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Anatomy, pathophysiology and localization of accessory pathways in the preexcitation syndrome

Bradley P Knight, MD, FACC
Section Editor
Peter J Zimetbaum, MD
Deputy Editor
Brian C Downey, MD, FACC


Conduction from the atria to the ventricles normally occurs via the atrioventricular node (AV)-His-Purkinje system. Patients with a preexcitation syndrome have an additional or alternative pathway, known as an accessory pathway, which directly connects the atria and ventricle and bypasses the AV node. AV conduction through an accessory pathway (most commonly a direct AV connection) results in the earlier activation of the ventricles than if the impulse had traveled through the AV node; hence the term preexcitation.

Accessory pathway is a generic term which may indicate either a "tract" which bypasses the AV node but inserts into the specialized conduction system (eg, the bundle of His, right or left bundles, or one of the fascicles), or a "connection" which bypasses the AV node and terminates directly within the myocardium. Other names that may be used include anomalous AV pathway, connection, or tract; accessory AV bypass pathway, connection, or tract; or simply AV bypass, tract, or pathway. (See "General principles of asynchronous activation and preexcitation".)

At other times, the specific sites of origin and termination are used. Examples include accessory atrioventricular connection, atrio-Hisian pathway or connection, or atriofascicular pathway or connection (table 1).

Preexcitation through an AV bypass tract, the bundle of Kent, produces the electrocardiographic pattern described by Wolff, Parkinson, and White in 1930 [1]. The terms preexcitation and Wolff-Parkinson-White (WPW) syndrome are often used interchangeably even though there are other forms of preexcitation. The electrocardiographic pattern of WPW should be differentiated from the "WPW syndrome," since patients with the latter have both the electrocardiographic pattern of preexcitation and paroxysmal tachyarrhythmias [2]. (See "Epidemiology, clinical manifestations, and diagnosis of the Wolff-Parkinson-White syndrome".)

This topic will review the anatomy and electrophysiologic properties of the accessory pathways. The related issue of asynchronous activation, the arrhythmias associated with WPW, and the pharmacologic and nonpharmacologic treatments of patients with this syndrome are discussed separately. (See appropriate topic reviews). A detailed discussion of electrophysiologic mapping techniques is found elsewhere. (See "Invasive cardiac electrophysiology studies", section on 'Mapping and ablation'.)


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Literature review current through: Sep 2016. | This topic last updated: Nov 19, 2015.
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