What is Wolff-Parkinson-White (WPW) syndrome?

Wolff-Parkinson-White (WPW) Syndrome

Wolff-Parkinson-White syndrome is a congenital cardiac condition characterized by the presence of an accessory electrical pathway between the atria and ventricles that bypasses the normal AV nodal conduction system, resulting in ventricular pre-excitation and increased risk of tachyarrhythmias and sudden cardiac death. 1, 2

Definition and Electrocardiographic Features

WPW syndrome is defined by:

• Specific ECG pattern (WPW pattern) showing:
  • Short PR interval (<120 ms)
  • Delta wave (slurring of the initial QRS upstroke)
  • Widened QRS complex (>120 ms)
• Presence of symptomatic tachyarrhythmias 2

The prevalence of WPW pattern on ECG ranges from 0.1% to 0.3% in the general population 1, 2.

Pathophysiology

WPW syndrome results from:

• Abnormal accessory pathway (AP) connecting atria and ventricles
• Bypass of the normal AV nodal delay
• Creation of a potential reentry circuit that can sustain tachyarrhythmias 2

Types of accessory pathways include:

• Manifest pathways (conduct antegrade, visible on ECG)
• Concealed pathways (conduct only retrograde, not visible on resting ECG)
• Decremental pathways (slow conducting, like PJRT) 1, 2

Clinical Manifestations and Associated Arrhythmias

Common arrhythmias in WPW syndrome:

1. Orthodromic AVRT (95% of cases):

   • Antegrade conduction through AV node
   • Retrograde conduction through accessory pathway
   • Presents as narrow QRS tachycardia 2

2. Antidromic AVRT (less common):

   • Antegrade conduction through accessory pathway
   • Retrograde conduction through AV node
   • Presents as wide QRS tachycardia 2

3. Atrial Fibrillation (AF):

   • Occurs in up to 50% of WPW patients
   • Can conduct rapidly through accessory pathway
   • Highest risk for sudden cardiac death 3, 2

4. Permanent Junctional Reciprocating Tachycardia (PJRT):

   • Involves slowly conducting posteroseptal accessory pathway
   • Characterized by long RP interval 1, 2

Risk Stratification

High-risk features for sudden cardiac death:

• Shortest pre-excited R-R interval <250 ms during atrial fibrillation
• History of symptomatic tachycardia
• Multiple accessory pathways
• Posteroseptally located pathways 1, 2

The 10-year risk of sudden cardiac death ranges from 0.15% to 0.24% in patients with WPW 1. The risk appears highest in the first two decades of life 1.

Low-risk features:

• Intermittent pre-excitation
• Abrupt loss of pre-excitation during exercise
• Loss of pre-excitation after drug administration (ajmaline, procainamide) 1, 2

Acute Management

For orthodromic AVRT:

1. Vagal maneuvers (first-line) 1
2. Adenosine (if vagal maneuvers fail) 1
3. Synchronized cardioversion for hemodynamically unstable patients 1

For pre-excited atrial fibrillation:

1. Immediate synchronized cardioversion for hemodynamically unstable patients 1
2. Ibutilide or IV procainamide for hemodynamically stable patients 1

CAUTION: AV nodal blocking agents (calcium channel blockers, beta-blockers, digoxin) should be avoided in pre-excited AF as they can enhance conduction through the accessory pathway and potentially precipitate ventricular fibrillation 2.

Definitive Management

Catheter ablation is the first-line definitive treatment for symptomatic WPW syndrome, with success rates exceeding 95% and complication rates of 1-2% in experienced centers. 1, 2

Indications for catheter ablation:

• Symptomatic tachyarrhythmias
• Documented atrial fibrillation with rapid ventricular response
• Survivors of ventricular fibrillation
• High-risk occupations (pilots, athletes, heavy machinery operators) 1, 2

For asymptomatic patients with incidental WPW pattern:

• Risk stratification should guide management
• Catheter ablation may be considered in high-risk professions or athletes
• Observation may be appropriate for truly low-risk patients 1, 2

Special Considerations

In athletes:

• Comprehensive risk evaluation before competitive sports participation
• Catheter ablation recommended for symptomatic athletes or those with high-risk features 1

Associated conditions:

• Ebstein's anomaly
• Hypertrophic cardiomyopathy
• Other structural heart diseases 2

Prognosis

With appropriate management:

• Excellent prognosis following successful ablation
• Normal life expectancy
• Low recurrence rate (5-10%) after ablation 2

Most asymptomatic patients with WPW pattern have a good prognosis, but sudden cardiac death can be the first manifestation of the disease in some cases 1.