The tricuspid valve is bicuspid.
A study of 100 normal human autopsy hearts confirms numerous variations in the configuration of the cusp tissue and chordal/papillary support of the tricuspid valve, making the interior of the right ventricle as unique to each individual as one's finger print. The tricuspid veil of tissue is split by clefts into varying number of scallops with confusing names. However, the tricuspid veil of cusp tissue lends itself into a neat subdivision functionally into two halves: a septal cusp usually with no clefts hanging down from the relatively immobile septal part of the tricuspid annulus, and a mural cusp hanging down from the annulus related to the atrioventricular groove. Since the mural part of the annulus changes its shape and size during the cardiac cycle, the related mural cusp needs to have clefts which vary in number and split it artificially into two to six segments. It appears logical to label this part of the cusp as 'mural cusp' which will include the classical 'anterior' and 'posterior' cusps and associated commissural scallops. The apparent endless variety in the papillary and chordal support also resolves into an orderly pattern if the tricuspid valve is divided on an embryologic basis by a line drawn through the maximum height of the 'anterior' and septal cusps. The superior half of the valve thus divided is derived from the anterior and posterior endocardial cushions with chordal support from the bulbar septum, sinus (inlet) and membranous part of interventricular septum (IVS). The inferior half is derived from the lateral endocardial cushions with chordal support from the trabecular part of IVS. Thus the 'tricuspid' valve can be bisected conveniently into two halves in two different ways either on a functional or an embryologic basis, bringing order out of apparent chaos inside the right ventricle.
Victor
S
S
Heart Institute, Madras, India.
Nayak
V M
VM
D002815:Chordae Tendineae / Q000033:anatomy & histology; D006801:Humans; D010210:Papillary Muscles / Q000033:anatomy & histology; D014261:Tricuspid Valve / Q000033:anatomy & histology* / Q000502:physiology