The characteristics of the electrocardiogram and the intracardiac electrogram in left bundle branch pacing.

Left bundle branch pacing (LBBP) has recently been reported to maintain left ventricular electrical synchrony with a low and stable threshold. However, the electrocardiogram (ECG) definitions of LBBP have not been well established. We report four cases to show the characteristics of the ECG and the intracardiac electrogram (EGM) in LBBP. Four patients, two with an atrioventricular block (AVB) and two with left bundle branch block (LBBB), were included in the study. LBBP was performed and the ECGs and EGMs were collected and compared at different pacing outputs. Selective LBBP (S-LBBP) was defined as only capturing the LBB with a typical RBBB morphology and a discrete component between the pacing stimulus and ventricular activation in the EGMs. While nonselective LBBP (NS-LBBP) captured both the LBB and the local myocardium, resulting in a narrow right bundle branch block (RBBB) morphology without the discrete component. The left bundle branch (LBB) potential was recorded in two cases during narrow QRS complex or LBBB correction by selective His bundle pacing and SLBBP (n = 3) was achieved. A constant and shortest stimulus to left ventricular activation time (LVAT) in LBBP was obtained at different pacing outputs. The ECG and EGM characteristics of LBBP can be summarized as: 1) RBBB pattern; 2) usually with the LBB potential; 3) SLBBP with specific ECG changes and a discrete component in EGM; and 4) with a constant and shortest stimulus to LVAT at different pacing outputs. Further studies are necessary to confirm these observations.

Chen X ，Wu S ，Su L ，Su Y ，Huang W ... -  《-》

Evaluation of the Criteria to Distinguish Left Bundle Branch Pacing From Left Ventricular Septal Pacing.

This study sought to assess the predictive value of the proposed electrocardiogram and intracardiac electrogram characteristics for confirmation of left bundle branch (LBB) capture. Previously proposed criteria to distinguish left bundle branch pacing (LBBP) and left ventricular septum (LVS) pacing (LVSP) have not been fully validated. A His bundle pacing lead, an LBBP lead, and a multielectrode catheter at the LVS were placed. Direct LBB capture was defined as demonstration of retrograde His potential on the His bundle pacing lead and/or anterograde left conduction system potentials on the multielectrode catheter during LBBP. The routinely used parameters-His, LBB potential, time from stimulus to peak ventricular activation (Stim-LVAT), and paced QRS morphology during LVSP and LBBP at various depths and outputs were analyzed. Thirty patients (21 non-left bundle branch block [LBBB], 9 LBBB) who demonstrated direct LBB capture using the defined criteria were included. The proportion of paced right bundle branch block was 100% during LBB capture in all patients compared to 23.4% in non-LBBB and 44.4% in LBBB during LVSP. LBB potential was recorded in all patients during intrinsic rhythm (non-LBBB group) or His corrective pacing in LBBB. Paced QRS duration was longer during selective LBBP compared to nonselective LBBP or LVSP only. All patients with characteristics of selective LBBP or abrupt decrease in Stim-LVAT of ≥10 ms demonstrated LBB capture. Direct LBB capture can be confirmed by recording retrograde His potential and anterograde left conduction system potentials. Abrupt decrease in Stim-LVAT of ≥10 ms and demonstration of selective LBBP could be used as simple criteria to confirm LBB capture.

Wu S ，Chen X ，Wang S ，Xu L ，Xiao F ，Huang Z ，Zheng R ，Jiang L ，Vijayaraman P ，Sharma PS ，Su L ，Huang W ... -  《-》

Left bundle branch pacing utilizing three dimensional mapping.

Permanent His bundle pacing is feasible and effective in patients with atrioventricular block or left bundle branch block. However, pacing thresholds to capture the distal His bundle is often higher. Recently left bundle branch area pacing (LBBP) has been shown to be feasible by advancing the lead transvenously, deep into the interventricular septum to reach the left ventricular endocardial surface. In this article we describe the utility of three dimensional (3D) mapping to achieve LBBP. Ensite Precision (Abbott) mapping system was used to perform LBBP. A decapolar catheter was used to create 3D map of right atrium and right ventricle (RV). Regions of interest (His bundle, potential LBBP sites of interest in RV) were tagged in the 3D map. The LBBP lead was implanted utilizing the 3D map. The lead depth in the septum was assessed in the 3D map. LBBP was performed in three patients: chronic LBBB and intermittent 2:1 atrioventricular block; atrioventricular (AV) node ablation and conduction system pacing; and bifascicular block and intermittent AV block in a patient with severe left ventricular hypertrophy. LBBP was successful in all three patients. The lead depth in the interventricular septum was 12, 11, and 21 mm, respectively as assessed by 3D mapping. Three-dimensional mapping was helpful in achieving LBBP in patients with LBBB, severe left ventricular hypertrophy or during AV node ablation. 3D mapping also facilitated easy assessment of lead depth during and after lead fixation. 3D mapping techniques may be a valuable tool to reduce the learning curve of implanters with minimal experience in LBBP.

Vijayaraman P ，Panikkath R ，Mascarenhas V ，Bauch TD ... -  《-》

Comparison of electrocardiogram characteristics and pacing parameters between left bundle branch pacing and right ventricular pacing in patients receiving pacemaker therapy.

This study explores the feasibility of left bundle branch pacing (LBBP) and characterizes electrocardiogram (ECG) patterns during the pacing in comparison with conventional right ventricular pacing (RVP). Forty pacing-indicated patients were prospectively enrolled. Twenty patients underwent LBBP (the LBBP group), and 20 patients underwent RVP (the RVP group). Left bundle branch pacing was achieved by transseptal method in the basal ventricular septum. Electrocardiogram characteristics, pacing parameters, pacing sites, and safety events were assessed at implantation and 3-month follow-up. In the LBBP group, the pacing lead was successfully placed near the endocardium of the left side of the septum. Electrocardiogram pattern during LBBP showed right bundle branch conduction delay. Left bundle branch block (LBBB) in two patients was corrected by LBBP. Post-implantation 3D echocardiography confirmed the pacing location. In the RVP group, ECG showed LBBB pattern. The paced QRS duration was 111.85 ± 10.77 ms in LBBP group and 160.15 ± 15.04 ms in the RVP group (P < 0.001). Pacing thresholds (at implantation: 0.73 ± 0.20 V in the LBBP group and 0.61 ± 0.23 V in the RVP group) remained low and stable at 3-month follow-up. No adverse event was observed during 3-month follow-up. This study demonstrates the clinical feasibility of LBBP. Left bundle branch pacing that has a low pacing threshold and produces narrow ECG QRS duration may be a new pacing strategy for patients in need of ventricular pacing.

Chen K ，Li Y ，Dai Y ，Sun Q ，Luo B ，Li C ，Zhang S ... -  《-》

Influence of Capture Selectivity and Left Intrahisian Block on QRS Characteristics During Left Bundle Branch Pacing.

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. Criteria for S-LBBP and NS-LBBP have not been validated with intracardiac mapping. 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. 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). 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.

Sun W ，Upadhyay GA ，Tung R 《-》