Cryoballoon Ablation and Phrenic Nerve Injury
How often does right phrenic nerve injury (PNI) occur when electromyographic monitoring is performed during cryoballoon ablation?
One hundred patients (mean age 63.6 years) with paroxysmal atrial fibrillation underwent cryoballoon ablation using a 28-mm second-generation cryoballoon catheter and single 3-minute freezes. Right diaphragmatic compound motor action potentials (CMAPs) during phrenic nerve pacing were monitored. Cryoablation was discontinued upon a >30% reduction in CMAP amplitude.
PNI occurred in eight patients during cryoablation around the right superior pulmonary vein (RSPV) and in one patient during the thawing process. A reduction in the CMAP always preceded weakening of diaphragmatic contraction. The distance between the RSPV ostium and the right peri-cardiophrenic bundle (RPCB) was measured on a preprocedure computed tomography scan and was significantly shorter in patients with than without PNI. The sensitivity and specificity of a 12.4-mm cutoff in distance between the RSPV ostium and the RPCB for PNI were 96.6% and 88.9%, respectively. The PNI resolved within 1 day in six patients and at 2-8 months in three patients.
There is a 3% risk of persistent PNI resolving at ≤8 months when CMAP monitoring is used during cryoballoon ablation of the RSPV with a 28-mm cryoballoon catheter. The distance between the RPCB and the RSPV ostium is predictive of PNI.
All cases of PNI in this study occurred during cryoablation of the RSPV. However, PNI also can occur during cryoablation of the right inferior pulmonary vein and it is important to monitor the CMAP during cryoablation of both right-sided pulmonary veins.
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