First degree AV block pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ahmed Elsaiey, MBBCH [2], Cafer Zorkun, M.D., Ph.D. [3]

Pathophysiology

Main article: Electrical conduction system of the heart

First degree AV block may be due to conduction delay in the AV node, His-Purkinje system (made up by the bundle of His and the Purkinje fibers), or a combination of the two. The majority of cases are due to a dysfuction of the AV node; however, when first degree heart block coexists with a bundle-branch block, the cause is more likely to be a conduction delay in the His-Purkinje system. There are no missed beats in first degree AV block and all the impulses from the atria are transmitted to the ventricles resulting in a regular ventricular beat rhythm.

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First Degree AV Block with Normal QRS Duration

First degree AV block with normal QRS duration, in majority of cases, results from atrial or AV nodal delay. Other probable sites include the bundle of His and infra-Hisian conduction system.

First Degree AV Block with Wide QRS Complex

First degree AV block with wide QRS complex most often results from delay in conduction in the bundle of His and in some patients, the AV node.

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