Lown-Ganong-Levine syndrome
Synonyms and keywords: Lown-Ganong-Levine Syndrome, LGL syndrome, Pre-excitation syndromes, Short PR Normal QRS Complex Syndrome, Clerc-Levy-Cristesco syndrome, Coronary nodal rhythm syndrome, Short PQ interval syndrome, Short P-R syndrome.

# Overview
Lown-Ganong-Levine syndrome (LGL) is actually a pre-excitation syndrome with EKG findings including short PR interval, narrow or normal QRS complex, and a normal P wave. It is caused by the presence of accessory bundles of fibers known as James fibers which lead to the development of abnormal conduction pathways. The LGL syndrome was named after Bernard Lown, William Francis Ganong, and Samual Levine who described it in 1952. Patients of LGL usually present with a history of palpitations, lightheadedness, shortness of breath, and sometimes chest pain. There is an increased risk of tachyarrhythmias and syncope. EKG is the principal modality of investigation for establishing a diagnosis. Usually, antiarrhythmics are given to prevent the development of tachyarrhythmias but recently radiofrequency ablation of the accessory pathways has been the mainstay of treatment with a good prognosis.

# Historical Perspective
- Following is the timeline of LGL syndrome with its discovery and developments of its bypass tracts:

# Classification
- LGL syndrome can be classified based on the accessory pathways into the following categories:

# Pathophysiology
- The pathophysiology of LGL syndrome is not yet understood completely.
- Multiple theories have been proposed to suggest the mechanism of LGL.
- The current theory supporting the mechanism of LGL is that it may result from numerous underlying causes that involve junctional pathways which partially or wholly bypass the AV node with subsequent normal conduction down the bundle of His.
- The three accessory pathways as discussed in the classification section have been proposed to be the main triggering factors for the development of LGL.
- Lown-Ganong-Levine pattern may occur including the following fibers:
Brechenmacher fibers (account for 0.03% of the patients presenting with LGL)
Intra-nodal bypass tracts
James fibers
- Brechenmacher fibers (account for 0.03% of the patients presenting with LGL)
- Intra-nodal bypass tracts
- James fibers
- The intra-nodal bypass tracts allow the rapid conduction of action potential through the AV node bypassing the other slow pathways.

# Causes
- The exact causes of LGL syndrome have not been completely understood yet.
- However, the presence of following accessory pathways can predispose a patient to the development of LGL syndrome:
James fibers
Brechenmacher fibers
Intra-nodal fibers
- James fibers
- Brechenmacher fibers
- Intra-nodal fibers
- Sometimes, patients with LGL syndrome have a history of congenital heart disease.

# Differentiating Lown-Ganong-Levine Syndrome from other Diseases
- The differential diagnosis for Lown-Ganong-Levine syndrome includes the following diseases as shown in the table below:

# Epidemiology and Demographics
- In a retrospective study conducted by Bernard Lown, William Francis Ganong, and Samual Levine,  200 electrocardiograms (EKGs) of 13500 patients showed EKG findings with the prevalence of just over 1%.

## Age
- There is currently insufficient data regarding age predilection of LGL syndrome.

## Gender
- There is currently insufficient data regarding gender predilection of LGL syndrome as the LGL pattern is not associated with an increased incidence in one particular sex.
- However, Lown in 1952 reported 70.9% of the 34 cases in women.

## Race
- There is currently insufficient data regarding race predilection of LGL syndrome as the LGL pattern is not associated with an increased incidence in one particular ethnic background.

# Risk Factors
- The data regarding the risk factors predisposing to LGL syndrome is insufficient. However, the following conditions or factors may lead to the various pre-excitation syndromes:
Presence of accessory bypass tracts
The high-risk population for sudden cardiac death in patients with pre-excitation syndromes includes the following:
Policemen
Athletes
Firemen
Pilots
Steelworkers
- Presence of accessory bypass tracts
- The high-risk population for sudden cardiac death in patients with pre-excitation syndromes includes the following:
Policemen
Athletes
Firemen
Pilots
Steelworkers
- Policemen
- Athletes
- Firemen
- Pilots
- Steelworkers

# Natural History, Complications and Prognosis

## Natural History
- LGL syndrome can be asymptomatic or can present with the following symptoms:
Palpitations
Lightheadedness
Shortness of breath
Syncope
- Palpitations
- Lightheadedness
- Shortness of breath
- Syncope
- In the case of congenital heart disease or genetic anomaly, it can also present as paroxysms of tachycardia or chest pain.

