What is Wolf Parkinson White (WPW) disease?

What is Wolff-Parkinson-White Syndrome?

Wolff-Parkinson-White (WPW) syndrome is a cardiac condition caused by an abnormal accessory electrical pathway connecting the atria and ventricles, bypassing the normal atrioventricular (AV) node, which creates ventricular pre-excitation and predisposes patients to potentially life-threatening tachyarrhythmias. 1

Anatomical Substrate and Pathophysiology

• The anatomical basis is a direct muscular connection (accessory pathway or bypass tract) between the atria and ventricles across the annulus fibrosus 1, 2
• These accessory pathways rarely show decremental conduction, allowing the electrical impulse to conduct prematurely to the ventricles, resulting in a short PR interval 1
• Simultaneous conduction through both the AV node and accessory pathway creates collision of two electrical wavefronts at the ventricular level, producing the characteristic delta wave and fusion QRS complex with prolonged duration 1
• The accessory pathway can conduct in the anterograde direction (atria to ventricles), retrograde direction (ventricles to atria), or both directions 2

Electrocardiographic Features

The diagnosis relies on specific ECG findings during sinus rhythm:

• PR interval less than 0.12 seconds (120 ms) due to bypass of the AV node 1, 3
• Delta wave - a slurring of the initial upstroke of the QRS complex, which is the defining feature and must be present for diagnosis 4, 3
• QRS complex widening with total duration greater than 0.12 seconds 3
• Secondary repolarization changes with ST segment-T wave changes directed opposite (discordant) to the major delta wave and QRS complex 3

Important caveat: Left lateral accessory pathways may show minimal delta waves due to fusion with normal AV nodal conduction, potentially appearing as intermittent pre-excitation when actually continuously present 4

Epidemiology

• Prevalence in the general population ranges from 0.1% to 0.3% 1, 5, 3
• The prevalence is not different in athletic populations 1
• In children with structural heart disease, prevalence is estimated at 0.33% to 0.5% 1
• Incidence of newly diagnosed cases is approximately 4 per 100,000 persons per year for all age groups 1

Clinical Manifestations

Asymptomatic vs. Symptomatic Disease

• Approximately 50% of patients with the WPW ECG pattern have no history of arrhythmias and most asymptomatic patients have a good prognosis 1
• The majority of patients with pre-excitation remain asymptomatic throughout their lives 6, 3
• When symptoms occur, they are secondary to tachyarrhythmias 6, 3

Common Symptoms

• Palpitations - the most common symptom, representing episodes of tachyarrhythmias 4
• Syncope or near-syncope - particularly concerning as it may indicate rapid conduction over the accessory pathway and risk of sudden death 4
• Dizziness during tachyarrhythmia episodes 4
• Chest pain during tachyarrhythmia episodes 4
• Shortness of breath indicating hemodynamic compromise during tachyarrhythmias 4
• Fatigue, especially during activities like driving 4

Arrhythmic Complications

Supraventricular Tachycardia

• Orthodromic AV re-entrant tachycardia (AVRT) is the most common arrhythmia, accounting for 95% of reentrant tachycardias in WPW patients 4
• The reentry circuit involves anterograde conduction through the AV node and retrograde conduction through the accessory pathway 1
• This produces a narrow QRS complex tachycardia 1

Atrial Fibrillation - The Most Dangerous Complication

• One-third of patients with WPW syndrome may develop atrial fibrillation 1
• Pre-excited atrial fibrillation occurs when AF conducts rapidly over the accessory pathway, which can degenerate into ventricular fibrillation 1, 4
• This is particularly dangerous when the shortest pre-excited R-R interval is less than 250 ms during AF 4

Other Arrhythmias

• Atrial flutter 1, 3
• Antidromic AVRT (wide QRS complex tachycardia with anterograde conduction over the bypass tract) 1
• Ventricular fibrillation (rare but potentially fatal) 6, 3

Risk of Sudden Cardiac Death

• The lifetime risk of sudden cardiac death in symptomatic WPW syndrome approaches 4% 4
• Annual sudden death rate is estimated at 0.15% to 0.5% during childhood 1
• The risk ranges from 0.15% to 0.39% over 3-10 years of follow-up 4
• Critical point: Sudden cardiac death may be the first manifestation of the disease in approximately 50% of cardiac arrest cases in WPW patients 4
• The highest risk appears in the first two decades of life 4

High-Risk Features

• Shortest pre-excited R-R interval less than 250 ms during atrial fibrillation 1, 4
• Accessory pathway refractory period less than 240 ms 4
• History of symptomatic tachycardia 1, 4
• Multiple accessory pathways 1, 4
• Posteroseptally located pathways 1
• History of syncope 4

Low-Risk Features

• Intermittent pre-excitation on resting ECG or ambulatory monitoring (90% positive predictive value for low risk) 4
• Abrupt loss of pre-excitation during exercise testing 1, 4

Associated Cardiac Conditions

WPW syndrome is associated with increased prevalence of certain structural heart diseases:

• Ebstein's anomaly of the tricuspid valve 1, 4
• L-transposition of the great arteries 1
• Hypertrophic cardiomyopathy 1
• Cardiac tumors 1
• PRKAG2-related familial WPW (glycogen storage cardiomyopathy) 4

Diagnostic Pitfalls

• The WPW ECG pattern can mimic pseudo-diaphragmatic (inferior) myocardial infarction, which should not be misinterpreted 7
• A short PR interval alone without delta waves does not constitute WPW syndrome and may represent normal variant conduction or enhanced AV nodal conduction 4
• Intermittent pre-excitation is not uncommon in newborns and infants 1
• Depending on the accessory pathway location and AV nodal conduction properties, even continuous pre-excitation may be subtle and only detected in mid-precordial leads 1

Critical Medication Contraindications

Absolute contraindications in pre-excited atrial fibrillation:

• Digoxin - shortens the anterograde effective refractory period of the accessory pathway and promotes rapid AV conduction during atrial flutter or fibrillation, potentially precipitating ventricular fibrillation 1, 4
• Verapamil - may increase ventricular response rate during atrial fibrillation and can cause cardiovascular collapse in infants and young children 1, 4
• Diltiazem - same mechanism as verapamil 4
• Beta-blockers - can precipitate ventricular fibrillation in pre-excited AF 4

These AV nodal blocking agents are contraindicated at any age in WPW patients with atrial fibrillation 1