Wolff-Parkinson-White (WPW)

Introduction and Pathophysiology

Wolff-Parkinson-White (WPW) syndrome is a congenital cardiac electrical abnormality characterized by clinical symptoms of tachyarrhythmias accompanied by specific electrocardiographic findings of a short PR interval and ventricular preexcitation.
The critical anatomical substrate in WPW syndrome is the presence of an electrically active myocardial fiber, known as an accessory bypass tract, that connects the atrium directly to the ventricle, effectively bypassing the normal delay of the atrioventricular (AV) node.
These accessory bypass tracts can exhibit antegrade conduction (from atrium to ventricle), retrograde conduction (from ventricle to atrium), or bidirectional conduction properties.
The presence of this dual conduction system (the native AV node and the accessory pathway) establishes a macro-reentrant circuit that predisposes the patient to atrioventricular reentrant tachycardia (AVRT).
During normal sinus rhythm, the electrical impulse is carried simultaneously over both the AV node and the accessory pathway, resulting in a fusion of the two depolarization fronts and an abnormal QRS complex.
Orthodromic reentrant tachycardia (ORT) occurs when the electrical impulse travels in an antegrade fashion down the native AV node and returns to the atrium in a retrograde fashion via the accessory pathway.
Antidromic reentrant tachycardia (ART) occurs when the impulse travels in an antegrade fashion down the accessory pathway and returns to the atrium in a retrograde fashion via the native AV node.
A highly critical pathophysiological risk in WPW syndrome is the development of preexcited atrial fibrillation, wherein rapid antegrade conduction of atrial fibrillation impulses across the accessory pathway bypasses the protective decrementing properties of the AV node.
Rapid antegrade conduction over the accessory pathway during atrial fibrillation can directly initiate life-threatening ventricular fibrillation.

Clinical Features and Associated Conditions

The clinical presentation of WPW syndrome is highly variable, ranging from completely asymptomatic individuals to those presenting with hemodynamic collapse or sudden cardiac death.
Reentrant tachycardias may trigger acutely with exercise, rest, or acute infections in infants, leading to sudden onset and abrupt termination of palpitations.
In older children and adolescents, the tachycardia rate generally exceeds 180 beats per minute, while infants may present with rates ranging between 240 and 300 beats per minute.
Prolonged episodes of unrecognized supraventricular tachycardia (SVT), particularly in non-verbal infants, can lead to tachycardia-induced cardiomyopathy, presenting with poor feeding, ashen color, restlessness, irritability, tachypnea, poor pulses, and severe hepatomegaly.
Syncope is considered a highly ominous symptom in patients with WPW syndrome, indicating a potentially high risk for life-threatening arrhythmias.
The incidence of sudden cardiac death in asymptomatic patients with WPW syndrome is estimated at 1 per 1,000 patient-years, though this rate may be higher in the pediatric population.
While WPW syndrome frequently occurs in structurally normal hearts, it has a well-documented association with Ebstein anomaly of the tricuspid valve, congenitally corrected transposition of the great arteries (ccTGA), and certain forms of hypertrophic cardiomyopathy.
Other systemic and genetic conditions associated with WPW syndrome include hypokalemic periodic paralysis, Danon disease, tuberous sclerosis (often associated with cardiac rhabdomyomas that act as accessory pathways), PRKAG2 mutations, and left ventricular noncompaction (LVNC).

