His bundle pacing to avoid electrical dyssynchrony with traditional right ventricular pacing: Importance of heart size

Background: His Bundle Pacing (HBP) is attracting interest as an alternative to traditional right ventricular pacing (RVP) because it avoids electrical dyssynchrony induced by RVP. This study aims to evaluate the effect of heart size on benefit from HBP compared to RVP in terms of achieving electrical synchrony. Methods: Fifty-nine patients with HBP and a RVP back-up lead underwent pre-implantation echocardiography to measure left ventricular end-diastolic volume (LVEDV). Electrical benefit from HBP was calculated as the difference in QRS duration (QRSd) between RVP and HPB. Results: LVEDV was significantly correlated with RVP QRSd (R = 0.53; p < 0.001). In contrast, LVEDV was unrelated to HBP QRSd (R = 0.16; p = 0.24). Electrical benefit of HBP over RVP was directly related with LVEDV (R = 0.43; p = 0.001). In addition, electrical benefit of HBP was larger for patients with LVEDV above median (99 mL) than below (49 ± 27 ms vs. 34 ± 19 ms, p = 0.014). Conclusions: This study is the first to demonstrate that patients with larger LV size may benefit most from HBP as a replacement of traditional RVP to avoid electrical dyssynchrony. Our results indicate that LV size impacts QRSd during RVP with slow cell-to-cell conduction, whereas it does not affect electrical synchrony during HBP with fast His-Purkinje conduction.