Impact of baseline QRS morphology on right ventricular function during long-term LBBAP in patients with atrioventricular block

Abstract Introduction Recent studies have described two possible mechanisms of right ventricular (RV) activation during left bundle branch area pacing (LBBAP): direct transseptal activation from the pacing site and retrograde activation via the conduction system. The latter may be absent in patients with infranodal atrioventricular block (AVB) and a wide baseline QRS complex. Purpose This study compared the long-term RV function in patients with AVB and successful LBBAP according to the baseline QRS morphology. Methods All patients with an LBBAP attempt for AVB between June 2020 and September 2022 were eligible for this study. The inclusion criterion was a paced QRS complex of QR morphology in lead V1 and transition from non-selective to selective pacing with decremental amplitude or recording and capture of a left bundle potential. In the end, 82 patients were prospectively evaluated. Patient and procedural characteristics were recorded at baseline and follow-up. Also, right atrial (RA) volume, RV diameter, tricuspid annulus peak systolic elevation (TAPSE), RV S` wave (RVS`W), and tricuspid regurgitation (TR) were evaluated before the procedure and at the end of the follow-up period. Results The mean age of the patients was 68.2 ± 11.1 years, and 63.4% were males. 41.5% had a baseline narrow QRS (Group 1), 29.3% had a right bundle branch block (Group 2), and 29.3% had a left bundle branch block morphology (Group 3). The three groups had no difference in baseline echo parameters. Also, the RV activation time (measured as the distance from stimulus to R wave peak time in lead V1) was similar between the three groups (123.9±12.1 vs. 118.6±12.7 vs. 124.9±13.2, p>0.1). The patients were followed over a mean period of 715.7 ± 194.8 days. In group 1, the echocardiographic evaluation showed non-statistically significant changes between the follow-up and the baseline values for RA volumes (59.4±32.8 vs. 57.3±22.6 ml, p=0.56), RV diameter (33±7 vs. 33.7±5.3 mm, p=0.56), RVS`W (12.1±3 vs. 13±6.2 cm/sec, p=0.46), and TR (1±0.9 vs. 1.2±0.9, p=0.44). TAPSE improved from 19.5±3.8 to 21.5±4.2 mm (p=0.014). In group 2, at follow-up, there were no statistically significant differences in RA volumes (50.2±19.7 vs. 50.9±17 ml, p=0.71), RV diameter (31.7±4.7 vs. 31.5±5.6 mm, p=0.90), RVS`W (17±21.8 vs. 15.9±13.7 cm/sec, p=0.84), and TAPSE (19.7±3.7 vs. 20.9±5 mm, p=0.18). TR worsened from 0.7±0.7 to 1±0.9 (p=0.04). The same observations were made in group 3 for RA volumes (51.9±26.8 vs. 58.3±37.6 ml, p=0.19), RV diameter (31.4±6 vs. 32.4±4.9 mm, p=0.49), RVS`W (13.1±3.3 vs. 13±3.4 cm/sec, p=0.94), and TAPSE (21±4.8 vs. 22±5.3 mm, p=0.39) with an increase in TR from 0.6±0.5 to 1±0.7 (p=0.02). When comparing the three groups, there was no significant difference between them regarding all follow-up echocardiography parameters. Conclusions LBBAP showed a similar long-term protective effect on RV function in patients with AVB, regardless of the baseline QRS morphology.