724-5 Retrograde Atrial Activation in Patients with Atrioventricular Nodal Reentry: Evidence for a Single Anterior Nodal Exit

Recent reports suggested different retrograde atrial break throughs during right ventricular apical (RVA) pacing at cycle lengths (CL) of g 600 and l 500 msec or change in the atrial electrogram morphology with critically timed ventricular premature beats (V2) during atioventricular nodal reentrant tacycardia (AVNRT). These Observations were attributed to the presence of anisotropic conduction properties and multiple anterior nodal exits. respectively. We evaluated the sequence of retrograde atrial activation in 12 consecutive patients (pts) with AVNRT. Using hexa- or decapolar catheters with 2 mm interelectrode spacing, multiple electrograms were recorded from the His bundle region, posteroseptal, and midseptal tricuspid annulus. Atrial activation was assessed during decremental (RVA) pacing at CL 700 to 400 msec (50 msec decrements) and down to the cycle length of block thereafter (10 msec decrements). and during diastolic scanning of AVNRT with V 2 (10 msec decrements). The mean cycle length of tachycardia was 366 msec. The atrial retrograde activation sequence during decremental RVA pacing was identical to that during AVNRT for all pts. At critical coupling intervals, V 2 could penetrate AVNRT circuit as indicated by resetting the tachycardia cycle length in 9 pts. In each patient, resetting or lack of resetting was associated with a change in morphology in all intracardiac electrograms when the local V 2 and A 2 were separated. The sequence of atrial activation remained unchanged and identical to that during tachycardia in all pts. Conclusion These observations suggest that only one retrograde pathway links the distal AV node to the anterior atrial septum. Change in electrogram morphology is most likely due to isolating ventricular from atrial activation.