Case 1:
A 35 years old woman with non-ischemic cardiomyopathy (NICM), left bundle branch block (LBBB) and left ventricular (LV) dysfunction (ejection fraction 28%) was referred for cardiac resynchronization therapy (CRT). After obtaining informed consent, LBBP was performed using C315 His sheath and 3830 Selectsecuretm lead (Medtronic, Minneapolis, MN). The pacing lead was positioned deep inside the septum 1.5 cm apical to the distal His bundle region by 4-5 rapid turns. PVCs with changing morphology were noted during lead advancement. Rotation was stopped immediately on observing a PVC (VES1) with narrow QRS duration and qR (right bundle branch [RBB] delay) pattern in lead V1 (Figure 1A). No potentials were noted during baseline LBBB rhythm. Non-selective to selective capture of left bundle branch (LBB) could be demonstrated by change in QRS morphology and discreet local ventricular electrogram at near threshold output (Figure 1C). Pacing threshold was 0.4V at 0.5ms and unipolar pacing impedance of 670 ohms. LBB paced QRS morphology mimicked VES1 with duration of 122ms and peak left ventricular activation time (pLVAT) in lead V5 of 65ms (Figure 1B). AV interval was optimized to correct the RBB delay (Figure 1D).