When does phrenic nerve injury recover after cryoballoon ablation? Data from Japanese multicenter registry

FUNDING ACKNOWLEDGEMENTS: Type of funding sources: None. BACKGROUND: Although phrenic nerve injury (PNI) is most frequently encountered complication in cryoballoon ablation, it recovered in most cases. However, the duration of persisting PNI has not been fully investigated yet. PURPOSE: This study sought to confirm the clinical course of PNI after the procedure in cases in which reduction of diaphragmatic compound motor action potential (CMAP)was confirmed during cryoballoon ablation of right-sided pulmonary veins (PVs). METHODS: We retrospectively analyzed a total of 237 patients who experienced right PNI confirmed by the CMAP amplitude reduction during cryoballoon ablation in 4 Japanese centers. Cryoballooon ablation of right-sided PVs were performed under CMAP monitoring in all cases, and once CMAP amplitude reduction was observed, freezing was immediately interrupted with a double stop technique. The recovery of PNI was confirmed by chest X-ray, and transient PNI was defined as one recovering before the discharge. RESULTS: Among 237 patients, PNI occurred during cryoballoon ablation of right superior PV and right inferior PV in 166 and 71 patients, respectively. The mean freezing time to PNI was 126.9±45.6 seconds and the mean balloon temperature when PNI occurred was -50.2±7.5°C. After PNI was confirmed, additional cryoballoon ablation of the same PV or the other ipsilateral PV was performed under CMAP monitoring in 29 and 97 patients, respectively. Transient PNI accounted for 53.2% of patients with PNI (126 out of 237 patients). Among the remaining 111 patients, the PNI recovery was confirmed within 3 months, 6 months or 12 months after the procedure in 42(37.8%), 55 (49.5%), 74 (66.7%) patients, respectively. When we excluded 32 patients who did not undergo sufficient follow-up of chest X-ray, only 5 patients (2.4%) still suffered from PNI at 12 months after the ablation, and the PNI recovery was confirmed after more than 12 months in 3 out of them. When we compared patients who suffered from PNI at 6 months after the procedure with those who did not, there was no significant difference in nadir balloon temperature (-50.4±6.9°C; for PNI recovery [-] vs -50.0±7.8°C; for PNI recovery [+], p=0.75). When freezing time was less than 60 seconds, PNI recovered within 6 months after ablation in all cases, although 23.2% of the patients in whom freezing time was 60 seconds or more still suffered from PNI at 6 months after the procedure (p=0.045). CONCLUSION: The right-sided PNI confirmed by the CMAP amplitude reduction during cryoballoon ablation recovers within a couple of days in half of cases, and it rarely persists more than 12 months after the procedure. When freezing was interrupted less than 60 seconds, it is highly expected that PNI recovers within 6 months.