Fibrous skeleton (heart, anatomy)

The fibrous skeleton of the heart is a connective tissue frame which functions to electrically isolate the atria from the ventricles. The atrioventricular conducting system is the only electrical connection between the atria and the ventricles in a normal heart. Also, it provides rigidity to prevent the dilatation of individual valves or outflow tracts. Finally, it provides a point of attachment for valve leaflets and the myocardium. The myocardium extends from the fibrous skeleton in a series of spirals that progress to the apex.

The fibrous skeleton consists of a set of fibrous rings of collagen which surround the atrioventricular canals and extends to the origins of the aorta and the pulmonary trunk. The majority of the skeleton lies within the plane of the base of the ventricles, roughly parallel to the coronary sinus. However, this is a simplification as there is a complex spatial arrangement of the atria, ventricles and valve outlets to each other:

• the atrioventricular valves tend to lie in the same plane as each other: this faces anteriorly, slightly to the left and inferiorly
• the aortic valve lies superior and to the right of the atrioventricular valve plane
• the pulmonary valve lies anterosuperior to the aortic valve, to its left but roughly at right angles

Consequently, the fibrous skeleton diverges from the atrioventricular orifices through a number of fibrous extensions. Therefore, it can be considered in terms of:

• fibrous annuli of the respective valves:
  • mitral
  • tricuspid
  • pulmonary
  • aortic
• connections between individual annuli