The conducting system of the heart is responsible for initiating and conducting electrical impulses to coordinate heart contractions. It consists of specialized cardiac muscle fibers including the sinoatrial node, atrioventricular node, bundle of His, and Purkinje fibers. The fibrous skeleton of the heart provides support and attachment points for the heart valves. It is composed of fibrous rings surrounding the atrioventricular, pulmonary, and aortic orifices that prevent dilatation and provide rigidity. The conducting system and fibrous skeleton work together to coordinate the pumping of blood through the heart.

1. CONDUCTING SYSTEM AND
FIBROSKELETON OF THE HEART
DR BHIMA NEUPANE

2. Conducting system
• Made up of specialized cardiac muscle fibres (not nervous tissue)
• Responsible for initiation and conduction of cardiac impulse.
• Consist of:
• 1. Sinuatrial node (SA node).
2. Atrioventricular node (AV node).
3. Atrioventricular bundle (of His).
4. Right and left branches of bundle of His.
5. Subendocardial Purkinje fibres.

4. Sinuatrial node (SA node or node of Keith
Flack
• Small horseshoe-shaped mass having
specialized myocardial fibres- clusters
of myocytes
• Location-wall of the right atrium in the
upper part of sulcus terminalis
• Just below the opening of superior
vena cava.

5. • It is known as natural pacemaker of the heart
• It generates electrical impulses (about 70/minute) and initiates the
contraction of cardiac muscle producing heart beat

6. Atrioventricular node /node of Tawara
• Smaller than the SA node
• location- Triangle of KOCH
• It conducts the cardiac impulse to the ventricle by the atrioventricular
bundle.
• The AV node is capable of generating impulses at the rate of about
60/min.
• The speed of conduction of cardiac impulse (about 0.11 sec) provides
sufficient time to the atria to empty their blood into the ventricle before
ventricles start contracting.

7. Atrioventricular Bundle (of His)
• It begins from AV node
• crosses the AV ring
• Runs along the inferior part of the
membranous part of the
interventricular septum
• Divides into the left and right
branches

8. Right and left branches of the bundle
• The right branch passes down the right side
of the interventricular septum
• Then becomes subendocardial on the right
side of the septum.
• A large part of it continues in the
septomarginal trabeculum (moderator band)
to reach the anterior papillary
muscle and anterior wall of the ventricle.
• Its Purkinje fibres then spread out beneath
the endocardium

9. Left branch
• The left branch descends on the left
side of the ventricular
septum, divides into Purkinje fibres
which are distributed to
the septum and left ventricle.

10. • Purkinje fibres:
• They are the terminal branches of
right and left branches of the
bundle of His
• Spread subendocardially
over the septum and the rest of the
ventricular wall.

11. • The SA node (a spontaneous source of cardiac impulse)
• Initiates an impulse which rapidly spreads to the muscle fibres
of the atria, making them to contract.
• The AV node picks up the cardiac impulse from atria
• Conducts it through atrioventricular bundle
• and its branches to the papillary muscles and the walls of the
ventricles.
• The papillary muscles contract first, to tighten the chordae tendinae
• Then the contraction of ventricular muscle occurs

12. • Conducting system defects:
• The defect/damage of conducting system causes cardiac arrhythmias.

13. Blood supply
• SA node-
• nodal br of Rt coronary artery (60%) cases
• circumflex br lt coronary artery (40%) cases
• AV node-
• -Br of rt coronary artery (90%)
• Circumflex br lt coronary artery
• AV bundle-
• -Septal br of rt coconary artery

14. • Rt bundle br-
• Septal br of lt coronary artery
• Left bundle br-
• Largely by septal br of lt coronary artery

15. SKELETON OF THE HEART
• Composed of fibrous tissue and forms the central support of the
heart.
• It consists of fibrous rings that surround the atrioventricular,
pulmonary, and aortic orifices.
• These rings provide circular form and rigidity to the atrioventricular
orifices
• and Roots of the aorta and pulmonary trunk.
• They also provide attachment to the valves and prevent dilatation of
these orifices.
•

16. • Pulm ring lies above , infront and
slightly to left of aortic ring
• Both rings set at right angle to each
other
• Connected by fibrous septum K/a
tendon of infundibulum

17. • The cardiac valves are firmly attached to this skeleton.
• The cardiac skeleton along with membranous part of interventricular
septum also provides attachments to the cardiac muscle fibres.

18. • The fibroskeleton disturbs the continuity between atrial and
ventricular muscles except at bundle of His of the conducting system.
• So for propagation of impulse from atria and ventricles , a specialized
cardiac muscle , conducting system of heart essential.
•

20. • 4 fibrous ring arranged in 4 collagenous
annuli
• Not in same plane
• Aortic annulus – central in position
• Closely interconnected to mitral and
tricuspid annuli
• Pulm annulus lies further apart from
aortic annulus
• Connected by tendon of infundibulum

21. • The fibrous skeleton is strongest at the
junction of the aortic, mitral and tricuspid
valves, the so-called central fibrous body

22. Aortic annulus
• Consist of 3 collagenous scallop-
1.anterior
• 2.Posterior- left post &rt posterior
• Attachment in inner surface to base
of aortic cusp
• Rt fibrous trigone-attachment to
post filum coronorium of mitral
annulus n both fila annulus
• So k/a central fibrous body
Post and left scallop
forms left fibrous
trigone –gives
attachment to ant
filum coronarium of
mitral ann
Botton
of post
n rt
scallop
-rt
fibrous
trigon
Mitral valve
annulus

23. Mitral annulus
• Includes left and rt fibrous trigone
• fila coronaria attached to, two trigone
• And weak sulcal conn tissue attached to
tips of both fila
• Between two fibrous trigone the subaortic
curtain forms part of mitral annulus

24. Tricuspid annulus
• Comprise of
• Ant and post fila coronaria
• Rt fibrous trigone (central fibrous body)
• Where both fila are attached
• And a weak sulcal conn tissue which connects
tips of two fila.
• Tricuspid and mitral annuli lie in same plane
making an angle of 45 degree in saggital
plane

25. Pulmonary annulus
• Set rt angle to aortic annulus
• Tripple scalloped
• Two infront, one behind
• Inner aspect of which provide
attachment to bases of pulm cusp
• Tip of sub vulvar span facing
aorticic annulus –attachment to
tendon of infundibulum (prevents
separation of both annuli during
ventricular ejection)

26. Functional significance:
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 and
prevent the valves from stretching and becoming incompetent. The
aortic ring is the strongest

27. • In prosthesis operation of heart valves,
the fibrous skeleton is capable of holding sutures under persistent
tension.