Europace Advance Access originally published online on April 26, 2007
Europace 2007 9(6):424-425; doi:10.1093/europace/eum063
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FASCICULAR PATHWAYS
A NavXTM -guided ablation of a nodo-fascicular fibre
Medizinische Klinik I, Klinikum Grosshadern, Universität München, Marchioninstr. 15, Munich, Germany
Manuscript submitted 17 July 2006. Accepted after revision 14 March 2007.
* Corresponding author. Tel: +49 89 7095 3060; fax. +49 89 7095 8830. E-mail address: christopher.reithmann{at}med.uni-muenchen.de
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The NavXTM system was used to guide mapping and successful ablation of a reciprocating antidromic tachycardia involving anterograde conduction over a nodo-fascicular fibre and retrograde conduction over the His bundle and AV node. This novel mapping system allowed visualization of the lower insertion site of the nodo-fascicular accessory pathway
1.5–2 cm away from the tricuspid annulus in a three-dimensional reconstruction of the right atrium and right ventricle.
Key Words: Accessory pathway, Arrhythmia, Three-dimensional, Catheter ablation
A 40-year-old woman presented with recurrent regular narrow QRS tachycardia and regular broad QRS tachycardia exhibiting a left bundle branch block (LBBB) pattern and leftward axis. During sinus rhythm, a ventricular pre-excitation was present. A right-sided free wall atrioventricular pathway with antegrade and retrograde accessory conduction was first successfully ablated at an antero-inferior location of the tricuspid annulus. After ablation of the accessory atrioventricular pathway, the broad QRS tachycardia with LBBB pattern was still inducible. The resting electrocardiogram was normal and showed no pre-excitation, but a subtle pre-excitation was induced by premature atrial extrastimuli or incremental atrial pacing. The broad QRS complex tachycardia was easier inducible by ventricular extrastimuli than by atrial extrastimuli. The tachycardia showed the electrophysiological characteristics of a reciprocating antidromic tachycardia involving anterograde conduction over a nodo-fascicular or nodo-ventricular pathway and retrograde conduction over the His bundle and AV node. Ventricular mapping of the pre-excited tachycardia showed earlier ventricular activation at the right ventricular (RV) apex rather than at the ventricular aspect of the tricuspid annulus. During the antidromic tachycardia, retrograde right bundle activation preceded retrograde His bundle activation, and ventricular premature beats were able to demonstrate retrograde His activation and to exclude a second accessory connection. The following findings indicated anterograde conduction over a nodo-fascicular or nodo-ventricular rather than an atrio-fascicular fibre: (a) late right atrial (RA) extrastimuli delivered during the pre-excited tachycardia (not advancing the atrial activation in the bundle of His or the coronary sinus region) did not advance the ventricular activation; (b) ventricular pre-excitation was not more readily exposed from the RA than from the coronary sinus; and (c) short periods of ventriculo-atrial dissociation were documented during the tachycardia.
In the few reported cases of nodo-fascicular or nodo-ventricular fibres, the earliest ventricular activation of the pre-excited beats was recorded at the ventricular aspect of the tricuspid annulus or close to it, which was suggestive of a ventricular rather than a fascicular lower insertion site. In our patient, a sharp His-like potential preceding the QRS complex was found in the RV septum, suggesting a fascicular lower insertion site of the accessory pathway (Figure 1, left). We used the NavXTM system to correlate the position of this accessory pathway potential in relation to the location of the tricuspid annulus and the His bundle/right bundle conduction system in a three-dimensional reconstruction of the RA and RV (Figure 2).
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The system uses externally applied, high-frequency electric fields from cutaneous patches. It requires three pairs of skin patches, one for each of X, Y, and Z-axes, thus creating a three-dimensional coordinate system. The patches and the mapping catheters were connected to the non-contact mapping workstation (St. Jude Medical, Saint Paul, MN, USA). Ablation at the position of the His-like potential preceding the QRS complex during the broad QRS tachycardia terminated the tachycardia after few seconds. The successful ablation site was found
1.5–2 cm away from the tricuspid annulus in the RV septum, indicating a nodo-fascicular rather than a nodo-ventricular fibre. In the following sinus beats, the potential of the nodo-fascicular fibre was no longer demonstrable and conduction over the ‘physiologic’ His bundle and right bundle was visible (Figure 1, right). The tachycardia could no longer be induced, and the patient was free of arrhythmias during the follow-up of 8 months.
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