Cardiac anatomy

Cardiac Conduction System

Primary components:
- Sinoatrial node (SA)
- Atrioventricular node (AV)
- Bundle of His
- Right and left bundle branches
- Purkinje system
Pacemaker nodal cells
- P cells or round cells
- Transitional or T cells

unknown original source; if this image is in violation of copyright, please inform us.

SA nodal location: in the right atrial wall at the junction of the right atrium with the superior vena cava (SVC)
- above image courtesy of Marquette Electronics
Connections between the SA and AV nodes: internodal conduction system composed of:
1. Anterior (Bachman's bundle)
2. Middle bundle
3. Posterior internodal systems
Left atrial activation: Bachman's bundle

AV nodal location: in the right atrial floor (near the coronary sinus ostium)

image from An Atlas and Practical Guide to Histology, by Dr. Kenneth Chan with technical assistance from Dr. Simon Cool and Mr. Duncan McCardle. The University of Queensland, Department of Anatomical Sciences © 1998

AV nodal anatomy: 3 regions
- A-N transitional zone (cells smaller than normal atrial cells)
- N region (consisting of round/P cells (similar to SA nodal cells))
- N-H region (transitional area, near the bundle of His)
Bundle of His pathway
1. Traverses the superior edge of the interventricular septum to the septal muscular portion apex
2. Divides into right and left bundle branches
3. Branches extend towards the subendocardium along ventricular surfaces
Right Bundle of His pathway
- Emerges in the right ventricular endocardium (near the base of the anterior papillary muscle)
  - One branch passes through the moderator band
  - The second branch traverses over the right ventricular endocardial surface
Left Bundle of His pathway
- Left bundle subdivision:
  - Anterior and posterior fascicles: division shortly after left bundle branch origin (medial fascicle come originating from the left bundle, just after the anterior fascicle)
    - Medial fascicle: activates septal myocardium
Right and left bundle branch Fascicle terminations:
- Subdividing, forming the Purkinje system
  - Left bundle branch fascicle:
    - Initial endocardium contact: interventricular septum, below the aortic valve
  - Right bundle-branch fascicle:
    - Initial anatomical contact: ventricular subendocardium (near anterior papillary muscle base)

**Summary**

unknown original source; if this image is in violation of copyright, please inform us.

Primary Reference: Lake, C.L. Cardiovascular Anatomy and Physiology, Third edition (Barash, PG, Cullen, BF, Stoelting, R.K, eds), Lippincott-Raven Publishers, Philadelphia, pp. 805-835, 1997
Primary Reference: Ross, AF, Gomez, MN. and Tinker, JH Anesthesia for Adult Cardiac Procedures in Principles and Practice of Anesthesiology (Longnecker, D.E., Tinker, J.H. Morgan, Jr., G. E., eds) Mosby, St. Louis, Mo., pp. 1659-1698, 1998.
Primary Reference: Shanewise, JS and Hug, Jr., CC, Anesthesia for Adult Cardiac Surgery, in Anesthesia, 5th edition,vol 2, (Miller, R.D, editor; consulting editors, Cucchiara, RF, Miller, Jr.,ED, Reves, JG, Roizen, MF and Savarese, JJ) Churchill Livingston, a Division of Harcourt Brace and Company, Philadelphia, pp. 1753-1799, 2000.
Primary Reference: Wray Roth, DL, Rothstein, P and Thomas, SJ Anesthesia for Cardiac Surgery, in Clinical Anesthesia, third edition (Barash, PG, Cullen, BF, Stoelting, R.K, eds), Lippincott-Raven Publishers, Philadelphia, pp. 835-865, 1997

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