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Ann Thorac Surg 2000;70:581
© 2000 The Society of Thoracic Surgeons

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Invited commentary

Invited commentary

^a Department of Neurology, Children’s Hospital, CA–503, Harvard Medical School, 300 Longwood Ave, Boston, MA 02115, USA,

e-mail: bellinger{at}al.tch.harvard.edu

Invited commentary

The results of this study by Dr Sharma and colleagues raise several important points regarding the potential neurological impacts of interventions used to repair congenital heart defects in children. First, they add to the substantial evidence that subtle neurological and cognitive dysfunctions may be evident even among children in whom cardiac repair is completely successful from a strictly medical standpoint.

Second, the results suggest that supporting vital organs using total circulatory arrest did not confer any additional risk beyond that associated with experiencing cardiopulmonary bypass (at least for arrest periods that ranged up to 69 minutes and averaged 27 minutes). This conclusion is based on the finding that neurologic status and global cognitive function (an IQ-like score) were equivalent among children for whom the method of vital organ support included total circulatory arrest and among children for whom the support method was low-flow cardiopulmonary bypass. This conclusion must be qualified, however, in light of recent evidence that total circulatory arrest is associated with worse outcomes in specific domains of child development, including gross and fine motor skills and oral-motor skills including speech production [1]. In the latter study, as in the study of Dr. Sharma and colleagues, treatment group differences were not apparent on IQ testing, although in both groups scores were below the population mean, a pattern implicating cardiopulmonary bypass as a critical factor.

Third, the results suggest that significant gaps remain in our understanding of the critical determinants of postoperative neurologic outcomes in children who undergo surgical repair of a congenital heart defect. The most serious neurologic outcomes were observed in two infants for whom surgery and postoperative course appeared to be completely routine. Some of the difficulty in identifying the most important predictors of outcome stems from the large number of factors that may be contributory and that sometimes vary widely across studies. Dr Sharma and colleagues controlled several of the most important factors by applying a relatively standard protocol to both groups of patients, including the strategies used to manage acid-base balance and hematocrit. In addition, all patients were operated on by the same surgical and anesthetic team over a relatively brief period of time (two years), minimizing the possibility of outcome variability attributable to surgical practices or to changes in practices over time. As always, however, the choice of a study design entails important tradeoffs. The patient accrual strategy employed by Dr Sharma and colleagues has two disadvantages. First, the diversity of lesions represented in the study cohort resulted in limited numbers of patients in some of the diagnosis groups. If support method is associated with outcome only among patients with particular lesions, combining patients with heterogeneous lesions will reduce the likelihood of detecting treatment group differences. Second, lesion type was confounded with support method, in some cases completely. For example, all patients with TGA were repaired with some period of total circulatory arrest, whereas no patients with CAVC underwent total circulatory arrest. If, perhaps for genetic reasons, lesion type is associated with neurologic outcome independent of support method, this confounding of lesion with support method in the study sample would distort an estimate of the impact of support method on neurologic outcome. An alternative approach to comparing the neurologic impacts of total circulatory arrest versus low-flow bypass would be to select a single lesion (eg, TGA) that can be repaired with equal facility by either method and employ random assignment to method. One of the trade-offs involved in the choice of this design, however, is the possible reduced generalizability of the findings to other lesions.

Doctor Sharma and colleagues are to be congratulated for getting us a little farther in the quest to understand some of these complex issues.

References

1. Bellinger D.C., Wypij D., Kuban K.C.K., et al. Developmental and neurological status of children at 4 years of age after heart surgery with hypothermic circulatory arrest or low-flow cardiopulmonary bypass. Circulation 1999;100:526-532.[Abstract/Free Full Text]

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