Characteristics of individuals in the cohort (n = 3897).

Notes: IQR interquartile range; Preterm birth - before 37 completed weeks of gestation; Additional cardiac defects - children who had at least one structural cardiac defect in addition to their primary cardiac diagnosis; Non-Down's syndrome non-cardiac malformations - a further 290 children had non-cardiac congenital malformations that were not Down's syndrome, including recognised syndromes such as Di George's (n = 61). Clinical status on first admission was defined as unstable if one or more of the following symptoms/signs were present: unwell = significant pallor, breathlessness or sweating, intubated, mechanically ventilated, hypotension = systolic blood pressure [SBP] <50 mmHg, hypertensive = SBP >100 mmHg, cardiac or respiratory arrest, metabolic acidosis, requiring adrenaline or high dose inotropic support. Characteristics of individuals in the cohort (n = 3897).