Wolff-Parkinson-White (WPW)
Definition and Pathophysiology
- Ventricular preexcitationpreexcitation 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 ( |
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:
- Loss of preexcitation (disappearance of delta wave).
- Persistent preexcitation throughout test.
- 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.