Cryoablation of 'delicate' accessory pathways

Abstract

Accessory bypass tracts are embryological remains of the atrioventricular connections based on an incomplete development of the atrioventricular (AV) annulus and incomplete fibrous separation of the atria and ventricles. Radiofrequency catheter ablation has become first-line therapy for patients with recurrent AV tachycardias. 1 Long-term outcome after catheter ablation of accessory pathways is excellent with a low complication rate. 2 However, different accessory bypass localizations still represent challenges for ablation. Ablation of superior paraseptal and midseptal bypass tracts is more difficult than others because of the complexity of anatomical structures involved. 3,4 The aggravating circumstances for ablation of superior paraseptal and midseptal bypass tracts may dictate the need for alternative ablation approaches. A possibly safer approach for elimination of those accessory pathways could be cryoablation. The use of cryoablation in ‘delicate’ accessory pathways as superior paraseptal and midseptal bypass tracts is described as safe and successful: 5,6 cryomapping is a ‘strategy tool’ for verifying the effectiveness and safety of ablation at different critical sites. It is performed at temperatures of about 2308C and can help to avoid AV block and locate the effective ablation site. A further distinctive feature of cryoablation is the stability (cryoadherence) of the catheter tip during temperatures at the desired location, even during tachycardia. Surprisingly, no large size, randomized, prospective studies exists which compared cryoablation and radiofrequency ablation of ‘delicate’ accessory pathways as superior paraseptal and midseptal bypass tracts. Several previous non-randomized, retrospective studies reported single-centre experience in small numbers of patients. It is within the context that we should evaluate the contribution by Bastani et al. 7 The authors report their single-centre, non-randomized experience with cryoablation of superior septal and septal accessory pathways. During a 5-year period, 27 out of 464 patients had superior posterior or septal accessory pathways and underwent cryomapping at 2308C before ablation with a 6 mm cryo tip catheter and a goal temperature of 2808C for at least 240 s. Acute success was reported in 26 (96%); 7 (27%) patients had a recurrence of the arrhythmia. Five out of seven patients with the recurrence underwent further cryoablation. In total, 89% patients had successful cryoablation after mean follow-up of 2 years. The authors have proved their clinical results by using a symptom questionnaire, which was returned by the majority of patients and demonstrated a freedom of arrhythmias in 88%. No permanent AV block was observed, although the number of treated patients was relatively small. The total procedure and fluoroscopy times were 163+ 61 and 30+ 22 min, respectively. The recurrence rate was significantly higher in patients with procedure-related transient mechanical accessory pathway block (6 of 7, 86%) due to catheter-induced trauma compared with those without mechanical block (5 of 20, 25%) (P ¼ 0.006). The authors have concluded that procedure-related transient mechanical accessory pathway block is a predictor of a higher recurrence rate. Furthermore, a previous radiofrequency ablation attempt is even a predictor for arrhythmia relapses. The paper by Bastani et al. describes the advantages and disadvantages of cryoablation in difficult accessory bypass tracts in a very concise and precise manner. There are four main aspects that should be further discussed. First, the authors used additional radiofrequency catheters in patients with additional accessory pathways, which did not have superior septal or midseptal locations. It is unclear why the authors used an additional conventional radiofrequency catheter for ablation, while they concluded that cryoablation is an effective tool for ablation of accessory pathways. One additional advantage of cryoablation is pain-free energy delivery with the absent necessity of analgesia. The use of an additional conventional radiofrequency catheter for ablation could impede the absent necessity of analgesia. The costeffectiveness of this ablation strategy is also questionable. Secondly, the authors reported a high incidence of mappinginduced mechanical trauma to an accessory pathway, which was related to worse clinical outcome and explained this by local tissue adherence of the cryo catheter compared with a radiofrequency catheter. This observation opens a field for speculation, for example, whether mechanical trauma was mostly induced by a lower proper positioning of the cryoablation catheter. In our experience, a potential explanation for an increased rate of