Effects of pharmacological autonomic blockade on dual atrioventricular nodal pathways physiology in patients with slow-fast atrioventricular nodal reentrant tachycardia

Dual atrioventricular nodal pathways physiology: a review of relevant anatomy, electrophysiology, and electrocardiographic manifestations

More than half a century has passed since the concept of dual atrioventricular (AV) nodal pathways physiology was conceived. Dual AV nodal pathways have been shown to be responsible for many clinical arrhythmia syndromes, most notably AV nodal reentrant tachycardia. Although there has been a considerable amount of research on this topic, the subject of dual AV nodal pathways physiology remains heavily debated and discussed. Despite advances in understanding arrhythmia mechanisms and the widespread use of invasive electrophysiologic studies, there is still disagreement on the anatomy and physiology of the AV node that is the basis of discontinuous antegrade AV conduction. The purpose of this paper is to review the concept of dual AV nodal pathways physiology and its varied electrocardiographic manifestations.

Differential effects of atropine and isoproterenol on inducibility of atrioventricular nodal reentrant tachycardia

BACKGROUND

Radiofrequency ablation of the "slow pathway" in atrioventricular nodal reentrant tachycardia (AVNRT) relies on tachycardia non-inducibility after ablation as success criterion. However, AVNRT is frequently non-inducible at baseline. Thus, autonomic enhancement using either atropine or isoproterenol is frequently used for arrhythmia induction before ablation.

METHODS

80 patients (57 women, 23 men, age 50+/-14 years) undergoing slow pathway ablation for recurrent AVNRT were randomized to receive either 0.01 mg/kg atropine or 0.5-1.0 microg/kg/min isoproterenol before ablation after baseline assessment of AV conduction. The effects of either drug on ante- and retrograde conduction was assessed by measuring sinus cycle length, PR and AH interval, antegrade and retrograde Wenckebach cycle length (WBCL), antegrade effective refractory period (ERP) of slow and fast pathway and maximal stimulus-to-H interval during slow and fast pathway conduction.

RESULTS

Inducibility of AVNRT at baseline was not different between patients randomized to atropine (73%) and isoproterenol (58%) but was reduced after atropine (45%) compared to isoproterenol (93%, P<0.001). Of the 28 patients non-inducible at baseline isoproterenol rendered AVNRT inducible in 21, atropine in 4 patients. Dual AV nodal pathway physiology was present in 88% before and 50% after atropine compared to 83% before and 73% after isoproterenol. Whereas both drugs exerted similar effects on ante- and retrograde fast pathway conduction maximal SH interval during slow pathway conduction was significantly shorter after isoproterenol (300+/-48 ms vs. 374+/-113 ms, P=0.012).

CONCLUSION

Isoproterenol yields higher AVNRT inducibility than atropine in patients non-inducible at baseline. This may be caused by a more pronounced effect on antegrade slow pathway conduction.

Clinical and electrophysiologic characteristics and long-term efficacy of slow-pathway catheter ablation in patients with spontaneous supraventricular tachycardia and dual atrioventricular node pathways without inducible tachycardia

OBJECTIVES

We sought to investigate the long-term efficacy of slow-pathway catheter ablation in patients with spontaneous, documented paroxysmal supraventricular tachycardia (PSVT) and dual atrioventricular (AV) node pathways but without inducible tachycardia.

BACKGROUND

The lack of reproduction of clinical PSVT by programmed electrical stimulation, which is not uncommon in AV node reentrant tachycardia (AVNRT), is a dilemma in making the decision of the therapeutic end point of radiofrequency catheter ablation.

METHODS

Twenty-seven patients (group A) with documented but noninducible PSVT and with dual AV node pathways were prospectively studied. Programmed electrical stimulation could induce a single AV node echo beat in 12 patients, double echo beats in 4 patients and none in 11 patients at baseline or during isoproterenol infusion. Of the patients in group A, 16 underwent slow-pathway catheter ablation and 11 did not. The clinical and electrophysiologic characteristics of the 27 patients were compared with those of patients with dual AV node pathways and inducible AVNRT (group B, n = 55) and patients with dual AV node pathways alone without clinical PSVT (group C, n = 47).

RESULTS

During 23+/-13 months of follow-up, none of the 16 patients with slow-pathway catheter ablation had recurrence of PSVT. However, 7 of the 11 patients without ablation had PSVT recurrence at 13+/-14 months of follow-up (p < 0.03 by Kaplan-Meier analysis). Compared with groups B and C, group A consisted predominantly of men who had better retrograde AV node conduction and a narrower zone for anterograde slow-pathway conduction.

CONCLUSIONS

Slow-pathway catheter ablation is highly effective in eliminating spontaneous PSVT in which the tachycardia is not inducible despite the presence of dual AV node pathways.