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Updated: May 7, 2026
Benefits of Cardiac Resynchronization Therapy in an Asynchronous Heart Failure Model Induced by Left Bundle Branch Ablation and Rapid Pacing
Published on: December 11, 2017
Interplay of electrical wavefronts as determinant of the response to cardiac resynchronization therapy in
Marc Strik1, Lars B van Middendorp, Patrick Houthuizen
1Department of Physiology, Cardiovascular Research Institute Maastricht, Maastricht University Medical Center, Maastricht, The Netherlands.
Insights
Optimal cardiac resynchronization therapy (CRT) hemodynamics depend on synchronized activation waves and mechanical resynchronization, not ventricular filling. This study clarifies CRT optimization in heart block models.
Area of Science:
- Cardiology
- Biomedical Engineering
- Electrophysiology
Background:
- The precise mechanisms driving optimal hemodynamic outcomes in cardiac resynchronization therapy (CRT) remain unclear.
- Understanding the interplay between electromechanical synchronization and ventricular filling is crucial for CRT timing adjustments.
Purpose of the Study:
- To investigate whether optimal hemodynamic effects in CRT necessitate the collision of pacing-induced and intrinsic activation waves.
- To determine the role of optimal left ventricular (LV) filling in achieving peak hemodynamic performance during CRT.
Main Methods:
- CRT was performed in canine models with left bundle-branch block (LBBB) or atrioventricular (AV) block.
- Multiple pacing combinations were tested, assessing total activation time (TAT) and mechanical dyssynchrony.
- Optimal settings (CRTopt) were defined by achieving ≥90% of maximal LVdP/dtmax, with LV end-diastolic volume (EDV) changes monitored.
Main Results:
- CRTopt yielded an average LVdP/dtmax increase of approximately 15% across all tested settings.
- In AV block, CRTopt was solely dependent on interventricular intervals, not AV intervals.
- In LBBB, CRTopt occurred when LV pacing fused with intrinsic activation; optimal settings reduced TAT and dyssynchrony with minimal EDV change.
Conclusions:
- Optimal hemodynamic function in CRT for LBBB and AV block is primarily driven by the synchronization of pacing and intrinsic activation waves.
- Mechanical resynchronization, achieved through this interplay, is more critical than ventricular filling for hemodynamic optimization in CRT.
Background:
The relative contribution of electromechanical synchronization and ventricular filling to the optimal hemodynamic effect in cardiac resynchronization therapy (CRT) during adjustment of stimulation-timings is incompletely understood. We investigated whether optimal hemodynamic effect in CRT requires collision of pacing-induced and intrinsic activation waves and optimal filling of the left ventricle (LV).
Methods And Results:
CRT was performed in dogs with chronic left bundle-branch block (n=8) or atrioventricular (AV) block (n=6) through atrial (A), right ventricular (RV) apex, and LV-basolateral pacing. A 100 randomized combinations of A-LV/A-RV intervals were tested. Total activation time (TAT) was calculated from >100 contact mapping electrodes. Mechanical interventricular dyssynchrony was determined as the time delay between upslopes of LV and RV pressure curves. Settings providing an increase in LVdP/dtmax (maximal rate of rise of left ventricular pressure) of ≥90% of the maximum LVdP/dtmax value were defined as optimal (CRTopt). Filling was assessed by changes in LV end-diastolic volume (EDV; conductance catheter technique). In all hearts, CRTopt was observed during multiple settings, providing an average LVdP/dtmax increase of ≈15%. In AV-block hearts, CRTopt exclusively depended on interventricular-interval and not on AV-interval. In left bundle-branch block hearts, CRTopt occurred at A-LV intervals that allowed fusion of LV-pacing-derived activation with right bundle-derived activation. In all animals, CRTopt occurred at settings resulting in the largest decrease in TAT and mechanical interventricular dyssynchrony, whereas LV EDV hardly changed.
Conclusions:
In left bundle-branch block and AV-block hearts, optimal hemodynamic effect of CRT depends on optimal interplay between pacing-induced and intrinsic activation waves and the corresponding mechanical resynchronization rather than filling.
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