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J Thorac Cardiovasc Surg 2007;133:880-887
© 2007 The American Association for Thoracic Surgery
Surgery for Congenital Heart Disease |
a Division of Pediatric Cardiology, University of Michigan, Ann Arbor, Mich
b Section of Cardiac Surgery, University of Michigan, Ann Arbor, Mich
c Division of Pediatric Psychology, University of Michigan, Ann Arbor, Mich
d School of Public Health, Department of Biostatistics, University of Michigan, Ann Arbor, Mich.
Read at the Eighty-sixth Annual Meeting of The American Association for Thoracic Surgery, Philadelphia, Pa, April 29-May 3, 2006.
Received for publication June 20, 2006; revisions received November 8, 2006; accepted for publication November 20, 2006. * Address for reprints: Caren S. Goldberg, MD, C.S. Mott Childrens Hospital, L1221 Womens Box 0204, 1500 East Medical Center Dr, Ann Arbor, MI 48109-0204. (Email: cgoldber{at}umich.edu).
| Abstract |
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Methods: A randomized trial was performed in infants with single ventricle anatomy undergoing the Norwood operation. Participants were randomized to deep hypothermic circulatory arrest or regional cerebral perfusion. Neurodevelopment was measured before second-stage surgery and at 1 year by the Bayley Scales of Infant Development-II, Psychomotor Development Index and Mental Development Index. Intent-to-treat analysis was performed.
Results: Seventy-seven patients were enrolled. Survival to hospital discharge was 88% and to 1-year follow-up, 75%, without a significant difference between groups. For the entire cohort, the mean (SD) psychomotor development index score was 77 (20) and the mean mental development index score was 92 (21), with psychomotor development index lower than mental development index both before second-stage surgery (P < .0001) and at 1 year (P < .0001). There were no statistical differences in mental development or psychomotor development scores between the groups at presecond-stage operation or 1-year follow-up, although the point estimates were consistently lower for the regional cerebral perfusion group.
Conclusion: Infant development is delayed after the Norwood operation. Pilot data do not suggest that regional cerebral perfusion improves infant development. Further study with a multicenter clinical trial is imperative to address this important question.
| Introduction |
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For infants undergoing the Norwood operation, DHCA has been the standard intraoperative perfusion technique used during aortic arch reconstruction. Circulatory arrest allows for a bloodless field and diminishes the risk of embolism. Deep hypothermia at nasopharyngeal temperatures of 18°C is used to lower the metabolic needs of the brain. However, despite this technique, the use of circulatory arrest has been associated with neurologic and developmental abnormalities.10-12
In an effort to protect the brain, regional cerebral perfusion (RCP) has been adopted by some centers as an alternative to DHCA. RCP is performed by cooling the patient as with DHCA. Through a polytetrafluoroethylene graft anastomosed to the innominate artery, blood can then be directed to the cerebral circulation. Flow rates of 20 mL · kg1 · min1 are generally used. RCP has been demonstrated to be technically feasible,13-15
but no randomized prospective study has compared functional neurodevelopmental outcomes for children undergoing the Norwood operation with the use of RCP with those after the Norwood operation with DHCA. The purpose of this study was therefore to determine whether the use of RCP rather than DHCA during aortic arch reconstruction in infants with HLHS and other functional single ventricle malformations is associated with improved neurodevelopment without increasing morbidity or mortality.
| Materials and Methods |
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Stratification and Randomization
Study participants were stratified by surgeon and by risk group. (Three congenital heart surgeons participated in this study). Patients with pulmonary venous obstruction, patients less then 36 weeks gestation and/or less than 2.5 kg, and patients with clinical shock or clinical seizures preoperatively were randomized within the higher risk strata. Within strata, randomization used block randomization with random block size.
Of note, although it was obviously not possible to blind the surgeon and the surgical team, the family and the other research team members, including the pediatric psychologists, were masked to the assigned technique.
Surgical Technique
Standard technique at the University of Michigan Congenital Heart Center at the time of this study was to perform a modified Norwood operation with a modified BlalockTaussig shunt as previously described by our group.16
DHCA involved active cooling during cardiopulmonary bypass to less than 18°C by nasopharyngeal temperature probe over a period of greater than 20 minutes. Topical cooling was also used by applying ice bags to the patients head.
All patients were managed throughout bypass with alpha-stat monitoring and underwent 10 minutes of modified ultrafiltration at the conclusion of bypass. Hematocrit was maintained at a target of 30% during bypass, with higher values at separation from bypass to achieve a postmodified ultrafiltration value in the mid to high 40s.
