Atrial Echo Beats in the Human Heart Elicited by Induced Atrial Premature Beats

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Abstract
In a patient with atrial septal defect and incomplete right bundle-branch block atrial echo beats were observed after atrial premature beats, induced with a gradually decreasing delay during regular driving of the atrium. The time relations of these atrial echo beats could be accurately defined. Considerable prolongation of the atrioventricular (A-V) conduction of the premature atrial response was found to be a necessary condition for the occurrence of atrial reciprocation, which was restricted to small and very circumscript delay ranges. Three types of atrial echo responses could be discerned. The concept of a dual A-V conduction system was not sufficient to explain the genesis of these three types. The assumption of a third pathway in the upper part of the A-V node was needed. Arguments in favor of a longitudinal dissociation of one of the two pathways postulated in the concept of dual A-V transmission were given.