Abstract 2104: The Critical Temperature, Distance and Balloon Size-Dependence of Phrenic Nerve Injury During Cryoballoon Ablation
Background: Previous in vivo studies have demonstrated occurrence of phrenic nerve injury resulting from cryoballoon ablation. It is unknown to what degree cryothermy penetrates target tissue and surrounding tissue to create this collateral damage.
Methods: This study was undertaken in the Mayo Translational EP Lab to characterize the phrenic nerve tissue temperature response during 23 and 28 mm cryoballoon ablation of the RSPV in a canine model. T-Type thermocouples were implanted at RSPV and phrenic nerve surface sites in 11 dogs. Phrenic nerve function was assessed by pacing in the SVC throughout the ablation.
Results: 39 cryoballoon ablations were performed at the RSPV, (32 with 23 mm/7 with 28 mm balloons). Phrenic nerve injury occurred in 3/32 (27%) of animals with 23 mm and 0/7 with 28 mm balloons. The phrenic nerve-RSPV distance was significantly smaller by anatomic measurement in animals with phrenic nerve injury compared to those without, (4.8 ± 1.6 mm and 8.6 ± 3.0 mm, p=0.02, respectively). The minimum temperature with phrenic nerve injury was significantly lower than without injury, (−16 ± 7.2 vs. 8.8 ± 12.7 °C, p< 0.005, respectively). Phrenic nerve temperatures colder than −10 ° C resulted in injury. Eight of 32 freezes (25%) had phrenic nerve temperatures <0 ° C when using the 23 mm balloon compared to 0/7 with the 28 mm balloon. The minimum temperatures at matched phrenic nerve locations using the 23 mm and 28 mm balloons was −0.5 ± 18.3 °C and 16.1 ± 12.2 ° C respectively, p=0.03, all related to balloon position outside the PV with 28 mm balloons.
Conclusion: As demonstrated by these data, phrenic nerve injury is dependent on the temperature achieved and distance of the nerve from the ablation site. This may be overcome by larger balloons limiting ablation to the veno-atrial junction or outside the vein.