Cardiac MRI Study

Cardiac MRI baby brain study

The Cardiac MRI study has been ongoing since 2002. The goal is to understand brain development and risks of brain injury in babies with congenital heart disease. The results so far include:

Newly acquired brain injury is as common BEFORE surgery as after

This is surprising because prior to this finding many people assumed that the period of greatest risk to the baby occurred during surgery when support with heart/lung bypass is needed to accomplish the repair.  Clearly two decades of advances in surgical technique and cardiopulmonary bypass have made surgery safer and more effective!  Now our challenge is to extend brain protection into the periods before and after surgery, as well as during surgery.

Acquired injuries most commonly take the form of small injuries to the developing white matter

This observation was very surprising because white matter injury had previously been thought to only occur in newborns born prematurely.  This led us to ask the question:  ‘Is brain development somehow delayed in newborns with congenital heart disease?’

Brain development is delayed in newborns with congenital heart disease

This has been the most surprising and influential study result to date.  This finding was reported inThe New England Journal of Medicine and led to many newspaper articles and TV coverage.  This finding has since been validated by other investigators.  Brain development begins to slow prenatally in the third trimester before birth.  The delay in brain development is mild (~ equivalent to being born one month premature – e.g. 34-36 weeks instead of 40 weeks gestation).  As with premature newborns, evidence suggests that infants with CHD have potential for recovery of developmental milestones as they grow up, with improvements noted during infancy and childhood as they are followed with repeated testing.

Figure: Normal Fetal Circulation and Changes with Congenital Heart Disease

Course of blood flow in a late gestation fetus with normal heart anatomy (A), d-transposition of the great arteries (B) and hypoplastic left heart syndrome due to aortic atresia (C).  Deoxygenated blood (blue-purple) flows to the placenta through the umbilical artery (UA) where gas exchange takes place.  Blood with higher oxygen content (red) returns through the umbilical vein (UV) and ductus venosus (DV) to the inferior vena cava (IVC).  The more highly saturated blood forms a stream in the IVC, which is preferentially directed across the foramen ovale into the left ventricle in the normal fetus and with d-TGA. Estimated hemoglobin oxygen saturation in percent is shown for each ventricle.  Blood flow to the fetal lungs is limited by elevated pulmonary vascular resistance. In the fetus with d-TGA, the aorta arises from the right ventricle such that the brain receives less oxygenated blood, while the higher saturated blood is directed to the descending aorta through the ductus arteriosus.  In HLHS, reduced or absent left ventricular ejection results in elevated left atrial pressure, limiting or reversing flow at the foramen and resulting in complete mixing of desaturated and well saturated blood in the right atrium and ventricle.  Blood flow the head and neck may occur in a retrograde fashion from the ductus arteriosus across the aortic isthmus.

Currently we hypothesize that delayed brain development may put newborns with CHD at risk of white matter injury around the time of surgery.  ‘White matter’ includes the connection between brain cells (neurons or ‘grey matter’) and the cells that produce ‘myelin’ to support and insulate the neurons.  We are focused on identifying interventions or medications to prevent any brain injury around surgery.  Selecting these interventions would not be possible without the information we have gathered from our study babies to date.

We are finding that children with heart disease repaired during infancy, share many aspects of behavior and learning styles noted at school age in children born prematurely.  Both groups score within the normal range on IQ testing, but are challenged by tasks that require attention, executive function and visual-motor integration.

Our present focus includes fetal MRI to understand how brain development is affected by congenital heart disease before birth.  We are also following infants and children after surgery to watch how they develop into school age and beyond to understand and achieve optimal brain development, or if needed, repair and recovery following newborn heart surgery.