Incessant narrow-QRS tachycardia mediated by ventriculo-fascicular accessory pathway

Figure 1. Tachycardia 12-lead electrocardiogram, intracardiac recordings, and reentry circuit diagram. A: After 2 normally conducted sinus beats a narrow QRS tachycardia with atrioventricular (AV) dissociation starts. Compared to sinus rhythm, tachycardia QRS complexes show lower R-wave amplitude in lead V1, Q-wave disappearance in leads V5–V6, and slight downward shift of the QRS axis. These findings are consistent with a right-to-left interventricular septal activation. B: From top to bottom, electrograms recorded from catheters placed in the coronary sinus (CS), His bundle region (HB), right ventricular septum (RVS), and right ventricular apex (RVA) are shown. P and 5 indicate the proximal recordings; d and 1 the distal ones; A, atrial electrogram; and H, HB electrogram. All measures are in ms and refer to consecutive deflections when not otherwise indicated. During sinus rhythm (first beat) HB activation is proximal-to-distal (HHBEd-HRVS4: 15 ms; asterisk indicates the earliest HB recording). Spontaneous tachycardia initiation (second beat) is associated with a change in the HB activation sequence (HHBEd-HRVS4: 0 ms), indicating a retrograde impulse propagation occurring along the…

Figure 2. Premature ventricular stimulation from the right ventricular apex and tachycardia reset curve. In panels A to C intracardiac recordings are arranged as in Figure 1. A: A premature ventricular beat (PVB) synchronous with the His bundle (HB) activation advances the next HB electrogram (to 290 ms) and resets the tachycardia. PVBs introduced with progressively shorter coupling intervals reset the tachycardia with varying degree of fusion at surface electrocardiogram (A–C). These findings prove the involvement of an accessory pathway with a distal attachment at the ventricular level in the tachycardia reentry circuit. D: PVBs with a coupling interval ≤280 ms reset the tachycardia. Progressive shortening of PVB coupling intervals (V1-V2) up to ventricular refractoriness (200 ms) is associated with increasing V2-H2 intervals, indicating slow conduction in the retrograde arm of the reentry circuit.

Figure 3. Tachycardia reset from the para-Hisian area and catheter cryoablation. In all panels intracardiac recordings are arranged as in Figure 1. A: A premature beat delivered from the His bundle (HB) catheter with a 285 ms coupling interval (H1-H2) directly captures the HB, advances the QRS complex, and reset the tachycardia. The ST-V interval is similar to the tachycardia HV interval, and the postpacing interval (ST-H) matches the tachycardia cycle length duration (315 ms). The subtle changes in the morphology of the advanced QRS (small S wave in lead 1, small Q wave in lead V5) are consistent with possible antidromic capture of the proximal HB. B: A very late coupled premature beat (V1-V2: 300 ms), delivered slightly more distally (RVS1) after the right bundle branch activation, locally captures the ventricle without producing QRS fusion at surface electrocardiogram, but it still advances the next HB electrogram and resets the tachycardia. These findings also support the reentry circuit depicted in Figure 1C. RVS = right ventricular septum. C: An HB potential is present on the mapping catheter (ABLd) at the ablation site. D: During cryoenergy delivery (at -30°C) tachycardia…