The bundle branches arise from the AV node and Bundle of His. The bundle branches are comprised of Purkinje cells, which are specialized cells that conduct very fast compared to conduction speed of contracting myocytes. There are a few key points:
- the right bundle rapidly conducts the depolarizing electrical charge to the RV
- the left bundle rapidly conducts the depolarizing electrical charge to the LV
- the left bundle also conduts the depolarizing electrical charge to the ventricular septum
- the conducting fibers are all located on the endocardial (inner) surface of the heart. This is extremely important to understand because:
- the wave of depolarization travels from endocardium (inner surface) to epicardium (outer surface) as a result of the anatomic location of the conducting fibers
- this pattern of depolarization is efficient because it would not be efficient to contract outer layer cells first if the cells on the inner layer were still relaxed
- understanding that the wave of depolarization travels from endocardium to epicardium is important in understanding other concepts such as Q waves, R wave progression, ST changes and other important concepts that we will cover in future modules. Ensure that you understand this concept.
The diagram below shows a simple representation of the conducting fibers of the heart:
