The Stereotaxis system is a “robotic” remote navigation catheter manipulation system that uses an externally applied 0.08-0.1 Tesla magnetic field to direct a system-specific highly flexible ablation catheter. Catheter tip direction is changed by altering the directional vector of the magnetic field generated by large movable permanent magnets placed on both sides of the patient. A motor drive unit performs advancement and retraction of the catheter. Remote navigation is done with a joystick or mouse. Because of its flexibility, the ablation catheter can move with the underlying tissue with less contact and shear force. This has the advantage of reducing perforation risk and improving power delivery in areas that prove challenging with respect to catheter stability, either because of morphologic issues (e.g., femoral approach to the tricuspid annulus) or significant cardiac or respiratory motion.1
Mahaim-type accessory pathways (AP) were initially described in 1937 as nodoventricular or His-ventricular bypass tracts.2 The definition has been expanded to include decrementally conducting atriofascicular accessory pathways.3 Hallmarks of diagnosis include: 1) Minimal to absent pre-excitation at baseline often with an rS complex in lead III4; 2) Wide complex tachycardia of a left bundle branch block (LBBB)-leftward axis morphology; 3) Progressive QRS widening with prolongation of the AV interval and shortening of the HV interval with incremental pacing from the right atrium. Pathway location is mapped either by identification of a Mahaim potential on the tricuspid annulus, or by identifying the location on the atrial side of the annulus which results in the shortest stimulus to QRS interval.5,6
A 21-year-old male college student was referred for management of recurrent palpitations and near syncope. Otherwise healthy, with normal echocardiogram, his past cardiac history was notable for catheter ablation approximately one year prior for supraventricular tachycardia that was noted to aberrate with LBBB morphology. Cryoablation was performed for what was diagnosed as orthodromic AVRT utilizing a concealed posteroseptal accessory pathway, and typical slow-fast AV node reentry. The patient remained symptom free for about 2-3 months before recurrence of symptoms, but did not immediately seek care for his arrhythmias as he was moving to change schools and was without health insurance.
With the beginning of school, his goal was for a curative procedure because of recurrent near-syncopal spells and the desire to participate in college-level competitive athletics.
He was brought to the EP lab for diagnostic testing and ablation, with the expectation that he had recurrence of one of the two previously ablated arrhythmias.
Baseline 12-lead ECG showed narrow QRS complexes with an rS complex in lead III (Figure 1). Incremental atrial pacing resulted in progressive QRS widening without shortening of the PR interval (Figure 2). Administration of adenosine during atrial pacing unmasked pre-excitation with a short HV interval but no shortening of the AV interval (Figure 3). No dual AVN physiology could be demonstrated, and with pacing from the RV, VA Wenckebach occurred at just over 400 msec with concentric retrograde activation (Figure 4). These findings argued against the recurrence of AVNRT or recovery of the previously ablated posteroseptal accessory pathway. With single extrastimuli, on isoproteronol, wide complex tachycardia was induced with His bundle activation during tachycardia occurring after QRS onset (Figure 5). Entrainment of the tachycardia from the right ventricle demonstrated a V-A-V response with retrograde septal activation occurring within the QRS complex.7 These findings supported antidromic AVRT utilizing a Mahaim-type atriofascicular accessory pathway with retrograde conduction up the fast AV nodal pathway.
To aid in accessory pathway mapping, a 20-pole “halo” catheter (Halo XP, Biosense Webster, Inc., a Johnson & Johnson company) was placed on the tricuspid annulus. During sinus rhythm, a Mahaim potential was recorded at approximately 8 o’clock on the annulus (Figure 6). Using a 4 mm tip bidirectional ablation catheter, stability at the target site proved challenging, and during positioning of a long sheath in the right atrium, the pathway was bumped and AP conduction interrupted. Numerous empiric ablation lesions were delivered at the poles of the halo catheter recording the AP potential prior to the “bump ablation.” Despite this, and though heating remained suboptimal, AP conduction did not recover after a waiting period in the lab, and the procedure was terminated.
Because of the issues with catheter stability encountered at the first procedure, we elected to use the Stereotaxis Niobe ES system for the repeat procedure. A decapolar catheter was placed in the coronary sinus, a quadripolar catheter in the RV apex, and a 20-pole halo catheter on the tricuspid annulus. A 3.5 mm open-irrigated tip ablation catheter (Celsius RMT ThermoCool, Biosense Webster, Inc., a Johnson & Johnson company) was introduced through an SR0 guiding sheath (Fast-Cath, St. Jude Medical) positioned at the IVC-RA junction. The EnSite NavX mapping system (St. Jude Medical) was used for non-fluoroscopic catheter tracking. A Mahaim potential was again recorded on the halo catheter and this site tagged on the NavX (St. Jude Medical) map. Activation mapping during tachycardia confirmed reentry with earliest ventricular activation at the posterolateral right ventricle (Figure 7). Radiofrequency energy was delivered at 40W during atrial pacing from the halo catheter with elimination of AP conduction during RF delivery. The patient has remained arrhythmia-free for 6 months to date.
Catheter ablation of Mahaim-type accessory pathways can be difficult due to challenges with accurate mapping of AP location. Conventional mapping and ablation techniques were used on the initial attempt, but technical issues rather than mapping or diagnostic ones ultimately hampered success. Non-fluoroscopic 3D mapping proved valuable for tagging pathway location, and the flexible nature of the Stereotaxis ablation catheter permitted stable catheter position against the endocardium with adequate energy delivery despite significant cardiac and respiratory motion. ■
Editor’s Note: This article underwent peer review by one or more members of EP Lab Digest®’s editorial board.
Disclosures: The author has no conflicts of interest to report regarding the content herein.
- Davis DR, Tang AS, Gollob MH, Lemery R, Green MS, Birnie DH. Remote magnetic navigation-assisted catheter ablation enhances catheter stability and ablation success with lower catheter temperatures. Pacing Clin Electrophysiol. 2008;31(7):893-898.
- Mahaim I, Benatt A. Nouvelles recherches sur les connections superieures de la branche du faisceau de His-Tawara avec cloison interventriculaire. Cardiologia. 1937;1:61-76.
- Tchou P, Lehmann MH, Jazayeri M, Akhtar M. Atriofascicular connection or a nodoventricular Mahaim fiber? Elucidation of the pathway and associated reentrant circuit. Circulation. 1988;77(4):837-848.
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- McClelland JH, Wang X, Beckman KJ, et al. Radiofrequency catheter ablation of right atriofascicular (Mahaim) accessory pathways guided by accessory pathway activation potentials. Circulation. 1994;89:2655-2666.
- Klein L, Hackett FK, Zipes DP, Miles WM. Radiofrequency catheter ablation of Mahaim fibers at the tricuspid annulus. Circulation. 1993;87:738-747.
- Knight BP, Zivin A, Flemming JM, et al. A technique for the rapid diagnosis of atrial tachycardia in the electrophysiology laboratory. J Am Coll Cardiol. 1999;33:775-781.