Biventricular endocardial pacing and left bundle branch area pacing for cardiac resynchronization: Mechanistic insights from electrocardiographic imaging, acute hemodynamic response, and magnetic resonance imaging

BACKGROUND Biventricular endocardial pacing (BiV-endo) has demonstrated superior cardiac resynchronization compared to con-ventional biventricular epicardial pacing (BiV-epi). Left bundle branch area pacing (LBBAP) may also achieve effective cardiac re -synchronization therapy (CRT). OBJECTIVE The purpose of this study was to compare the acute electrical and hemodynamic effects of BiV-epi, BiV-endo, and LBBAP delivered from the LV endocardium and to assess how myocardial scar affects response. METHODS Eleven patients with heart failure and indications for CRT underwent a temporary pacing study with electrocardiographic im-aging (ECGi) and hemodynamic assessment. BiV-endo was delivered by stimulation of the left ventricular (LV) lateral wall, and LBBAP was delivered by stimulation of the LV septum, at the site of a Pur-kinje potential. LV activation time (LVAT-95), LV dyssynchrony in-dex (LVDI), biventricular activation time (BIVAT-90), and biventricular dyssynchrony index (BIVDI) were calculated. Myocar-dial scar was assessed using magnetic resonance imaging (MRI). RESULTS The protocol was completed in 10 patients. Compared to BiV-epi (LVAT-95: 79.2 +/- 13.1 ms; LVDI: 26.6 +/- 3.4 ms) LV resynch-ronization was superior during BiV-endo (LVAT-95: 48.5 +/- 14.9 ms; P = .001; LVDI: 16.6 +/- 6.4 ms; P = .002) and LBBAP (LVAT-95: 48.9 +/- 12.5 ms; P = .001; LVDI: 15.3 +/- 3.4 ms; P = .001). Biven-tricular resynchronization was similarly superior during BiV-endo and LBBAP vs BiV-epi (BIVAT-90 and BIVDI; P <.05). The rate of acute hemodynamic responders was higher during BiV-endo (90%) and LBBAP (70%) vs BiV-epi (50%). The benefits of LBBAP (but not BiV-endo) on LV resynchronization were attenuated when septal scar was present in a subset of 8 patients who under-went MRI. CONCLUSION Our findings suggest superior electrical resynchroni-zation and a higher proportion of acute hemodynamic responders during BiV-endo and LBBAP compared to BiV-epi. Electrical resynch-ronization was similar between BiV-endo and LBBAP; however, septal scar seemed to attenuate response to LBBAP.