What is the role of underlying mechanisms 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

The modern view of LGL is that no convincing evidence suggests that this is a syndrome separate from other known and independently characterized electrophysiologic phenomena. LGL was identified as a clinical syndrome prior to the advent of catheter-based electrophysiologic (EP) studies. EP studies and histopathologic studies have identified several underlying mechanisms that can account for the presence of a short PR interval and normal QRS. These mechanisms include enhanced AV nodal conduction, several types of fibers that bypass all or part of the AV node, and an anatomically small AV node. Studies incorporating electrophysiologic data have separately identified several types tachycardias that occur in patients with LGL. The most common tachycardias include AV nodal reentry, accessory pathway mediated tachycardia, atrial fibrillation, atrial flutter, and ventricular tachycardia. [24, 27]

To date, the underlying mechanisms that generate a short PR interval in LGL have not been found to be necessary for the development of the tachycardias identified in patients with LGL. In the case of enhanced AV nodal conduction, the short PR interval reflects anterograde conduction over the fast AV nodal pathway; however, during the most common form of AV nodal reentry, which is the most common tachycardia in patients with LGL, conduction occurs anterograde over the AV nodal slow pathway and retrograde up the AV nodal fast pathway.

Enhanced conduction over the fast pathway is not necessary for existence of the tachycardia (normal fast pathway conduction would suffice). Even the rate of the tachycardia is largely determined by slow pathway conduction, which is independent of the short PR interval mechanism. [25] Similarly, the presence of fibers that bypass all or part of the AV node is not necessary for the occurrence of atrial fibrillation or atrial flutter; functionally, these fibers may facilitate more rapid conduction of atrial arrhythmias to the ventricles.

Mutations in several ion channel genes have been linked to short-QT syndrome, the mechanisms of which are obscure. [28]

In summary, LGL is a clinical diagnosis born of the era before EP study. Many mechanisms have been identified to describe the coexistence of a short PR interval and normal QRS and many tachycardias have been identified in patients with LGL. However, none of the identified short PR interval mechanisms is necessary for the generation of LGL tachycardias.


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