The cardiac conduction system is a collection of nodes and specialised conduction cells that initiate and co-ordinate contractivity of the heart muscle. It is composed of:

Sinoatrial nodeAtrioventricular nodeAtrioventricular bundle (bundle of His)Purkinje fibres

In this article, we shall look at the anatomy of the cardiac conduction system – its structure, feature and also clinical correlationships.

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Fig 1 – Animation of the spreview of conduction via the heart


The sequence of electric occasions during one complete contraction of the heart muscle:

An excitation signal (an action potential) is produced by the sinoatrial (SA) node.The wave of excitation spreads throughout the atria, bring about them to contract.Upon getting to the atrioventricular (AV) node, the signal is delayed.It is then conducted into the bundle of His, down the interventricular septum.The bundle of His and also the Purkinje fibres spreview the wave impulses alengthy the ventricles, resulting in them to contract.

We will certainly currently comment on the anatomy of the individual components associated in the conducting system.


Contents of the Cardiac Conduction System

Sinoatrial Node

The sinoatrial (SA) node is a arsenal of specialised cells (pacemaker cells), and is located in the upper wevery one of the ideal atrium, at the junction wright here the superior vena cava enters.

These pacemaker cells can spontaneously generate electric impulses. The wave of excitation developed by the SA node spreads via gap junctions across both atria, resulting in atrial contraction (atrial systole) – via blood relocating from the atria into the ventricles.

The price at which the SA node generates impulses is influenced by the autonomic nervous system:

Sympathetic nervous system – rises firing price of the SA node, and for this reason increases heart price.Parasympathetic nervous system – decreases firing rate of the SA node, and also for this reason decreases heart price.

Atrioventricular Node

After the electric impulses spreview throughout the atria, they converge at the atrioventricular node – situated within the atrioventricular septum, near the opening of the coronary sinus.

The AV node acts to delay the impulses by approximately 120ms, to ensure the atria have sufficient time to totally eject blood into the ventricles prior to ventricular systole.

The wave of excitation then passes from the atrioventricular node into the atrioventricular bundle.

Atrioventricular Bundle

The atrioventricular bundle (bundle of His) is a extension of the specialised tissue of the AV node, and also serves to transmit the electrical impulse from the AV node to the Purkinje fibres of the ventricles.

It descends down the membranous component of the interventricular septum, prior to separating into 2 major bundles:

Right bundle branch – conducts the impulse to the Purkinje fibres of the appropriate ventricleLeft bundle branch – conducts the impulse to the Purkinje fibres of the left ventricle.
By TeachMeSeries Ltd (2021)
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Fig 2 – Outline of the individual components of the heart conduction pathway


Purkinje Fibres

The Purkinje fibres (sub-endocardial plexus of conduction cells) are a network of specialised cells. They are plentiful via glycogen and also have extensive gap junctions.

These cells are situated in the subendocardial surface of the ventricular walls, and also are able to promptly transmit cardiac activity potentials from the atrioventricular bundle to the myocardium of the ventricles.

This quick conduction permits coordinated ventricular contraction (ventricular systole) and also blood is relocated from the best and also left ventricles to the pulmonary artery and also aorta respectively.


Clinical Relevance: Artificial Pacemaker

An fabricated pacemaker is a small electric device typically fitted to monitor and also correct heart price and also rhythm. It is inserted right into the chest under the left clavicle, via wires associated to the heart using the venous mechanism.

The the majority of prevalent indication for a pacemaker is bradycardia. Once placed, the pacemaker monitors the heart price, and only fires if the price becomes as well sluggish. Pacemachines deserve to likewise be provided to treat some tachycardias, specific types of heart block and various other rhythm abnormalities.

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By Npatchett (Own work) , by means of Wikimedia Commons
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Fig 3 – There are various types of pacemakers; the the majority of widespread are dual-chamber and single-chamber.