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

Wolff-Parkinson-White (WPW) Syndrome

Definition and Pathophysiology

WPW syndrome is a cardiac pre-excitation disorder caused by an abnormal accessory electrical pathway (bypass tract) that directly connects the atria to the ventricles, bypassing the normal AV node and allowing premature ventricular activation. 1, 2

• The accessory pathway creates a direct muscular connection between atrial and ventricular myocardium across the annulus fibrosus, conducting electrical impulses faster than the normal AV nodal pathway 1, 3
• This dual conduction system results in collision of two electrical wavefronts at the ventricular level, producing the characteristic ECG findings 1
• The prevalence is approximately 0.1-0.3% in the general population, with higher rates (0.55%) in first-degree relatives suggesting genetic predisposition 4, 2, 5

Electrocardiographic Features

The diagnosis relies entirely on surface ECG findings with three cardinal features 2:

• PR interval <0.12 seconds (120 ms) due to rapid conduction through the accessory pathway that bypasses the AV node 2
• Delta wave - a slurred upstroke of the initial QRS segment representing early ventricular pre-excitation 1, 2
• QRS complex widening >0.12 seconds from fusion of pre-excited and normally conducted ventricular activation 2
• Secondary ST-T wave changes that are typically discordant (opposite direction) to the major QRS deflection 2

Important diagnostic pitfall: Left lateral accessory pathways may show minimal delta waves due to fusion with normal conduction, potentially appearing as intermittent pre-excitation when actually continuously present 6

Clinical Spectrum and Terminology

Critical distinction between two entities 6:

• WPW pattern: ECG findings of pre-excitation without symptoms - an electrocardiographic diagnosis only 6
• WPW syndrome: Pre-excitation pattern PLUS documented tachyarrhythmias or symptoms - establishes clinical disease requiring intervention 6, 4

Most patients remain asymptomatic throughout their lives, but when symptoms occur they are typically from tachyarrhythmias. 2

Associated Arrhythmias

WPW predisposes to multiple life-threatening tachyarrhythmias 7, 2:

• Atrioventricular re-entrant tachycardia (AVRT) - the most common arrhythmia (95% of reentrant tachycardias), typically orthodromic with antegrade conduction through the AV node and retrograde through the accessory pathway 6, 7, 3
• Pre-excited atrial fibrillation - occurs in up to 50% of WPW patients and represents the most dangerous arrhythmia due to risk of degeneration to ventricular fibrillation 1, 7
• Atrial flutter - less common but can conduct rapidly over the accessory pathway 1
• Ventricular fibrillation - the terminal event in sudden cardiac death, typically precipitated by rapid AF conduction 1, 7

Risk Stratification for Sudden Cardiac Death

The lifetime risk of sudden cardiac death in symptomatic WPW approaches 4%, with an annual incidence of 0.15-0.39% over 3-10 years. 6, 4

High-Risk Features Requiring Immediate Intervention 6, 4:

• Shortest pre-excited R-R interval <250 ms during atrial fibrillation - the single strongest predictor of life-threatening events 6, 4
• Accessory pathway effective refractory period <240 ms 6
• History of symptomatic tachycardia or syncope - syncope is particularly ominous as it may indicate rapid pathway conduction 6, 4
• Multiple accessory pathways 1, 6, 4
• Associated Ebstein's anomaly 1, 6, 4
• Familial WPW syndrome (rare but high sudden death incidence) 6, 4

Low-Risk Features 6:

• Intermittent pre-excitation on resting ECG or ambulatory monitoring (90% positive predictive value for low risk) 6
• Abrupt loss of pre-excitation during exercise testing - indicates long accessory pathway refractory period 6, 4

Diagnostic Evaluation

Initial Assessment 6:

• 12-lead ECG - essential for diagnosis; obtain during tachycardia episodes whenever possible 6
• Echocardiography - mandatory to exclude associated structural heart disease including Ebstein's anomaly, hypertrophic cardiomyopathy, and PRKAG2-related familial WPW 6
• Family history - focus on pre-excitation in first-degree relatives, sudden cardiac death in young family members, and cardiomyopathy 6

Risk Stratification Testing 6:

• 24-hour Holter monitoring - detects paroxysmal arrhythmias and intermittent pre-excitation (90% positive predictive value for low risk if intermittent) 6
• Exercise ECG - evaluates if pre-excitation disappears with exercise, suggesting long anterograde refractory period and low sudden death risk 6
• Electrophysiological study - the gold standard for risk stratification in both symptomatic and asymptomatic patients 6