For participants randomized to RCP, at the time of the aortic arch reconstruction, the patients body and head were cooled to 18°C, as with DHCA. The proximal end of the BlalockTaussig shunt was anastomosed at the distal innominate artery. The arterial bypass cannula was placed into the BlalockTaussig shunt and RCP initiated at 5 mL · kg1 · min1, gradually increasing to 20 mL · kg1 · min1 (Figure 1). Near-infrared spectroscopy (INVOS 5100A; Somanetics, Troy, Mich) was used to measure cerebral oxygenation. At the conclusion of the arch reconstruction, the patient was returned to cardiopulmonary bypass and rewarmed, as with the standard technique.
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Outcome Measurements
Measures of safety
Safety information was collected in multiple ways. Each day while the patient was in the hospital, a member of the study team rounded on that patient to collect any information relating to morbidities. In addition, each family was contacted by telephone before the second-stage operation and again at 10 months of age. During all hospitalizations, including at the time of the second-stage operation, the patients were tracked as well. Echocardiograms and catheterizations are performed routinely as part of the clinical practice at the University of Michigan Congenital Heart Center before the second-stage procedure. The echocardiographic data were reviewed at hospital discharge after the Norwood operation and before the second stage to assess diaphragm function. Catheterization data before the second stage were used to determine the presence of aortic recoarctation. Need for cardiopulmonary resuscitation, need for extracorporeal membrane oxygenation, cardiac transplantation, vocal cord paresis, and/or diaphragm paresis before the second-stage operation were noted.
All mortalities were categorized as follows: (1) death before discharge after the Norwood operation, (2) interstage death before the second-stage procedure, or (3) death after the second-stage procedure.
Measures of neurologic and developmental outcome
Infant development was measured before the second-stage operation and again at 1 year of age with the Bayley Scales of Infant Development II (BSID-II). The BSID-II was administered by one of three pediatric psychologists. (E.M., E.S., S.T.) The pediatric psychologists were masked to the perfusion technique assignment. The BSID-II includes two scales or indices, the Mental Development Index (MDI) and the Psychomotor Development Index (PDI). The MDI is used primarily to assess memory, habituation, problem solving, early receptive and expressive language, social skills, and early number concepts. The PDI measures primarily gross and fine motor functioning. The mean score for the general population for each index is 100 points with a standard deviation of 15 points.17
Socioeconomic status was measured using the Hollingshead Four Factor Index of Social Status for all participants who returned for developmental assessment before the second stage and/or at 1 year.
Statistical Analysis
The primary method of analysis was based on intention-to-treat methods to compare those participants randomly assigned to RCP with participants randomly assigned to DHCA.
2 or Fisher exact analysis was used to compare the differences in dichotomous variables between treatment groups. All normally distributed variables, such as scores on the PDI and MDI, were compared between treatment groups by the Student t test. Paired t test was used to compare two continuous variables between two time points or on two indices, the MDI before second-stage operation to the MDI at 1 year, or the MDI to PDI. Regression modeling was performed to adjust for impact of demographic variables on the BSID II scores, such as fetal diagnosis and socioeconomic status.
| Results |
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Preoperative demographics showed no statistical difference in sex, gestational age, birth weight, or cardiac anatomy. Socioeconomic status measured with the Hollingshead Four Factor Index was not different between groups for the participants who returned for developmental follow-up. All participants had a single ventricle and required a Norwood operation. The majority of the participants had HLHS (67/77); 32 (84%) of 38 in the DHCA treatment group and 35 (90%) of 39 in the RCP treatment group. Overall, the diagnosis was made by prenatal ultrasound in 77% of the participants. A fetal diagnosis was made in 66% of patients randomly assigned to DHCA and 85% of those randomly assigned to RCP (P = .06). Thirty percent of the study cohort were within the high-risk strata, 31% of the RCP group and 29% of the DHCA group (P = .86) (Table 1).
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Survival
Overall hospital survival for the study cohort was 88%. There were 3 predischarge deaths in the RCP subgroup (8%) and 6 predischarge deaths in the DHCA subgroup (16%) (P = .31). After discharge, but before the second-stage operation, 8 patients died from the RCP group (8/36, 22%) and 2 from the DHCA subgroup (2/32, 6%), P = .08. At 1 year, survival was 75% for the entire cohort, 69% for the RCP group, and 79% for the DHCA group (P = .33) (Figure 2).
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Before the second-stage operation, the mean (SD) MDI and PDI scores for the entire cohort were 87.4 (14) and 71.5 (15), respectively. There was a tendency toward higher scores for the entire study group at 1 year, 91.8 (21) and 77.1 (21) for the MDI (P = .21) and PDI (P = .07), respectively. The MDI scores were significantly higher than the PDI scores both before the second-stage (P < .0001) operation and at 1 year (P < .0001) (Figure 3).
