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Ann Thorac Surg 2004;78:1517
© 2004 The Society of Thoracic Surgeons
Trakya University, Medical Faculty, Department of Cardiovascular Surgery, 22030 Edirne, Turkey
scanbaz2001{at}yahoo.com
To the Editor:
We read with great interest the article by Deng and collaborators [1] regarding right phrenic nerve injury during mammary artery harvesting. In this well-conducted retrospective data analysis, the authors showed that the right phrenic nevre could be injured during high mammary artery harvesting, and diaphragm plication might be recommended if the patient is symptomatic. Although the development of right phrenic nerve injury during cardiac surgery has been known for many years, this comprehensive and detailed study by Dr Deng and coworkers is a valuable supplement to the literature. We wish to add some comments on this topic.
Some studies have suggested that hypothermic cardiopulmonary bypass (CPB) has a role in phrenic nerve injury [2, 3]. If beating heart patients were included in the study together with CPB patients, it would be shown that CPB is not a factor in the etiology of nerve injury. Except in cases where the nerve is transected intraoperatively, the lesions can generally be described as neuropraxia. Whereas neuropraxia is reversible, the spectrum of nerves injuries during mammary artery harvesting extend from mild demyelinization to severe axonal damage [4].
In Table 1 of the paper [1], 31 PNI + 754 non-PNI = 785 patients; this number is given as 783 in the results section.
The authors [1] used posteroanterior chest roentgenogram, spirometry, and fluoroscopy for diagnosis of phrenic nerve injury. Taking the spirometric results, diagnosis of the phrenic nerve injury was confirmed if the forced vital capacity and forced expiratory volume in 1 second ratios were more than 80% of predicted values. However, many factors—especially CPB—partially suppress respiratory functions during the postoperative period. We consider that reliance on spirometry and fluoroscopy does not provide a safe or adequate basis for recommending surgical intervention to the patient. Confirmation of the diagnosis by a nerve conduction study would be helpful for patients who are to undergo diaphragm surgery [2, 3].
In a recent prospective study that included both CPB and beating heart patients, we performed preoperative and postoperative bilateral electrophysiologic studies on the phrenic nerves of about 100 patients. We did not observe right phrenic nerve injury in any patients who underwent left mammary but not right mammary artery harvesting as standard procedure. Also, no phrenic nerve injury was detected in the approximately 30 beating heart patients in which the left mammary artery was harvested. Although there were signs of diaphragm paralysis on chest roentgenogram and spirometry in 20 of approximately 50 patients in which hypothermic CPB and ice-slush application around the heart had been used, only 5 patients failed to show an electrophysiologic response to an applied stimulus. Three months later, we observed a response to phrenic nerve stimulation in 1 of these 5 patients; thus, spontaneous recovery had occurred in this patient.
Invasive electrophysiologic study of the phrenic nerve could be performed quickly near the bed or in the laboratory. Both phrenic nerves could be stimulated transcutaneously with surface electrodes inserted into the neck, and nerve conduction could also be recorded with another electrode inserted into the chest at the level of the diaphragm [3, 4].
In view of our findings, we suggest that when phrenic nerve injury is suspected, based on low-sensitive methods such as chest roentgenogram, spirometry, and abnormal diaphragm movements, the diagnosis might be confirmed by a simple electrophysiologic study.
References
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