The tricuspid annulus is displaced downward into
the right ventricle such that part of the right ventricle becomes
“atrialized” (i.e., lies above the valve). The anterior and septal valve
leaflets are affected the most and may be severely dysplastic, resulting in
tricuspid regurgitation. The distal ends of the valve leaflets may be fused,
resulting in a variant degree of tricuspid stenosis. The anterior leaflet may
obstruct the right ventricular outflow tract. Atrial septal defect (ASD) or enlarged patent foramen
ovale (PFO) is present in almost all cases. Most often, the tricuspid lesion
results in tricuspid insufficiency, but stenosis also is possible. Tricuspid
regurgitation causes distention of the atrium and the atrialized ventricular
portion, which is usually thin-walled with paradoxical movement during
ventricular systole. Even distention may be seen during atrial systole.
Because part of the right ventricle is atrialized, the functional right
ventricle is smaller than normal, and secondary dilatation may result in
thinning of the wall, predisposing to right ventricular failure. Forward
flow of blood is also affected by the fact that, during atrial contraction,
part of the blood from the right atrium is pumped into the atrialized
portion of the right ventricle causing its dilatation, whereas during
ventricular contraction the blood in the atrialized part is pushed back into
the (dilated) atrium. Right-to-left shunting occurs across the ASD or PFO,
leading to a variable degree of cyanosis. Cyanosis is thus a common feature
of this anomaly occurring in more than 50% of patients.