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Mahaim fiber tachycardias

Philip J Podrid, MD, FACC
Section Editor
Brian Olshansky, MD
Deputy Editor
Brian C Downey, MD, FACC


The term cardiac preexcitation was originally used to describe premature activation of the ventricles in patients with the Wolff-Parkinson-White (WPW) pattern. This term has been broadened to include all conditions in which antegrade ventricular activation or retrograde atrial activation occurs partially or totally via an anomalous pathway distinct from the normal cardiac conduction system.

The classic form of cardiac preexcitation is the WPW pattern, which is characterized by a short PR interval and a broad QRS complex with a delta wave. The anatomic substrate for this is a band of myocytes that bridges the fibrous atrioventricular junction, also known as the bundle of Kent [1]. The electrocardiographic features are a result of premature ventricular activation due to conduction over the accessory pathway. (See "Anatomy, pathophysiology, and localization of accessory pathways in the preexcitation syndrome".)

Several other pathways, including a bundle of James (which links the atrial myocardium to the bundle of His and is responsible for Lown-Ganong-Levine syndrome [a short PR interval and a normal QRS complex]) and Mahaim fibers (which link the His bundle to the ventricular myocardium), have been postulated to result in cardiac preexcitation. However, most lack the histopathologic correlation that has been demonstrated for the WPW pattern. This topic will discuss the Mahaim fiber tachycardias. WPW and other non-WPW forms of preexcitation are discussed separately. (See "Epidemiology, clinical manifestations, and diagnosis of the Wolff-Parkinson-White syndrome" and "Lown-Ganong-Levine syndrome and enhanced atrioventricular nodal conduction".)


In 1937, during pathologic examination of the heart, Mahaim and Benatt identified islands of conducting tissue extending from the His bundle tissue into the ventricular myocardium [2]. These fibers were termed Mahaim or fasciculoventricular fibers [2]. This description was subsequently expanded to include connections between the atrioventricular (AV) node and the ventricular myocardium (nodoventricular fibers) (figure 1). These findings have been confirmed by other investigators, but true continuity of these pathways is less common than was initially suspected [1,3,4].

Mahaim fibers were originally classified into two main groups depending upon their site of origin [1]:

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Literature review current through: Oct 2017. | This topic last updated: Sep 22, 2017.
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