Brain Injury in Congenital Heart Disease

Abstract

Mortality rates for virtually all forms of congenital heart disease have declined with dramatic advances in medical, transcatheter, and surgical therapies. 1 As the population of congenital heart disease survivors has burgeoned, however, their long-term functional morbidities have become the focus of increasing concern. Among the foremost morbidities are adverse neurodevelopmental outcomes, with their profound personal and societal costs. 2 Article p 280 Neurological and developmental outcomes of congenital heart patients are influenced by many factors, both innate and acquired, with cumulative effects. Genetic syndromes such as trisomy 21 or 22q11 microdeletion3–5 may affect both the heart and the brain. Cerebral dysgenesis is reported to occur in 10% to 29% of children with congenital heart disease in autopsy series, with the incidence varying by lesion 6–8 ; findings may range from microdysgenesis to gross abnormalities such as agenesis of the corpus callosum, incomplete operculization, and microcephaly. During fetal life, congenital heart lesions may be associated with changes in cerebrovascular blood flow distribution and resistance. For example, fetuses with hypoplastic left heart syndrome, whose cerebral perfusion is supplied retrograde through the ductus arteriosus, have lower cerebrovascular resistance than normal. 9 Postnatal neurodevelopmental risk factors may derive from the sequelae of congenital heart disease itself—eg, chronic severe hypoxemia, failure to thrive, arrhythmias with cardiac arrest or hypotension—or from the procedures used for cardiac correction or palliation.10 Neuropathological studies have revealed both focal and diffuse infarction. Focal infarction has been ascribed to thromboembolic events, whereas a diffuse pattern of cerebral injury has been attributed to hypotension and hypoperfusion.11 More recent neuropathological data in infants who underwent reparative or palliative cardiac surgery reveals that not only are these children at increased risk of gray matter injury but also nascent white matter is at risk. For instance, in a series of infants who died after cardiac surgery, cerebral white matter damage (periventricular leukomalacia or diffuse white matter gliosis) was the most significant lesion in terms of severity and incidence. 12 Similarly, MRI performed in patients with congenital heart disease after surgery has revealed findings consistent with both gray matter injury and widely distributed white matter injury. 13 Risk factors for brain injury during infant heart surgery have been particularly well studied. Cardiopulmonary bypass carries the risks of particulate and gaseous microemboli, macroemboli, and hypoperfusion with accompanying diffuse ischemia/reperfusion injury. In neonates and infants undergoing surgery with use of hypothermic bypass techniques, the risk of brain injury may be influenced by perfusion variables such as the duration of total circulation arrest,14 the depth of hypothermia, 15 the rate and duration of core cooling, 16 pH management during core cooling (alpha-stat versus pH stat), 17,18 and the level of hemodilution. 19 Disruption of cerebral vasoregulation in the early postoperative period renders the brain more vulnerable to hemodynamic instability. 20–22 After infant heart surgery, longer length of stay in the intensive care unit or hospital is associated with worse neurodevelopmental outcome on mid-term follow-up. 23,24