Quantitative CT Geometry of the Patent Ductus Arteriosus in Infants with Congenital Heart Disease: Association with Aortic Arch Obstruction or Hypoplasia

Background/Objectives: Quantitative patent ductus arteriosus (PDA) geometry in congenital heart disease (CHD), particularly in relation to aortic arch abnormalities, is incompletely characterized. We evaluated CT-derived PDA geometry. Methods: This retrospective exploratory single-center study included 168 infants with CHD and a PDA on cardiovascular CT. Aortic-end, pulmonary-end, and mid-duct diameters and ductal length were measured. The Ductal Length-to-Diameter Index (LDI), selected during exploratory analysis, was defined as ductal length divided by the mean end diameter. Seventy-three patients had CT-documented aortic arch obstruction or hypoplasia. Results: LDI was lower in patients with arch obstruction/hypoplasia than in those without these findings (2.04 [1.39–2.84] vs. 3.51 [2.23–4.89]; p < 0.001; rank-biserial r = −0.473) and remained associated after adjustment for age, weight, and sex (OR per +1 LDI, 0.534; 95% CI, 0.412–0.693; p < 0.001). The association remained robust with a conservative definition restricted to coarctation or interrupted aortic arch. LDI had an interobserver ICC of 0.843 (95% CI, 0.685–0.954), with wide limits of agreement (−1.98 to +2.45). Conclusions: CT-documented aortic arch obstruction or hypoplasia is associated with lower LDI. This exploratory geometric association warrants prospective external validation before clinical use.