Patient 3
This patient was a 50 year old man. He suffered from palpitation for 12 years. He was otherwise healthy. Either atrial or ventricular EPS could induce the tachycardia with CL variation from 260 to 275 ms. This tachycardia had three patterns including a narrow QRS pattern, a complete left bundle branch block pattern (CLBBB) with superior axis and a CRBBB pattern with superior axis (Figure 3A). All 3 patterns could switch to each other incessantly. Cycle length of the narrow QRS pattern equaled to that of the CLBBB pattern (265 ms), while CL of the CRBBB pattern was longer (275ms). V-A dissociation was observed during all 3 patterns of tachycardia which excluded atrial tachycardia and AVRT. H-V intervals of all 3 patterns of tachycardia and sinus rhythm were equal (46 ms, Figure 3B). Activation sequence of His on both sides during tachycardia was from the proximal to the distal which suggested that the tachycardia was a supra-ventricular one. His bundle refractory period ventricular stimuli could reset H-H interval, indicating the existence of an AP that did not connect to the atrium (Figure 3C). RVA pacing during sinus rhythm produced V to H sequential conduction without V to A conduction, and the proximal H was earlier than the distal H (Figure 3C). This phenomenon further suggested that there was an AP which was not connected to the atrium. Since CL of the tachycardia was longer during CRBBB than during CLBBB (Figure 3A), it could be deduced that the AP located on the right side [4]. RVA entrainment at 240 ms generated a more fully captured QRS morphologies than that at 250 ms (Figure 3D). This phenomenon suggested that the AP was an NV fiber, but not an nodo-fascicular (NF) fiber. This tachycardia was an orthodromic reentrant tachycardia mediated by a concealed NV fiber which located on the right side. Sketch maps of the tachycardia are shown in Figure 3E.
After thermo-controlled ablation (55°C, 40 watt, 100 seconds) of the slow pathway of AV node at the lower 1/3 of the triangle of Koch, the tachycardia could not be induced, and repeated EPS did not cause “jump-up” phenomenon of A-H interval any more.
All three patients survived up till now without any symptoms of recurrences.