• Accessory Pathways
• Lown-Ganong-Levine (LGL) Syndrome
• LGL Syndrome and Shortened PQ Interval
• Accelerated AV Conduction and Shortened PQ Interval
• ECG and LGL Syndrome

Accessory Pathways

• Physiologically, the atria are electrically isolated from the ventricles
• The only electrical connection is the AV junction
• If the AV junction is disrupted, a third-degree AV block occurs (electrical isolation of the atria from the ventricles)
• 0.5% of the population has an additional accessory pathway besides the AV junction
• Thus, the atria and ventricles are electrically connected via two pathways:
• AV junction
• Accessory pathway
• 10% of patients with an accessory pathway have an additional secondary accessory pathway
• which is often inactive
• Based on location, there are three main accessory pathways:
• Kent bundle
• Connects the atria and ventricles
• (Atrio-Ventricular bypass)
• Creates WPW syndrome
  
  
• James bundle
• Connects the atria to the His bundle
• (Atrio-Hisian bypass)
• Creates LGL syndrome
  
  
• Mahaim bundle
• Connects the AV junction to the ventricles
• (Nodo-Ventricular bypass)
• Creates Mahaim syndrome

LGL Syndrome and Shortened PQ Interval

• James Bundle
• Connects the atria to the His bundle, bypassing the AV node
• (Atrio-Hisian bypass)
• The PQ interval is shortened (<0.12s)
• Because the impulse reaches the ventricles without slowing (bypasses the AV node)
• Narrow QRS complex
• The ventricles are activated through the conduction system (as in sinus rhythm)
• May lead to Atrioventricular Reentry Tachycardia (AVRT)
  
  
• The same ECG pattern can be seen in Accelerated Junctional Conduction

ECG and LGL Syndrome

• Shortened PQ interval (< 0.12s)
• Narrow QRS complexes (< 0.12s)
  
  
• Sometimes the shortened PQ interval is evaluated as follows:
• Accelerated AV conduction:
• Shortened PQ interval + Normal QRS complex
• LGL syndrome:
• Shortened PQ interval + Normal QRS complex + Frequent AVRT
• Atria and ventricles are connected via 2 pathways
• therefore AV reentry tachycardia (AVRT) can occur

LGL Syndrome

• Shortened PQ interval (< 0.12s)
• Narrow QRS complex (< 0.12s)
• It may also be due to accelerated AV conduction
• Differential diagnosis is performed using electrophysiological examination