Fig. 3

a Three-D activation mapping showed the earliest ventricular activation site near the His bundle during HRA pacing (black line; suspected tricuspid valve area, light blue dot; ablation site making prolongation of AV conduction, red dot; His bundle area, white spot; the earliest ventricular activation site). The ablation catheter was positioned under the His bundle when sudden AV conduction delay occurred. Left 3D and angiographic image is taken by RAO 30 degree and right 3D and angiographic image is taken by LAO 40 degree. b PR interval was prolonged from 86 to 216 ms by the ablation under the His bundle. The QRS morphologies were changed in lead III (from Rs to rS) and aVF (from Rs to RS), but the delta-like wide QRS was persisted. c The AH interval was prolonged from 53 to 114 ms and the HV interval was from 35 to 61 ms. ABL: ablation catheter (d: distal, p: proximal), CS: coronary sinus (9, 10: proximal site, 1, 2: distal site), H and HIS: His bundle, LAO: left anterior oblique, RAO: right anterior oblique, Ref: reference catheter, RV: right ventricle, V: ventricle