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Models including fetal diagnosis and socioeconomic status were created to determine whether adjustment for these factors would provide a different understanding of the impact of RCP on MDI and PDI scores at the presecond-stage and 1-year evaluations. The magnitude of the differences between groups was unchanged.
| Discussion |
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Myung and colleagues18
compared the impact of RCP to DHCA on neurologic function in a fetal pig model. Fetal pigs were randomized to a 90-minute period of either RCP or DHCA. The authors found that postoperative neurobehavioral scores were more likely to be abnormal in the DHCA group than in the RCP group and that the RCP subgroup had less evidence of apoptosis on autopsy. However, there have been no data demonstrating improved outcomes with the use of RCP in infants.
Dent and colleagues19
from the University of Cincinnati have performed head magnetic resonance imaging studies of children with HLHS preoperatively and after the Norwood operation to determine whether RCP protects against hypoxic-ischemic injury evident structurally. Head magnetic resonance imaging was performed before the Norwood operation and during the early postoperative period in 15 newborn infants, all of whom had aortic arch reconstruction performed with the use of RCP. The investigators found that 73% of study participants had worsened or new evidence of cerebral ischemia after the Norwood operation despite the use of RCP during aortic arch reconstruction.19
There was no direct control group in this study and the RCP time averaged 83 minutes, significantly longer than the 41 minutes of DHCA time that Wypij and colleagues20
found to be relatively safe.
The primary aim of this study was to investigate the hypothesis that RCP would improve neurodevelopmental outcomes without significantly affecting morbidity and mortality. We have studied too few patients thus far to draw definitive conclusions regarding the impact of RCP rather than DHCA on neurodevelopmental outcome on survival for children undergoing Norwood palliation. However, our data do not support the hypothesis that RCP improves neurodevelopmental outcomes. Since its initial description, RCP has been adopted by surgeons at some congenital heart centers with the belief that cerebral perfusion will provide better protection of the brain than DHCA.
Although we measured no statistical difference in morbidity and mortality outcomes between the two treatment groups, we could not demonstrate any beneficial effect of RCP on neurodevelopment.
This study was stratified for a composite high-risk group and for surgeon. Fetal diagnosis was not stratified and was somewhat different between the two groups. Mahle and colleagues21
have found that fetal diagnosis is associated with lower rates of neurologic events in patients with HLHS. In this study there was a higher rate of fetal diagnosis in the RCP subgroup. This may be expected to bias the RCP group to improved neurodevelopment. Adjustment for fetal diagnosis was therefore performed with regression modeling, but although the tendency was for improved scores in patients with a fetal diagnosis, the difference between the RCP and DHCA treatment groups was not found to be statistically different.
There are a number of limitations to our study. Whereas the exposure to DHCA or RCP occurs during the newborn period at the Norwood operation, the primary outcome measure was performed at 1 year of age. Thus, all participants underwent a second-stage operation, before the 1-year BSID-II evaluation. It was for this reason that the BSID-II was administered before the second stage as well. It is interesting to note that many of the participants had higher scores on the BSID-II at 1 year than at the presecond-stage evaluation, suggesting that the second stage is not typically associated with new neurologic insults. By the 1-year follow-up, more time generally has passed since the last hospitalization and thus the patient has potentially had more time to progress developmentally. Longer-term follow-up will be important to discern if developmental catch-up will be more likely to occur in either the RCP or DHCA treatment groups.
This study is also limited by the relatively small sample size. When the findings of a planned early look at the data were analyzed, the estimated required sample size to address the study hypothesis was substantially increased and it was determined that a multicenter study would be more appropriate to address this question efficiently. However, although the sample size is relatively small, there was a consistent trend for the RCP treatment group to have lower developmental scores.
As with all trials comparing a new technique with a standard technique, this study is subject to a learning curve bias. Although RCP was used at our center selectively for approximately 1 year before the initiation of this trial, we recognize that this is still limited experience compared with the experience with DHCA at our center. To further investigate for evidence of a developing learning curve, we have analyzed the total bypass time for patients randomized to RCP over time and find that there is no change in bypass time over the study period (data not shown).
Finally, the method of RCP used in this study was based on the published experience at the time this trial was developed. Since that time, the method of RCP delivery has evolved at some centers. We do recognize that this study has only tested a single method of providing RCP and that there may be variations that would lead to different results.
The data from this trial do demonstrate that mental and psychomotor development as measured by the BSID-II is delayed in infants after the Norwood operation. These data also demonstrate significantly lower scores on the PDI than on the MDI, as previously shown.22,23
The reason for this result remains unclear, although the finding is consistently reproducible and likely represents a predisposition for particular areas of central nervous system insult.
| Conclusions |
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| Footnotes |
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* Hollingshead AB. Four-factor index of social status. Unpublished manuscript, Yale University, Department of Sociology, New Haven [CT]. 1975. ![]()
| References |
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