Makindo Medical Notes

About WPW Syndrome

• WPW syndrome involves an abnormal electrical connection between the atrium and ventricle via the accessory Bundle of Kent.
• This pathway bypasses the AV node, allowing fast conduction from the atria to the ventricles, resulting in early ventricular depolarization (pre-excitation).
• Patients may experience episodes of reentrant tachycardia, which can sometimes present as narrow or wide complex tachycardia depending on the conduction pathway.

Pathophysiology and Mechanisms

• Normally, electrical impulses travel through the AV node without retrograde conduction.
• With WPW, the accessory pathway can conduct impulses in either direction, leading to reentrant tachycardias (anterograde or retrograde through the AV node and accessory pathway).
• In atrial fibrillation (AF), the accessory pathway may conduct impulses rapidly to the ventricles, posing a risk of ventricular fibrillation (VF), which can be life-threatening.

Associations with WPW

• Septum secundum Atrial Septal Defect (ASD)
• Ebstein anomaly of the tricuspid valve
• Hypertrophic Cardiomyopathy (HCM)
• Mitral Valve Prolapse (MVP)

Clinical Presentation

• Many individuals remain asymptomatic throughout life, despite characteristic ECG findings.
• Common symptoms: palpitations, syncope, presyncope, dizziness.
• Rarely, sudden cardiac death can occur due to rapid AF conducting down the accessory pathway.

ECG Findings

• Resting ECG
  • Concealed pathway: Normal ECG between arrhythmias with no delta wave.
  • Manifest pathway: Short PR interval with slurred delta wave. Different ECG patterns may appear depending on the location of the accessory pathway.
• Arrhythmias
  • Atrioventricular Reentrant Tachycardia (AVRT): Typically narrow complex due to reentrant pathway involving the accessory pathway.
  • Atrial Fibrillation (AF) with Pre-excitation: Irregularly irregular rhythm with delta waves; risk of rapid ventricular rates and progression to VF.

ECG Examples - Pre-excitation and WPW Patterns

ECG Example - AVNRT

Investigations

• Blood tests: FBC, U&E, TFTs, CRP
• ECG to detect pre-excitation patterns and arrhythmias
• Imaging: Echocardiogram or Cardiac MRI to evaluate associated structural abnormalities
• Electrophysiological (EP) studies to identify the accessory pathway and guide management decisions

Atrial Fibrillation in Patients with WPW

Acute Management Scenarios

• Regular Narrow Complex Tachycardia (AVRT SVT):
  • Initial treatment includes vagal maneuvers. If unsuccessful, administer Adenosine or, if unstable, perform DC cardioversion.
  • The reentrant pathway may be antidromic (going through the AV node and back through the accessory pathway).
• Pre-excited AF:
  • Recognize by wide complex irregular rhythm with delta waves; ventricular rates can exceed 200 bpm.
  • If the patient is hemodynamically compromised, immediate DC shock is indicated.
  • Pharmacologic treatment options include IV Procainamide, Ibutilide, Propafenone, or Flecainide.
  • Note: Avoid Digoxin, Beta Blockers, Calcium Channel Blockers, and Adenosine.

Definitive Management

• Patients with pre-excited AF or recurrent SVT should be referred for radiofrequency catheter ablation of the accessory pathway.
• This procedure has a high success rate (approximately 95%) and significantly reduces symptoms and the risk of sudden cardiac death.
• In rare cases (1%), ablation near the AV node may lead to complete heart block, requiring pacemaker insertion.

References

• StatPearls on WPW Syndrome