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

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

Wolff-Parkinson-White syndrome is a cardiac condition characterized by documented supraventricular tachycardia or symptoms consistent with SVT in a patient with ventricular pre-excitation during sinus rhythm, caused by an abnormal accessory electrical pathway directly connecting the atria and ventricles. 1

Anatomical Substrate and Pathophysiology

The fundamental abnormality in WPW syndrome is a direct muscular connection (accessory pathway) between the atria and ventricles that bypasses the normal atrioventricular node 1. This accessory pathway creates several key physiologic consequences:

• The electrical impulse conducts prematurely to the ventricles because accessory pathways rarely show decremental conduction, resulting in earlier ventricular activation than would occur through the normal AV node 1
• Simultaneous conduction occurs through both the AV node and accessory pathway, creating collision of two electrical wavefronts at the ventricular level 1
• This dual conduction produces the characteristic ECG findings: short PR interval (<100-120 ms), delta wave (slurring of initial QRS upstroke), widened QRS complex (>80-120 ms), and secondary ST-T wave changes directed opposite to the delta wave 1, 2

Epidemiology and Clinical Significance

The prevalence of WPW syndrome ranges from 0.1-0.3% in the general population, with an incidence of approximately 4 newly diagnosed cases per 100,000 persons per year 1, 3. The condition affects all age groups but is particularly important to recognize because:

• Lifetime risk of sudden cardiac death in symptomatic WPW approaches 4% 4
• Population-based studies show sudden death risk of 0.15-0.2%, while symptomatic patients face higher risk at 2.2% 1
• Sudden cardiac death may be the initial presentation in approximately half of cardiac arrest cases in WPW patients 4

Critical Distinction: Pattern vs. Syndrome

It is essential to differentiate between two related but distinct entities 1, 4:

• WPW pattern (asymptomatic pre-excitation): Pre-excitation ECG findings without documented arrhythmias or symptoms
• WPW syndrome: Pre-excitation pattern PLUS documented supraventricular tachycardia or symptoms consistent with SVT 1

Associated Arrhythmias and Mechanisms

WPW syndrome predisposes patients to multiple life-threatening tachyarrhythmias 1, 5:

Orthodromic AVRT (Most Common)

• Accounts for 95% of reentrant tachycardias in WPW patients 4
• Uses the AV node anterogradely and accessory pathway retrogradely 1
• Produces narrow QRS complex tachycardia 1

Antidromic AVRT (Less Common)

• Uses accessory pathway anterogradely and AV node retrogradely 1
• Produces wide QRS complex (maximally pre-excited) 1

Pre-excited Atrial Fibrillation (Most Dangerous)

• Occurs in up to one-third to 50% of WPW patients 1, 5
• Can degenerate into ventricular fibrillation when rapid ventricular rates occur over the accessory pathway 1
• Shortest pre-excited R-R interval <250 ms during AF is the strongest predictor of sudden death risk 6, 4

Associated Cardiac Conditions

WPW syndrome shows increased prevalence with specific structural heart diseases 1:

• Ebstein's anomaly of the tricuspid valve (classical association) 1, 4
• Hypertrophic cardiomyopathy 1
• L-transposition of the great arteries 1
• Cardiac tumors 1

In children with structural heart disease, prevalence increases to 0.33-0.5% 1.

High-Risk Features Requiring Immediate Attention

The following characteristics identify patients at elevated risk for sudden cardiac death 6, 4:

• Shortest pre-excited R-R interval <250 ms during atrial fibrillation (strongest predictor) 6, 4
• History of symptomatic tachycardia or syncope 6, 4
• Multiple accessory pathways 6, 4
• Accessory pathway refractory period <240 ms 4
• Ebstein's anomaly or familial WPW 6, 4

Conversely, intermittent pre-excitation or abrupt loss during exercise indicates lower risk, with 90% positive predictive value for benign course 4.

Critical Management Pitfalls

Certain medications are absolutely contraindicated in WPW with pre-excited atrial fibrillation because they can precipitate ventricular fibrillation 1, 6:

• Digoxin (shortens accessory pathway refractory period) 1
• Verapamil (may cause cardiovascular collapse, especially in infants) 1
• Diltiazem 6
• Beta-blockers 6

These AV nodal blocking agents preferentially block the normal pathway, forcing more conduction through the accessory pathway and potentially causing life-threatening ventricular rates 1, 6.

Definitive Treatment

Catheter ablation has become the preferred definitive therapy, particularly for symptomatic patients, with success rates exceeding 95% and major complication rates of only 0.1-0.9% 1, 6, 4. Five-year arrhythmic event rates demonstrate dramatic benefit: 7% in ablated patients versus 77% in non-ablated patients 4.