Utility of Cooled-tip Radiofrequency Ablation for Accessory Pathways Refractory to Standard Radiofrequency

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Accessory pathways are formed embryologically during cardiogenesis and may be broad, slanted,1 and occasionally particularly challenging to ablate. Right-and left-sided pathways are derived differently with right-sided pathways characteristically subendocardial as opposed to subepicardial.2 Successful ablation of right-sided pathways is frequently limited by catheter stability and ablation attempts are associated with a lower acute success and higher recurrence rate.3,4 The authors report a challenging case of a right-sided accessory pathway with interesting surface echocardiographic (ECG) manifestations, suggesting a long slanted pathway. Location and characteristics presented a challenge using standard ablation techniques and required complex catheter manipulation and cooled-tip energy application to create the effective lesion formation necessary for pathway elimination.

Background

The patient is a 17-year-old male who has been diagnosed with ventricular pre-excitation since the age of nine. Initially, he only complained of intermittent palpitations, but more recently demonstrated an adenosine-sensitive sustained supraventricular tachycardia. Although he was well controlled on ╬▓-blocker therapy, he was a competitive swimmer, and preferred non-pharmacologic curative therapy.

The patient underwent diagnostic electrophysiology testing eight months prior to the curative ablation. This evaluation diagnosed a manifest posteroseptal pathway (see Figure 1), and a concealed right free-wall (RFW) pathway. Unfortunately, ablation attempts were unsuccessful. A repeat procedure six months later was also unsuccessful, despite the use of a unidirectional cooled-tip catheter.

Eight months after the initial procedure the subject presented for repeat electrophysiology testing and ablation at the authorsÔÇÖ institution.

Electrophysiology Study
  • Written informed consent was obtained.
  • Conscious sedation was used throughout the procedure.
  • Diagnostic catheters were placed in the coronary sinus.
  • The subjectÔÇÖs bundle position, tricuspid annulus (Halo), and right ventricle (RV) and the electrophysiologic properties of the pathway were assessed.
  • Earliest antegrade activation appeared to be in the distal halo (see Figure 2).
  • Pacing the RV demonstrated earliest retrograde activation in the low lateral right atrium (see Figure 3).

 

Ventricular pacing reproducibly initiated orthodromic atrioventricular tachycardia (a tachycardia cycle length of 320ms). In addition to being observed spontaneously, supraventricular tachycardia was also induced with ventricular premature depolarizations, atrial pacing, and atrial premature depolarizations. Retrograde effective refractory period (ERP) was 260ms. Antegrade ERP was 280ms at a paced cycle length of 400ms.Attempts to assess antegrade 2:1 block in the pathway resulted in atrial fibrillation. Atrial fibrillation (requiring electrical cardioversion) was observed at different times during the procedureÔÇöthe shortest R-R interval was 320ms (see Figure 1).

Electroanatomic mapping with a 4-mm Navistar catheter was performed. Detailed antegrade and retrograde mapping was completed. Earliest antegrade activation (19ms pre-delta) was in the posteroseptal right atrioventricular junction, whereas earliest retrograde activation was in the low lateral right atrium. The coronary sinus was mapped. Subsequently, the mapping catheter was placed retrograde across the aorta into the left ventricle (LV) and the left posteroseptal region was mapped in detail. The earliest antegrade location remained in the right posterior septum. Repeat mapping of retrograde accessory pathway conduction from the RV aspect of the tricuspid was also performed with earliest atrial activation confirmed to be in the low lateral tricuspid annulus.

Radiofrequency (RF) application to the right posterior septum at the site of earliest pre-excitation failed to eliminate accessory pathway conduction. Catheter stability targeting the low lateral tricuspid annulus was difficult to maintain. A MullinÔÇÖs sheath modified to remove the distal curve was inserted into the right heart to provide support and improve stability of the catheter. RF energy delivered with a standard 4-mm tip ablation catheter in this region was limited either by continued difficulty with maintaining catheter tip stability at the annulus or maximum power delivery of 10W with a target tip temperature of 55┬║C when ablating the atrial aspect of the annulus. Despite RF energy application, antegrade and retrograde conduction persisted. A bi-directional cooled-tip catheter (Chilli II) was inserted through the modified sheath and a stable tricuspid annular catheter position was obtained. Power-controlled RF energy was delivered along the right inferolateral tricuspid annulus, starting at 15W, with an incremental titration of power with maximum target temperature of 38┬║C and maximum impedance drop of 8Oh.Antegrade and retrograde conduction were eliminated over the accessory pathway without additional lesions to the posterior septal region. Only poor AV nodal conduction was evident retrograde, and supraventricular tachycardia was no longer inducible.

Discussion

Many features of this case highlight the difficulties that may be encountered with accessory pathway ablation. Manifest pre-excitation for this patient is consistent with a posteroseptal pathway,5 but the retrograde activation is mapped to the posterolateral tricuspid annulus. The wide disparity between antegrade and retrograde activation lead to the suspicion of two separate pathways. However, a single lesion was able to terminate conduction in both directions, implying a single slanted pathway of significant length.1 The inability of prior ablation to the posterior tricuspid annulus suggested that the pathway was indeed protected from easy elimination with endocardial ablation. The procedure also highlights the technical difficulties in ablating on the lateral tricuspid annulus, both in terms of catheter stability and/or power delivery.

Elevated tip temperatures limited adequate power delivery with a standard 4-mm catheter and may have impeded successful ablation. Although the use of an irrigated tip catheter ablation is rarely necessary for accessory pathway elimination, prior studies have demonstrated the safety and efficacy of using irrigated tipped catheters for pathways refractory to standard techniques. An irrigated tipped catheter was previously used with this patient, though ineffectively. This was possibly related to the location of the pathway and the difficulty of keeping the catheter in a stable position with good contact using a unidirectional catheter. The recently released bi-directional cooled-tip Chilli II catheter allowed for a wider range of catheter manipulation, better contact, and effective power delivery to eliminate accessory pathway conduction.

Conclusion

Right-sided accessory pathways may be difficult to successfully ablate. An unusual case of a long right posterior slanted pathway illustrates many of these difficulties. The case highlights the utility of a bi-directional cooled-tip catheter to facilitate catheter stability and effective power delivery in successfully eliminating accessory pathway conduction refractory to standard ablation tools and techniques.Ôûá

References
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