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J Thorac Cardiovasc Surg 2008;135:546-551
© 2008 The American Association for Thoracic Surgery
Surgery for Congenital Heart Disease |
a Department of Pediatrics, Division of Pediatric Cardiology, Duke University Medical Center, Durham, NC
b Duke Clinical Research Institute, Durham, NC
c Congenital Heart Institute of Florida (CHIF), University of South Florida, All Children's Hospital
d Pediatric Cardiovascular Surgery, St Christopher's Hospital for Children, Philadelphia, Pa
e Division of Cardiothoracic Surgery, Oregon Health and Science University, Portland, Ore
f Division of Cardiovascular Surgery, Duke University Medical Center, Durham, NC
Received for publication May 4, 2007; revisions received August 30, 2007; accepted for publication September 14, 2007. * Address for reprints: James Jaggers, MD, Box 3474, DUMC, Durham, NC 27710. (Email: james.jaggers{at}duke.edu).
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Abstract |
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Methods: We analyzed mortality in 3022 infants ages 0 to 90 days weighing 1 to 2.5 kg (n = 517) and greater than 2.5 to 4 kg (n = 2505) who underwent cardiac surgery from 2002 through 2004 at 32 participating centers. Patients were grouped according to the primary procedure performed and analyzed according to their weight at the time of surgical intervention. Patients were also analyzed according to Risk Adjustment for Congenital Heart Surgery-1 and Aristotle Basic Complexity scores.
Results: Compared with infants weighing 2.5 to 4 kg, infants weighing less than 2.5 kg had a significantly higher mortality for the following operations: repair of coarctation of the aorta, total anomalous pulmonary venous connection repair, arterial switch procedure, systemic to pulmonary artery shunt, and the Norwood procedure. Lower infant weight remained strongly associated with mortality risk after stratifying the population by Risk Adjustment for Congenital Heart Surgery-1 levels 2 through 6 and Aristotle Basic Complexity levels 2 through 4.
Conclusions: Low weight at the time of surgical intervention is associated with increased mortality in patients undergoing several types of cardiovascular procedures. These data do not allow assessment of specific risks or benefits of any particular treatment strategy. However, they do support the need for prospective analysis of specific treatment strategies for these high-risk patients.
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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of improved survival in this difficult group, the significance of weight as a risk factor for mortality remains unclear. Studies that report surgical outcomes in low-weight infants have been limited to single institutions with limited numbers of patients. These studies typically examine weight as an independent risk factor without including a comparison group of normal-weight infants. In this study we used of the Society of Thoracic Surgeons (STS) Congenital Heart Surgery Database to evaluate the hypothesis that low-weight infants have increased operative mortality when compared with children of normal weight with similar defects. |
Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Study Population
Using the Congenital Heart Surgery Database, we analyzed mortality in infants up to 90 days of age who underwent cardiovascular surgery between January 2002 and December 2004. Data from participating centers with greater than 10% missing data for discharge mortality or postoperative length of stay were excluded. This left 18,253 patients from 32 centers with complete diagnosis and procedure data for the first cardiovascular operation during their index admission. From these, we excluded patients with age greater than 90 days (n = 11,681), weight less than 1 kg or greater than 4 kg (n = 1743), missing primary procedure data (n = 1760), or missing discharge mortality status (n = 47). The remaining patient population for analysis was 3022.
Patients were further grouped according to primary cardiovascular diagnosis and procedures (
Table 1). The primary procedure was defined as the procedure with the highest Aristotle Basic Complexity (ABC) score. If there were multiple procedures with equal complexity scores listed, the procedure designated as the primary procedure on the data collection form was used. Because the Risk Adjustment for Congenital Heart Surgery 1 (RACHS-1) score was not a required field in the database in 2004, this score was assigned by the investigators.6
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Table 2). Age was described as a median and interquartile range (IQR; defined as 25th to 75th percentile), and sex and ethnicity were described as frequencies. The distribution of age was compared by using a stratum-adjusted Wilcoxon rank-sum test, although sex and ethnicity were compared by using stratum-adjusted 
2 tests. Mortality rates were calculated by weight category for all combinations of diagnoses and procedures with a sample size of at least 15. Relative risks and approximate 95% confidence intervals were constructed to compare mortality risk between groups. The hypothesis of no association between weight group and mortality was assessed by using a 2 test. Identical analyses were performed by using stratification with the RACHS-1 system and ABC scores. SAS Statistical software (Cary, NC) was used for analysis.
