Figure Legends:
Figure 1. Surface electrocardiogram (I, aVF, V1, V6) and intracardiac electrograms - His bundle electrogram distal and proximal (HISD, HISP), coronary sinus (CS) 9,10 dipoles at CS ostium, & CS 1,2 dipoles at distal CS. Pacing is being done from HBD and is followed by tachycardia; both show identical eccentric atrial activation patterns (marked by arrows) with earliest activation at CS 3,4 channel.
Figure 2. Left panel. Fluoroscopic image showing location of left ventricle pacing site and ablation catheter positioned at the mitral annulus transeptally in RAO 30 (left upper panel) and LAO 40 (left lower panel). Right panel. 12-lead surface electrocardiogram at the initiation of radiofrequency energy delivery depicting sudden change in QRS morphology after the 6th beat.
Figure 3. Left panel. Surface electrocardiogram (I, aVF, V1, V6) and intracardiac electrograms recorded from catheters as depicted in figure 2 left panel. The arrow after the 2nd beat denotes the artefact at the initiation of radiofrequency energy delivery. The orthodromically captured His bundle potentials on the HISD channel and the ventricular/atrial potentials on the RFD channel are marked with H, V and A respectively. Note the sudden change in QRS morphology and width with loss of ventriculo-atrial conduction after the 6th beat. Right panel. The shaded beat on the left panel at a higher speed of 300 mm/sec to demonstrate a short HV interval of 20 ms suggesting fusion between wavefronts originating from the ongoing othrodromic re-entrant tachycardia and the LV pacing.