Method discussion for steadily right phrenic nerve pacing with cryoballoon ablation for atrial fibrillation

Abstract

Objective Cryoballoon ablation to achieve pulmonary vein isolation is effective for patients with atrial fibrillation. Right phrenic nerve palsy (PNP) is a common complication during the procedure. Continuous monitoring the right phrenic nerve activity can reduced incidence of PNP. We try to explore an effective method for sustained right phrenic nerve pacing. Methods The 32 patients underwent cryoballoon ablation of atrial fibrillation were enrolled in the study. The deflectable pacing catheter were placed in the supra vena cava (SVC) region in an invertedUshape. In the right anterior oblique position, the SVC region was longitudely divided into upper, medium, and lower regions according to the subclavian intervertebral space, and was horizontally separated into posterior, free, and anterior wall. The modified lead Ⅰ was used to record the diaphragmatic compound motor action potential (CMAP) when pacing with 5 mA output. Results The phrenic nerve could be steadily captured by the pacing catheter in the SVC region with the invertedUfashion. No persistent PNP was observed in any of the 32 patients. A total of 285 pacing sites were tested. The phrenic nerve was captured in 175 sites (61.4%, 175/285). Pacing at the posterior (84.2%, 80/95) and the free wall (80.0%, 76/95) of the SVC region were more easily to capture the phrenic nerve than at anterior wall (20.0%, 19/95). With the stable pacing output of 5 mA, the CMAP was significantly higher when pacing at the posterior and free wall than in the anterior wall (P<0.001). The CMAP amplitude was negatively correlated with the pacing threshold (r=-0.267, P=0.005). Conclusions The phrenic nerve can be steadily captured with pacing catheter placed at the posterior and free wall of the SVC region with invertedUfashion. And pacing at site with lowest threshold can be present with clear CMAP in modified lead Ⅰ, which can be helpful to predict PNP during cryoablation. Key words: Atrial fibrillation; Catheter ablation; Phrenic nerve palsy; Phrenic nerve pacing; Pacing threshold; Compound motor action potential