Spontaneuos Interruption of Reentrant Intranodal Tachycardia. Electrophysiological Mechanisms

pp 461-469

Abstract

Background and objectives

In the common type of atrioventricular nodal reentrant tachycardia anterograde conduction occurs via a "slow" pathway, whereas retrograde conduction takes place via a fast pathway. The exact conformation of the reentrant circuit and its component tissues, particularly of the so-called retrograde "fast"pathway, has not yet been conclusively defined. The main goal of the study was to explore the site and characteristics of conduction blockade provoking spontaneous interruption of the common type of atrioventricular nodal reentrant tachycardia, to assess the functional properties of the pathways in-volved in the mechanisms of arrhythmia.

Method and results

Sixteen patients with recurrent self-terminating atrioventricular nodal reentrant tachycardia were evaluated. The arrhythmia was repeatedly induced by programmed atrial stimulation. Its total duration as well as the AA, AH and HA intervals were measured to assess the site and features of conduction blockade leading to interruption of the reentrant mechanism. Isoproterenol was infused and the stimulation protocol was repeated in 4 cases in which the arrhythmia could not be induced at baseline. Self-limited episodes of atrioventricular nodal reentrant tachycardia were provoked by programmed atrial stimulation at baseline in 12/16 patients and during isoproterenol administration in the remaining 4 patients. Two groups of patients could be identified: group I, consisting of 9 patients in whom the arrhythmia ceased due to a Mobitz I type block in the anterograde "slow" pathway, and group II, composed of 7 patients in whom the arrhythmia ended as a Mobitz II type block de in the retrograde "fast" pathway. Blockade of impulse propagation in either the anterograde "slow" or the retrograde "fast" pathways was clearly time-dependent.

Conclusions

Our results in a very selected group of patients with self-limited episodes of atrioventricular nodal re-entrant tachycardia suggest that different cell populations may integrate the pathways involvedin the reentrant mechanism. Spontaneous interruption of the arrhythmia in the anterograde "slow" pathway in a Mobitz I type modality is in accordance with the well known AV nodal properties of this pathway. Conversely, the occurrence of a Mobitz II type blockade in the retrograde "fast"pathway strongly suggests that this pathway involves, at least in part, a fast response tissue.