Figure 2. 12-lead and intracardiac electrocardiograms (ECG) during LBB pacing in a 96-year-old III° AVB patient. A:Intrinsic rhythm showed a QS morphology in V1 lead. B: LBB potential recorded by pacing tip (black circle ) when the lead reached LV subendocardium. C: p-LVAT measured by unipolar pacing after fixation. Under different pacing output, QRS showed similar RBB block pattern and p-LVAT stayed short, indicating capture of LBB.D: Postprocedure ECG recording. A QR pattern was shown in V1 lead. Paced QRS duration was similar to intrinsic.