## Complications
- There is an increased risk of developing tachyarrhythmias.
- Certain medications such as sympathomimetics should be used with caution in patients of LGL syndrome.
- Digitalis does not produce any effect on LGL syndrome but it can slow down the conduction in the AV node which prevents AVRT in these patients.
- Although beta-blockers do not directly affect the accessory pathway, however, they can slow conduction through the AV node similar to digitalis.

## Prognosis
- The overall prognosis of patients with LGL syndrome is good.
- Patients are usually asymptomatic but some can develop certain clinical features such as:
Palpitations
Shortness of breath
Occasional episodes of:
Atrial fibrillation
Atrial flutter
AVRT
Other tachyarrhythmias
They can also lead to the development of ventricular arrhythmias in rare cases.
- Palpitations
- Shortness of breath
- Occasional episodes of:
Atrial fibrillation
Atrial flutter
AVRT
Other tachyarrhythmias
They can also lead to the development of ventricular arrhythmias in rare cases.
- Atrial fibrillation
- Atrial flutter
- AVRT
- Other tachyarrhythmias
- They can also lead to the development of ventricular arrhythmias in rare cases.

# Diagnosis

## Diagnostic Criteria
- Characteristic ECG findings of LGL syndrome are 
Short PR interval (<120ms)
Normal P wave axis
Normal/narrow QRS morphology in the presence of paroxysmal tachyarrhythmia
- Short PR interval (<120ms)
- Normal P wave axis
- Normal/narrow QRS morphology in the presence of paroxysmal tachyarrhythmia

## History and Symptoms
- LGL syndrome is usually asymptomatic.
- The symptoms of LGL syndrome usually overlap with those of pre-excitation syndrome and may include the following:
Palpitations
Dizziness
Lightheadedness
Shortness of breath
Racing heart
Syncope
Chest pain or tachycardia (in case of an underlying cardiac structural defect)
- Palpitations
- Dizziness
- Lightheadedness
- Shortness of breath
- Racing heart
- Syncope
- Chest pain or tachycardia (in case of an underlying cardiac structural defect)

## Physical Examination
- Patients with LGL syndrome usually appear normal.
- Physical examination findings are limited in LGL syndrome.
- During cardiac auscultation or palpation of peripheral pulses, there can be irregular rhythm.

## Imaging Findings

### ECG
- The diagnosis of LGL syndrome can be made by the use of resting EKG. EKG findings usually show:
Short PR interval (<120ms)
Normal P wave axis
Normal/narrow QRS morphology in the presence of paroxysmal tachyarrhythmia
- Short PR interval (<120ms)
- Normal P wave axis
- Normal/narrow QRS morphology in the presence of paroxysmal tachyarrhythmia

## Other Diagnostic Studies
- Holter monitors or implantable loop recorders may provide insight into the underlying conduction abnormalities.

# Treatment

## Medical Therapy
- The mainstay of therapy for LGL syndrome is the use of antiarrhythmic medications to prevent tachyarrhythmias.
- Medications such as digitalis, beta-blockers, calcium channel blockers and Class I and III antiarrhythmic drugs have been used to slow down AV conduction and prevent AVRT and other arrhythmias.
- Drugs such as sotalol and amiodarone have promising effects as a treatment option for LGL syndrome but are still under investigation and need further studies.

## Surgery
- Patients refractory to medical management can be managed by the use of radiofrequency catheter ablation as it has become a primary treatment option in various pre-excitation syndromes.
- This can be further implicated by the implantation of a permanent pacemaker.

## Prevention
- There are no primary preventive measures available for LGL syndrome.