Mahaim fibers

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Vendhan Ramanujam M.B.B.S [2]

Synonyms and keywords: Atypical bypass tracts, fasciculoventricular fibers, Mahaim physiology, nodoventricular fibers, paraspecific fibers of Mahaim

Overview

Mahaim fibers refer to the connecting fibers originating from the atrioventricular node (AV node), bundle of His, or left bundle branch that join the ventricular myocardium. The myocardial fibers resemble the tissue of origin and gradually take over the characteristics of the ventricular myocardial cells.^[1] Mahaim fibers may be present from the AV node to the right, left, or middle part of the interventricular septum. They may serve as the substrate for a variety of pre-excitation syndromes.

Historical Perspective

Mahaim and Benatt described the islands of conducting tissue extending from the bundle of His to the ventricular myocardium in 1937.^[2] These fasciculoventricular fibers as well as the nodofascicular fibers are referred to as Mahaim fibers. However, Gillette and his colleagues provided evidences suggesting anatomic substrates of the preexciation variants previously attributed to Mahaim fibers may be actually atriofascicular or atrioventricular pathways that possess anterograde decremental conduction properties.^[3]

Pathophysiology

There are two varieties of Mahaim fibers namely nodoventricular and fasciculoventricular connections. Nodoventricular accessory connections connect AV node to ventricular myocardium and fasciculoventricular connections connect bundle of His (distal part of junctional area) to ventricular myocardium. Both mediate the atrioventricular bypass through the normal conducting system. These accesory pathways lack the rate-slowing property of AV node. So a rapid conduction through there fibers will lead to short PR interval and reentrant tachycardia.

Conditions Involving Mahaim Fibers

Mahaim tachycardia is a reentrant tachycardia that occurs using the Mahaim fibers as antegrade limb and AV node as retrograde limb.^[4]

Treatment

Mahaim tachycardia is sensitive to adenosine but not to other agents that predominately affect the AV node. However, AV nodal blocking agents like calcium channel blockers and beta blockers may be effective in preventing tachycardia by affecting the retrograde AV nodal conduction in the retrograde limb of tachycardia. Both class of IA and IC antiarrhythmic agents may also slow Mahaim fiber tachycardia.
Catheter ablation of the atrioventricular junction may be useful for treating recurrent tachycardia in patients with Mahaim fibers.

References

↑ A. John Camm MD FRCP FESC FACC FAHA FHRS; Sanjeev Saksena MBBS MD FACC FESC FHRS FAHA (2011). Electrophysiological Disorders of the Heart: Expert Consult - Online and Print, 2e. Philadelphia: Saunders. ISBN 1-4377-0285-6.
↑ Mahaim, Ivan; Benatt, Alfred (1937). "Nouvelles recherches sur les connexions supérieures de la branche gauche du faisceau de His-Tawara avec la cloison interventriculaire". Cardiology. 1 (2): 61–73. doi:10.1159/000164567. ISSN 1421-9751.
↑ Gillette PC, Garson A, Cooley DA, McNamara DG (1982). "Prolonged and decremental antegrade conduction properties in right anterior accessory connections: Wide QRS antidromic tachycardia of left bundle branch block pattern without Wolff-Parkinson-White configuration in sinus rhythm". American Heart Journal. 103 (1): 66–74. PMID 7055047. Unknown parameter |month= ignored (help)
↑ Tchou P, Lehmann MH, Jazayeri M, Akhtar M (1988). "Atriofascicular connection or a nodoventricular Mahaim fiber? Electrophysiologic elucidation of the pathway and associated reentrant circuit". Circulation. 77 (4): 837–48. PMID 3127077. Unknown parameter |month= ignored (help)