Wolff-Parkinson-White Syndrome

Definition

• WPW syndrome is a congenital cardiac conduction disorder characterized by the presence of an accessory pathway that directly connects the atria and ventricles.
• The aberrant pathway bypasses the normal AV node system, in which the atria and ventricles are electrically isolated, thereby causing ventricular myocardial preexcitation and a unique ECG pattern characterized by a shortened PR interval, a slurred upstroke of the QRS complex (delta wave), and QRS widening.
• Criteria for terming as WPW pattern or syndrome:
  • Pattern: Characteristic ECG preexcitation changes without symptomatic arrhythmia
  • Syndrome: Preexcitation on ECG AND symptomatic arrhythmia.¹

Incidence

• The prevalence of WPW pattern is estimated to be around 0.1-0.3%, but can be up to 0.55% among first-degree relatives, suggesting a familial component that can be associated with hypertrophic cardiomyopathy.²
• Among those with WPW pattern, the incidence of arrhythmia resulting in WPW syndrome is ~1-2% per year.
• Most patients with accessory AV pathways do not have coexisting structural cardiac abnormalities; if present, Ebstein anomaly is the most strongly associated congenital condition.^1,3

Mechanism

• Accessory pathways are believed to originate from the chamber myocardium due to abnormal early atrial and ventricular folding during cardiac embryogenesis.
• The accessory pathway allows electrical conduction to bypass the AV nodal delay and reach the ventricles prematurely.²
• The characteristic WPW pattern of the delta wave arises because a portion of the ventricular myocardium is prematurely activated due to the accessory pathway rather than utilizing the AV node to the His-Purkinje system.¹

• Tachyarrhythmias associated with WPW may be classified as those that require or do not require the accessory pathway for initiation and maintenance.
  • Accessory path required: AV reentrant tachycardia (AVRT), of which there are two types:
    • Orthodromic AVRT: electrical impulse travels antegrade through the AV node and retrograde through the accessory pathway (narrow QRS)
    • Antidromic AVRT: electrical impulse travels antegrade through the accessory pathway and retrograde through the AV node (wide QRS).
  • Accessory path NOT required: The accessory path may serve as a route for atrial or ventricular activation, but it is not necessary for perpetuation of the arrhythmia. These tachyarrhythmias include atrial fibrillation or flutter, junctional rhythms including AV nodal reentrant tachycardia, ventricular tachycardia, and ventricular fibrillation.^1,3

Diagnosis

• Surface ECG is usually sufficient for diagnosing WPW pattern, based on characteristic ECG findings: a shortened PR interval (less than 120ms) and a slurred QRS upstroke (delta wave) with QRS widening (more than120ms).
• Rarely, invasive electrophysiology (EP) testing can help confirm the presence of an accessory pathway, at the discretion of expert cardiology or EP input.
• The diagnosis of WPW syndrome is made in a patient with preexisting WPW pattern on ECG who develops a symptomatic arrhythmia as above, with clinical manifestations that may include lightheadedness, palpitations, chest pain, syncope, or sudden cardiac arrest.
• Suspicion for this diagnosis should be increased among child or young adult patients with an arrhythmia and rapid ventricular rate.¹

Management

• For asymptomatic patients with WPW pattern:
  • If intermittent preexcitation findings are present on ECG, the risk for sudden cardiac death is likely low, and routine outpatient cardiology follow-up may be appropriate.
  • If persistent findings on surface and exercise ECG, the patient may be at increased risk for sudden cardiac death and should be considered for invasive EP testing and potential accessory pathway ablation as appropriate with expert consultation.^2,5
• For WPW syndrome:
  • Acute treatment
    • Hemodynamically stable
    • Regular narrow QRS complex arrhythmia: stepwise escalation of therapy as needed with vagal maneuvers, intravenous (IV) adenosine, IV verapamil, IV procainamide, or beta blocker
    • Regular wide complex: stepwise escalation of therapy as needed with vagal maneuvers, IV procainamide
    • Irregular wide complex: IV procainamide, IV ibutilide
  • AV nodal blocking agents are contraindicated in patients experiencing atrial fibrillation with preexcitation, as they will promote conduction through the accessory pathway, which can increase the rate, leading to hemodynamic instability and degeneration into ventricular fibrillation
    • Hemodynamically unstable
    • Direct current cardioversion^2,5
  • Chronic treatment
• Consideration for catheter ablation of the accessory tract is generally preferred due to the efficacy and safety of ablation rather than long-term use of antiarrhythmics, which is less effective in preventing recurrent arrhythmias and have risk for adverse effects.^3,5