Recordings of diaphragmatic electromyograms during cryoballoon ablation for atrial fibrillation accurately predict phrenic nerve injury

BACKGROUND Cryoballoon ablation has been associated with a significant incidence of phrenic nerve injury (PNI). OBJECTIVE The purpose of this study was to evaluate whether recordings of diaphragmatic compound motor action potentials (CMAP) on a modified Lead I during ciyoballoon ablation can predict PNI. METHODS Cryoballoon ablation was performed in 109 patients with atrial fibrillation (AF). During ablation of the right-sided pulmonary veins, the phrenic nerve was paced from the superior vena cava. The right and left arm electrodes from a 12-lead ECG were positioned 5 cm above the xiphoid process and 16 cm along the right costal margin. The amplitude of CMAP was recorded on Lead I during ablation. RESULTS Cryoballoon was applied 424 times in 211 right-sided veins. PNI occurred in 7 (6.4%) patients. The average CMAP amplitude did not significantly change in patients without PNI from the initial average CMAP amplitude of 0.34 +/- 0.18 mV to 0.32 +/- 0.17 mV (P =.58). In patients who developed PNI, there was a significant decrease in the initial average CMAP amplitude during the ablation from 0.33 +/- 0.14 mV to 0.09 +/- 0.05 mV (P <.001). The maximal percent change in the average CMAP amplitude in patients with PNI was higher (70% 10%) than in patients without PNI (7.6% +/- 7%; P <.001). In any patient without PNI, the CMAP amplitude did not decrease more than 35% from baseline. CONCLUSION Recording of CMAP amplitude on a modified lead I is reliable and could be early and sensitive method for predicting PNI in patients undergoing cryoballoon ablation for AF.