Statistics
Differences in the atrial septum and pulmonary artery band parameters were assessed using the paired student t-test and differences between the two groups (AS and HLHS) was assessed using the independent student t-test. Inter- and intra-user variability was assessed using the intraclass correlation coefficient. Statistical analysis was performed using Stata version 14.1 (StatCorp, Texas). Change in variables over time was modelled using multilevel mixed effects linear regression, with time modelled as a categorical variable. All models included patient age as a covariate. Change over time was expressed using 3 P values: time, group (left versus right) and group-time interaction (see table 3 legend for further explanation).