Fibrous skeleton of heart and clinical importance

Heart

1. Anatomy Of Fibrous Skeleton Of Heart And It’s Importance Presenter: Dr. Himanshi Moderator: Prof. Subodh Satyarthi

2. THE FIBROUS SKELETON OF HEART The fibrous skeleton of heart is concentrated at the base of the ventricular mass . It provides electrical insulation at the atrioventricular level and fibrous continuity for the leaflets of the mitral, aortic, and tricuspid valves. Its components include the fibrous trigones, the fibrous area of aortic-mitral continuity, the subvalvar collar of the mitral valve, the membranous septum, the interleaflet triangles, the tendon of Todaro , and likely the conus ligament.

3. Principal elements of the fibrous skeleton of the heart. The view is from the right posterosuperior aspect. This Perspective causes the pulmonary anulus to appear smaller than the aortic anulus , whereas, in fact, the reverse is the case.

4. THE FIBROUS TRIGONES

5. The right fibrous trigone is then continuous with the membranous septum, the conjoined structure being known as the central fibrous body. From the two fibrous trigones, cords of fibrous tissue extend around the orifices of the mitral valve. It is rare, however, to find these cords encircling the entirety of the valvar orifice to provide uniform support for the attachments of the mural leaflet of the mitral valve. When well formed, the fibrous tissue frequently takes the form of a short fibrous strip, rather than a circular cord.  

6. At the fibrous trigone the atrioventricular bundle (  AV bundle  of HIS), a part of the conducting system of the heart, passes over from the right atrium to the interventricular septum. The fibrous skeleton stabilizes the valves and serves as an electrical insulator between the atria and the ventricles. The electrical impulse reaches the ventricles exclusively through the AV bundle.

7. FIBROUS AREA OF AORTIC-MITRAL CONTINUITY

8. The aortic, mitral and tricuspid valves form one continuous structure, with each valve in close approximation to the other and connected by the fibrous skeleton of the heart. They are arranged as a triangle at the base of the heart; the pulmonary valve is separate and placed anteriorly. The fibrous skeleton of the heart surrounds the aortic valves and partially surrounds the mitral and tricuspid valves. The anulus of each valve is therefore not homogenous, but is made of a combination of fibrous tissue for some of its diameter and muscular tissue for the remainder, which results in asymmetrical dilation of each valve under pressure and/or volume loading.

9. LV Outflow tract opened anteriorly and spread to reveal the area of fibrous continuity between the leaflets of aortic and mitral valves. The ends of the area of continuity are thickened to form the fibrous trigones, with the continuity between the right trigone and the membranous septum forming the central fibrous body.

10. Running at the ventricular base is a complex framework of dense collagen with membranous, tendinous and fibroareolar extensions, intimately related to atrioventricular valves and the aortic orifice. The leaflets of the pulmonary valve are supported on a free-standing sleeve of right ventricular infundibulum (conus arteriosus) that can easily be removed from the heart without disturbing either the fibrous skeleton or the left ventricle. Moreover, the fibrous skeleton of the heart does not incorporate the entirety of the atrioventricular and arterial anuli .

11. SUBVALVAR COLLAR OF THE MITRAL VALVE

12. The majority of the mitral annulus is fibrous, but the only true fibrous part of the tricuspid annulus is where the valvar leaflets are attached to the central fibrous body. At the aortic annulus, the fibrous elements support only the noncoronary aortic sinus and parts of the right and left coronary sinuses. The ring-shaped annulus of the arterioventricular valves as localized with imaging techniques (imaging annulus) differs from the crown-shaped hemodynamic annulus of the arterial valves.

13. Much of the insulation between the atrial and ventricular chambers is provided by the fibroadipose tissues within the atrioventricular sulci. There is some collagenous tissue in the mitral valvular anulus , but it is not always continuous with the fibrous structure. The tricuspid valvular anulus is almost exclusively composed of fibroadipose tissue. The only true fibrous part of the tricuspid anulus is where the valvular leaflets are attached to the central fibrous body . Another point of confusion is the idea that the fibrous skeleton provides the support for the cardiac valves.

14. In reality, it is the overall structure of the atrioventricular junctions that supports the mitral and tricuspid valves, whereas the arterial valves are hinged within the valvular sinuses. The fibrous skeleton is strongest at the central fibrous body, which is the junction of the aortic, mitral and tricuspid valves. Two pairs of curved, tapering, collagenous, fila coronaria extend from the central fibrous body. They are stronger on the left, where they pass partially around the mitral and tricuspid orifices. These orifices are almost co-planar and incline to face the cardiac apex.

