SAN FRANCISCO (FRONTLINE MEDICAL NEWS) Lower doses and conservative applications eliminated phrenic nerve palsy with Medtronic’s Arctic Front Advance cryoballoon ablation catheter at the University of Florida, Gainesville.

Cardiologists there were accustomed to performing atrial fibrillation pulmonary vein isolation with the first-generation device – the Arctic Front – when they switched to the second-generation Advance catheter in 2012; they had 2 phrenic nerve palsies in the first 33 patients (6%), a doubling from the 2 cases in 74 patients (2.7%) with the first-generation device.

The second-generation catheter is more powerful, with a cooling jet in the front of the balloon that delivers colder temperatures deeper into pulmonary veins. “We realized we needed to change the way we were using these catheters. You can use them safely, but you have to respect” their power, said lead investigator Dr. Robert Gibson.

“We reduced freezing times from 240 seconds to 180 seconds, and made that a hard rule. We limited the number of ablations” to two complete occlusions per vein, down from four to seven with the first-generation Arctic Front. “We also implemented a nadir cutoff to stop ablation when catheter temperatures fell below –55° C, and we tried to stay as proximal as possible to the pulmonary vein antra while still maintaining complete occlusion.” To help with that, cardiologists stopped using the 23-mm catheter, opting instead for the 28-mm catheter, Dr. Gibson said at the Heart Rhythm Society annual meeting.

Since making the changes, the team has performed 140 ablations, and there has not been a single phrenic nerve palsy. “We haven’t experienced a diaphragm paralysis” with the new approach. “We are very happy with these results. The changes make physiologic sense. You stay back; you use fewer freezes,” he said.

Phrenic nerve injury also decreased, from 3 cases in the first 33 second-generation patients (9%) to 9 in the 140 (6.4%) with the refined technique. Total phrenic nerve complications are now fewer in Gainesville than with the original, less powerful first-generation Arctic Front.

The team didn’t report ablation success with their new approach, but a 2015 review of Arctic Front Advance in more than 3,000 patients suggested long-term success with similar refinements ( Heart Rhythm. 2015 Jul;12[7]:1658-66 ).

Patients in the University of Florida review were in their early 60s, on average, and about two-thirds were men. About 30% had prior ablations. Phrenic nerve injury was determined by continuous phrenic nerve stimulation and manual diaphragm palpation during cryoablation.

The investigators had no relevant financial disclosures. Medtronic helped with the statistical analysis.