title: Subclavian vein pacing and venous pressure waveform measurement for phrenic nerve monitoring during cryoballoon ablation of atrial fibrillation.
abstract: OBJECTIVE
  The phrenic nerves may be damaged during catheter ablation of atrial fibrillation. Phrenic nerve function is routinely monitored during ablation by stimulating the right phrenic nerve from a site in the superior vena cava (SVC) and manually assessing the strength of diaphragmatic contraction. However the optimal stimulation site, method of assessing diaphragmatic contraction, and techniques for monitoring the left phrenic nerve have not been established. We assessed novel techniques to monitor phrenic nerve function during cryoablation procedures.
  
  
  RESULTS
  Pacing threshold and stability of phrenic nerve capture were assessed when pacing from the SVC, left and right subclavian veins. Femoral venous pressure waveforms were used to monitor the strength of diaphragmatic contraction. Stable capture of the left phrenic nerve by stimulation in the left subclavian vein was achieved in 96 of 100 patients, with a median capture threshold of 2.5 mA [inter-quartile range (IQR) 1.4-5.0 mA]. Stimulation of the right phrenic nerve from the subclavian vein was superior to stimulation from the SVC with lower pacing thresholds (1.8 mA IQR 1.4-3.3 vs. 6.0 mA IQR 3.4-8.0, P < 0.001). Venous pressure waveforms were obtained in all patients and attenuation of the waveform was always observed prior to onset of phrenic nerve palsy.
  
  
  CONCLUSIONS
  The left phrenic nerve can be stimulated from the left subclavian vein. The subclavian veins are the optimal sites for phrenic nerve stimulation. Monitoring the femoral venous pressure waveform is a novel technique for detecting impending phrenic nerve damage.
authors.affiliation: The Mater Hospital, Sydney, Australia The Royal Prince Alfred Hospital and University of Sydney, Sydney, Australia.
authors.forename: Justin
authors.initials: J
authors.lastname: Ghosh
authors.affiliation: The Royal Prince Alfred Hospital and University of Sydney, Sydney, Australia.
authors.forename: Suresh
authors.initials: S
authors.lastname: Singarayar
authors.affiliation: The Royal Prince Alfred Hospital and University of Sydney, Sydney, Australia.
authors.forename: Peter
authors.initials: P
authors.lastname: Kabunga
authors.affiliation: The Mater Hospital, Sydney, Australia The Royal Prince Alfred Hospital and University of Sydney, Sydney, Australia mark.mcguire@email.cs.nsw.gov.au.
authors.forename: Mark A
authors.initials: MA
authors.lastname: McGuire
mesh_terms: D001281:Atrial Fibrillation / Q000601:surgery*; D002304:Cardiac Pacing, Artificial / Q000379:methods; D015331:Cohort Studies; D003452:Cryosurgery / Q000009:adverse effects / Q000379:methods; D003964:Diaphragm / Q000294:innervation*; D004558:Electric Stimulation; D005268:Femoral Vein / Q000502:physiology*; D006801:Humans; D016343:Monitoring, Intraoperative / Q000379:methods*; D009119:Muscle Contraction / Q000502:physiology*; D059348:Peripheral Nerve Injuries / Q000517:prevention & control*; D010791:Phrenic Nerve / Q000293:injuries / Q000502:physiology*; D063177:Pulse Wave Analysis; D013350:Subclavian Vein; D014683:Vena Cava, Superior; D014690:Venous Pressure / Q000502:physiology*
keywords: Atrial fibrillation; Cryoballoon; Phrenic nerve palsy