AVNRT Ablation: Aiming for 100/0, and for Comfort!

In this issue of PACE,1 Chan and colleagues compare radiofrequency (RF) and cryo ablation for atrioventricular nodal reentry tachycardia (AVNRT) ablation. The authors draw attention to the stresses on both the patient and on the operator. They conclude that operator stress is higher with RF than cryo, probably because of the need for intensive and continuous and simultaneous monitoring of catheter position, electrograms, electrocardiograms, and ablation settings. As the authors point out, it is difficult to achieve 100%“cure” of AVNRT or 0% atrioventricular block (AVB). Some of the challenges are anatomical. Patients with “short septums” (between the His area and the coronary sinus os) may offer little room for error in catheter position, and sudden deep breath or other cause for catheter movement can have serious consequences. One of the advantages here of cryo is that the lead tends to become stuck in place at lower temperatures (–60°C–80°C) so that inadvertent movement is less of a problem. It is also known that a small percentage of patients will have both the fast and slow pathways well posterior to the His position; hence, the suggestion by some that anterograde and retrograde septal mapping should be done prior to delivering RF2,3 and presumably cryo as well. The findings regarding greater patient discomfort with RF may be context related. It is now fairly routine to use sedation during electrophysiology study, and few sedated patients have much memory of their procedures. Chan et al. did not use sedation, and thus were able to query patients on their perception of procedural pain. The authors did not indicate why they did not use sedation: (1) their routine practice? (2) to permit comparison of RF-cryo discomfort levels? (3) to ensure that patients could be told not to take deep breaths or move during delivery of RF or cryo? The reduced operator stress using cryo is also interesting. The reduction in catheter movement when the tip freezes is reassuring. Cryo has the reputation of causing less irreversible AV block than cryo, but all things are relative. This editor is aware of documented but unpublished instances of AVB using cryo, and one wonders whether operator overconfidence may have played a role. Although the cryo technique is more forgiving, operators should avoid a false sense of security, and maybe aim for just a little higher stress than reported by Chan and colleagues.