Change in mechanical dyssynchrony during fusion pacing for the left bundle branch block and its relationship with QRS duration and morphology
H Hara, G Susukita, S Suzuki, K Kato, H Hara, M Murakami, H Ito, Y Naruse, Y MaekawaAbstract
Background
In patients with left bundle branch block (LBBB) and preserved atrioventricular (AV) conduction, cardiac resynchronization therapy (CRT) can shorten QRS duration through fusion pacing. However, the change in dyssynchrony during fusion pacing and the association of dyssynchrony with QRS duration and morphology remain unclear.
Purpose
This study aimed to evaluate the changes in left ventricular (LV) mechanical dyssynchrony, QRS duration, and morphology in patients with LBBB when AV delay (AVD) was shortened during LV-only fusion pacing.
Methods
A total of 20 patients (age 72 ± 12 years, 12 males) who underwent CRT for LBBB (QRS duration: 155 ± 18 ms, PQ interval: 198 ± 51 ms) were included in this study. The LV lead position was in the anterior-lateral (n=13) or inferior-lateral (n=7). The time from QRS onset to sensing in the LV lead (Q-LV) was 128 ± 29 ms. Atrial pacing (AP) and atrial-LV sequential pacing (AP-LVP) were performed at a rate of 5–10 bpm faster than the intrinsic heart rate. In AP-LVP, AVD was shortened every 20 ms, and the shortest AVD at which the LV pacing spike did not occur earlier than the QRS onset (AVDQ) was determined. On echocardiography, longitudinal strain was evaluated in 18 LV segments. Contraction observed during the pre-ejection period was identified as early systolic contraction (ESC). The first negative peak that appeared after aortic valve opening was identified as late systolic contraction (LSC). The time from QRS onset to the peak of the LSC (Q-Peak) was measured in each segment (Fig. A). In the 4-chamber view, Q-Peaks of the two segments in the inferoseptal, apical, and anterolateral regions were averaged. Dyssynchrony was calculated as the difference between the maximum and minimum values of the average Q-Peaks across three regions. QRS duration and amplitude of the initial positive deflection of the QRS complex (i.e. r or R wave) in lead V1 (V1-Ramp) were measured on 12-lead electrocardiography.
Results
During AP, the Q-Peak was shortened in the septum and prolonged in the lateral wall. Although the dyssynchrony was reduced during AP-LVP at AVDQ, ESC or slurring was still observed in the septum, and the Q-Peak remained short in the septum and prolonged in the lateral wall. The dyssynchrony was minimal at the AVD shortened by 20 ms from the AVDQ (AVDQ–20ms). On the other hand, the QRS duration was minimal during the AP-LVP at AVDQ. The V1-Ramp showed no change during AP-LVP at AVDQ compared with that during AP, but increased at the AVDQ–20ms.
Conclusions
The QRS duration and LV mechanical dyssynchrony in LBBB were reduced by LV-only fusion pacing. However, the AVD at which these parameters reached their minimum values differed. Confirming the timing of QRS onset and observing the change in V1-Ramp may assist in establishing CRT settings with reduced dyssynchrony.Fig. A to CFig. D and E