Wolf-Parkinson-White (WPW) Pattern

Overview

• WPW is a type of heart arrhythmia.
• Caused by an accessory electrical conduction pathway (bundle of Kent).
• Connects atria and ventricles, bypassing the normal AV node delay.

Normal Heart Conduction

• Electrical signal starts at SA node in right atrium.
• Propagates through atria, including Bachmann's bundle in left atrium.
• Delayed at AV node before passing through the bundle of His and Purkinje fibers.
• Causes contraction of ventricles.
• ECG indicators:
  • P wave: Atrial contraction
  • PR interval: Delay at AV node
  • QRS complex: Ventricular contraction

WPW Conduction

• Bundle of Kent allows early ventricle contraction (pre-excitation).
• Types of pre-excitation:
  • Type A (left side)
  • Type B (right side)
• ECG indicators in WPW:
  • Short PR interval (<120 ms)
  • Delta wave
  • QRS prolongation (>110 ms)
  • ST segment and T-wave directed opposite QRS complex

Symptoms and Risks

• Typically benign, may cause no symptoms.
• Can facilitate severe arrhythmias, potentially leading to sudden cardiac death.
• Example: Atrial arrhythmias with rates 200-300 bpm.
  • Normally AV node regulates signal transfer to ventricles.
  • Bundle of Kent causes ventricles to contract at atrial rate, possible cardiogenic shock.

Re-entry Circuits

• Signal can move back up the accessory pathway (bundle of Kent).
• Atrioventricular Reentrant Tachycardia (AVRT):
  • Orthodromic conduction (ventricle to atrium)
  • Antidromic conduction (opposite direction)
• Initiated by premature atrial or ventricular contractions.

Prevalence and Treatment

• WPW pattern present in about 1 in 1000 people (congenital).
• Small proportion develop symptoms that require treatment.
• Treatment:
  • Pharmacological options for tachyarrhythmias.
  • Definitive treatment: Radio-frequency catheter ablation of bundle of Kent.

Conclusion

• Ablation leaves AV node as the sole pathway between atria and ventricles.
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