What is the role of structural anomalies in the pathophysiology of Lown-Ganong-Levine syndrome (LGL)?

Updated: Dec 09, 2020
  • Author: Daniel M Beyerbach, MD, PhD; Chief Editor: Jose M Dizon, MD  more...
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Answer

No single structural anomaly has been implicated directly as the cause of the short PR interval and normal QRS in LGL. Indeed, most authors believe that LGL does not exist as a phenomenon separate from other known conditions. Several structural anomalies have been proposed as the possible basis for LGL, [18, 19] including the presence of James fibers, [20] Mahaim fibers, [21] Brechenmacher-type fibers, [7] and an anatomically underdeveloped (hypoplastic) [22] or small AV node. [16, 23]

James fibers run from the upper portion of the AV node and insert into the lower portion of the AV node, or into the bundle of His. [6] Thus, conduction over James fibers bypasses some of the intrinsic AV nodal delay, which shortens the PR interval; the QRS configuration remains normal, as ventricular activation occurs normally via His-Purkinje system.

Mahaim fibers are muscular bridges, almost exclusively right-sided in occurrence, that may originate in the lower portion of the AV node, the upper portion of the bundle of His, or the bundle branches. Mahaim fibers terminate in the interventricular septum or in a bundle branch.

Brechenmacher described fibers that run from the atrium to the His bundle, bypassing the AV node altogether.

Each of these fibers has been identified histologically. However, none of these anomalous communications has been uniquely linked to the presence of LGL. Moreover, the histologic presence of fibers does not speak to whether these fibers are functional, with conductive properties.


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