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Conducting System of the Heart

The heart generates its own electrical impulses and has its own specially devised pathway that helps spread an action potential through the cardiac muscle. This article will explain the conducting system of the heart and touch upon the possible pathological ailments that directly relate to it.

Anatomy

The cardiac conducting system is composed of five main elements which are mentioned here in the order of which an action potential reaches them.

Sinoatrial node

The sinoatrial node is the pacemaker of the heart and is situated superior to the sulcus terminalis of the right atrium, next to the opening of the superior vena cava. This special myocardial tissue that is difficult to distinguish histologically from surrounding cardiac muscle, propagates the electrical impulses and therefore governs the sinus rhythm from minute to minute. If this node should fail, the atrioventricular node has the capacity to undertake the role of pacemaker.

Sinoatrial node (Branch to it) - ventral view

Sinoatrial node (Branch to it) - ventral view

Atrioventricular node

The atrioventricular node is also located in the right atrium at a level that places it posteroinferior to the interatrial septum and next to the septal cusp of the tricuspid valve. It picks up and continues the action potentials produced by the sinoatrial node and in some cases will even propagate a few of its own. Its innovative area covers the atria of the heart, just as the sinoatrial node does.

Bundle of His

The bundle of His is a specialized bundle of cardiac muscle fibers, that is seated within the interatrial septum. These fibers run along the interventricular septum to the apex of the heart, where they branch further as conducting (Purkinje) fibers that extend into the myocardium of the ventricles.

The right side has a single bundle that reaches the apex of the right ventricle before curving around it and travelling back along the right side of the heart.

The left side has an anterior and a posterior division. The anterior division cuts across the left ventricle by running through its anterosuperior wall, while the posterior division behaves as the right bundle does and circles around the left side of the heart after reaching its apex.

Heart conductive system - histological slide

Heart conductive system - histological slide

Purkinje fibers

The terminal strands of nervous tissue are known as the purkinje fibers and these are responsible for making sure that every small group of cells is reached by an electrical stimulus, so that a maximum muscular contraction can occur.

Bundle of purkinje fibers - histological slide

Bundle of purkinje fibers - histological slide

Cardiac arrhythmia

Cardiac arrhythmia occurs when the sinoatrial node produces action potentials that fail to or exceed the normal range of a sinus rhythm which is between sixty to one hundred beats per minute.

Sinus bradycardia is observed when the electrical impulses occur less than sixty times in a minute, while sinus tachycardia is the opposite at over one hundred impulses in a minute. It should be noted that in athletes undergoing vigorous exercise, sinus tachycardia is not seen to be pathological, but rather as an effort to keep the body in its natural homeostasis by compensating for prolonged increased activity.

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Show references

References:

  • Frank H. Netter, MD, Atlas of Human Anatomy, Fifth Edition, Saunders - Elsevier, Chapter 3 Thorax, Subchapter 22 Heart, Guide Thorax: Heart Page 114.
  • Ramin Assadi, MD, Richards A. Lange, MD. Conduction system of the Heart. Emedicine. November 6, 2013.
  • Cardiology teaching package. University of Nottingham.

Author:

  • Dr. Alexandra Sieroslawska

Illustrators:

  • Sinoatrial node (Branch to it) - ventral view  - Yousun Koh
  • Heart conductive system - histological slide - Smart In Media
  • Bundle of purkinje fibers - histological slide - Smart In Media
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