Bundle of His

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	The Bundle of His plays an important role in atrioventricular conduction in the natural excitation of the heart.  Upon depolarization the cardiac action potential proceeds from the sinoatrial (SA) node to the atrioventricular (AV) node via internodal pathways in the atrium.  At the AV node the nodal fibers merge with the Bundle of His, which is the beginning of the specialized ventricular conduction system.  The bridging of this gap between the AV node and the Bundle of His is normally the only way for conduction to proceed normally from the atria to the ventricles.  See diagram p. 32


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Sample Problems:





Explain the importance of the significance of the Bundle of His in determination of the degree of Atrioventricular (AV) block.  Hint: See box on p. 35 for details.



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Answers:





His bundle electrograms have been shown to determine whether the site of AV block is above or below the bundle of His.  Blocks below the bundle are more serious because it can evolve into a 3rd degree block (or complete heart block) where impulse is unable to travel from the atria to the ventricles.  Artificial pacemakers are often required for blocks below the bundle of His.



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For more information on this topic, please refer to Berne & Levy , Text pgs. 32 & 35

Also, check out the following links that may be helpful:

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This page was written by Bryan D. Lambird , a student in this course.

BME 403 Pages maintained by the T.A., Douglas Miles.