Cryoablation of the para-Hisian region

Basis: the ablation of the para-Hisian region is a challenge due to the risk of inadvertent lesion of a bundle of His. Cryoablation, due to its slower progression, allows interruption of the application in case of signs of undesired lesions and catheter adhesion during the applications, which has made cryoablation the ideal method for these patients. Objectives: to demonstrate the results of an initial series of patients referred for cryoablation of para-Hisian pathways. Patients and methods: From April 2015 to August 2017, 13 patients were referred for cryoablation due to the necessity for a para-Hisian approach detected in previous ablation procedures. Of the 13 patients, seven were submitted a radiofrequency ablation attempt (RF) and presented failure or recurrence, fi ve performed only electrophysiological studies, and no ablation was attempted, and one was indicated primarily. The mean age was 32 ± 16 years. Eleven patients had manifest anomalous pathways (APs), one hidden and one nodal reentrant tachycardia (NRT) with a transient atrioventricular block (AB) during RF. A cycle of 4 minutes followed by one more cycle in case of a positive result. Results: Of the 13 patients, 11 had an acute success in eliminating the accessory pathway. One patient had multiple accessory pathways, one right side, and one left side. In this patient, it was possible only the ablation of the left pathway. In all others, it was observed exuberant Hisian potential at the point of application with success. The patient with NRT was ablated in the M region without intercurrences. Four applications were required on average to eliminate the accessory pathway successfully. The mean local temperature was -74 oC. In fi ve patients, the occurrence of third-degree right branch block (RBB) was observed. In one patient, early application of RBB was interrupted and the bonus application was not applied. This was the only acutely successful patient who presented clinical recurrence. Transient AB was not observed in any patient. No complications were observed. Conclusion: Cryoablation of para-Hisian pathways and NRTs in regions surrounding the His was an eff ective method for treatment in this population of patients refractory or refused for RF treatment. The occurrence of acute RBB does not seem to be a criterion for the interruption of applications.


PALAVRAS-CHAVE:
Th e mean scan time was 6 minutes.
In one patient, the RBB application was stopped early (130 seconds) and the booster application was not performed. Th e return of ventricular pre-excitation was observed 14 days after the procedure. Th is was the only acutely successful patient who presented recurrent pre-excitation or recurrence of palpitation symptoms.
No transient AP block of any degree was observed in any patient. Measurements of the HV intervals did   The patients did not a present recurrence of tachycardia or ventricular pre-excitation or AP block at follow-up.

DISCUSSION
Para-Hisian accessory pathways have always been a challenge for electrophysiology in the era of RF ablation because of the risk of irreversible AP node damage during RF pulse release.
The AP node lesion can install quickly without warning signs.
Several RF mapping and ablation techniques have been described in an attempt to increase the success of ablation and decrease the risk of the procedure in the right anteroseptal pathways. Mapping and ablation of the right coronary cusp, use of electroanatomic mapping and energy release with low power, approach by superior access (jugular or subclavian) and use of magnetic navigation system were published in case reports.
The cryoablation procedure is very similar to the RF ablation procedure in relation to the access pathway, sedation and the use of radioscopy. The handling of the cryoablation catheter is very similar to that of the RF catheter, which makes the technique easy to perform for licensed electrophysiologists.
Cryoablation has proven to be an effective and safe method in arrhythmias in which the region to be injured is contiguous to the bundle of His. The technique proved safe even in children and with high rates of long-term cure in several series of patients reported in the literature.
The cryoablation procedure is similar to the RF ablation pattern with respect to femoral venous access and the use of radioscopy.
There are no direct published comparative studies of RF ablation and cryoablation. Our initial case series shows a high success rate and safety of cryoablation in para-Hisian accessory pathways in accordance with current literature.

AUTHORS' CONTRIBUTION
All the authors contributed equally to this article.