Conduction system of heart

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.
Friday, May 4, 2018

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

7. INTERATRIAL TRACT
(BACHMAN BUNDLE)
Band of specialised
muscle fibre from SA
node to left atrium.
Causes Depolarization
of Atria.
Friday, May 4, 2018

8. INTERNODAL CONDUCTION
PATHWAY.
Anterior (Bachman)
Middle
( Wenchebach)
Posterior (Thorel)
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9. ATRIOVENTRICULAR NODE.
Location – just
beneath the
endocardium on right
side of lower part of
atrial septum.
Convey impulses from
internodal tracts to
ventricles.
Friday, May 4, 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.
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11. PURKINJE FIBRES
Spread deep to
Endocardium & reach
all parts of ventricles
including bases of
papillary muscles.
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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.
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13. INNERVATIONAL
CHARACTERISTIC OF HEART
Both SA & AV node
supplied by
sympathetic &
parasympathetic
Sympathetic – stellate
ganglion
Parasympathetic -
Vagus
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14. INNERVATIONAL
CHARACTERISTIC OF HEART
SA node – supploied
by
Right vagus
Right sympathetic
AV node
Left vagus
Left sympathetic.
Friday, May 4, 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.
Friday, May 4, 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
Friday, May 4, 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.
Friday, May 4, 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.
Friday, May 4, 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.
Friday, May 4, 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.
Friday, May 4, 2018

21. ROLE OF ANS IN CONTROLLING
HEART RHYTHM
Vagal tone
Effect of
parasympathetic
stimulation.
Effect of sympathetic
stimulation.
Friday, May 4, 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.
Friday, May 4, 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.
Friday, May 4, 2018

24. EFFECT OF SYMPATHETIC
STIMULATION.
Causes release of NE –


Ca permeability -
rate & force of
contraction.
Friday, May 4, 2018

25. SPREAD OF CARDIAC IMPULSE.
SA node & atria
AV node
Ventricular
conduction.
Friday, May 4, 2018
SA NODE
AV NODE
BUNDLE BRANCHES
PURKINJE FIBRES
ENDOCARDIAL &
EPICARDIAL SURFACE
OF VENTRICLES.