LETTER TO THE EDITOR
Reply
David Amar, MD
Memorial Sloan-Kettering Cancer Center, Anesthesiology, 1275 York Ave., Rm M-304, New York, NY 10021, USA
Alan H. Kadish, MD
amard{at}mskcc.org
We thank Dr. Stein for her interest and comments. Although we would like to study nonlinear methods in our patients, this task was prohibitive in the time frame required for this response. We appreciate the suggestions and will explore our data using these methods in the future.
Dr. Stein suggests that postoperative patients behave similarly to healthy volunteers in whom increased randomness of the heart-period signal was attributed to increasing doses of norepinephrine (1) and that the increases in both time- and frequency-domain parameters of heart rate variability (HRV) observed in our study do not represent vagal resurgence (2). We disagree with this hypothesis for several reasons.
First, in a study of patients undergoing major thoracic or abdominal surgery, we showed persistent downregulation and desensitization of the lymphocyte beta-adrenergic receptor/adenylyl cyclase system, which correlated with decrements in time- and frequency-domain indices of HRV throughout the first week after surgery (3). These changes occurred in the absence of change in perioperative epinephrine or norepinephrine levels.
Second, to suggest that our atrial fibrillation (AF) patients (n = 48) had a significantly different perioperative neurohumoral response than did that of controls (n = 48) matched for age, gender, and identical operation, appears unlikely. Finally, the HRV response seen in our control group was very similar to that seen in other patients undergoing major thoracic surgery, supporting the presence of parasympathetic withdrawal and not resurgence (4).
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References
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1. Tulppo MP, Makikallio TH, Seppanen T, et al. Effects of pharmacological adrenergic and vagal modulation on fractal heart rate dynamics. Clin Physiol. 2001;21:515–523[CrossRef][Medline]
2. Amar D, Zhang H, Miodownik S, Kadish AH. Competing autonomic mechanisms precede the onset of postoperative atrial fibrillation. J Am Coll Cardiol. 2003;42:1262–1268[Abstract/Free Full Text]
3. Amar D, Fleisher M, Pantuck CB, et al. Persistent alterations of the autonomic nervous system after noncardiac surgery. Anesthesiology. 1998;89:30–42[CrossRef][Medline]
4. Amar D, Zhang H, Leung DHY, Ginsburg I. Effects of left and right pneumonectomy on time- and frequency-domain parameters of heart rate variability. Ann Noninvas Electrocardiol. 1999;4:325–332
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