Systematic analysis of the atrioventricular canal in 129 heart specimens identified anatomic and microarchitectural advantages in Down syndrome.

Abstract

To systematically analyze the macroscopic and microscopic anatomic characteristics of the common atrioventricular valve in patients with Down syndrome (DS) and those without DS. Such findings could explain the difference in outcomes between these 2 groups. We reviewed the clinical records and examined archived heart specimens with unrepaired common atrioventricular canal (AVC) defect. The common atrioventricular valve (CAVV) annulus and leaflets were measured for dimensions and area. The histology of leaflets at age <1 month, 3 months, and 6 months were reviewed. Leaflet nuclear density was calculated and used as an objective marker of maturation. Histologic findings were compared with normal controls. A total of 129 hearts with an AVC defect, including 47 DS hearts and 82 non-DS hearts, were studied. The DS hearts had a greater proportion of complete AVC (CAVC), particularly Rastelli type C, and fewer unbalanced AVC. The CAVV leaflet area-to-annulus area ratio (LA/AA) was significantly larger in the DS group than in the non-DS group overall and in patients age <12 months with CAVC. Leaflets in DS hearts showed a near-normal stratification by age 6 to 7 months; however, leaflets in the non-DS hearts remained quite amorphous at the same age. Leaflet interstitial nuclear density decreased more rapidly in the DS hearts, such that the nuclear density was similar to normal by 6 to 7 months; however, it remained significantly higher in non-DS hearts. The AVC defect in DS hearts compared with non-DS hearts was characterized by more CAVCs, fewer unbalanced defects, more Rastelli type C defects, larger LA/AA ratio, and histologically more organized and mature leaflets by 6 months. These characteristics might explain the better outcomes in DS patients. Our findings offer potential opportunities for optimizing surgical management.