMD was 85 and 40% in LBBB and RBBB, respectively. Ejection fraction, scar severity, and LBBB morphology independently explained 70% of variance seen in PhaseBW. Ejection fraction had the highest area under the curve (AUC 0.918) in the receiver operating characteristics analysis of LVMD with an optimal cut-off of 47% (sensitivity 73% and specificity 98%). Notably, QRSd was not predictive.
Conclusion:
LV mechanical dysfunction plays a greater role than conduction abnormality in the genesis of LVMD, a finding that is intriguing in the context of contemporary literature which suggests that QRSd is the parameter that is most predictive of CRT response.
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