LETTER TO THE EDITOR
Reply
James T. Niemann, MDa
a Professor of Medicine, Department of Emergency Medicine, Box 21, Harbor-UCLA Medical Center, 1000 West Carson Street, Torrance, California 90509, USA
jniemann{at}emedharbor.edu
We appreciate the insightful review of our article (1) by Sun et al. and wish to offer the following comments regarding their concerns.
The baseline mean aortic pressure (MAP) and cardiac output that we reported are typical for swine anesthetized with isoflurane and nitrous oxide and approximate those recorded in awake animals (2). Although not reported in the article, the observed control heart rate in our animals, approximately 100 beats/min, also approximates that observed in conscious swine. We believe that these values are reflective of stable anesthesia with inhaled agents that are preferred by many for cardiovascular research. In our opinion, control values should ideally reflect those observed in conscious animals. The MAP values as well as left ventricular dP/dt observed by Sun et al. using intermittent intravenous pentobarbital anesthesia are, in fact, excessive when compared to values reported in the literature for swine anesthetized with pentobarbital (3). This suggests that the "control" values reported by Sun et al. are supranormal, possibly reflecting enhanced sympathetic tone of uncertain etiology. We would therefore agree with Sun et al. that these differences of concern to them are due to differences in experimental procedures between our laboratories. However, they are not reflective of inadequate technical skills in our laboratory used in the acquisition and interpretation of hemodynamic data.
Our data do, in fact, support the observations of Sun et al. In a prior publication (4), they reported no differences between defibrillation waveform groups with respect to first shock success or clinically important indexes of postresuscitation cardiac function after a 4-min period of ventricular fibrillation (VF). Observed differences appear to resolve rather than evolve during extended observation. Sun et al. have previously acknowledged the effect of prolonged pentobarbital anesthesia on cardiac mechanics (5). We likewise observed no differences during observation after a 5-min VF period. It would appear that the "best" defibrillation waveform for the treatment of VF of 4- to 5-min duration would be the one that is first available.
We have not systematically investigated the differences between defibrillation waveforms in the management of VF of >5-min duration. It is very likely that if we administered monophasic waveform energy doses similar to those used by Sun et al. in their 7-min swine model (4), an average dose approximating 57 J/kg, we would observe results similar to what they have reported. In our hospital’s recent six-year clinical experience with out-of-hospital sudden cardiac death, the largest energy dose used in any patient has been approximately 33 J/kg delivered with seven countershocks. Since the energy doses reported by Sun et al. far exceed what is encountered clinically, our laboratory has no intention of pursuing a similar experimental design due to its lack of clinical relevance.
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References
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1. Niemann JT, Burian D, Garner D, Lewis RJ. Monophasic versus biphasic transthoracic countershock after prolonged ventricular fibrillation in a swine model. J Am Coll Cardiol. 2000;36:932–938[Abstract/Free Full Text]
2. Lundeen G, Manohar M, Parks C. Systemic distribution of blood flow in swine while awake and during 1.0 and 1.5 MAC isoflurane anesthesia with or without 50% nitrous oxide. Anesth Analg. 1983;62:499–512[Abstract/Free Full Text]
3. Stanton HC. Development of cardiovascular control and function. Swine in Cardiovascular Research. 1st ed. Boca Raton, FL: CRC Press; 1986. p. 49–71
4. Tang W, Weil MH, Sun S, et al. The effects of biphasic and conventional monophasic defibrillation on postresuscitation myocardial function. J Am Coll Cardiol. 1999;34:815–822[Abstract/Free Full Text]
5. Gazmuri RJ, Weil MH, Bisera J, Tang W, Fukui M, McKee D. Myocardial dysfunction after successful resuscitation from cardiac arrest. Crit Care Med. 1996;24:992–1000[CrossRef][Medline]
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