Electrocardiograms of right ventricular pacing, bi-ventricular pacing, and His bundle pacing

Example ECG tracings of (A) RV apical pacing (B) bi-ventricular pacing and (C) His bundle pacing.
(A) Classic features for RV apical pacing include the left bundle branch block pattern in V1 with leftward superior axis in the limb leads, negative pre-cordial concordance in V1 to V6 and widened QRS approximately 200 ms in duration.
(B) The bi-ventricular paced QRS complex is comparatively more narrow ~160 to 170 ms with a right bundle branch block morphology in V1 and overall rightward, horizontal axis in the limb leads. Contrast the rS pattern in the inferior limb leads III and aVF, as well as lateral precordial lead V6 with the deeply negative Q waves in present in the RV apical paced ECG.
(C) The His bundle paced QRS complex is comparatively more narrow than the QRS complexes in both tracings above, measuring approximately ~110 to 120 ms in duration with a leftward inferior axis in the limb leads and pre-cordial R wave transition in V4. This tracing most closely replicates native ventricular activation present in a normal ECG.