The Practice of Catheter Cryoablation for Cardiac Arrhythmias

Case 5.2 A 73-year-old woman with refractory paroxysmal atrial fibrillation

A 73-year-old woman was undergoing ablation with the 28 mm cryoballoon for refractory paroxysmal atrial fibrillation. After isolation of both left pulmonary veins, the right upper pulmonary vein was occluded with the 28 mm balloon, which was perfectly centered. Using the upside-down technique and a deflectable quadripolar 6F stimulation catheter in the superior caval vein, the phrenic nerve was stimulated in 2-second intervals. The amplitude of diaphragmatic excursion palpated through the abdominal wall was noted to decrease after 200 seconds of freezing.

• 1. How should one respond to this phenomenon?

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  Correct answer:
  The freezing period has to be stopped immediately.
  Diminishing diaphragmatic contraction is indicative of an imminent threat of phrenic nerve paralysis and coincides with a decreasing amplitude of the electric summation potential on phrenic nerve monitoring. At no time should time be wasted with maneuvers aimed to ascertain catheter-related factors. Freezing has to be aborted immediately. In most cases, phrenic nerve function will recover within several minutes, even with normal thawing. We terminated the freezing period and asked our patient to take a deep breath, which was fluoroscopically monitored (Video Case 5.2). To our surprise, the right hemidiaphragm could still be stimulated from the superior vena cava, albeit only very weakly so. As can be seen from the excursion of the left hemithorax, voluntary inspiration was associated with activation of only the left hemidiaphragm.

  This disparity once again underlines the need for electrical monitoring in all cases where general anesthesia is used.

  Whenever the freezing cycle is stopped as described above, we do not recommend a second freeze after phrenic nerve recovery if the pulmonary vein is successfully isolated. We believe that one may subsequently isolate the right inferior vein without undue risk, but in such cases, phrenic nerve monitoring should also be employed during right inferior pulmonary vein isolation.