Abstract 17710: Phrenic Nerve Injury Despite High-Output Pacing in Patients Undergoing Radiofrequency Catheter Ablation of Atrial Fibrillation

Abstract

Introduction: High-output pacing has been advocated as a strategy to avoid injury to the phrenic nerve (PN) during antral pulmonary vein (PV) isolation. We assessed the hypothesis that pacing does not prevent PN injury in patients undergoing radiofrequency (RF) ablation of atrial fibrillation (AF). Methods: The medical records of 198 consecutive patients (age=63±12 years, 129 men, ejection fraction=57±10%, LA=44±6mm, paroxysmal=49%) undergoing their first ablation procedure for AF were reviewed. All patients underwent antral PV isolation using a 3D mapping system (CARTO XP or CARTO 3) and a 3.5 mm irrigated-tip ablation catheter (maximum power, 25 W). Prior to RF energy delivery, high-output pacing (20 mA @ 10 ms, maximum output) was performed to asses for PN capture. Sites that afforded PN capture were avoided and RF energy was delivered at adjacent sites without PN capture. The 3-D maps were reviewed to identify the prevalence and sites of PN capture. Results: High-output pacing along the anterior right antrum resulted in PN capture in 35 patients (18%). The most common site with a positive response was the crux between the upper and lower PVs (60%), followed by the right superior PV (43%), and the right inferior PV (20%). Of the patients with PN capture, 49% had only one site of capture, 20% with two sites, and 31% had 3 or more sites. All PVs were isolated at the end of the procedure. Two patients (1%) developed PN injury (symptom onset on the day after the procedure), which was confirmed on radiography. In neither case was there evidence of PN capture during the procedure. Symptoms resolved in both patients within 3 months, with normalization of radiographic findings. Conclusions: High-output pacing along the anterior right PV antrum yields PN capture in roughly one-fifth of the patients undergoing PV isolation. Despite a negative response to pacing and alteration of the lesion set, PN injury may occur. The reason for this discordance is unknown, but may include the possibility that the capture threshold of the PN exceeds the maximum output of the stimulator, or that RF energy may injure the pericardiophrenic artery, which accompanies the PN. Avoiding high-power or long-duration lesions and high contact force in this region may minimize the risk of PN injury.