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Results |
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Patients undergoing repair of total anomalous pulmonary venous connection (29.2% vs 9.9%), coarctation of the aorta repair (7.1% vs 2.7%), arterial switch procedure for transposition of the great arteries (TGA; 11.8% vs 2.6%), systemic to pulmonary artery shunt placement for pulmonary atresia with ventricular septal defect (PA/VSD; 14.8% vs 2.8%), and systemic to pulmonary artery shunt (24.4% vs 6.2%) and the Norwood procedure (30% vs 21.1%) for other single-ventricle diagnoses demonstrated increased risk of mortality for those infants weighing 2.5 kg or more (
Table 3). Patients with PA/VSD and TGA with intact ventricular septum weighing less than 2.5 kg had the highest risk ratios. For all other diagnosis–procedure categories analyzed, there was no statistically significant difference in mortality for those infants weighing less than 2.5 kg. The inverse association between infant weight and outcomes persisted after we stratified the population using the RACHS-1 and ABC scoring systems. Weight less than 2.5 kg was consistently associated with 1.5 to 3.0 times higher mortality risk in all levels of RACHS-1 and ABC scoring, with the exception of ABC level 1 (
Table 4).
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The New England Regional Infant Cardiac Program,7 as well as Kramer and colleagues,8 demonstrated infants with congenital heart disease (CHD) were more likely to be small for gestational age or of low birth weight when compared with normal-weight infants. The incidence of being small for gestational age is 15% and that of low birth weight is 8.6% in infants with CHD compared with 4.5% and 6%, respectively, in the healthy population. After adjusting for other potential confounding factors, the New England Regional Infant Cardiac Program concluded that there was a direct relationship between mortality and birth weight of less than 2 kg. They assigned a prognostic value from 1 (best) to 4 (worst) in an attempt to risk stratify the various diagnoses and then calculated crude 1-year mortality rates according to these diagnostic severity groups, analyzing infants with a birth weight of less than 2 kg as a group of interest. Calculated mortality rates in the less than 2-kg group ranged from 70% to 100% compared with 27% to 86% for the same diagnostic severity groups.7 Since that time, there have been multiple attempts to further examine the relationship between birth weight and mortality for infants with CHD. However, these studies have been limited to single institutions with limited numbers of patients or have examined weight as an independent risk factor without careful case-control procedures.1-5 Analysis of the STS Congenital Heart Database affords the opportunity to further examine these clinical questions with sample sizes larger than has been previously possible.
The combination of low birth weight, prematurity, and CHD makes the management of these patients challenging. It is unclear whether a strategy of medical management and deferment of surgical intervention is beneficial over more expeditious intervention. Preoperative management of infants with ductal-dependent pulmonary or systemic blood flow requires intravenous prostaglandin E1 and carries the associated risks of infection, apnea, vasodilation, seizures, and necrotizing enterocolitis. Furthermore, the altered physiologic state of unrepaired CHD leads to increased energy expenditure, failure to thrive, and further difficulty in weight gain. The long-term effects of abnormal cardiovascular physiology, including volume overload and hypoxemia, are difficult to quantify.9 Conventional surgical wisdom might suggest that delaying surgical intervention until a higher weight is attained might decrease the risk of bypass-related morbidities, including intracranial hemorrhage, renal dysfunction, and coagulopathy. At the present time, however, there are insufficient data to predict the risk/benefit ratio of deferring surgical intervention until some arbitrary weight gain. In a small series of patients, Chang and colleagues10 demonstrated not only that this management strategy was ineffective but that in their experience it was associated with increased mortality. In another single-institution study by Reddy and associates,4 an analysis of approximately 100 infants weighing less than 2.5 kg led to the inference that delaying repair conferred higher preoperative morbidity without any associated benefit. Unfortunately, given the limitations of the present study, we are unable to adequately address and answer the question of whether a strategy of deferring surgical intervention for weight gain is beneficial. Further prospective investigation to determine how the risk of delaying surgical intervention on these patients compares with the risk of repair is still necessary.
