Diagnosis
The diagnosis of whether the PR prolongation is due to AV nodal disease or diffuse conduction system disease is typically made by an electrophysiology study of the conduction system. In an electrophysiology study, trifascicular block due to AV nodal disease (true trifascicular block does not involve the AV node) block is represented by a prolonged AH interval (denoting prolonged time from impulse generation in the atria and conduction to the bundle of His) with a relatively preserved HV interval (denoting normal conduction from the bundle of His to the ventricles). Trifascicular block due to distal conduction system disease is represented by a normal AH interval and a prolonged HV interval.
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