Histology of the tricuspid valve annulus and right atrioventricular muscle distance.

Objectives: Histologically, the mitral valve annulus comprises a collection of collagen fibres. However, the existence of collagen fibres in the tricuspid valve annulus has not been elucidated. Our goal was to clarify the histology of the tricuspid annulus.

Methods: Fifty human hearts without heart disease that were autopsied at Osaka City University Hospital between January 2009 and December 2017 were examined. The tricuspid valve was sectioned at 12 sites around the annulus, and the atrioventricular junction distance was measured.

Results: None of the tricuspid valve annulus samples had a continuous aggregation of collagen fibres that could be called an annulus. The interventricular space between the right atria and ventricles was composed of adipose tissue only on the anterosuperior and inferior sides, and no adipose tissue was found on the septal side. Comparing the atrioventricular muscle distance of the anterosuperior and inferior sides, the distance at the inferior side was statistically significantly larger than that of the anterosuperior side in 47 cases (P < 0.0001).

Conclusions: There was no continuous circumferential aggregation of collagen fibres in the right atrioventricular junction. The distance between the right atrial and ventricular myocardium was greater at the inferior side than that at the anterosuperior side, which might lead to more inferior annular dilation versus anterosuperior dilation. These anatomical features will be fundamental for future discussions of the suturing method used in prosthetic ring annuloplasty for tricuspid regurgitation.