Electrical And Mechanical Synchronization Of Left Bundle Branch Pacing

Part ⅠThe Relationship of Paced Left Bundle Branch Pacing Morphology with Anatomic Location and Physiologic OutcomesBackground.Left bundle branch pacing(LBBP)is an emerging physiologic pacing modality.The feasibility and short-term safety is now well established.However,little is known regarding pacing at different locations on the left bundle brach.Objective.The present study was designed to explore pacing and physiologic characteristics associated with different LBBP locations.Methods.The study included 68 consecutive patients with normal unpaced QRS duration and successful LBBP implantation.Patients were divided into three groups according to the paced QRS complex:left bundle branch trunk pacing(LBTP),left posterior fascicular pacing(LPFP)and left anterior fascicular pacing(LAFP).ECG characteristics,pacing parameters and fluoroscopic localization at implant were collected and analyzed.Results.There were 17(25.0%),35(51.5%)and 16(23.5%)patients in the LBTP,LPFP and LAFP groups,respectively.All subgroups had relatively narrow paced QRS complex(128.6±9.1 ms vs.133.7± 11.2 ms vs.134.8±9.6 ms,P=0.170),fast left ventricular activation(70.4±9.0 ms vs.70.6± 10.2 ms,vs.71.0±9.0 ms,P=0.986),as well as low and stable pacing thresholds.Delayed right ventricular activation and inter-ventricular dysynchrony were similar between groups.Fluoroscopic imaging indicated that the lead tip was located most commonly in the basal-middle region of the septum(67.7%)and this was independent of paced QRS morphology group(88.2%vs.57.1%vs.68.8%,P=0.106).Conclusions.Pacing at different sites of the left bundle brach resulted in similar intraventricular and interventricular electrical synchrony in patients with intact conduction system.Fluoroscopic imaging alone could not predict specific LBBP paced ECG morphology.Part Ⅱ Feasibility and Electrophysiological Parameters of Bilateral Bundle Branch Area Pacing(BBBP-I)Background.Left bundle branch pacing(LBBP)is a technique for conduction system pacing,but it often results in right ventricular activation delay(RBBD)morphology on the electrocardiogram.Objectives.This study was designed to assess simultaneous pacing of the left and right bundle branch areas to achieve more synchronous ventricular activation.Methods.In symptomatic bradycardia patients,the distal electrode of a bipolar pacing lead was placed at the left bundle branch area via a trans-ventricular septal approach.This was used to pace the left bundle branch area,while the ring electrode was used to pace the right bundle branch area.Bilateral bundle branch area pacing(BBBP)was achieved by stimulating the cathode and anode in various pacing configurations.QRS duration,delayed right ventricular activation time(dRVAT),peak left ventricular activation time(LVAT)and inter-ventricular conduction delay were measured.Pacing stability and short-term safety were assessed at three-month follow-up.Results.BBBP was successfully performed in 22 of 36 patients.Compared with LBBP,BBBP resulted in greater shortening of QRS duration(109.3±7.1 ms vs.118.4±5.7 ms,P<0.001).LBBP resulted in a paced RBBD configuration,with a dRVAT of 115.0±7.5 ms and inter-ventricular conduction delay of 34.0±8.8 ms.BBBP fully resolved the RBBD morphology in 18 patients.In the remaining 4 patients,BBBP partially corrected the RBBD with dRVAT and IVD decreasing from 120.5±4.7 ms and 39.0±1.2 ms during LBBP to 106.1 ±4.2 ms(P=0.005)and 28.8±4.7 ms(P=0.030)during BBBP,respectively.Conclusions.LBBP results in a relatively narrow QRS complex,but with an inter-ventricular activation delay.BBBP can diminish the delayed right ventricular activation,producing more physiological ventricular activation.Part Ⅲ Comparison of mechanical synchrony between bilateral bundle branch area pacing and left bundle branch pacing(BBBP-II)Background.Bilateral bundle branch area pacing(BBBP)can diminish the left bundle branch pacing(LBBP)-induced right ventricular activation delay(RBBD)by stimulating both left and right bundle branch areas simotanously,producing more physiological ventricular activation.However,it is unknown whether the difference of electrical synchrony between LBBP and BBBP can be further transformed into difference of mechanical synchrony.Objectives.The aim of this study is to compare the mechanical synchrony between these two pacing modes by comparing echocardiogram.Methods.The BBBP-Ⅱ study was an explorative data collection study in paitents who received BBBP implantation.Symptomatic bradycardia patients with successful BBBP implantation and without serious structural heart disease were concecutively enrolled.LBBP and BBBP were determined by electrocardiogram and all enrolled patient were evaluated whether they met the criteria of LBBP and BBBP firstly.The pacing threshold of both pacing modes were determined meanwhile.The inter-ventricular mechanical delay(IVMD)and systolic dssychrony index(SDI)were used to evaluate the inter-ventricular and intra-ventricular mechanical synchrony under different pacing modes,respectively.Results.A total of 25 patients(mean age 60.7±13.3 years,10 males)were enrolled in this study.Of 25 enrolled patients,RBBD was completely eliminated in 14 cases(56.0%)and partially eliminated in 11 cases(44.0%)during BBBP.The pacing threshold of LBBP was significantly lower than that of BBBP(0.8±0.3V/0.4ms vs.5.2±2.0V/0.4ms,P<0.001).IVMD of BBBP was similar to that of intrinsic rhythm,slightly better than that of LBBP(intrinsic rhythm vs.LBBP vs.BBBP,-0.5±9.8ms vs.7.32±13.8ms vs.1.4± 13.2ms,P=0.009).No significant differences on SDI were observed among intrinsic rhythm,LBBP and BBBP[intrinsic rhythm vs.LBBP vs.BBBP,2.6(1.7,4.9)vs.3.3(2.4,5.6)vs.3.1(1.9,5.9),P=0.242].Conclusion.Compared with LBBP,BBBP can achieve an inter-ventricular mechanical synchronization more similar to intrinsic conduction.Both LBBP and BBBP exert a similar influence on intra-ventricular mechanical synchrony of the left ventricle,which is consistent with manifestation of the electrocaridogram.