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J Thorac Cardiovasc Surg 2005;129:192-198
© 2005 The American Association for Thoracic Surgery
Surgery for Congenital Heart Disease |
a Division of Cardiovascular, Thoracic, and Pediatric Surgery, Department of Cardio-pulmonary and Vascular Medicine, Kobe University Graduate School of Medicine, Kobe, Japan
b Department of Cardiothoracic Surgery, Kobe Children's Hospital, Kobe, Japan
Received for publication February 24, 2004; revisions received May 7, 2004; accepted for publication May 13, 2004.
* Address for reprints: Yutaka Okita, MD, Division of Cardiovascular, Thoracic, and Pediatric Surgery, Department of Cardio-pulmonary and Vascular Medicine, Kobe University Graduate School of Medicine, Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan
yokita{at}med.kobe-u.ac.jp
| Abstract |
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METHODS: A prospective observational cohort study conducted over 2.5 years was performed in 98 consecutive patients (51 infants and 47 children) undergoing cardiac surgery for ventricular septal defects. Serial measurements of serum levels of heart fatty acidbinding protein and the respective areas under the curve were obtained, with particular reference to age and aortic crossclamp time. Assessment of clinical outcomes included inotropic support, ventilatory support, and intensive care unit stay.
RESULTS: There was a linear dependence of the logarithm of age and the logarithm of heart fatty acidbinding protein release(r = 0.737, P < .0001). This logarithm-logarithm plot showed a power function of age for heart fatty acidbinding protein release. The exponent and amplitude parameter of the power function was the aortic crossclamp time. Compared with children, infants had significantly more myocardial damage and worse clinical outcomes, and these factors were related to the aortic crossclamp time.
CONCLUSIONS: The younger the age of patients, the more vulnerable are their myocardia to injury caused by ischemia during definitive repair of congenital heart disease. Therefore, perioperative management for pediatric patients after cardiac surgery should be performed, taking into consideration the dependence of the myocardial damage on age and ischemic time.
In this study we analyzed the severity of myocardial injury in pediatric cardiac surgery by measuring HFABP release and assessed the effects of age and ischemic time on the release of HFABP.
| Methods |
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24 months of age) underwent transatrial repair of VSD at Kobe Children's Hospital. This age criterion was selected from the median age of all patients. Preoperative characteristics are summarized in Table 1. No patients required preoperative respiratory or inotropic support. Approval from the local ethics committee was obtained, as was informed consent from all participating patients or their guardians.
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Protocol of myocardial protection
Myocardial protection was achieved with intermittent cold blood cardioplegia with topical cardiac cooling in all patients. An initial dose of 300 mL/m2 body surface area was initially infused into an aortic root at a pressure of 30 mm Hg to achieve cardiac arrest, with subsequent doses of 150 mL/m2 body surface area infused every 20 minutes. In all patients, an additional 300 mL of warm (35°C) blood cardioplegic solution per square meter of body surface area was infused into the aortic root just before the aortic declamping.7 Blood cardioplegic solution4 was made by mixing hyperkalemic crystalloid solution8 with oxygenated blood in a 1:2 ratio and cooled to 9°C (Table 2). At the start of reperfusion, the aorta was partially declamped for 3 minutes, and the aortic root pressure was maintained at less than 30 mm Hg to reduce reperfusion injury. The aorta was then fully declamped. If ventricular fibrillation persisted beyond a few minutes after the aortic declamping, electrical defibrillation was applied to restore normal sinus rhythm.
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Assessment of clinical outcome
The relationship between serum peak levels of HFABP and intraoperative and postoperative clinical variables was evaluated. Intraoperative variables included duration of cardiopulmonary bypass, aortic crossclamp (AoX) time, and lower rectal temperature. Postoperative variables included inotropic score, duration of intubation, and intensive care unit stay. Inotropic score was defined as follows: the sum of doses of dopamine (in micrograms per kilogram per minute), dobutamine (in micrograms per kilogram per minute), and epinephrine (in micrograms per kilogram per minute x 100) multiplied by the number of hours that each drug was used.10
Statistical analysis
Database management and statistical analysis were performed with the Statview (version 5.0) software package (Abacus Concepts Inc). Normally distributed data are reported as means ± SEM; data that were not normally distributed are reported as medians with interquartile ranges. The methods of analysis included Mann-Whitney U tests for continuous variables and
2 tests for dichotomous parameters. The relationships between preoperative patient characteristics and preoperative serum HFABP levels and serum peak HFABP levels were analyzed with forward stepwise regression. Spearman rank correlation coefficients (2-tailed) were used to evaluate whether serum peak HFABP levels were correlated with operative clinical variables. HFABP-AUC and age showed some degree of positive skewness, and we therefore performed statistical analysis on the basis of logarithmic transformation of these variables to get an approximately normal distribution. Linear or nonlinear regression analysis was performed to determine the relationship between HFABP-AUC and age. For this analysis, the age data were evaluated as continuous variables. In addition, to quantify the independent effects of age and ischemic time and to examine their interactive effect, we used a general linear regression model.11
| Results |
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![]() | (1) |
and
, with a correlation coefficient (r) of 0.738. A highly significant negative correlation was found between the logarithm of HFABP release and the logarithm of age (P < .0001). The dotted lines in Figure 2, A, show the confidence intervals and prediction limits for the regression lines.
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![]() | (2) |
. Data were back-transformed to get the usual relationship in the original scale and plotted in Figure 2, B. The solid line in Figure 2, B, denotes equation 2, which is the nonlinear regression model of the data. It has been shown that the relationship between HFABP release and age follows a negatively accelerating power function.
