Cardiac dissection
Conduction tissue

Author: R. Amita, M.D.(see Authors page)

Revised: 19 March 2018, last major update December 2015

Copyright: (c) 2015-2018, PathologyOutlines.com, Inc.

PubMed Search: Conduction tissue [title] heart
Cite this page: Amita, R. Conduction tissue. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/heartconductiontiss.html. Accessed April 21st, 2018.
Definition / general
  • The specialized tissues of the heart (neuromyocardial cells) that initiate and conduct the cardiac impulse consist of:
    1. Sinus node (SA node, sinoauricular node, node of Keith-Hack)
    2. Atrioventricular junctional area, including the AV node (node of Twara) and His bundle
    3. Bundle branches (branching portion of AV bundle, bifurcation, ventricular conduction tissue) and Purkinje fibers
Gross description
  • Sinus node:
    • An oval shaped, elongated mass 10-20 mm long and up to 5 mm thick
    • The "head" of the node extends toward the interatrial groove while its "tail" extends toward the orifice of the inferior vena cava
    • In most hearts, it is located in the subepicardial region (less than 1 mm from the epicardial surface) at the lateral junction of the superior vena cava and right atrium
    • Supplying the sinus node is a prominent artery ("sinus node artery") arising from the right coronary artery in 55 - 60% of cases and from the left circumflex coronary artery in 40 - 45%

  • Atrioventricular (AV) node:
    • Situated in the inferomedial right atrium and forms the top of the only normal electrical connection between atria and ventricles
    • Blood supply is from the right coronary artery in 90% of cases, the left circumflex in the remainder

  • His-Purkinje System:
    • Located at the crest of the interventricular septum
    • The AV node terminates in the top of the His bundle which then branches into a left and right bundle branch
    • The right bundle branch is a cord-like structure insulated from surrounding myocardium for most of its length
    • When it reaches the right ventricular apex it makes its initial electrical contact with myocardial cells of the anterior papillary muscle
    • In contrast, the left bundle branch is usually a fan-like structure, dividing soon after its origin into anterior and posterior fascicles
    • These fascicles then further ramify into the rest of the Purkinje network
    • Blood supply is almost entirely from the left anterior descending artery
    • The proximal His bundle may have dual supply, from both right and left coronary arteries
Diagrams / tables
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Purkinje network

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Compact atrioventricular node

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Conduction system

Microscopic (histologic) description
    Sinus node:
  • Cells include nodal cells, transitional cells and atrial muscle cells

  • Nodal cells (P cells) are small ovoid, pale staining and poorly striated compared with the general myocardial cells
  • The nodal cells are grouped together in interconnecting fascicles placed in a background of fibrous matrix
  • Nodal cells are thought to be the source of normal impulse formation in the sinus node
  • In the infant sinus node, the nodal cells predominate relative to the fibrous matrix; in contrast, in the adult sinus node, the fibrous tissue is predominant with the nodal cells scattered within the connective tissue

  • Transitional cells (T cells) are elongated with characteristics intermediate between the packed nodal cells and the individual atrial myocardial cells
  • Transitional cells are located at the margins of the node where the nodal cells become contiguous with atrial myocardium
Microscopic (histologic) images
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Sinoatrial (SA) node

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Sinus node fibrosis

Additional references