136-67: Incidence and Predictors of Phrenic Nerve Stimulation following Cardiac Resynchronization Therapy System Implantation of a Quadripolar Lead

Abstract

Introduction: Quadripolar (quad) left ventricular (LV) pacing leads are routinely used during cardiac resynchronization therapy (CRT). When phrenic nerve stimulation (PNS) occurs in patients with a quad LV lead, reprogramming is often sufficient to eliminate the problem. However, the incidence and predictors of PNS remain less understood. Methods: Patients implanted with CRT-D during a prospective Investigational Device Exemption study of the Boston Scientific ACUITY X4 quad LV lead were evaluated. Electrical performance including pacing capture thresholds (PCT) and PNS were evaluated intra-operatively, at pre-discharge, and 3 months. The IO PNS safety margin was calculated between PNS (tested up to 7.5V) and PCT. Complications were tracked for 6 months. Results: Clinically documented PNS occurred in 58 (8%) of 744 CRT patients. In 14 (24%) of these patients, PNS occurred within the first day of implant; overall, the median time to PNS was 5.5 days [IQR 0.75, 53]. PNS most commonly occurred when the distal electrode was used (30 of 205 [15%] cases vs 28 of 539 [5%] for non-distal pacing, p < 0.001). In 51 (88%) of the 58 patients, PNS was not present intra-operatively at even maximal pacing output. In the remaining 7 patients, a safety margin between PNS and PCT failed to prevent PNS. When the safety margin was < 2 V, there was 35% risk of PNS. Device reprogramming (lowering pacing output or changing pacing electrode) was sufficient to eliminate the issue in 55 (95%) cases. Conclusion: With an ACUITY X4 quad LV lead, PNS was observed in 8% of patients, often within days of device implantation. When possible, avoidance of the distal electrode for pacing and avoidance of accepting a small “safety margin” for pacing output may mitigate against PNS. However, most patients had no measureable PNS at implant, suggesting an inability of current intra-operative techniques to ensure subsequent absence of PNS.