Wolff-Parkinson-White (WPW)

Definition and Pathophysiology

• Ventricular preexcitation syndrome first described in 1915.
• Characterized by paroxysms of tachycardia.
• Caused by presence of accessory bypass tracts.
• Bypasses normal atrioventricular (AV) node conduction.
• Allows direct conduction of atrial depolarization to ventricle.
• Bypass tracts exhibit antegrade conduction only, or bidirectional (antegrade and retrograde) conduction properties.
• Forms substrate for Atrioventricular Reentrant Tachycardia (AVRT).

Types of Atrioventricular Reentrant Tachycardia (AVRT)

• Dependent on direction of conduction through accessory pathway and AV node.

AVRT Type	Antegrade Conduction	Retrograde Conduction	QRS Morphology
Orthodromic AVRT	AV Node	Accessory Pathway	Narrow QRS complex
Antidromic AVRT	Accessory Pathway	AV Node	Wide QRS complex

Electrocardiographic (ECG) Manifestations

Baseline ECG (Sinus Rhythm)

• Short PR interval.
• Delta wave (slow upstroke of widened QRS complex).
• Functional bundle branch block pattern.
• Features may be intermittent.
• Delta wave may not be evident in every ECG lead.

Arrhythmia ECG

• Orthodromic AVRT: Narrow QRS complex tachycardia with retrograde P waves.
• Antidromic AVRT: Wide QRS complex tachycardia.
• Atrial Fibrillation: Irregularly irregular ventricular response.
• Wide QRS complexes during atrial fibrillation indicate rapid ventricular conduction and full preexcitation.

Clinical Presentation

• Paroxysms of tachycardia.
• Syncope. Ominous symptom requiring immediate evaluation.
• Sudden cardiac death. High risk in specific subsets.
• Ventricular fibrillation (VF) leading to cardiac arrest.

Physical Examination

• Heart sounds: Delayed P2 component of second heart sound (S2).
• Delayed P2 associated specifically with left-sided accessory pathways.

Associated Conditions and Syndromes

• High-yield associations for pediatric cardiology evaluation.

Congenital Heart Disease (CHD)

Defect	Association Details
Ebstein Anomaly	Most common CHD association. WPW more commonly associated with Ebstein anomaly than any other CHD.
Congenitally Corrected Transposition (ccTGA)	Known anatomic association with ventricular preexcitation.

Genetic, Metabolic, and Systemic Syndromes

Syndrome / Disease	Genetic/Molecular Basis	Clinical Features
PRKAG2 Syndrome	Autosomal dominant; PRKAG2 gene ($\gamma$2 subunit of AMPK)	Glycogen-accumulating cardiomyopathy. Conduction delay, advanced heart block, cardiac hypertrophy, sudden cardiac death.
Danon Disease	Xq24; LAMP2 mutation	Lysosomal storage disorder. Associated with Hypertrophic Cardiomyopathy (HCM).
Tuberous Sclerosis	-	Associated with cardiac rhabdomyomas and preexcitation.
Hypokalemic Periodic Paralysis	-	Episodic muscle weakness associated with WPW.

Mitochondrial Diseases

Disease Entity	Genetic Variant	Cardiac Phenotype
MELAS	tRNALeu point variant	Encephalopathy, stroke-like episodes, HCM, WPW.
MERRF	tRNALys point variant	Myoclonus, ataxia, HCM, WPW.
Mitochondrial Ribosomal Subunit Deficiencies	MRPS22, MRPl3, MRPL44	Leukoencephalopathy, seizures, HCM, WPW.

Cardiomyopathies

• Hypertrophic Cardiomyopathy (HCM): Certain forms associated with prominent voltages and ventricular preexcitation.

Risk Stratification

• Essential for differentiating patients at higher risk for sudden cardiac death.

Ambulatory Monitoring

• 24-hour Holter monitoring utilized.
• Intermittent preexcitation on monitoring does not necessarily decrease patient risk profile.

Exercise Stress Testing (EST)

• Previously utilized to risk stratify WPW patients.
• Preexcitation responds in one of three ways during EST:
  1. Loss of preexcitation (disappearance of delta wave).
  2. Persistent preexcitation throughout test.
  3. Persistent preexcitation triggering SVT.
• Historical Paradigm: Response 1 previously identified as lower risk.
• Current Evidence: Response 1 does not necessarily indicate low risk.
• Current Utility: Rare to use EST for risk stratification due to shifting treatment paradigms.

Management and Intervention

Electrophysiology Study (EPS)

• Strongly indicated for patients presenting with syncope.
• Indicated for patients surviving Ventricular Fibrillation (VF) unless clearly reversible cause identified.

Catheter Ablation

• Definitive treatment.
• Consideration strongly advised for any patient with syncope.
• Indicated if WPW syndrome noted after VF survival.
• Evidence-based trend supports catheter ablation for both symptomatic and asymptomatic patients.