PULMONARY ARTERY WALL THICKNESS IN CHILDREN WITH FONTAN PHYSIOLOGY – AN OPTICAL COHERENCE TOMOGRAPHY CASE CONTROL STUDY

Abstract

Fontan failure in patients with preserved ventricular function is not well understood. Loss of pulsatile flow in the pulmonary arteries leads to lack of shear stress, which is believed to result in endothelial dysfunction. This endothelial dysfunction may further promote vascular remodelling. Subsequent increased pulmonary vascular resistance is considered to be a potential contributing mechanism for Fontan failure. We sought to perform an in vivo case control study to evaluate structural changes in the pulmonary arteries of children with a Fontan circulation compared to those with a normal pulmonary circulation. Since May 2016, we have recruited patients undergoing cardiac catheterization at BC Children’s Hospital. The control group comprised of children with normal pulmonary circulation undergoing cardiac catheterization or invasive electrophysiology evaluation. We performed intravascular imaging of the pulmonary arteries using Optical Coherence Tomography (OCT, Abbott). For quantitative OCT image analyses, we identified a series of 10 cross-sectional frames that were each ≥0.5 mm apart along the vessel. Using digital planimetry, we measured lumen diameter (mm), lumen cross-sectional area (CSA, mm2), wall CSA (mm2), vessel CSA (lumen+wall CSA, mm2) and mean wall thickness (mm) for each frame. To standardize wall thickness by vessel size, we calculated wall CSA to vessel CSA ratios. We calculated median values across frames for each case. Between-group differences were assessed by Mann-Whitney U tests; associations by Spearman Rank correlation (Stata v. 14.0; p < 0.05). We quantitatively analysed OCT images of the pulmonary arteries in 10 children with a Fontan circulation (10.8±3.9yrs at OCT, 40% female) and 8 control children (10.5±4.2yrs at OCT, 75% female). Overall, there were no significant differences between groups in terms of wall thickness (overall median 0.11mm, interquartile range 0.10-0.15) or wall/vessel ratio (0.13, IQR 0.11-0.15). There was no association between wall thickness or wall/vessel ratio with age at OCT, age at Fontan completion, or time since Fontan completion. Median pulmonary artery pressure at time of OCT was 11.8mmHg (10.5-14.0), which was not associated with normalized wall thickness. OCT findings suggest that during childhood, pulmonary artery wall dimensions are normal in children with Fontan physiology and reassuring hemodynamic status. Further evaluation of vascular function and correlating structure with function in this population would be worthwhile. Serial evaluation of pulmonary artery structure and correlation with clinical course into adulthood is needed.