CONDUCTION SYSTEM OF HEART

1. DR NILESH KATE
MBBS,MD
ASSOCIATE PROF
ESIC MEDICAL COLLEGE, GULBARGA.
DEPT. OF PHYSIOLOGY
CONDUCTION
SYSTEM OF
HEART

2. OBJECTIVES.
 Introduction.
 Anatomic consideration.
 Mechanism of origin of rhythmic cardiac
impulse.
 Spread of cardiac impulse.

3. INTRODUCTION.
 Cardiac muscle shows
4 properties
 Auto Rhythmicity
 Conductivity
 Excitability
 Contractility.
Thursday, April 26, 2018

4. INTRODUCTION.
 Auto Rhythmicity
 Heart initiate its own
impulse at constant
rhythm.
 Due to pacemaker
tissue that initiate
rhythm & forms
conduction system.
Thursday, April 26, 2018

5. ANATOMIC CONSIDERATION.
 Conducting system of
heart.
 Sinuatrial node.
 Interatrial tract ( Bachman
bundle)
 Internodal conduction
pathway.
 Atrioventricular node.
 Atrioventricular bundle of His
 Purkinje fibres
Thursday, April 26, 2018

6. SINUATRIAL NODE.
 Location – In wall of
right atrium right to
opening of superior
venacava.
 Dimensions –
15×2×1mm
 Spread to cardiac
muscle, interatrial &
internodal.
Thursday, April 26, 2018

7. INTERATRIAL TRACT
(BACHMAN BUNDLE)
 Band of specialised
muscle fibre from SA
node to left atrium.
 Causes Depolarization
of Atria.
Thursday, April 26, 2018

8. INTERNODAL CONDUCTION
PATHWAY.
 Anterior (Bachman)
 Middle
( Wenchebach)
 Posterior (Thorel)
Thursday, April 26, 2018

9. ATRIOVENTRICULAR NODE.
 Location – just
beneath the
endocardium on right
side of lower part of
atrial septum.
 Convey impulses from
internodal tracts to
ventricles.
Thursday, April 26, 2018

10. ATRIOVENTRICULAR BUNDLE OF
HIS
 Arises from A-V node
& divide into right &
left for right and left
ventricles.
 Becomes continuous
with plexus of
purkinje fibres.
Thursday, April 26, 2018

11. PURKINJE FIBRES
 Spread deep to
Endocardium & reach
all parts of ventricles
including bases of
papillary muscles.
Thursday, April 26, 2018

12. CHARACETRISTIC HISTOLOGICAL
FEATURES OF CONDUCTING SYSTEM
 Consists of modified
cardiac muscle – few
striations & indistinct
boundaries.
 P cells (Pacemakers)
- SA node & AV node
contains small round
cells connected by
GAP junctions.
Thursday, April 26, 2018

13. INNERVATIONAL
CHARACTERISTIC OF HEART
 Both SA & AV node
supplied by
sympathetic &
parasympathetic
 Sympathetic – stellate
ganglion
 Parasympathetic -
Vagus
Thursday, April 26, 2018

14. INNERVATIONAL
CHARACTERISTIC OF HEART
 SA node – supploied
by
 Right vagus
 Right sympathetic
 AV node
 Left vagus
 Left sympathetic.
Thursday, April 26, 2018

15. MECHANISM OF ORIGIN OF
RHYTHMIC CARDIAC IMPULSE.
 Pacemaker – part of
cardiac muscle from
which rhythmic impulse
produced.
 SA node is Pacemeaker –
as impulse generated by
it highest.
 Ectopic pacemaker –
pacemaker other than SA
node.
Thursday, April 26, 2018

16. MECHANISM OF ORIGIN OF
RHYTHMIC CARDIAC IMPULSE.
 Rate of production of rhythmic impulses
 SA node – 70-80/min
 AV node – 40-60/min
 Atrial Muscle - 40-60/min
 Ventricular muscle -20-40/min
Thursday, April 26, 2018

17. ELECTRICAL POTENTIAL IN
PACEMAKER TISSUE.
 In pacemaker tissue –
RMP is -55 to -60 mv
 Not steady.
 Always slow rise in RMP
due to slow
depolarization up to
-40 mv (threhold)
 Then depolarization upto
+5mv followed by
repolarization.
Thursday, April 26, 2018

18. ELECTRICAL POTENTIAL IN
PACEMAKER TISSUE.
 Then reach to RMP
which is not stable –
again start raising.
 This slow rising RMP
is called Prepotential
or pacemaker
potential.
 This is cause for –
AUTORHYTMICITY.
Thursday, April 26, 2018

19. IONIC BASIS OF PACEMAKER POTENTIAL
AND ACTION POTENTIAL IN SA NODE
 SA node & AV node contains
slow fibres
 Other myocardial fibers
contains – fast fibers.
 Slow fibres – contains leaky
“Na” channels
 Causes – diffusion of Na at
RMP – so this raises
potential to -55 mv – this is
Initial pacemaker
potential.
Thursday, April 26, 2018

20. IONIC BASIS OF PACEMAKER POTENTIAL
AND ACTION POTENTIAL IN SA NODE
 then T Ca channels opens up
– influx of Ca – threshold
level of -40 mv reached.
 At threshold all Ca channels
opens up – Depolarization.
 Then Ka Channels opens up
– K diffuses out –
Repolarization.
 Again due to “Leaky Na
channels” – slow
depolarization.
Thursday, April 26, 2018

21. ROLE OF ANS IN CONTROLLING
HEART RHYTHM
 Vagal tone
 Effect of
parasympathetic
stimulation.
 Effect of sympathetic
stimulation.
Thursday, April 26, 2018

22. VAGAL TONE
 SA node supplied by right
Vagus.
 Vagus releases Ach –
Increases permeability for
K – efflux of K – Hyper
polarization
 Slows firing rate of SA node
from 90-120 to 60—90
 This is Vagal Tone.
Thursday, April 26, 2018

23. EFFECT OF PARASYMPATHETIC
STIMULATION.
 HR by decreasing rate of
sinus rhythm.
 excitation of conducting
system transmission of
impulse – ventricles may
stop beating
 Then Purkinje fibres initiate
own rhythm @ 15-40/min –
this is Vagal Escape.
Thursday, April 26, 2018

24. EFFECT OF SYMPATHETIC
STIMULATION.
 Causes release of NE –
Ca permeability -
rate & force of
contraction.
Thursday, April 26, 2018

25. SPREAD OF CARDIAC IMPULSE.
 SA node & atria
 AV node
 Ventricular
conduction.
Thursday, April 26, 2018
SA NODE
AV NODE
BUNDLE BRANCHES
PURKINJE FIBRES
ENDOCARDIAL &
EPICARDIAL SURFACE
OF VENTRICLES.