Electrophysiologic characteristics and clinical correlation of right ventricular activation during left bundle branch area pacing (RV-LBBAP study)

Background: Left bundle branch area pacing (LBBAP) results in a right bundle branch (RBB) delay pattern because of preexcitation of the left bundle. The mechanism of right ventricular (RV) activation during LBBAP is largely unknown.

Objective: The aim of the study was to analyze the electrophysiologic characteristics of RV activation by mapping the RBB during LBBAP and its clinical correlation.

Methods: Consecutive patients who underwent successful LBBAP were included. RBB block, RV paced rhythm, and suboptimal intracardiac electrograms were excluded. LBBAP was performed with continuous recording of His bundle (HB) and RBB electrograms. RV activation was classified into 3 types based on the intracardiac electrogram: type I, RBB mediated; type II, transseptal activation; and type III, fusion pattern.

Results: Overall, 86 patients (94% left bundle branch pacing [LBBP]; 6% left ventricular septal pacing) were included. The mean age was 59.6 ± 12.8 years. Nonselective to selective capture transition was noted in 85% (n = 73). In patients with baseline normal QRS (n = 47), during selective LBBP (S-LBBP; n = 39), the most common pattern was type I (n = 34 [87%]), whereas during nonselective LBBP (NS-LBBP; n = 44), type III pattern (n = 40 [91%]) was common. In patients with left bundle branch block (n = 39), type III pattern was common during both S-LBBP and NS-LBBP. Type I pattern was noted only in patients with retrograde HB activation during S-LBBP. Left ventricular septal pacing showed type II activation in both groups. Patients without retrograde HB activation had higher left ventricular end-diastolic diameter, lower left ventricular ejection fraction, and prolonged HV interval compared with those with retrograde HB activation.

Conclusion: Physiologic RBB-mediated (type I) activation of the right ventricle was the most common pattern observed during S-LBBP in patients with intact retrograde HB activation. Type III pattern was the most common pattern observed during NS-LBBP with fusion of multiple wavefronts from anterograde RBB activation, myocardial, and transverse interbundle connections.