Influence of Capture Selectivity and Left Intrahisian Block on QRS Characteristics During Left Bundle Branch Pacing
Weiping Sun1, Gaurav A Upadhyay2, Roderick Tung2
1Center for Arrhythmia Care, Pritzker School of Medicine, University of Chicago Medicine, Chicago, Illinois, USA; Heart Center, Beijing Anzhen Hospital, Capital Medical University, Beijing, China.
Insights
Nonselective left bundle branch pacing (NS-LBBP) achieves narrower QRS duration than selective LBBP by recruiting the right ventricular septum. Narrow QRS during LBBP depends on nonselective capture or AV fusion, not intrinsic synchrony.
Area of Science:
- Electrophysiology
- Cardiac Pacing
- Heart Rhythm Disorders
Background:
- Selective (S) and nonselective (NS) left bundle branch pacing (LBBP) criteria lack validation via intracardiac mapping.
- Understanding LBBP mechanisms is crucial for optimizing pacing strategies.
Purpose of the Study:
- To investigate QRS characteristics and intracardiac electrograms during S-LBBP and NS-LBBP using direct left septal recordings.
- To compare the efficacy of S-LBBP versus NS-LBBP in achieving narrow QRS duration across different baseline conduction statuses.
Main Methods:
- Pacing from multielectrode Purkinje recordings below the His bundle in patients with various QRS durations.
- Measuring QRS duration from stimulus onset (QRSst) and intrinsicoid deflection (QRSid).
- Assessing retrograde left bundle branch conduction via stimulus-to-His intervals.
Main Results:
- NS-LBBP yielded significantly narrower QRSst (163 ms vs 181 ms) and QRSid (125 ms vs 150 ms) compared to S-LBBP (P < 0.001).
- Left ventricular activation time was shorter with NS-LBBP (88 ms vs 97 ms; P = 0.019).
- Wider QRSst during NS-LBBP was observed in patients with complete conduction block (181 ms vs 157 ms; P = 0.022).
Conclusions:
- NS-LBBP promotes narrower QRS by recruiting the basal right ventricular septum, unlike S-LBBP which can cause delayed RBB synchronization.
- Achieving narrow QRS during LBBP relies on nonselective capture or programmed AV fusion, not solely on intrinsic left bundle branch activation.
- Bidirectional left intrahisian block can lead to wider paced QRS morphology.
Objectives:
This study sought to examine QRS and intracardiac characteristics during selective (S) and nonselective (NS) left bundle branch pacing (LBBP) from direct left septal recordings.
Background:
Criteria for S-LBBP and NS-LBBP have not been validated with intracardiac mapping.
Methods:
Pacing was performed from multielectrode Purkinje recordings below the left-sided His. S-LBBP and NS-LBBP were performed in patients with narrow QRS (n = 9), right bundle branch block (n = 3), intraventricular conduction delay (n = 5), and left bundle branch block (n = 10). QRS duration was measured from stimulus onset (QRSst) and from the intrinsicoid deflection of the R-wave in V1-V2 (QRSid) to QRS end. Retrograde left bundle branch conduction was assessed by stimulus-to-retrograde His intervals.
Results:
Among 27 patients analyzed, 20 demonstrated both NS- and S-LBBP and were studied in paired comparisons. NS-LBBP resulted in narrower QRS compared to S-LBBP (QRSst: 163 ms [interquartile range (IQR): 144-179 ms] vs 181 ms [IQR: 173-203 ms]; P < 0.001; QRSid: 125 ms [IQR: 117-142 ms] vs 150 ms [IQR: 135-157 ms]; P < 0.001). Left ventricular activation time was also significantly shorter for NS-LBBP compared to S-LBBP (88 ms [IQR: 75-111 ms] vs 97 ms [IQR: 82-123 ms]; P = 0.019). Left intrahisian block was bidirectional in 10 patients with long retrograde stimulus-to-His intervals. QRSst duration was significantly longer in patients with complete conduction block compared to those with intact Purkinje activation during NS-LBBP (181 ms [IQR: 162-195 ms] vs 157 ms [IQR: 139-168 ms]; P = 0.022).
Conclusions:
In contrast to His-bundle pacing, S-LBBP predominantly yields a wide QRS as a result of delayed RBB synchronization, whereas NS-LBBP results in shorter QRS duration because of recruitment of the basal right ventricular septum. A wider-paced morphology of LBBP was noted in patients with complete conduction block caused by bidirectional left intrahisian block. Achievement of narrow QRS during LBBP is predicated upon capture nonselectivity or programmed atrioventricular fusion, rather than intrinsic physiologic synchrony from left bundle branch stimulation.
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