Electrophysiology Study Results:
Bilateral femoral venous access was obtained, and catheters were positioned in the high right atrium, the His bundle region, and the coronary sinus. A mapping/ablating catheter was introduced after the diagnosis was established.
At baseline, intracardiac recordings from the His-bundle region revealed a single atrial electrogram followed by two distinct His deflections (H1 and H2) and two ventricular electrograms (Figure 2A). At a sinus cycle length of 1150 ms, the AH1 and AH2 intervals were consistently 90-100 ms and 435-450 ms, and the HV1 and HV2 intervals were 55 ms and 65 ms, respectively (see Table). On the surface ECG, the first His signal conducted with a narrow QRS complex (QRS duration 75 ms) and the second His signal conducted with either a narrow QRS complex or right-bundle branch block morphology (QRS duration 130 ms), due to rate related RBBB aberrancy. Atrial burst pacing at a cycle length of 780 ms resulted in “double fire, with a ventricular rate of 155 BPM (figure 2B). Atrial burst pacing at a faster cycle length of 450 ms revealed persistent block in the slow pathway, leading to sustained 1:1 AV conduction over the fast pathway and a paradoxical slowing of the ventricular rate to 133 BPM (figure 2C). Ventricular burst pacing demonstrated absence of retrograde conduction.
It was observed on multiple instances that the patient had athird , even wider QRS (140 ms) following some sinus P waves (figure 3), similar to what was observed on telemetry (figure 1C). The intracardiac electrograms on the His bundle catheter demonstrated athird His bundle deflection preceding the 3rdQRS, representing triple AV nodal conduction from the preceding atrial impulse (so-called “triple fire”). Each instance of the 3rd response conducted with markedly prolonged AH interval of 730ms; each “triple fire” was followed by a sinus P waves with a single QRS response.
Table: The electrophysiologic characteristics associated with the 3 AV nodal pathways are summarized in the Table: