Objective After the arterial switch operation (ASO), disproportional neo-aortic growth during childhood has been reported. Even though it has been suggested neo-aortic dilation will stabilise in adulthood, data are lacking. The aim of this study was to assess the change in neo-aortic dimensions, prevalence of neo-aortic dilation >40 mm and long-term outcome in adults who underwent ASO in childhood.

Methods All 116 ASO patients operated in a tertiary referral centre and born before 1995 were included. Of these, 83 (72%) survived to adulthood (>17 years) and six were lost to follow-up. Neo-aortic measurements performed in adulthood were collected from available echocardiographic, cardiovascular magnetic resonance and CT images. The time trend was analysed using a mixed model, adjusted for imaging modality.

Results Clinical data with at least one measurement of the neo-aortic diameter were available in 77 (93%) adult patients and serial measurements in 65 (78%). At baseline (median age 18.1 years), mean neo-aortic diameter was 36±5 mm. Mean neo-aortic growth was 0.31 mm/year (p<0.001 compared with normal value 0.08 mm/year) and was linear over time. Freedom from neo-aortic dilation beyond a diameter of 40 mm was 23% at 28 years of age. During a mean clinical follow-up in adulthood of 7.2 years (IQR 4.0 to 10.1), 3 (4%) patients underwent neo-aortic replacement. No other neo-aortic complications occurred.

Conclusions In early adulthood, neo-aortic growth was on average linear and did not stabilise over time.