Evaluation Of Left Ventricular Synchrony Between Left Bundle Branch Pacing And Right Ventricular Mid-septum Pacing By Three-dimensional Speckle Tracking Imaging

Objective:The purpose of this study is to compare the left ventricular strain and synchrony between left bundle branch pacing（LBBP）and right ventricular mid-septum pacing（RVSMP）by three—dimensional speckle tracking imaging（3D-STI）,so as to provide theoretical basis for clinical selection of appropriate pacing sites.Methods:Patients diagnosed with sick sinus syndrome type A or type B who were implanted with dual-chamber pacemaker in our hospital from 2018-09-01 to2020-10-31 were enrolled in the study.According to different pacing sites,patients were divided into LBBP group and RVSMP group,19 patients in LBBP group and 22 patients in RVSMP group,excluding those with abnormal preoperative echocardiography and electrocardiogram or complicated with other diseases affecting cardiac function.The electrocardiogram and echocardiographic information of patients was collected 2 months after operation during outpatient follow-up.The information was collected in two states of self-conduction and ventricular pacing.The duration of QRS wave in lead II used as a parameter to evaluate cardiac electrical synchronization was obtained by electrocardiograph.Left ventricular ejection fraction,left ventricular global longitudinal strain,left ventricular global radial strain,left ventricular global circumferential strain,16-segmental maximum difference and standard deviation of the time when left ventricular 16 segments reached the minimum systolic volume after correction by RR interval were obtained by 3D-STI.The left ventricular global longitudinal,radial and circumferential strain were used as strain parameters to evaluate the left ventricular contractility.The 16-segmental maximum difference and standard deviation of the time when left ventricular 16 segments reached the minimum systolic volume after correction by RR interval were used as parameters to evaluate the mechanical synchronization of the left ventricular contraction.Results:1.C om pari so n o f el ect ri cal s yn ch ro ni zati on param eters 2 m on ths aft e r operation:Compared between groups,there was no significant difference in QRS wave duration between LBBP group and RVSMP group during self-conduction[（98.74±12.30）ms vs（96.82±13.02）ms,t=0.48,P>0.05)].During ventricular pacing,QRS wave duration of LBBP group was narrower than that of RVSMP group[（107.37±14.13）ms vs（130.00±13.85）ms,t=5.17,P<0.01].In LBBP group,the QRS wave had no right bundle branch block pattern during self-conduction,while the QRS wave in lead V₁ showed the pattern of QR or r SR’during ventricular pacing.The QRS wave duration has no significant difference between self-conduction and ventricular pacing in LBBP group[（107.37±14.13）ms vs（98.74±12.30）ms,t=2.08,P>0.05].In RVSMP group,the QRS wave duration of ventricular pacing was wider than that of self-conduction,and the difference was statistically significant[（130.00±13.85）ms vs（96.82±13.02）ms,t=14.39,P<0.01].2.Comparison of left ventricular ejection fraction 2 months after operation:Left ventricular ejection fraction of LBBP group was not significantly different from that of RVSMP group during self-conduction or ventricular pacing[（61.55±3.46）%vs（62.10±3.23）%,（60.75±4.00）%vs（60.55±4.16）%,t=0.52、0.16,P>0.05].Left ventricular ejection fraction has no significant difference between self-conduction and ventricular pacing in LBBP group or RVSMP group[（60.75±4.00）%vs（61.55±3.46）%,（60.55±4.16）%vs（62.10±3.23）%,t=1.36、1.97,P>0.05].3.Comparisons of strain parameters and the mechanical synchronization parameters 2 months after operation:There was no significant difference in strain or mechanical synchronization parameters between LBBP group and RVSMP group during self-conduction[（-21.00±3.36）%vs（-20.90±3.26）%,（-30.45±3.10）%vs（-31.75±3.14）%,（51.00±4.14）%vs（51.15±4.13）%,（8.45±1.72）%vs（9.47±2.46）%,（3.26±1.12）%vs（3.79±1.29）%,t=0.10-1.52,P>0.05].Left ventricular global longitudinal and circumferential strain（absolute value of strain and the strain in following paragraphs refers to its absolute value）of LBBP group were greater than that of RVSMP group during ventricular pacing,and the difference was statistically significant[（-20.60±3.02）%vs（-17.95±2.37）%,（-31.00±3.68）%vs（-27.40±3.45）%,t=3.09、3.19,P<0.01].16-segmental maximum-minimum difference and standard deviation of the time when left ventricular 16 segments reached the minimum systolic volume after correction by RR interval of LBBP group were less than that of RVSMP group during ventricular pacing,and the difference was statistically significant[（9.04±2.27）%vs（24.18±3.91）%,（3.82±1.42）%vs（8.96±1.13）%,t=14.96、12.68,P<0.01].There was no significant difference in strain or mechanical synchronization parameters between self-conduction and ventricular pacing in LBBP group[（-20.60±3.02）%vs（-21.00±3.36）%,（-31.00±3.68）%vs（-30.45±3.10）%,（50.50±4.25）%vs（51.00±4.14）%,（9.04±2.27）%vs（8.45±1.72）%,（3.82±1.42）%vs（3.26±1.12）%,t=0.90-1.90,P>0.05].Left ventricular global longitudinal and circumferential strain of ventricular pacing were less than that of self-conduction in RVSMP group,and the difference was statistically significant[（-17.95±2.37）%vs（-20.90±3.26）%,（-27.40±3.45）%vs（-31.75±3.14）%,t=7.62、6.31,P<0.01].Mechanical synchronization parameters of ventricular pacing were greater than that of self-conduction in RVSMP group,and the difference was statistically significant[（24.18±3.91）%vs（9.47±2.46）%,（8.96±1.13）%vs（3.79±1.29）%,t=26.25、26.44,P<0.01].Conclusion:LBBP might be more physiological than RVSMP.3D-STI technique can quantitatively evaluate left ventricular systolic function.Longitudinal strain and circumferential strain can reflect the change of left ventricular systolic function earlier than left ventricular ejection fraction.