What is Wolff-Parkinson-White (WPW) syndrome and its clinical profile?

Wolff-Parkinson-White Syndrome: Definition and Clinical Profile

Definition and Pathophysiology

Wolff-Parkinson-White (WPW) syndrome is defined as the presence of ventricular pre-excitation on ECG combined with symptomatic paroxysmal arrhythmias, caused by an accessory electrical pathway that bypasses the normal AV node conduction system. 1, 2

• The syndrome affects 0.15-0.25% of the general population, with higher prevalence (0.55%) in first-degree relatives, suggesting genetic predisposition 2
• The accessory pathway creates a direct electrical connection between atria and ventricles, allowing impulses to bypass the AV node 3
• Pre-excitation degree varies based on relative conduction through the AV node versus the accessory pathway 2

Electrocardiographic Features

The diagnostic ECG criteria include four key features that must be recognized 3:

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

Important diagnostic pitfall: 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

Clinical Presentations and Arrhythmias

Common Arrhythmias

The tachyarrhythmias in WPW syndrome include 1, 5:

• Orthodromic AVRT (90-95% of episodes) - narrow QRS complex tachycardia using the AV node anterogradely and accessory pathway retrogradely 1
• Antidromic AVRT (5% of episodes) - wide QRS complex tachycardia with anterograde conduction via the accessory pathway 1
• Atrial fibrillation - occurs in up to 50% of WPW patients and is particularly dangerous due to risk of rapid ventricular response 5
• Atrial flutter - less common but can also conduct rapidly over the accessory pathway 1
• Ventricular fibrillation - rare but life-threatening complication, particularly when triggered by pre-excited AF 1

Symptom Profile

Patients typically present with 4:

• Palpitations - most common symptom, representing tachyarrhythmia episodes 4
• Syncope or near-syncope - particularly concerning, indicating rapid conduction and sudden death risk 4
• Dizziness during tachyarrhythmias 4
• Chest pain during episodes (less common) 4
• Shortness of breath indicating hemodynamic compromise 4
• Fatigue, especially during activities like driving (57% experience episodes while driving) 4

Critical point: Many patients remain asymptomatic throughout their lives, but sudden cardiac death may be the first presentation in approximately half of cardiac arrest cases in WPW patients 4, 3

Risk Stratification for Sudden Cardiac Death

High-Risk Features Requiring Immediate Attention

The following features identify patients at increased risk of sudden death and should prompt consideration for catheter ablation 4, 2:

• Shortest pre-excited R-R interval <250 ms during atrial fibrillation - strongest predictor of life-threatening events 1, 4, 2
• Accessory pathway refractory period <240 ms 4
• History of symptomatic tachycardia - increases sudden death risk from 0.15-0.2% to 2.2% 1
• Multiple accessory pathways 1, 4
• Associated Ebstein's anomaly 1, 4
• Familial WPW (PRKAG2-related) - associated with high sudden death incidence 4
• Young age - highest risk in first two decades of life 1

Low-Risk Indicators

Features suggesting lower risk include 4, 2:

• 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 - suggests long anterograde refractory period 4

Overall Mortality Risk

• Population-based sudden cardiac death risk: 0.15-0.24% over 10 years 1
• Symptomatic WPW patients: 2.2% risk 1
• Lifetime risk in symptomatic WPW: approaching 4% 4

Associated Structural Heart Disease

Echocardiography is essential to exclude associated conditions 4:

• Ebstein's anomaly - congenital tricuspid valve abnormality 1, 4
• Hypertrophic cardiomyopathy 1, 4
• PRKAG2-related familial WPW - glycogen storage cardiomyopathy 4

ECG Mimics and Diagnostic Challenges

WPW syndrome can mimic other conditions on ECG 3, 6:

• Pseudo-inferior myocardial infarction - should not be misinterpreted 7
• Bundle branch block - particularly right bundle branch block 6
• Ventricular hypertrophy 6
• Conduction disease - can lead to diagnostic dilemmas in syncope evaluation 6

Important distinction: A short PR interval (<0.12 seconds) without a delta wave does NOT constitute WPW and may represent normal variant conduction, enhanced AV nodal conduction, or other conditions like Lown-Ganong-Levine syndrome 4

Dangerous Arrhythmia: Pre-Excited Atrial Fibrillation

Pre-excited AF is the most life-threatening arrhythmia in WPW syndrome 5, 8:

• Characterized by irregular rhythm, very rapid ventricular response (often >200 bpm), presence of delta waves, and wide bizarre QRS complexes 8
• Can degenerate into ventricular fibrillation when the accessory pathway conducts rapidly 1
• Absolutely contraindicated medications: AV nodal blocking agents (digoxin, diltiazem, verapamil, beta-blockers) can precipitate ventricular fibrillation 2, 8
• Appropriate acute treatment: procainamide or ibutilide for stable patients; immediate electrical cardioversion for unstable patients 1, 2, 8

Evaluation Algorithm

For patients with suspected or confirmed WPW 1, 4:

1. History and physical examination focusing on palpitations, syncope, family history of sudden death or pre-excitation 4
2. 12-lead ECG to identify pre-excitation pattern 4
3. Echocardiography to exclude structural heart disease 1, 4
4. 24-hour Holter monitoring to detect paroxysmal arrhythmias and assess for intermittent pre-excitation 4
5. Exercise testing to evaluate if pre-excitation disappears with exercise 4
6. Electrophysiological study - gold standard for risk stratification in both symptomatic and asymptomatic patients 4