Wolff-Parkinson-White Syndrome

Table of Contents

  1. Overview
  2. Epidemiology
  3. The Bundle of Kent (Accessory Pathway)
  4. ECG Features: Pre-excitation Pattern
  5. Arrhythmias in WPW
  6. Sudden Cardiac Death Risk
  7. Clinical Presentation
  8. Diagnosis and Risk Stratification
  9. Acute Management
  10. Catheter Ablation — Curative Treatment
  11. Asymptomatic WPW Management
  12. Research Papers
  13. Connections
  14. Featured Videos

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1. Overview

Wolff-Parkinson-White (WPW) syndrome is defined as the combination of ventricular pre-excitation on the resting ECG (delta wave, short PR interval, wide QRS) with symptomatic tachyarrhythmias. It is caused by an abnormal accessory atrioventricular pathway — the Bundle of Kent — that bypasses the AV node's physiologic conduction delay and directly connects the atrial myocardium to ventricular myocardium across the AV groove.

The distinction between WPW pattern (ECG findings without symptoms) and WPW syndrome (ECG pattern + documented tachyarrhythmias) is clinically important: asymptomatic individuals with a WPW pattern require risk stratification but not necessarily immediate treatment.

WPW syndrome is the most common cause of atrioventricular reentrant tachycardia (AVRT) and carries a unique risk: when atrial fibrillation occurs in the setting of a rapidly conducting accessory pathway (refractory period <250 ms), extremely rapid ventricular rates can develop, potentially degenerating into ventricular fibrillation and sudden cardiac death. Catheter ablation of the accessory pathway is curative in the vast majority of cases.

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2. Epidemiology

The WPW ECG pattern is present in approximately 1–3 per 1,000 individuals in the general population. WPW syndrome (symptomatic pre-excitation with tachyarrhythmias) has a prevalence of approximately 0.1–0.3%. It is more common in men (male-to-female ratio approximately 2:1) and in young adults, with a peak incidence in the second decade of life.

The annual risk of sudden cardiac death (SCD) in WPW syndrome is approximately 0.1–0.6% (higher in symptomatic patients, lower in those with intermittent pre-excitation). Over a 10-year follow-up, SCD as the first manifestation of WPW occurs in approximately 0.15% of cases, making SCD risk stratification a key aspect of management.

Familial WPW may be associated with PRKAG2 mutations (glycogen storage cardiomyopathy) or other congenital heart disease (Ebstein anomaly in ~30% of patients with left-sided accessory pathways, hypertrophic cardiomyopathy).

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3. The Bundle of Kent (Accessory Pathway)

The accessory pathway (AP) is a strand of embryologically retained myocardial tissue crossing the normally insulating AV fibrous ring. These pathways can be located anywhere around the AV groove:

The AP conducts bidirectionally in most patients: antegrade (atrium → ventricle, producing delta wave) and retrograde (ventricle → atrium, enabling AVRT). Some APs conduct only retrograde ("concealed bypass tract" — no delta wave, only capable of supporting orthodromic AVRT).

AV nodal physiology vs. accessory pathway: The AV node slows conduction (physiologic delay) and has a refractory period of ~300–500 ms. Accessory pathways bypass this delay and may have refractory periods as short as 150–180 ms — enabling rapid conduction rates during AF that would otherwise be blocked by the AV node.

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4. ECG Features: Pre-excitation Pattern

The resting 12-lead ECG in WPW shows three characteristic features:

  1. Short PR interval (<120 ms): The AV node's conduction delay is bypassed, so atrial impulses activate the ventricle earlier.
  2. Delta wave: A slurred, initial upstroke of the QRS complex, representing early ventricular activation via the accessory pathway (before the main wavefront arrives through the His-Purkinje system).
  3. Wide QRS complex (>120 ms): The combined result of delta wave + normal His-Purkinje activation ("fusion complex" — part accessory pathway, part normal conduction).

Secondary ST-T wave changes: Abnormal repolarization in pre-excited zones produces ST depression and T-wave inversions in leads where the delta wave is positive, and ST elevation where the delta wave is negative.

Localization of accessory pathway using delta wave polarity:

Intermittent pre-excitation (delta wave intermittently present or disappearing with exercise/increased heart rate) suggests a pathway with a relatively long antegrade refractory period and lower SCD risk.

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5. Arrhythmias in WPW

Orthodromic AVRT (most common, ~95% of AVRT in WPW):
Antegrade conduction proceeds normally through the AV node → His-Purkinje → ventricles (narrow QRS). Retrograde conduction returns via the accessory pathway to the atria. ECG: narrow complex tachycardia, retrograde P wave visible in ST segment (RP interval ~100–160 ms), HR 150–250 bpm. Regular, abrupt onset/offset.

Antidromic AVRT (~5% of AVRT in WPW):
Antegrade conduction down the accessory pathway → ventricles (wide, fully pre-excited QRS). Retrograde conduction up the AV node or another accessory pathway. ECG: wide complex regular tachycardia, maximally pre-excited QRS. Can resemble ventricular tachycardia. Requires differentiation — patients with antidromic AVRT are at particularly high risk for SCD.

Atrial Fibrillation with WPW (life-threatening emergency):
When AF occurs in a WPW patient, atrial impulses can conduct rapidly over the accessory pathway (bypassing AV nodal rate limitation). If the accessory pathway has a short antegrade refractory period (<250 ms), ventricular rates can exceed 300 bpm → ventricular fibrillation → sudden cardiac death.
ECG signature of AF with WPW: wide complex, irregular tachycardia with varying QRS morphologies (fusion between pathway-conducted and normally conducted beats). Ventricular rate >200 bpm with irregular RR intervals is a medical emergency.

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6. Sudden Cardiac Death Risk

SCD in WPW results from AF conducting rapidly over the accessory pathway, triggering ventricular fibrillation. Risk factors for SCD in WPW:

Low-risk features: Intermittent pre-excitation (spontaneous loss of delta wave during sinus rhythm or with exercise), inducible PR normalization with procainamide or adenosine, SPERRI >250 ms during induced AF.

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7. Clinical Presentation

WPW syndrome presents primarily through its tachyarrhythmias:

Asymptomatic WPW (no palpitations, no documented tachyarrhythmia) may be discovered incidentally on ECG obtained for sports/military screening, insurance, or unrelated cardiac evaluation.

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8. Diagnosis and Risk Stratification

Resting 12-lead ECG: Confirms pre-excitation (delta wave, short PR, wide QRS).

Exercise stress test: Abrupt loss of pre-excitation during exercise (at a specific heart rate threshold) indicates the accessory pathway's antegrade refractory period exceeds the sinus cycle length at that rate — suggests relatively benign pathway. Persistence of pre-excitation at high heart rates (pathologic finding) suggests short refractory period.

Holter/event monitor: Documents clinical SVT or AF episodes.

Electrophysiology study (EPS): Gold standard for risk stratification:

Echocardiography: Excludes associated structural disease (Ebstein anomaly, hypertrophic cardiomyopathy).

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9. Acute Management

Orthodromic AVRT (narrow complex, stable):

AF with WPW (wide complex irregular tachycardia, potential emergency):

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10. Catheter Ablation — Curative Treatment

Catheter ablation of the accessory pathway is the definitive, curative treatment for WPW syndrome:

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11. Asymptomatic WPW Management

Management of incidentally found WPW pattern without symptoms is debated:

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Research Papers

The following PubMed topic searches return current peer-reviewed literature relevant to this condition. Each link opens a live PubMed query.

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Connections

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