0474: Inner architecture of the right ventricle: the role of the tricuspid valve

Abstract

A major anatomic characteristic of the right ventricle (RV), in addition to coarse and few apical trabeculations, is the presence of muscular bands arranged in a semicircular fashion: parietal band and subpulmonary conus, septal band (SB), moderator band (MB). The embryologic origin of SB, MB and anterior papillary muscle of the tricuspid valve (APM) is still controversial: primitive muscular tricuspid gully, or condensation of the ventricular trabeculations. In order to determine if the presence of SB, MB and APM could be related with the degree of development of the tricuspid valve, we reviewed 32 postnatal and 26 fetal human heart specimens with tricuspid atresia (TA). Forty-two hearts had ventriculo-arterial concordance, 14 had D-transposition. There were 52 muscular TA (musTA, including 6 without any RV cavity), and 6 membranous TA (mbTA) with imperforate valvar tissue in the floor of the right atrium. All 52 hearts with a RV cavity had a well-developed ventriculo-infundibular fold (VIF). A rudimentary SB (with demonstrable limbs in 3) was present in 6/46 (13%) musTA vs 6/6 (100%) mbTA (p=0.000), rudimentary MB in 3/46 (6.5%) musTA vs 6/6 (100%) mbTA (p=0.000), rudimentary APM in 3/46 (6.5%) musTA vs 3/6 (50%) mbTA (p<0.02). Left juxtaposition of the atrial appendages was found in 2% musTA vs 33% mbTA (p=0.02). SB and MB are absent in the vast majority of hearts with musTA but are found in all mbTA, while VIF is always present. These anatomic findings confirm the hypothesis of the muscular tricuspid primordium, itself developed from the posterior part of the primary fold, at the origin of SB, MB and AMP, while the VIF has a different origin (the inner curvature of the heart).