Effect of age and ischemic time on HFABP release
The 2 subgroups were divided according to AoX time (group S, <75 minutes; group L,
75 minutes). The criterion of AoX time was selected from the median AoX time of all patients. Total HFABP release in infants was significantly greater than that in children (medians of 1133 vs 425 ng/mL, P < .0001). The HFABP-AUC level in group L was higher than that in group S (infants, medians of 1331 vs 873 ng/mL, P = .005; children, medians of 461 vs 368 ng/mL, P = .011). The HFABP-AUC level was dependent on AoX time. Moreover, the difference in HFABP release between the subgroups showed a trend toward a greater increase in infants than in children (Figure 3). The interaction between age and AoX time might cause this effect on HFABP release.
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![]() | (3) |
To estimate the effect of AoX time, M is a dummy variable defined as follows: M = 0 for group S, and M = 1 for group L. Table 4 shows the result of this analysis. In the model of equation 3, as well as equation 1, a highly significant negative correlation was found between the logarithm of age and the logarithm of HFABP release (P < .0001). Also, the logarithm of HFABP release correlated significantly with AoX time (P = .0012). There was a significant negative interaction with age and AoX time (P = .0361).
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) and group L (
) showed a greater increase in infants than in children.
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| Discussion |
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In this study we showed that serum HFABP levels after pediatric cardiac surgery were significantly influenced by the age of the patients. It should be emphasized that infants (<24 months of age) displayed significantly greater amounts of serum HFABP than did children (
24 months of age) at each time point analyzed. Interestingly, we observed a negative power-law relationship between age and HFABP release. The validity of this relationship was demonstrated by a highly significant correlation between age and HFABP release in the ln-ln plot. Previously, Taggart and colleagues1 have shown that the accumulation of TnT release shows a power-law relationship to age, as do our results relative to HFABP release. We can say with fair certainty that the younger the age of the patients, the more vulnerable are their myocardia to injury during definitive repair of congenital heart disease.
Generally, myocardial metabolic response to surgical stress seems greater in the younger heart. In addition to HFABP and TnT, Smolenski and coworkers14 reported a much greater release of lactate, phosphate, and purines in coronary sinus effluent in children aged 2 to 10 years undergoing cardiac surgery than in adults. Alcaraz and associates15 showed that newborn patients displayed significantly greater amounts of serum interleukin 10 than did older children in response to cardiac surgery. These findings support the view that the immaturity or the fine sensibility of pediatric myocardium results in much more myocardial metabolic injury and a greater stress response. On the basis of this view, it is reasonable to postulate that surgical stress by ischemic time could promote a more biochemical response in infants than in children.
Ischemic time was also a highly significant explanatory variable for the release of HFABP. In both infants and children, there were positive correlations between ischemic time and HFABP release. We found that the ischemic time was the exponent and amplitude parameter of the power function between age and HFABP release. Interestingly, the effect of ischemic time on HFABP release was greater in infants than in children. This fact implied the presence of an interaction between age and ischemic time. Actually, our general linear model for HFABP release showed that myocardial damage was dependent on not only age and ischemic time but also on their interaction. We demonstrated statistically that the heart was more vulnerable to injury caused by myocardial ischemia in infants than in children.
Postoperative clinical outcomes were related to serum concentrations of HFABP after aortic declamping. In particular, we showed that inotropic support correlated significantly with serum peak HFABP levels in infants and children. In our study infants displayed significantly greater amounts of serum HFABP than did children after cardiac surgery, and the former had clinical outcomes that were not as good as those of children. It is also possible to say that clinical outcomes in pediatric cardiac surgery are dependent on the age of the patient. Recently, definitive repair for patients with congenital heart disease tends to favor the younger patients because of the advances in surgical technique, myocardial preservation, and postoperative care. In our experience with VSD repair, the mean age of the patients was 4.4 ± 0.3 years between 1996 and 1998 versus 3.3 ± 0.2 years between 1999 and 2001. The percentage of patients aged less than 2 years of all patients with VSD repair was 30.4% between 1996 and 1998 versus 46.1% between 1999 and 2001. In this tendency it is important to manage perioperative care for pediatric patients with congenital heart disease, taking into consideration the dependence of the myocardial damage on age and ischemic time.
This study population was carefully selected to evaluate the effects of age and ischemic time on the release of HFABP in pediatric cardiac surgery. Because of this selectivity, the limitation of the study is an absence of patients with repair of congenital heart disease, except for a single VSD. Neonatal patients and patients with cyanosis were not included in the study. In addition, the analysis was limited with respect to the presence of large volume overload and pulmonary hypertension. The severity of VSD is certainly intensified by pulmonary hypertension, in which case patients often need surgical repair in infancy rather than in childhood. Although these factors did not correlate with the baseline of serum HFABP levels before the operation or serum peak HFABP levels after aortic declamping, further studies including the abovementioned patients are intended to better characterize HFABP in pediatric cardiac surgery. Another possible limitation is that postoperative clinical variables can be subjective according to the clinician managing the patient. Clinician bias is, however, unlikely to have been a confounding factor because the postoperative management was strictly in accordance with our unit protocol, and the results were not available to the clinician.
In conclusion, this study expands current knowledge on myocardial injury in pediatric cardiac surgery and demonstrates a pattern of HFABP release in infants and children with dependence on age and ischemic time. Our results indicated that the younger the age of patients, the more vulnerable are their myocardia to injury caused by ischemia during definitive repair of congenital heart disease. Therefore, we should manage perioperative care for pediatric patients with congenital heart disease by taking into consideration the dependence of the myocardial damage on age and ischemic time.
| Acknowledgments |
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| References |
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