Successful use of "cryo-mapping" to avoid phrenic nerve damage during ostial superior vena caval ablation despite nerve proximity

Background: The SVC may require ablation to treat atrial fibrillation. Phrenic nerve proximity identified with pacing maneuvers may preclude ablation. Methods: We tested a new method using "cryo-mapping" to ablate despite nerve proximity. Results: Of 833 patients undergoing ablation, 110 (12%) had arrhythmogenic substrate at the SVC/RA junction. Of these 110 patients, 66 (60%) had consistent diaphragmatic stimulation when pacing at 10 mA at the prospective site of ablation. Of these 66 patients, 7 had continued arrhythmogenicity despite attempts to modify this substrate. For these 7 patients, we paced 4 cm into the SVC where consistent phrenic nerve stimulation was obtained, and cryoablation at -30°C was performed at sites requiring ablation. In 6 of 7 patients (86%), with continued diaphragmatic capture, cryoablation at -70/-80°C was then performed. In 1 of 7 patients (14%), diaphragmatic stimulation ceased at -30°C, and energy delivery stopped. In the 6 patients in whom cryoablation was completed, the arrhythmogenic substrate was successfully ablated without phrenic nerve injury. Conclusions: A novel "cryo-mapping" technique during phrenic nerve pacing can be used to successfully ablate arrhythmogenic substrate at the SVC/RA junction despite phrenic nerve proximity.