In the Search of Noninvasive Methods Delineating Left Bundle Branch Block Amendable With Conduction System Pacing
Tadej Žlahtič1,2, Vito Starc2, David Žižek1,2
1University Medical Centre Ljubljana, Ljubljana, Slovenia.
Insights
Conduction system pacing (CSP) shows promise for cardiac resynchronization therapy (CRT). Analyzing equivalent dipole trajectories in patients with left bundle branch block (LBBB) can identify those best suited for CSP, improving CRT outcomes.
Area of Science:
- Cardiology
- Medical Imaging
- Biomedical Engineering
Background:
- Conduction system pacing (CSP) is an emerging cardiac resynchronization therapy (CRT) but is ineffective for approximately one-third of patients with left bundle branch block (LBBB) due to distal conduction disease.
- Tailored patient selection for CRT is crucial, necessitating advanced analysis of ventricular depolarization patterns.
Purpose of the Study:
- To evaluate the utility of equivalent dipole (ED) trajectories derived from high-resolution electrocardiograms (hrECGs) in differentiating proximal LBBB (pLBBB) from distal LBBB (dLBBB).
- To assess the correlation between ED trajectory characteristics and CRT response in heart failure patients with LBBB undergoing CSP.
Main Methods:
- Retrospective analysis of 12-lead hrECGs, ED trajectories, and echocardiograms in 18 heart failure patients with LBBB indicated for CRT and randomized to CSP.
- Patients were categorized into pLBBB and dLBBB groups based on left bundle branch capture and left ventricular activation time.
- Comparison of baseline characteristics, ED trajectory parameters (direction, velocity), QRS duration, and echocardiographic measures post-6 months of CRT.
Main Results:
- The pLBBB group (n=12) exhibited distinct ED trajectories with an initial leftward direction (p=0.03) and slower, uniform velocity (p<0.001) compared to the dLBBB group (n=6).
- Patients in the pLBBB group demonstrated significantly greater QRS duration shortening (26% vs. 14%, p<0.02) and improved left ventricular volumes (41.3% vs. 15.8%, p=0.004) and ejection fraction (17.1% vs. 5.5%, p=0.02) after 6 months.
- ED trajectories differentiated pLBBB from dLBBB more effectively than standard 12-lead ECG criteria.
Conclusions:
- Equivalent dipole trajectories from hrECGs offer a superior method for distinguishing proximal from distal LBBB compared to standard ECG analysis.
- This advanced ECG analysis can aid in selecting appropriate candidates for conduction system pacing, optimizing cardiac resynchronization therapy outcomes.
Abstract:
Conduction system pacing (CSP) is an emerging new method of cardiac resynchronization therapy (CRT), however, one third of patients with left bundle branch block (LBBB) have distal conduction disease, which is not amenable to correction with CSP. There is an emerging need for tailored analysis of ventricular depolarization patterns for patient selection for CRT pacing modality. We retrospectively analyzed 12 lead hrECGs, equivalent dipole (ED) trajectories and standard transthoracic echocardiograms of 18 heart failure patients fulfilling Strauss criteria for LBBB and indication for CRT randomized to the CSP arm of the ongoing CSP-Sync study (NCT05155865). Based on achievement of left bundle branch capture with shortening of left ventricular activation time, 12 patients had proximal LBBB (pLBBB group), and 6 had intact proximal LBBB conduction (dLBBB group) with similar average baseline QRS durations between the groups (179±14 ms in the pLBBB and 165±20 ms in the dLBBB group, p = 0.1). All patients fulfilled the Strauss criteria with no significant difference in the additional criterion (R wave > 0.1 mV in V1; p = 0.7). In the pLBBB group ED trajectory had an initial leftward direction (six vs. zero patients, p = 0.03) with a uniform (12 vs. one patient, p < 0.001) and slower (0.57 ± 0.12 m/s in the pLBBB vs. 0.75 ± 0.15 m/s in the dLBBB group, p = 0.01) velocity. After 6 months the pLBBB group achieved greater relative QRS duration shortening (26% ± 8% vs. 14% ± 9%; p < 0.02) and relative reductions in end left ventricle systolic volumes (41.3% ± 17.6% vs. 15.8% ± 6.1%; p = 0.004) with better improvement in ejection fraction (17.1% ± 11.0% vs. 5.5% ± 1.0%; p = 0.02). The ED trajectories from 12-lead hrECGs could better differentiate patients with proximal or distal LBBB than standard 12-lead ECG alone.
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