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Fetal MRI

Fetal Transposition of the Great Arteries by Phase Contrast MRI

MRI Shows Limited Mixing Between Systemic and Pulmonary Circulations in Fetal Transposition of the Great Arteries - A Potential Cause of In Utero Pulmonary Vascular Disease
Presentation at the upcoming SPR 2014

To investigate the relationship between fetal hemodynamics and postnatal clinical presentation in patients with transposition of the great arteries using phase contrast cardiovascular magnetic resonance.

Summary

A severe and irreversible form of persistent pulmonary hypertension of the newborn occurs in up to 5 per cent of patients with transposition and is now the leading cause of morbidity and mortality in these infants. Restriction at the foramen ovale and ductus arteriosus has been identified as a risk factor for the development of pulmonary hypertension and this can now be studied with MRI using a new technique called metric optimized gating.

We found significantly reduced flows in the ductus arteriosus (p<0.001) and foramen ovale (p=0.01) and increased ascending aortic (p<0.01) and aorto-pulmonary collateral (p<0.01) flows in fetuses with transposition compared with normals. The fetus with the lowest foramen ovale shunt and highest aorto-pulmonary collateral flow developed fatal pulmonary vascular disease.
We found limited mixing between the systemic and pulmonary circulations in a small group of late gestation fetuses with transposition. We propose that the resulting hypoxia of the pulmonary circulation leads to increased aorto-pulmonary collateral flow and may contribute to the development of pulmonary vascular disease in some fetuses with transposition.

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Flows in fetuses with transposition versus normal hearts. 
Normal fetal flows (black bars) are compared with TGA (coloured symbols) as percentage of combined ventricular output (CVO). 

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Mean normal flows (gray bars) are also shown. 
Significance level is indicated (* p < 0.05, ** p < 0.01, *** p < 0.001). GA- gestational age, EFW- estimated fetal weight, MPA- main pulmonary artery, AAo- ascending aorta, SVC- superior caval vein, DA- arterial duct, DAo- descending aorta, PBF- pulmonary blood flow, UV- umbilical vein, FO- oval foramen.