The term “atrioventricular septal defect” (AVSD) covers a spectrum of congenital heart malformations characterised by a common atrioventricular junction coexisting with deficient atrioventricular septation. In ostium primum atrial septal defect (ASD) there are separate atrioventricular valvar orifices despite a common junction, while in complete AVSD the valve itself is also shared.

The estimated incidence of the condition in the era of two-dimensional echocardiography varies from 0.24/1000^w1 live births to 0.31/1000^w2 live births. There is a strong association with Down’s syndrome, with half of patients with AVSD in the population of Bohemia also complicated by Down’s syndrome.^w3 Conversely in a Toronto study about one third of patients with Down’s syndrome had a complete AVSD and 5% had an ostium primum ASD.^w4 In a prospective screening study within the relatively static Northern Irish population the incidence of AVSD in Down’s syndrome was 17% and the overall incidence of congenital heart disease in Down’s syndrome was 42%.¹

Three different genetic patterns are described in AVSD: the association with Down’s syndrome, as an autosomal dominant trait, and isolated. Molecular studies of patients with congenital heart disease and partial duplications of chromosome 21 have proposed DSCAM (Down’s syndrome cell adhesion molecule) as a candidate gene causing congenital heart disease in Down’s syndrome.² Cases with autosomal dominant inheritance, however, are not linked to chromosome 21.^w5

Over the past four decades the management of the complete form of the condition has evolved from palliative pulmonary artery banding in infancy with later repair to primary repair in early infancy to prevent the development of pulmonary vascular obstructive disease. Decreasing operative mortality has significantly altered the prognosis of these patients with and without Down’s syndrome. The improved prognosis for patients with Down’s syndrome and AVSD has implications for the management of patients …