Characterization of the phrenic nerve course within the epicardial substrate of patients with nonischemic cardiomyopathy and ventricular tachycardia

Background: Patients with nonischemic cardiomyopathy and ventricular tachycardia (VT) often have low-voltage areas in the lateral left ventricular (LV) epicardium that serve as the VT substrate. The course of the left phrenic nerve in this region may pose a challenge to successful and safe ablation. Objective: The purpose of this study was to delineate the left phrenic nerve course in patients with nonischemic cardiomyopathy and suspected epicardial VT and to characterize its relationship with the VT substrate. Methods: In 10 patients with nonischemic cardiomyopathy undergoing epicardial VT mapping and ablation, the course of the phrenic nerve was defined by pacing. The extent of epicardial LV low-voltage areas (<1.0 mV) was characterized by electroanatomic voltage mapping. Results: Eight of 10 patients had low-voltage areas involving the lateral epicardial LV, and 7 of these 8 patients had sites of phrenic capture within these areas. Ablation was limited due to location of the phrenic nerve in two patients. In one of these patients, a balloon catheter was successfully used to mechanically protect the phrenic nerve during ablation. In the other five patients, adjacent ablation sites were targeted at which no phrenic capture with high-output pacing was demonstrated prior to ablation. In all patients undergoing ablation, the targeted VT became noninducible, and no patient demonstrated phrenic nerve injury. Conclusion: In most patients with nonischemic cardiomyopathy undergoing epicardial VT ablation, the phrenic nerve courses through a lateral LV low-voltage area in proximity to potential sites for ablation. Strategies to identify and protect the phrenic nerve are important.