Diagnostic Investigations

Modality	Specific Findings and Diagnostic Utility
Electrocardiogram (ECG) - Sinus Rhythm	The classic triad of WPW syndrome on a resting ECG includes a short PR interval, a widened QRS complex, and a slurred upstroke of the QRS complex known as a delta wave. Secondary clues may include left axis deviation, an absence of anterior and lateral Q waves, or variation in QRS morphology following a premature atrial contraction.
ECG - Orthodromic AVRT (ORT)	Demonstrates a narrow QRS complex tachycardia (as antegrade conduction occurs via the normal His-Purkinje system) accompanied by retrograde P waves. The retrograde P wave typically has a negative axis in leads II, III, and aVF, with a ventriculoatrial (VA) interval greater than 70 milliseconds.
ECG - Antidromic AVRT (ART)	Demonstrates a wide QRS complex tachycardia because the ventricles are depolarized entirely outside of the normal specialized conduction system via the accessory pathway.
ECG - Preexcited Atrial Fibrillation	Demonstrates an irregularly irregular rhythm with wide, fully preexcited QRS complexes and extremely rapid ventricular response rates, mimicking polymorphic ventricular tachycardia.
Echocardiography	Indicated for all patients presenting with WPW syndrome to rule out associated structural or functional cardiac abnormalities, such as Ebstein anomaly, congenitally corrected transposition of the great arteries, or hypertrophic cardiomyopathy.
Ambulatory Monitoring & Exercise Testing	24-hour Holter monitoring and exercise stress testing are utilized to detect intermittent preexcitation or the triggering of SVT, aiding in noninvasive risk stratification. The abrupt loss of preexcitation during exercise was historically considered a marker of a low-risk pathway, though recent evidence suggests this response does not guarantee zero risk for life-threatening events.
Cardiac Catheterization (Electrophysiology Study)	An invasive electrophysiology study (EPS) maps the exact anatomical location of the accessory pathway, evaluates the antegrade and retrograde conduction characteristics, and determines the effective refractory period of the bypass tract. It is the definitive diagnostic and therapeutic tool.

Medical Management

Acute Management of Tachyarrhythmias

The acute management of narrow-complex orthodromic AVRT in a hemodynamically stable patient begins with vagal maneuvers, such as applying an ice bag to the face in infants or performing the Valsalva maneuver in older children.
If vagal maneuvers fail, adenosine is administered via a rapid intravenous push at an initial dose of 0.1 mg/kg (maximum 6 mg), which can be increased to 0.2 mg/kg (maximum 12 mg) if the initial dose is ineffective.
Because adenosine can rarely initiate atrial fibrillation, it must only be administered when equipment for direct current (DC) cardioversion is immediately available.
The acute management of wide-complex antidromic AVRT differs significantly; intravenous procainamide is the drug of choice for acute termination in a hemodynamically stable patient.
In cases of preexcited atrial fibrillation in a stable patient, procainamide is also the most effective medication as it safely slows conduction across the accessory pathway and may directly terminate the atrial fibrillation.
For any patient with WPW syndrome presenting with hemodynamic instability (shock, hypotension, poor perfusion), regardless of the tachycardia mechanism, immediate synchronized DC cardioversion at 0.5 to 2 Joules/kg is the mandatory first-line treatment.

Contraindicated Medications

Digoxin, verapamil, and other calcium channel blockers are strictly contraindicated in the management of WPW syndrome.
These medications selectively block the AV node, which can paradoxically increase the rate of antegrade conduction of impulses through the accessory bypass tract.
The administration of these AV-nodal blocking agents in WPW syndrome increases the risk of precipitating rapid preexcited atrial fibrillation, progressing to ventricular fibrillation, and causing sudden cardiac death.

Chronic Pharmacological Management

In patients requiring chronic preventive medical therapy, beta-blockers are the preferred first-line agents.
For patients with drug-resistant tachycardias or those who cannot tolerate beta-blockers, acceptable next-line antiarrhythmic agents include flecainide, propafenone, sotalol, and amiodarone.
Flecainide and propafenone should be strictly limited to patients possessing a structurally normal heart with normal baseline cardiac function due to the risk of proarrhythmia.

Interventional Management

Invasive electrophysiology study with transcatheter ablation is the definitive, curative treatment for WPW syndrome.
Ablation can be performed using either radiofrequency energy (which uses heat to destroy the pathway) or cryoablation (which destroys the tissue via freezing).
The overall initial success rate for catheter ablation in experienced pediatric laboratories is exceptional, ranging from 90% to 98%, dependent upon the specific anatomical location of the accessory pathway.
Any patient presenting with WPW syndrome and a history of syncope must undergo an immediate electrophysiology study with consideration for catheter ablation, as syncope is a marker for an elevated risk of sudden cardiac death.
Prior to clearing a patient with WPW syndrome for competitive sports, catheter ablation of the accessory pathway is strongly indicated if the patient has a history of paroxysmal atrial fibrillation or possesses a short refractory period bypass tract capable of rapid antegrade conduction.
For asymptomatic patients with preexcitation, invasive electrophysiological evaluation with ablation is reasonable if the bypass tract is deemed high risk for sudden cardiac death, specifically defined as having a refractory period of less than 250 milliseconds.
In patients with underlying congenital defects such as Ebstein anomaly, an electrophysiology study mapping and ablating the accessory pathway is highly recommended prior to surgical tricuspid valve repair or replacement.