Can cryofreezing energy be an absolute alternative to radiofrequency energy for treating atrioventricular nodal re‐entrant tachycardia? We have to further recognize the advantageous as well as disadvantageous aspects of cryofreezing energy

The advent of cryofreezing energy has had a vast influence on the clinical field of catheter ablation for treating atrial fibrillation as well as various kinds of atrial tachyarrhythmias up to now. The cryoablation system has become one of the established treatment options for catheter ablation in guideline‐directed medical therapy and has provided comparable clinical results. Previous studies of radiofrequency (RF) ablation have attempted to answer whether a patient population may exist whereby the effectiveness of this procedure would be sufficiently high, and the procedure risk sufficiently low, in cases undergoing ablation of atrioventricular re‐entrant tachycardia (AVNRT). In contrast to RF energy, the lesion formation with cryofreezing ablation occurs through convective cooling, whereby the cryorefrigerant absorbs heat from the tissue surrounding the catheter. The cryofreezing system possesses not only destroying effects but also transient injurious ones on the myocardial tissue namely “cryomapping. ” Cryomapping is a very useful clinical tool when the ablation target tissue is located in close vicinity of the normal conduction system such as the His bundle. Permanent injurious effects on the normal conduction system could be avoided by the cryomapping procedure, and unnecessary lesion formation could also be spared by observing the reversible findings provoked by a mild cryofreezing application at a temperature of −30°C to −40°C. Fukuda et al., in this issue of the Journal of Cardiovascular Electrophysiology, tested the safety and efficacy aspects of the cryofreezing ablation system in a relatively small volume of patients. We congratulate the authors for bringing this additional important information to light in this article. The authors were able to identify a “dangerous” area in Koch's triangle regarding provoking damage to the normal conduction system. They could also provide very important information with regard to how to perform a safe and successful ablation of AVNRT by investigating the ratio of the atrial/ventricular electrograms recorded through the tip of a roving catheter, the distance between safe and successful ablation sites, and the His recording site, which exhibited second‐ or third‐degree AV block during the cryoablation that recovered within 10min even though the cryofreezing energy was applied to an area very close to the His recording site with an average distance of 4 mm. Of interest, the previous reports failed to delineate the reason why the distance between the successful site for eliminating the AVN slow pathway and His recording site is significantly shorter during cryofreezing ablation than that RF applications. This difference might be derived from the difference in the lesion size or degree of energy penetration into the cardiac tissue between that with cryofreezing and that with RF energy. As a result, the successful ablation site might differ along the anatomical course of the AVN slow pathway in which the width and depth also may differ. In the present study, only a 6‐mm tip cryoablation catheter was used. If an 8‐mm tip cryoablation catheter, which is able to create a larger and deeper lesion, was used instead, the final results including the safety and long‐term efficacy might have differed. If an injurious effect is provoked by the RF energy application in the vicinity of the His bundle, we cannot expect a full recovery from any impairment of the AV conduction. In the present study, no conduction disturbance of the AV node was observed in any of the 45 study patients during the follow‐up period. Other reports also demonstrated this safety aspect of the cryofreezing system. However, this characteristic of the cryofreezing system could be associated with a lower clinical efficacy of this ablation system, when we change our perspective regarding this ablation system (the good news is also the bad news). We may say that the cryofreezing system has preserved safety by sacrificing clinical efficacy. Unlike the RF ablation system, cryofreezing energy cannot be titrated (due to the single fixed temperature setting) according to the target tissue. The only way to overcome this drawback of the cryofreezing system may be a larger number and longer duration of the cryofreezing applications than that for RF energy. In the present article, the cryofreezing duration was 4min, and the average number of applications was 4. A further greater number of cryofreezing applications might be recommended to further reduce the recurrence rate of AVNRT. The incidence of spontaneous episodes of AVNRT is relatively lower compared to the other kinds of tachyarrhythmias. A longer follow‐up period is desirable to evaluate the clinical outcome of the catheter ablation of AVNRT. The authors followed up the study patients for approximately 25 months on average. This length of