eMedicine Specialties > Cardiology > Arrhythmias

Lown-Ganong-Levine Syndrome

Author: Daniel M Beyerbach, MD, PhD, Consulting Staff, Florida Electrophysiology Associates
Coauthor(s): Christopher Cadman, MD, Director of Arrhythmia Service, Assistant Professor, Department of Internal Medicine, Division of Cardiology, University of New Mexico
Contributor Information and Disclosures

Updated: Sep 6, 2006

Introduction

Background

The Lown-Ganong-Levine syndrome (LGL) is usually considered in a class of preexcitation syndromes that includes the Wolff-Parkinson-White syndrome (WPW), LGL, and Mahaim-type preexcitation. Investigations into WPW have revealed that an accessory pathway for conduction, called a bundle of Kent, from the atria to the ventricles underlies the preexcitation observed in patients with WPW. Less is known regarding the structural anomalies underlying LGL. Theories proposed to explain LGL have centered around the possible existence of intranodal or paranodal fibers that bypass all or part of the atrioventricular (AV) node.

In 1938, Clerc et al first described the occurrence of frequent paroxysms of tachycardia in patients with a short PR interval and normal QRS duration. This syndrome was again described in 1952 by Lown, Ganong, and Levine, whose names form the eponym now used to describe it. In 1946, Burch and Kimball proposed that an atrio-His (AH) bundle pathway might explain the findings of the syndrome, although no such pathway had yet been identified anatomically. In 1961, James described fibers that originate in the low atrium and terminate low in the AV node. Brechenmacher et al reported anatomic findings of an AH bundle in 1974. Subsequent investigations into the origin of LGL have largely involved invasive electrophysiologic studies that have sought to identify structural and functional anomalies that might explain the findings of LGL.

Criteria for LGL include PR interval less than or equal to 0.12 second (120 ms), normal QRS complex duration, and occurrence of supraventricular tachycardia but not atrial fibrillation or atrial flutter.

Historically, some authors have referred to patients with a short PR interval and normal QRS duration as having LGL. However, this practice has been largely abandoned as more evidence has accumulated demonstrating that such patients without a history of tachycardia likely fall into a class of normal variants. Patients with an isolated finding of short PR interval may be characterized as having accelerated atrioventricular nodal conduction.

The term enhanced atrioventricular nodal conduction (EAVNC) refers to a set of functional criteria which includes an AH interval less than or equal to 60 ms, 1-to-1 AV nodal conduction at rates as high as 200 beats per minute, and an abnormally small increase in AH interval as atrial pacing rate is increased.

EAVNC represents a functional characterization of the AV node, whereas LGL refers to a syndrome of supraventricular tachycardia in association with a short PR interval. The short PR interval in LGL may be related to the presence of EAVNC. LGL and EAVNC may coexist, or either may exist alone in a given patient.

Pathophysiology

No single structural anomaly has been implicated directly as the cause of 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, including the presence of James fibers, Mahaim fibers, Brechenmacher-type fibers, and an anatomically underdeveloped (hypoplastic) or small AV node. James fibers run from the upper portion of the AV node and insert in the lower portion or in the bundle of His. Mahaim fibers may originate in the lower portion of the AV node, the bundle of His, or the bundle branches, and they terminate in the interventricular septum or in a bundle branch. Each of these fibers has been identified histologically. However, none of these anomalous communications has been linked causally to the presence of LGL. The histologic presence of fibers does not speak to whether these fibers are functional, with conductive properties.

EAVNC has been investigated as a possible functional basis for LGL. The criteria for EAVNC were established arbitrarily on the basis of observations of some patients with what seemed to be abnormally rapid AV nodal conduction times. In 1983, however, Jackman et al provided convincing evidence that EAVNC does not exist as a phenomenon separate from normal AV nodal physiology, but that AV nodal conduction physiology comprises a spectrum of AH intervals. In their series of 160 consecutive patients, they failed to identify a distinct group of patients with abnormally rapid AV nodal conduction. Rather, they found a broad spectrum of AH intervals in a unimodal, continuous distribution.

The modern view of LGL is that no convincing evidence suggests that this is a syndrome separate from other known phenomena. LGL was identified as a syndrome prior to the advent of catheter-based electrophysiologic (EP) studies. EP studies have led to several realizations. The short PR interval of LGL likely represents one end of the spectrum of normal PR intervals. Most patients with putative LGL are found at EP study to have another basis for paroxysmal tachycardia. Most have AV nodal reentrant tachycardia. Others have concealed accessory pathways, usually near the septum.

Thus, unless further studies demonstrate definitive structural or functional anomalies, the diagnosis of LGL remains a clinical diagnosis of the era before EP study.

Frequency

United States

Lown and associates described tachyarrhythmias in 17% of patients with a short PR interval. Some 2-4% of the adult population has a PR interval less than or equal to 0.12 second. Taken together, these data provide an estimate of the frequency of LGL as 0.5% of the adult population.

International

Frequency mirrors that in the United States.

Mortality/Morbidity

Paroxysms of tachycardia represent the primary morbidity of LGL. Few data are available regarding the frequency of these paroxysms. Data regarding mortality from LGL are scant. Numbers in published studies are too small to estimate mortality rate with significant accuracy or confidence. In the absence of significant structural heart disease, the mortality rate appears to be very low.

Clinical

History

Symptoms of paroxysmal tachycardia may be elicited. The manifestations of these paroxysms include palpitations, lightheadedness, and shortness of breath. In cases of underlying structural heart disease or coronary artery disease, episodes of tachycardia may induce cardiac stress and produce symptoms of chest pain or possibly of hypotension or other hemodynamic instability.

Physical

Findings are normal except during tachycardic episodes; cardiovascular examination may then reveal a rapid heart rate. However, absence of this finding does not exclude LGL as a possible diagnosis, as the tachycardia of LGL is paroxysmal.

Causes

No environmental factors that contribute to occurrence of LGL have been identified. Some evidence suggests that both WPW and LGL may be hereditary in certain families.

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