Involvement of a Nodofascicular Connection in Supraventricular Tachycardia with VA Dissociation

Abstract

We present the case of a patient with episodes of supraventricular tachycardia and atrial dissociation that were terminated by either adenosine or verapamil. Involvement of an accessory pathway was shown by ventricular extrastimuli, elicited during His-bundle refractoriness, that interrupted the tachycardia or advanced the next His potential. The tachycardia circuit was demonstrated to be confined to the nodofascicular region based on the exclusion of surrounding tissues. Atrial activity, including that in the perinodal region, was totally dissociated during tachycardia. The lowest part of the circuit was determined to be located above the Hisian bifurcation, as multiple episodes with either a right or left bundle branch configuration during tachycardia did not modify the HH cycle. The ventricular septum summit was determined not to be involved, as no preexcitation was present during tachycardia or atrial pacing, and the right bundle branch was not part of the circuit. Radiofrequency current applied beneath the tricuspid valve at the His region successfully eliminated the nodofascicular connection with preservation of 1:1 AV conduction. The anatomical substrate underlying the abnormal connection may be either nodofasciculoventricular Mahaim fibers or a duality or dispersion of the nodo-Hisian conducting system.

Cardiac Mapping in Variants of the Ventricular Preexcitation Syndrome

“…Reversal of the depolarization sequence of the His and the right bundle branch potentials was observed by Haissaguerre et al [68]. During ventricular pacing the right bundle branch potential preceded the recording of the His bundle potential.…”

“…Since the 1980s, when it became clear that the majority of the previously called nodoventricular fibers were in reality atriofascicular pathways, some authors even doubted the very existence of such structures. In the last 25 years we have learned that nodoventricular and nodofascicular fibers do exist, but only a few well-studied cases were reported [60][61][62][63][64][65][66][67][68][69][70][71][72][73][74]. Nodoventricular fibers were recently described in the autopsy of a patient who had a PRKAG2 gene mutation.…”

“…The differential diagnosis between an AVNRT and a tachycardia using a concealed nodofascicular (NF) fiber can be difficult [75]. Factors that favor a Mahaim NF fiber include: 1 intermittent anterograde preexcitation [64] 2 absence of His-bundle activation when the tachycardia is initiated by ventricular extrastimuli [76] C H A P T E R 2 4 Mapping in Variants of the Ventricular Preexcitation Syndrome 3 tachycardia initiation with a single atrial premature beat producing a dual ventricular response (1: 2 A:V) [76] 4 increase in the tachycardia cycle length at the occurrence of bundle branch block [65] 5 ability of a ventricular extrastimulus during His-bundle refractoriness to advance the next His bundle activation [68] 6 reproducible termination with adenosine supports participation of the AV node as the anterograde limb in the tachycardia circuit 7 catheter ablation of the AV node or the Mahaim fiber with elimination of the tachycardia (Figure 24.38). Intra-Hisian reentry may occur in a diseased His bundle, with prolongation of the HV interval and the occurrence of a split His potential.…”

“…In one patient a slow AV nodal pathway was ablated in addition to the NV fiber. Haissaguerre et al [68] successfully ablated a nodo-His fiber positioning the ablation catheter beneath the tricuspid valve, at a site with a clear His bundle potential and a very low voltage atrial deflection (Figure 24.38). Hluchy et al [71] ablated a concealed nodofascicular fiber at the right midseptal region, where an AP potential was found during tachycardia.…”

The 12‐Lead ECG in Patients with Mahaim Fibers

“…It is not possible to preexcite ventricular activation, because the AP is taking off from the AV node. [9][10][11][12] Those cases showed no preexcitation at baseline ECG and a narrow QRS tachycardia with ventriculoatrial block or AV dissociation, and a midseptal concealed NF/NV fiber was successfully ablated. However, Porkolab et al 55 showed failure of decremental right atrial Figure 13.…”