Histology of the tricuspid valve annulus and right atrioventricular muscle distance

Figures

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  Figure 1:. Preparation of the sections. (A) The mitral annulus was divided into 6 sections. A is the midpoint of the annulus on the anterior leaflet side; AL is the anterolateral commissure; PM is the posteromedial commissure; and P1-P3 are the midpoints of each posterior leaflet. AL: anterolateral; PM posteromedial. (B) The tricuspid annulus was divided into 12 sections as follows: each commissure (AI, IS, SA) and the quadrants between the commissures (A1–3, I1–3, S1–3). AI: anterosuperior–inferior; IS: inferior–septal; SA: septal–anterosuperior.

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  Figure 2:. Histology of the mitral and tricuspid valve annuli. (A) Six sections (A/AL/PM/P1-P3) of a typical mitral annulus in a representative case. The red circles are aggregations of collagen fibres, which are visible in all sections. On the AL site, fibrous tissue is present but not between the atrioventricular muscles, and on the P1 site, fibrous tissue can be seen like a curtain. Elastic van Gieson (EVG) staining; magnification ×20. Scale bar indicates 500 µm. AL: anterolateral; LA: left atrium; LV: left ventricle; MV: mitral valve; PM: posteromedial. (B) Twelve sections (A1–SA) of a typical tricuspid annulus in a representative case. No circumferential tissue characteristic of a valve annulus, such as collagen fibre aggregation, was observed. The asterisk indicates adipose tissue. The area within the red circle is the central fibrous body. Scale bar indicates 1 mm. EVG staining; magnification ×20. A: anterior; RA: right atrium; RV: right ventricle; S: septal; TV: tricuspid valve.

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  Figure 3:. Partial aggregation of collagen fibres. A case of localized collagen fibre aggregation (red circle) at the valve attachment only in the SA and A1 sections. Elastic van Gieson staining; magnification: ×20. Scale bar indicates 1 mm. A: anterosuperior; SA: septal–anterosuperior.

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  Figure 4:. Histology of the right atrioventricular area. (A, B) The area between the atrial and ventricular muscles at the anterosuperior and inferior sides is composed of adipose tissue (blue circles). Sections are A2 (A) and I2 (B). (C, D) The area between the atria and ventricle at the septal side is connected via a central fibrous body (outlined in red), without intervening adipose tissue. Sections are S2 (C) and S3 (D), and (D) is at the site of the membranous septum. A: anterosuperior; I: inferior; MS: membranous septum; RA: right atrium; RV: right ventricle; S: septal; TV: tricuspid valve; VS: ventricular septum.

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  Figure 5:. Right atrioventricular muscle distance. The edges of the right atrial muscle (blue dot) and right ventricular muscle (green dot) were identified, and the distance (µm) between these muscles was measured as the atrioventricular muscle distance (AVMD; red arrow).

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  Figure 6:. Comparison of the anterosuperior AVMD and inferior AVMD. Comparison of the mean anterosuperior AVMD and the mean inferior AVMD in each case. Wilcoxon’s signed rank sum test was performed using the difference between the mean AVMD values, which showed that the mean AVMD at the inferior side was larger than that at the anterosuperior side (P < 0.0001). A: anterosuperior; AVMD: atrioventricular muscle distance; I: inferior.