FROM THE JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY
Using a newer form of MRI to investigate oxygen levels in newborns with congenital heart disease, researchers in Canada reported that these patients may have impaired brain growth and development in the first weeks of life because of significantly lower cerebral oxygen delivery levels.
These findings suggest that oxygen delivery may impact brain growth, particularly in newborns with single-ventricle physiology, reported Jessie Mei Lim, BSc, of the University of Toronto, and her colleagues from McGill University, Montreal, and the Hospital for Sick Children, Toronto. The findings were published in the October issue of the Journal of Thoracic and Cardiovascular Surgery ( 2016;152:1095-103 ). Ms. Lim and her colleagues used cine phase-contrast (PC) MRI to measure cerebral blood flow in newborns with congenital heard disease (CHD). Previous studies used optical measures of tissue oxygenation and MRI arterial spin labeling to suggests that newborns with severe CHD have impaired CBF and cerebral oxygen delivery (CDO2) and CBF.
This single-center study involved 63 newborns from June 2013 to April 2015 at the Hospital for Sick Children. These subjects received an MRI of the head before surgery at an average of age 7.5 days. The scans were done without sedation or contrast while the infants were asleep. The study compared 31 age-matched controls with 32 subjects with various forms of CHD – 12 were managed surgically along a single-ventricle pathway (SVP), 4 had coarctation of the aorta, 13 had transposition of the great arteries (TGA), and 3 had other forms of CHD.
The researchers validated their method by reporting similarities between flows in the basilar and vertebral arteries in 14 controls, “suggesting good consistency and accuracy of our method for measuring CBF,” Ms. Lim and her coauthors noted. A comparison of CBF measured with an unpaired Student t test revealed no significant differences between the CHD group and controls. The average net CBF in CHD patients was 103.5 mL/min vs. 119.7 mL/min in controls.
However, when evaluating CDO2 using a Student t test, the researchers found significantly lower levels in the CHD group – an average of 1,1881 mLO2/min. vs. 2,712 mL O2/min in controls (P less than .0001). And when the researchers indexed CDO2 to brain volume yielding indexed oxygen delivery, the difference between the two groups was still significant: an average of 523.1 mL O2/min-1 .100 g-1 in the CHD group and 685.6 mL O2/min-1.100 g-1 in controls (P = .0006).
Among the CHD group, those with SVP and TGA had significantly lower CDO2 than that of controls. Brain volumes were also lower in those with CHD (mean of 338.5 mL vs. 377.7 mL in controls, P = .002).
The MRI findings were telling in the study population, Ms. Lim and her coauthors said. Five subjects in the CHD group had a combination of diffuse excessive high-signal intensity (DEHSI) and white-matter injury (WMI), 10 had an isolated finding of DEHSI, two had WMI alone and five others had other minor brain abnormalities. But the control group had no abnormal findings on conventional brain MRI.
The researchers acknowledged that, while the impact of reduced cerebral oxygen delivery is unknown, “theoretical reasons for thinking it might adversely impact ongoing brain growth and development during this period of rapid brain growth are considered.”
Cardiovascular surgeons should consider these findings when deciding on when to operate on newborns with CHD, the researchers said. “Further support for the concept that such a mechanism could lead to irreversible deficits in brain growth and development might result in attempts to expedite surgical repair of congenital cardiac lesions, which have conventionally not been addressed in the neonatal period,” they wrote.
Ms. Lim and her coauthors had no financial relationships to disclose.