Management Algorithm

Symptomatic Patients (WPW Syndrome) 6, 4:

Catheter ablation is the first-line definitive therapy (Class I recommendation) for all symptomatic WPW patients, particularly those with syncope, documented AF, or short bypass tract refractory period <250 ms. 6, 4

• Success rate approximately 95% with 6 months to 8 years follow-up 6
• Major complication risk 0.1-0.9% (complete heart block, bundle branch blocks) 6
• 5-year arrhythmic event rates: 7% in ablated patients versus 77% in non-ablated patients 6

Asymptomatic Patients (WPW Pattern) 6:

Two reasonable approaches (both Class IIa):

• Observation without further testing - acceptable for truly asymptomatic patients as most adults have benign course with low sudden death risk 6
• Electrophysiological study for risk stratification - reasonable to identify high-risk features given low complication risk versus potential for fatal arrhythmias 6

Critical decision point: If EP study reveals shortest pre-excited RR interval <250 ms during AF, accessory pathway refractory period <240 ms, multiple pathways, or inducible sustained AVRT, proceed to catheter ablation even in asymptomatic patients 6

Acute Management of Tachyarrhythmias

Pre-Excited Atrial Fibrillation - Hemodynamically Unstable 1, 4:

Immediate electrical cardioversion (Class I recommendation) - this is the only appropriate intervention for unstable patients. 1, 4

Pre-Excited Atrial Fibrillation - Hemodynamically Stable 1, 4:

First-line pharmacological treatment: Intravenous procainamide or ibutilide (Class I recommendation). 1, 4

Absolutely Contraindicated Medications in Pre-Excited AF 1, 4:

NEVER administer AV nodal blocking agents in WPW with pre-excited AF as they can precipitate ventricular fibrillation (Class III: Harm). 1, 4

Specifically contraindicated drugs 1, 4:

• Digoxin (oral or IV) - shortens accessory pathway refractory period and promotes rapid conduction 1
• Diltiazem and verapamil (oral or IV) - may increase ventricular response rate and cause cardiovascular collapse, especially in infants 1
• Beta-blockers - accelerate ventricular rate during pre-excited AF 1
• Amiodarone (IV) - potentially harmful in acute pre-excited AF 1
• Adenosine - can precipitate AF and accelerate ventricular rate 1

Orthodromic AVRT (Narrow Complex Tachycardia) 3, 8:

• Adenosine - can terminate AVRT in emergency situations 3
• Class IC antiarrhythmics (flecainide, propafenone) - first choice for patients with rapid anterograde conduction through accessory pathway 8
• Beta-blockers (atenolol, nadolol) - indicated for patients with re-entrant tachycardias and low conduction capacity through bypass tract 8

Special Populations and Considerations

Pediatric Patients 1:

• Prevalence in children with structural heart disease: 0.33-0.5% 1
• Incidence of sudden death estimated at 0.5% during childhood 1
• Cardiac arrest may be the initial presentation 1
• Digoxin and verapamil are absolutely contraindicated at any age - verapamil may cause cardiovascular collapse in infants and young children 1

Associated Structural Heart Disease 1, 6:

Higher prevalence of WPW with 1:

• Ebstein's anomaly of the tricuspid valve
• L-transposition of the great arteries
• Hypertrophic cardiomyopathy
• Cardiac tumors
• PRKAG2-related familial WPW (glycogen storage cardiomyopathy) 6

Pregnancy and Driving 6:

• Women with WPW require special monitoring during pregnancy 6
• 57% of patients with supraventricular tachycardia experience episodes while driving, representing significant safety concern 6

Key Clinical Pitfalls

Sudden cardiac death may be the first manifestation in approximately half of cardiac arrest cases in WPW patients, emphasizing the importance of risk stratification even in asymptomatic individuals. 6

• Misdiagnosing pre-excited AF as ventricular tachycardia can lead to administration of AV nodal blockers, potentially inducing ventricular fibrillation 7
• Short PR interval without delta wave does not constitute WPW and may represent normal variant, enhanced AV nodal conduction, or require evaluation for other conditions only if recurrent unexplained tachyarrhythmias occur 6
• Intermittent pre-excitation in newborns and infants is not uncommon and may be subtle, detected only in mid-precordial leads 1