SURGICAL-PROCEDURE FOR THE CURE OF ATRIOVENTRICULAR JUNCTIONAL (AV NODE) REENTRANT TACHYCARDIA - ANATOMIC AND ELECTROPHYSIOLOGIC EFFECTS OFDISSECTION OF THE ANTERIOR ATRIONODAL CONNECTIONS IN CANINE MODEL

Objectives. This study was undertaken to examine the electrophysiologi c and anatomic effects of a surgical procedure that cures the anterior (common) type of atrioventricular (AV) junctional reentrant tachycard ia. Background. The procedure was designed to interrupt the reentrant circuit at the point of earliest atrial activation during AV junctiona l reentrant tachycardia, the anterior atrionodal connections. Methods. Atrioventricular node function and the sequence of electrical excitat ion of Koch's triangle were examined in 18 dogs. Excitation of Koch's triangle was mapped using a 60-channel mapping system. Surgical dissec tion was performed in 10 dogs and a sham procedure in 8. After 28 to 3 5 days, AV node function and the atrial excitation pattern were reasse ssed. The AV junction was examined using light microscopy. Results. So me degree of AV node damage was visible in all dogs in the dissection group, but it was minor in 40% of cases. The anterior part of the AV n ode was disconnected from the anterior atrionodal connections in all c ases. Anterograde AV node function was mildly impaired. The median AH interval was increased (62 vs. 76 ms [interquartile ranges 48 to 72 an d 64 to 104, respectively], p = 0.05), and the AV Wenckebach cycle len gth was increased (210 vs. 245 ms [interquartile ranges 200 to 230 and 210 to 260, respectively], p = 0.02). The degree of impairment of con duction was directly proportional to the length of dissection (p < 0.0 5) but not to the degree of damage to the AV node. Ventriculoatrial (V A) conduction was destroyed in 50% of dogs undergoing dissection but i n none of those with a sham operation (p < 0.04). The AV node remained responsive to autonomic blocking drugs, and atrial mapping during ven tricular pacing revealed that the site of exit from the AV node had be en altered. Conclusions. The atrionodal connections closest to the His bundle are the preferred route of conduction through the AV node duri ng normal AV or VA conduction. Destruction of these connections modifi es AV node conduction. The surgical procedure selectively interrupts t hese connections, and this interruption is likely to be the mechanism of cure.