Electrophysiologic mechanisms for modification and abolition of atrioventricular junctional tachycardia with simultaneous and sequential atrial and ventricular pacing.

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Abstract
The role of simultaneous and sequential atrioventricular (AV) stimulation in prevention of tachycardia induction, and the underlying electrophysiologic mechanisms involved, were studied in 10 patients with documented paroxysmal reentrant supraventricular tachycardia (PSVT). Reentry circuit was localized to the AV node in 7 of 10. The remaining 3 cases had Wolff-Parkinson-White (WPW) syndrome and the reentrant circuit retrogradely incorporated an accessory pathway. Progressively earlier atrial premature beats (A2) were introduced while the basic cycle length (BCL) consisted of atrial pacing alone or simultaneous A and V pacing. Compared to atrial pacing alone, simultaneous A and V pacing during the basic drive completely abolished the PSVT zone in 2 of 7 with AV nodal reentrant PSVT, narrowed the zone in 4 of 7 and facilitated PSVT induction in the other patient. In all patients with AV nodal reentry, significant shortening of AV nodal refractoriness caused by simultaneous antegrade and retrograde AV nodal excitation was responsible for the results. In the 3 patients with ventricular preexcitation, simultaneous A and V pacing abolished or shortened the PSVT zone in the 2 cases with type B WPW, but had no effect in the other case (with type A WPW). Introduction of programmed ventricular premature complexes after A2 capable of initiating PSVT (sequential AV premature stimulation) prevented PSVT induction by prematurely interrupting the reentry pathway in all instances. Sequential AV premature stimulation was more effective in preventing PSVT when the BCL consisted of simultaneous A and V pacing than was atrial pacing alone. Simultaneous or sequential AV pacing can abolish or significantly narrow the PSVT zone, although paradoxical facilitation of reentrant process can occur.