In this investigation we have demonstrated an increased mortality associated with low-weight infants undergoing specific cardiovascular procedures for coarctation of the aorta, total anomalous pulmonary venous connection, TGA, PA/VSD, and the presence of a single ventricle. Roussin and coworkers11 demonstrated similar findings, with operative mortality of 16% in patients weighing less than 2000 g with TGA undergoing the arterial switch operation. Overall operative mortality in patients with hypoplastic left heart syndrome is approximately 20%, whereas some investigations have shown a mortality rate in low-weight patients to be as high as 45%.12 In the present investigation the mortality rate for low-weight patients undergoing a Norwood procedure was 30%. Findings in our study would suggest that there is a subset of low-weight patients with increased risk of operative mortality. At the same time, the data suggest that some cardiovascular procedures can be performed without substantial difference in mortality.
Both the ABC and RACHS-1 scoring systems were designed to facilitate meaningful comparisons of outcomes in children undergoing surgical intervention for CHD.6,13 Analysis of mortality based on either of these scoring systems and stratified by weight has not previously been performed. Mortality rates for nearly all infants of weight less than 2.5 kg is increased throughout the various levels of complexity, as stratified by using both of these tools. The high absolute mortality rates for both weight categories in ABC level 1 were not statistically significant and lack power for meaningful interpretation of these data because of the small sample sizes.
Further stratification within the diagnosis–procedure categories, as well as the RACHS-1 and ABC scores, by age at the time of surgical intervention was not feasible because of the small sample size of low-weight patients. For low-weight patients undergoing a Norwood procedure, there was a trend toward increased mortality for those who were taken to surgical intervention within the first week of life. However, within this age stratification, overall sample sizes were too small to provide meaningful data.
The limitations of the study are primarily related to the observational and voluntary nature of the database, which is still in evolution. The STS databases are observational and were established principally for the purpose of health care quality improvement. We investigated the feasibility of adjusting for potential confounding variables, such as preoperative risk factors and associated noncardiac anomalies. Unfortunately, attempts at a multivariate analysis to examine the interaction for these potential confounders were unsuccessful because of a high percentage of missing data. Also, it was not possible to determine whether some patients had been operated on after a period of nonoperative management or if there was any survival benefit to this approach. Because the STS Congenital Database is a procedural database, patients who did not survive to a surgical procedure are not included. Many of the previous reports are based on birth weight; however, at the time of the data harvest used in our analysis, birth weight and gestational age were not components of the data set, thereby making parallel comparisons difficult. Additionally, the inability to stratify by age within both diagnosis–procedure and risk scoring made analysis of the effect of delayed intervention with medical management infeasible. Therefore this study cannot make any conclusions or recommendations regarding any particular management strategy regarding low-birth-weight infants with CHD.
Low weight at the time of surgical intervention is associated with increased mortality for repair of coarctation of the aorta, total anomalous pulmonary venous connection, arterial switch procedure for TGA, systemic to pulmonary artery shunt placement for PA/VSD, and systemic to pulmonary artery shunt and the Norwood procedure for single-ventricle palliation. Notwithstanding several important limitations, this study is nonetheless one of the largest to date to examine the relationship between low birth weight and the risk of operative mortality in congenital heart surgery. It highlights the need for prospective analyses of specific treatment strategies as a means of improving outcomes for these high-risk patients.
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Footnotes |
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References |
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