Interfascicular concealment at the beginning of atrioventricular node reentrant tachycardia

Abstract

An electrophysiologic study and radiofrequency ablation were performed in a 38-year-old female patient with 12month history of paroxysmal palpitations in the absence of heart disease or syncope. Her resting electrocardiogram (ECG) showed sinus rhythm with normal intervals and incomplete right bundle-branch block (RBBB). The tachycardia depicted in Fig. 1 started because of mechanical stimulation during placement of the catheters. The arrows show P waves at the beginning of the arrhythmia, whereas these deflections are not discernible at the right. Fig. 2 shows the coronary sinus electrograms (from proximal to distal) when the His bundle recording catheter had not yet been positioned. The atrial electrograms confirm the existence of 2:1 block at the left followed by 1:1 conduction at the end of the tracing. Later electrophysiologic evaluation demonstrated dual atrioventricular (AV) node physiology and reproducible inducibility of common (slow/fast) AV node reentrant tachycardia that was eliminated with slow pathway ablation. The findings were reproducible (because they occurred 3 times during placement of the catheters). However, no further episodes of 2:1 atrioventricular block occurred after the His bundle recording catheter had been positioned. Which is the explanation of the wide QRS complexes numbered 5 and 7?