Download pacing the phrenic nerves from the right and left

PACING THE PHRENIC NERVES FROM THE RIGHT AND LEFT
SUBCLAVIAN VEINS IS SUPERIOR TO PACING FROM THE SUPERIOR
VENA CAVA ALLOWING RIGHT AND LEFT PHRENIC NERVE
MONITORING DURING BALLOON CRYOABLATION
Ghosh J, Singarayar S, McGuire MA, The Royal Prince Alfred Hospital and Mater Hospital, Sydney,
Australia.
Introduction:Phrenic nerve palsy is the most common complication of balloon cryoablation.
Monitoring the right phrenic by pacing at the lateral SVC is recommended. No data exist regarding the
benefits of this site versus other pacing sites. Furthermore despite reports of persistent left phrenic nerve
palsy due to balloon cryoablation, the incidence of left phrenic nerve dysfunction remains unknown. We
describe the novel approach of phrenic nerve monitoring by stimulating the right and left phrenic nerves
from the subclavian veins during balloon cryoablation procedures.
Methods:1)Prior to cryoablation of the left sided pulmonary, a quadrapolar pacing catheter was
positioned posterior to the left sternoclavicular junction in the left subclavian vein. High output pacing
was delivered to a widely spaced bipole (poles 1&4 at 25mA). Pacing output was then decreased until
reliable capture (detectable diaphragmatic contraction throughout the entire respiratory cycle) was lost.
Constant pacing was delivered at twice threshold during left sided cryoablation. 2)Prior to ablation of
the right sided pulmonary veins, phrenic nerve capture thresholds were assessed at both the subclavian
vein position and the lateral superior vena cava. During cryoablation, right phrenic pacing was from the
subclavian vein position.
Results:1) left phrenic nerve capture was achieved in 71/75 consecutive patients. Pacing was not
possible due to permanent pacemaker lead obstruction in 2 patients and inability to locate the left
subclavian vein in 2 patients. The median capture threshold was 2.8mA (IQR 1.5-6mA). Left phrenic
nerve dysfunction due to cryoablation did not occur during the initial 75 cases. 2)In 25 consecutive
patients the threshold obtained at the right subclavian vein was compared with the lateral SVC. The
median threshold was lower at the subclavian vein than the SVC (2mA IQR 0.85-4 vs 6 IQR 3-8mA
p<0.001)
Conclusions:Phrenic nerve stimulation at the subclavian veins is a novel technique which provides
stable capture at lower pacing outputs than the recommended SVC position, and also allows monitoring
of the left phrenic nerve. The true incidence of left phrenic nerve dysfunction due to cryoablation is
unknown, but may be quantified by the this technique.