PMC5420030_01
A: Preprocedure electrocardiogram showing sinus rhythm with dual conduction down the fast and slow AV nodal pathways resulting in 2 QRS complexes for each P wave. Ladder diagram created from lead II shows the fast pathway with solid lines and the slow pathway with dashed lines. B: Postprocedure electrocardiogram showing sinus rhythm with right bundle branch block.
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After transfer, the patient's ECG, as shown in Figure 1A, was initially interpreted as sinus rhythm with fascicular bigeminy. AV nodal pathways, resulting in 2 QRS complexes for each P wave (Figure 1A). As the patient had a preexisting RBBB, both QRS complexes conduct with RBBB. ECG after the procedure showed sinus rhythm with RBBB without any evidence of dual AV nodal conduction (Figure 1B).
Preprocedure telemetry recording showing evidence of P waves that conduct down the fast AV nodal pathway only (black arrow), both the fast and slow AV nodal pathways (red arrow), and the slow AV nodal pathway only (blue arrow). P waves are marked with orange star. PP, PR via fast pathway, and PR via slow pathway are shown. Ladder diagram created from lead II shows the fast pathway with solid lines and the slow pathway with dashed lines.
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Telemetry recordings were interpreted as ventricular (fascicular) tachycardia owing to the presence of more QRS complexes than P waves (Figure 2). Similarly, careful evaluation of the telemetry recording shows evidence of P waves that conduct down the fast AV nodal pathway only, both the fast and slow AV nodal pathways, and the slow AV nodal pathway only (Figure 2).
A: Spontaneously observed intracardiac electrograms during electrophysiology study demonstrating conduction of the first 2 sinus complexes down only the slow AV nodal pathway and conduction of the third sinus complex down both the fast and slow AV nodal pathways. The AH interval of the slow AV nodal pathway remains fairly constant at approximately 530 msec. B: Anteroposterior view of the site of successful ablation. Quadripolar catheters are positioned in the right atrial appendage and at the bundle of His. A decapolar catheter is in the coronary sinus. The radiofrequency ablation catheter (for mapping) is positioned in the right ventricular apex, and the cryoablation catheter (white arrow) is positioned in the region of the slow AV nodal pathway.
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However, the intracardiac electrograms confirmed sinus rhythm with conduction down both the fast and slow AV nodal pathways (Figure 3A). Cryoablation was performed in the area of the slow pathway with elimination of dual AV nodal conduction (Figure 3B).