Cerebral development may be impaired in fetuses with congenital cardiovascular malformations, particularly hypoplastic left heart syndrome (HLHS) and aortopulmonary transposition (APT). The decreased cerebral arterial pusatility index observed in some of these fetuses led to the belief that cerebral vascular resistance was reduced as a result of arterial hypoxemia and cerebral hypoxia is thought to be responsible for impaired cerebral growth. However, other hemodynamic factors could affect pulsatility index. I propose that cerebral blood flow is reduced in fetuses with HLHS and that reduced glucose, rather than oxygen, delivery interferes with cerebral development. This is based on the fact that most of these fetuses do not have lactate accumulation in the brain. In fetuses with APT, umbilical venous blood, containing oxygen and glucose derived across the placenta, is distributed to the lungs and lower body; venous blood, with low oxygen and glucose content, is delivered to the ascending aorta and brain. Oxygen and glucose delivery may further be reduced by decreased cerebral blood flow resulting from run-off of aortic blood through the ductus arteriosus to the pulmonary circulation during diastole. In APT fetuses, lack of lactate in the brain also supports my proposal that glucose deficiency interferes with cerebral development.
Increased frequency of neurodevelopmental disabilities has been noted in children born with congenital cardiovascular malformations. It had been attributed to cerebral damage resulting from cardiac failure or hypoxemia during the neonatal period, or following complicated surgical procedures (1-3). Recently, it has been recognized that abnormalities in cerebral development may occur before birth in association with congenital cardiovascular malformations.Unfortunately, most studies have grouped a variety of malformations and compared the observations with those in normal fetuses (4-6). However, it did appear that the most significant abnormalities were noted in fetuses with aortopulmonary transposition (APT) and hypoplastic left heart syndrome (HLHS). Head size at birth was noted to be reduced in infants with APT and particularly in those with HLHS (7).Hinton et al. (8) noted a significant reduction of head growth in fetuses with HLHS during the latter half of gestation; also, in 11 fetuses aborted electively, histopathology revealed diffuse cerebral white matter injury. Quantitative magnetic resonance imaging at 25-37 wk gestation showed a decrease in brain volume in fetuses with various congenital cardiovascular malformations compared with normal fetuses. These differences were most prominent in those with HLHS (5) This evidence of prenatal disturbance in cerebral development has raised questions regarding possible mechanisms. Genetic disturbances with which the cardiovascular malformations are associated could be responsible; this requires further study. Recently, there has been considerable interest in the possibility that altered circulatory dynamics could result in cerebral injury....