• Accessory Pathways
• Pre-excitation Syndrome
• ECG and Pre-excitation Syndrome
• Wolff-Parkinson-White (WPW) Syndrome
• Lown-Ganong-Levine (LGL) Syndrome
• Mahaim Syndrome
• Malignant Accessory Pathway
• Benign Accessory Pathway

Accessory Pathways

• Physiologically, the atria are electrically isolated from the ventricles
• The only electrical connection is the AV junction
• If the AV junction is interrupted, AV block III degree (electrical isolation of the atria from the ventricles) occurs
• 0.5% of the population have an additional accessory pathway in addition to the AV junction
• The atria and ventricles are electrically connected through 2 pathways:
• AV junction
• Accessory pathway
• 10% of patients with an accessory pathway also have an additional secondary accessory pathway
• which is often inactive
• Based on localization, there are 3 main accessory pathways:
• Kent bundle
• Connects the atria and ventricles
• (Atrio-Ventricular bypass)
• Creates the WPW syndrome
  
  
• James bundle
• Connects the atria with the His bundle
• (Atrio-Hisian bypass)
• Creates the LGL syndrome
  
  
• Mahaim fibers
• Connects the AV junction and ventricles
• (Nodo-Ventricular bypass)
• Creates the Mahaim syndrome

ECG and Pre-excitation Syndrome

• Accessory Pathways
  • Conduct impulses to the ventricles without delay (non-decremental conduction)
  • The ventricles are activated earlier through the accessory pathway
• Pre-excitation syndromes produce:
• Shortened PR interval
• Delta wave

Lown-Ganong-Levine (LGL) Syndrome

James Bundle and LGL Syndrome

• LGL Syndrome features the James bundle
• It connects the atria to the His bundle, bypassing the AV node (Atrio-Hisian bypass)
• Absence of Delta Wave
• The delta wave is absent because the ventricles are activated through the conduction system
• Shortened PR Interval < 0.12s
• The impulse bypasses the AV node and reaches the ventricles more quickly

Malignant Accessory Pathway

• It has a short refractory period, which allows it to conduct impulses at high frequencies
• Malignant accessory pathway in supraventricular tachycardia
• Conducts impulses to the ventricles at a frequency of 200-300/min.
• Progressively leads to ventricular fibrillation and the heart ceases to function as a pump
• Patients with WPW syndrome are at risk from any supraventricular tachycardia, most commonly
• Atrial fibrillation
• Atrial flutter

Atrial Fibrillation and WPW

• Impulses pass to the ventricles through the accessory pathway (without slowing down)
• Results in irregular wide-complex tachycardia (QRS > 0.12s)
• with a frequency of 200-300/min.
• May result in
• Fusion beat (Fusion beat)
• Capture beat (Capture beat)

WPW Syndrome

• Shortened PQ interval < 0.12s
• Delta wave
• Extended QRS complex (>0.12s)
• Dominant R waves in V1-3
• It is not right ventricular hypertrophy
• It is a sign of WPW Syndrome

Mahaim Syndrome

• Normal PQ interval (0.16s)
• Delta wave
• Wide QRS complex (>0.12s)
• Mahaim pathway confirmed by electrophysiological examination
• ECG resembles left bundle branch block
• Because the Mahaim pathway is in the right ventricle