15. In contrast, the aortic valve faces superiorly, lying anterosuperior and to the right of the mitral orifice. Two of the leaflets of the aortic valve (left coronary and non-adjacent) are in fibrous continuity with the aortic leaflet of the mitral valve; this subaortic curtain is also an integral part of the fibrous skeleton. The two ends of the fibrous curtain are strengthened as the right and left fibrous trigones, which are the strongest parts of the skeleton. The right trigone and the membranous septum constitute the central fibrous body, which is penetrated by the atrioventricular bundle (His). The membranous septum is crossed on its right aspect by the attachment of the tricuspid valve leaflets, dividing the septum into atrioventricular and interventricular parts .

16. The pulmonary valve possesses no fibrous continuity with the other three valves; however, in few cases a small fibrous band, known as the tendon of the conus, extends between the aortic and pulmonary valvar sinuses. The line of proximal fusion is the longitudinal raphe sometimes seen in the muscular subpulmonary infundibulum.

17. Similar fibrous triangles separate the sinuses of the pulmonary trunk but they are significantly less robust. Use of the terms mitral and tricuspid anuli implies that the atrioventricular valves are supported by discrete circular fibrous rings, when, in reality, the valves are D-shaped structures integrally attached at the atrioventricular junctions. It is therefore inaccurate to consider these valvular orifices as circular. Rather, the straight edge of the ‘D’-shaped mitral valve represents a fibrous continuity between the aortic leaflet and the aortic root, and the remainder supports the mural leaflet.

18. The straight edge of the ‘D’-shaped tricuspid valve represents the attachment of the septal leaflet, marking the inferior border of the triangle of Koch, and the remainder supports the anterosuperior and inferior leaflets. The attachments of the atrioventricular valves are not simple, rigid collagenous structures but dynamic, deformable lines that vary greatly at different peripheral points and change considerably with each phase of the cardiac cycle, and with increasing age. The tricuspid valvular leaflet attachments are even less robust than those of the mitral valve. At several sites, only fibroareolar tissue separates the atrial and ventricular muscular masses.

19. Often, the fibrous tissue fades out completely at various sites around the ring, with the atrial and ventricular muscle masses then being separated from each other in these locations by the fibrofatty tissue of the left atrioventricular groove . The mitral valvar leaflets then take origin from the ventricular myocardium, rather than from a fibrous skeleton. This arrangement is the rule rather than the exception in the right atrioventricular junction, where it is usually the fibrofatty tissues of the atrioventricular groove that serve to insulate the atrial from the ventricular musculature. Taken together, therefore, the so-called fibrous skeleton of the human heart is poorly formed, being a firm structure only within the aortic root.

20. The Membranous Septum

21. THE INTERLEAFLET TRIANGLES

22. INTERLEAFLET TRIANGLES The aortic root is central and is like an annulus integrated within the fibrous skeleton. The structure of the aortic root corresponds to the triple fibrous semilunar attachments of its valvular leaflets. Within this complex circumferential zone, three crucially important triangular areas separate, on the ventricular aspect, the aortic sinuses that house the valvular leaflets . Collectively , the three interleaflet triangles can be conceptualized in terms of a three-pointed coronet; their triangular apices correspond to the tips of the valvular commissures and their walls, significantly thinner than those of the aortic sinuses, consist variously of collagen or admixed muscle strands and fibroelastic tissue. They form the subvalvular extensions of the aortic vestibule.

23. The first triangle is the interval between the non-adjacent and left coronary sinuses/leaflets that is filled with the deformable subaortic curtain. The second triangle between the non-adjacent and right coronary sinuses/leaflets is continuous with the anterior surface of the membranous septum. The third triangle, between the two coronary aortic sinuses/leaflets, is filled with loose fibroelastic tissue and separates the extension of the subaortic root from the wall of the free-standing subpulmonary infundibulum.

24. TENDON OF TODARO

25. The tendon of TODARO is the connection between the valve of the inferior vena cava to the central fibrous skeleton.

26. ANNULUS FIBROSUS

27. CLINICAL IMPORTANCE

28. The skeleton of the heart allows cardiac muscle to contract against the rigid base. The fibrous rings support the bases of the cusps of the valves to prevent the valves from stretching and becoming impaired. The aortic ring is the strongest

29. Ultimately, the effect of valvular and ventricular disease processes is to lead to pathological changes in the structures of the tricuspid and mitral valves. Pressure and/or volume overload of the chambers of the heart will lead to chamber enlargement and then to anular dilation. The normal shape of the valve anulus becomes distorted and enlarged, and these changes, which are initially reversible, become progressive and irreversible. It is thought that 10% of patients with degenerative mitral valve disease will go on to develop regurgitation (leaking) through the valve that is sufficiently severe to warrant surgical intervention.

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