CorpusHuman Anatomy
CardiovascularOrgan part

Fibrous skeleton of the heart

Skeleton fibrosum cordis

Also known as: cardiac skeleton, annuli fibrosi, central fibrous body

The fibrous skeleton is a framework of dense collagen in the plane of the atrioventricular groove. Four fibrous rings joined by fibrous trigones anchor the valves and myocardium and electrically insulate the atria from the ventricles.

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Overview

The fibrous skeleton has five components. There are four fibrous rings (anuli fibrosi), one around each of the mitral, tricuspid, aortic and pulmonary orifices. The right fibrous trigone, also called the central fibrous body, lies between the aortic, mitral and tricuspid rings and is the strongest part. The smaller left fibrous trigone lies between the aortic and mitral rings. The membranous parts of the interatrial and interventricular septa are also part of the skeleton. Finally, the conus (infundibular) tendon links the aortic and pulmonary rings.

The leaflets of all four valves attach to the rings. The atrial and ventricular myocardium insert separately on either side.

The skeleton is also an electrical insulator. It separates the atrial myocardium from the ventricular myocardium, so the only normal route for the cardiac impulse is the bundle of His, which pierces the central fibrous body. This forces conduction through the AV node, with its built-in delay, and ensures that the ventricles contract only after the atria have emptied.

Location

At the base of the heart, in the plane between the atria and ventricles, surrounding the four valve orifices.

Parts & subdivisions

  1. Fibrous rings (anuli fibrosi)
    Surround the four valve orifices, preventing dilatation and anchoring the cusps.
  2. Right fibrous trigone (central fibrous body)
    Junction of the aortic, mitral and tricuspid rings. The bundle of His passes through it.
  3. Left fibrous trigone
    Lies between the aortic and mitral rings at the aortomitral continuity.
  4. Membranous septum
    Thin fibrous part of the ventricular and atrioventricular septa, just below the aortic valve.

Anatomy

Histology

Dense irregular collagenous connective tissue, mainly type I collagen. Fibrocartilage or calcification may appear with age.

Function

  • Provides firm attachment for the valve leaflets and keeps the orifices patent and competent.
  • Provides a fixed base against which the myocardium contracts.
  • Electrically insulates the atria from the ventricles, so conduction must pass through the AV node and bundle of His.

Clinical significance

Accessory pathways (Wolff–Parkinson–White)

A muscular accessory pathway (bundle of Kent) can bridge the fibrous rings and bypass the AV node. It pre-excites the ventricles, producing a short PR interval and a slurred upstroke (delta wave). It can also sustain a re-entrant tachycardia (AVRT). Catheter ablation of the pathway is curative.

Heart block after valve procedures

The bundle of His runs close to the aortic and tricuspid annuli. Aortic valve surgery, TAVI, an aortic root abscess or mitral annular calcification can therefore damage it and cause complete heart block.

Compiled from standard anatomy and physiology references — see the Cardiovascular System sources. For education only; not medical advice.