Conduction Of Cardiac Impulse

CONDUCTION OF CARDIAC IMPULSE

BY

RERA_AVIS

TRANSMISSION OF IMPULSE FROM SA NODE TO ATRIA

 Impulse is transmitted directly to atrial muscle fibers of right

atrium like ripples over pond.

 Impulse is transmitted to left atrium through anterior

interatrial band of bachmann.

TRANSMISSION OF IMPULSE FROM SA NODE TO AV NODE Impulse is transmitted from SA node to AV node through 3 specialized conduction bundles  Anterior internodal bundle of Bachman  Middle internodal bundle of Wenckhebach  Posterior internodal bundle of Thorel

AV NODE  AV node is located in the posterior wall of right atrium behind

the opening of tricuspid valve.  It is also called as AV node of Tawara  It is 22 mm long, 10mm wide and 3mm thick  AV node has three portions Atrionodal portion ( AN portion) Nodal portion ( N portion) Nodal His portion ( NH portion )

AV node continues with the common bundle of His ( AV bundle). Cardiac impulse is delayed for 0.09 seconds in AV node because of reduced conduction velocity in the node mainly in N and NH portions.

AN

N N H

COMMON BUNDLE OF HIS ( AV NODAL BUNDLE)  Bundle of His has two portions

Proximal (penetrating) portion Distal portion  Further delay for 0.04 seconds occurs in the bundle of His mainly in the proximal penetrating portion.  Thus a total delay of 0.13 seconds occur during transmission

through AV node and proximal portion of bundle of His.  This delay occurs because of reduced number of gap junctions

in this part of conduction system which increases the resistance  This delay allows atria to contract 0.16 seconds ahead of

ventricles. So that the blood present in atria is pushed in the ventricles before they start contracting.

TRANSMISSION THROUGH BUNDLE BRANCHES  Common bundle of His after penetrating through the

atrioventricular fibrous tissue (AV Septum) passes down in the interventricular septum for 5-15 mm and then divides in two branches RIGHT BUNDLE BRANCH LEFT ANTERIOR FASICLE LEFT BUNDLE BRANCH LEFT POSTERIOR FASICLE

 Each of three bundles ( RBB,LAF,LPF) spread down towards the

apex of heart and progressively divides in smaller branches.

 These branches supply impulse to all parts of ventricular

myocardium through specialized Purkinje fibers.

 Conduction of cardiac impulse is very quick once it passes

through the AV node and common bundle. Rapid transmission is due to very high permeability of gap junctions present in this part of conductive system  Purkinje fibers are broadest cells in the heart. Their diameter

is 70 to 80 um and their conduction velocity is up to 4 m/sec  The ends of Purkinje fibers penetrate into the muscle fibers of

ventricles and become continuous with them and then impulse continues from one muscle fiber to the other.  This transmission is slightly slow at a rate of 0.5m/s

ONE WAY TRANSMISSION OF IMPULSE IN AV NODE AND AV BUNDLE

 INABILITY OF ACTION POTENTIALS TO

TRAVEL BACKWORDS INTO ATRIA

 TRANSMISSION OF IMPULSE FROM ATRIA TO

VENTRICLES OCCURS THROUGH AV NODE ONLY

SPREAD OF IMPULSE IN VENTRICLES  First part to be activated is interventricular septum  Second is anteroseptal portion of ventricles  Third is bulky anterior and apical portion  Finally posterobasal portion  Transmission of impulse occurs from endocardiun to

epicardium i.e. inside out

CONDUCTION VELOCITIES OF DIFFERENT PARTS

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