Unusual resetting patterns in response to single atrial extrastimuli during AV junctional reentrant tachycardia.

Introduction: Two unusual resetting patterns were observed in two patients with slow-fast AV junctional reentrant tachycardia (AVJRT) submitted to an electrophysiologic study.

Methods And Results: After AVJRT induction, resetting was evaluated by introducing single extrastimuli at progressively shorter coupling intervals from the high right atrium (HRA) and the proximal coronary sinus (CS). An alteration in the return cycle length duration allowed demonstration of resetting. In the first patient, during and AVJRT with a large excitable gap, properly timed extrastimuli delivered both from the HRA and CS simultaneously reset the tachycardia and advanced the H electrogram of the preceding tachycardia beat. In the second patient, both HRA and CS stimulation apparently failed to reset AVJRT (return cycle length unchanged), but, at critical coupling intervals, the cycle length duration of the tachycardia beat following the return cycle was consistently shortened.

Conclusion: During slow-fast AVJRT, single atrial stimulation from sites remote to the reentrant circuit may result in unusual resetting patterns. Further studies are required to evidence the full spectrum of resetting in AVJRT.