Neuropsychological complications after cardiac surgery in children

Full text

Although the surgical morbidity of infants who must undergo cardiac surgery has declined, follow-up studies have identified major neurodevelopmental abnormalities in as many as 25% of survivors. The prevalence of subtle dysfunctions is likely to be even higher. An important source of morbidity may be operative events, particularly the support techniques used to protect vital organs during cardiac repair, including deep hypothermia with either total circulatory arrest (TCA) or continuous low-flow cardiopulmonary bypass (LFB). Drawing conclusions about the central nervous system (CNS) sequelae of cardiac surgery in children has been impeded, however, by a variety of methodological limitations of many published studies, including small sample sizes, diverse cardiac defects and ages at repair, retrospective study design, comparison of operative techniques used at different time periods, and lack of uniformity in the age at which children are followed up and in the test instruments used.

For more than a decade, our group at the Children's Hospital (Boston) has conducted studies to evaluate the CNS sequelae among infants with congenital heart lesions. This presentation focused primarily on the results to date of our single-center trial of infants with d-TGA who were randomized to undergo the arterial switch operation at less than 3 months of age using either TCA or LFB. The original cohort consisted of 171 infants (42 of whom also had a ventricular septal defect). Neurodevelopmental evaluations were completed on 155 children at 1 year of age and 158 children at 4 years of age. In addition, information was obtained on interim developmental status by means of parent-completed questionnaires when children were 2.5 years of age. Evaluations at age 8 years are ongoing and have been completed for approximately 135 children.

Our findings to date suggest two major conclusions. First, children assigned to TCA tend to have worse neurodevelopmental outcomes than do children assigned to LFB. In the perioperative period, they were at increased risk of clinical seizures; at 1 year of age, they achieved lower scores on a standardized test of motor development (Bayley Scales of Infant Development) and were at higher risk of having abnormalities on neurologic examination; at 2.5 years, they had worse expressive language development; and at 4 years of age they scored lower on tests of gross and fine motor function, and were at increased risk of oromotor apraxia and other abnormalities of speech production. Treatment group comparisons at 8 years of age will not be made until all eligible children have been evaluated.

Our second major conclusion is that the performance of the full cohort (ie children in both treatment groups) is below expected levels in several specific neuropsychological domains, placing them at substantially increased risk of academic failure. Interestingly, on global standardized tests such as IQ, the children's scores tend to be well within the normal range, although shifted slightly toward lower values. They express substantial deficits, however, in the following areas: visual-spatial/visual-motor skills, working memory, hypothesis generation and testing, vigilance and sustained attention, motor function, and higher-order language skills (verbal fluency, generation of connected discourse). We speculate that the neurodevelopmental vulnerabilities of children who undergo cardiac surgery in infancy are most prominent on tasks that call upon so-called 'executive functions'. Such tasks require that information be held, organized, manipulated, and integrated, and that strategies be designed, implemented, and modified in service of a goal.

One possibility is that a long period of cardiopulmonary bypass, regardless of whether or not TCA is involved, is detrimental to CNS development. Data from a small non-randomized study that are consistent with this hypothesis is presented. Children with atrial septal defects (ASDs) that were closed surgically scored significantly lower than children with ASDs that were closed by means of a catheter-delivered device, particularly in terms of visual-spatial skills. A randomized trial comparing the neuropsychological sequelae of surgical and transcatheter closure of ASDs is planned.