Purpose or Case Report: Infants with one functional cardiac ventricle often undergo the Norwood procedure which seeks to create unobstructed outflow from the single ventricle to aorta using a complex aortic arch reconstruction. The distal region of the patch used to fashion the neo-aorta terminates near the aortic isthmus, and represents an area of extensive challenge and manipulation for cardiothoracic surgeons. Re-coarctation in this region is common after the Norwood procedure and may be linked with longer-term morbidity and mortality. Echocardiography (TTE) is the primary means of surveillance of the aortic isthmus, though measurements are often difficult due to poor acoustic windows and lack of patient cooperation. To date, there have been no studies that assess how accurately TTE measures the aortic isthmus relative to a computed tomography (CT) derived gold standard.
Methods & Materials: A retrospective chart review identified infants with single ventricle physiology status post Norwood procedure that had both TTE and CT performed less than 14 days apart between 1/1/2010 and 9/15/2015. TTE images were reviewed in order to measure the aortic isthmus using the suprasternal notch window. CT measurements of the aortic isthmus were made using multi-planar reconstruction. The relationship between TTE and CT measurements were assessed by linear and intra-class correlation (ICC) coefficients.
Results: 22 pairs of studies met inclusion criteria over the study period. TTE was unable to identify and measure the aortic isthmus in 13 cases (60%). Of the remaining 9 cases, 66% had Hypoplastic Left Heart Syndrome and 56% had a BT shunt. Compared to CT measurements, TTE measurements of the aortic isthmus had extremely poor linear correlation and agreement (R = 0.05, p = 0.90, ICC = 0.01, figure). There were no aortic interventions required. The median radiation dose received was 0.3 mGy (CTDI vol).
Conclusions: In this study of infants with single ventricle physiology status post Norwood procedure, TTE-derived measurements of the aortic isthmus were challenging to obtain and poorly reflective of the true isthmus diameter using CT as a gold standard. Further studies are needed to determine the impact of poor linear correlation and agreement on morbidity and mortality. In this high-risk population for aortic arch obstruction after the Norwood procedure, CT may be a more accurate and timely modality for routine surveillance or imaging upon clinical concern of re-coarctation.