Wolff-Parkinson-White (WPW) syndrome

Etiology

• accessory tract bypassing AV node, generally congenital
• generally no underlying heart disease
• clinical associations
  • Ebstein's anomaly
  • mitral valve prolapse
  • cardiomyopathy

Epidemiology

• incidence of accessory pathway is 0.3% in the general population

Pathology

• pre-excitation & paroxysmal supraventricular tachycardia (PSVT)
• an accessory bypass tract sets up a circuit which allows either:
  • orthodromic conduction through the AV node with retrograde conduction through the accessory pathway (orthodromic PSVT)*
  • anterograde conduction through the accessory pathway with retrograde conduction through the AV node (antidromic PSVT)*
  • accessory path may be intermittently anterograde or retrograde
• tachycardia develops in 70% of these patients
  • the tachycardia is due to atrioventricular reentrant tachycardia**
• increased tendency towards atrial fibrillation
• combined atrial fibrillation & ventricular pre-excitation (i.e. anterograde conduction through the accessory pathway) may predispose patients to ventricular fibrillation

* Also orthodromic & antidromic reciprocating tachycardia. ** a delta wave makes atrioventricular nodal reentrant tachycardia unlikely

Diagnostic procedures

• electrocardiogram:
  • ventricular pre-excitation*
    • slurring of the initial part of the QRS complex (delta wave)
      • may just appear in ECG as a widening of the QRS complex (no slurring)
    • due to anterograde conduction through the accessory pathway
      • patients with accessory pathways that conduct only in the retrograde direction do NOT have a pre-excitation delta wave
    • pre-excitation may be enhanced by slowing conduction through the AV node
      • carotid sinus massage
      • vagal maneuvers
      • short-acting AV nodal blocking agents
    • pre-excitation may resolve with exercise (low risk)
  • short PR interval (< 120 msec)*
  • wide QRS complex (> 120 msec)*
  • paroxysmal supraventricular tachycardia (PSVT)*
  • may be Q-wave in V1-V3
  • may be R in V1
  • ST & T wave changes opposite in polarity to QRS complex
  • wide complex tachycardias
    • orthodromic tachycardia with bundle-branch block
    • antidromic tachycardia
      • inverted p-wave prior to every QRS
      • short, but constant PR interval
      • no isoelectric PR segment
      • wide & bizarre QRS morphology
        • may resemble ventricular tachycardia
    • atrial fibrillation
      • irregular baseline & rhythm
      • no p-waves
      • QRS variable from normal to wide, bizarre (pre-excited) complexes
      • rate may be rapid
    • atrial flutter
  • narrow complex tachycardia (most common)
    • orthodromic conduction in the absence of bundle-branch block
    • orthodromic PSVT (AV reentrant tachycardia/AV reciprocating tachycardia) with normal QRS (no pre-excitation)#
• exercise stress testing prior to participation in competitive sports
  • normalization of the QRS complex during exercise indicates low risk for sudden cardiac arrest
• electrophysiology
  • asymptomatic patients with WPW in sinus rhythm do not necessarily require electrophysiology studies
  • if QRS complex does not normalize during exercise stress testing, electrophysiology studies indicated
  • symptomatic &/or high-risk of sudden cardiac death

* defining criteria for WPW

# AV nodal reentrant tachycardia is caused by dual nodal AV physiology not WPW

Complications

• atrial fibrillation can convert to ventricular fibrillation

Differential diagnosis

• hypertrophic cardiomyopathy
  • deep inverted T-waves in V2-V4

Management

• acute episodes are managed similar to AVNRT
  • vagal maneuvers
    • carotid massage
    • Valsalva maneuver
  • AV nodal blocking agents (short-acting) *see below*
    • adenosine 6-12 mg IV
    • verapamil 5 mg IV every 5 min for a maximum of 3 doses
    • diltiazem 15-20 mg IV over 2 min for a maximum of 2 doses
  • adenosine may potentiate short periods of atrial fibrillation
    • DC cardioversion should be available
  • cardioversion for any unstable patient
• wide complex tachycardia
  • lidocaine may precipitate ventricular tachycardia
  • synchronized cardioversion is hemodynamically unstable
  • procainamide agent of choie in hemodynamically stable patient
• atrial fibrillation
  • AV blocking agents contraindicated
    • Ca+2-channel antagonists, beta-blockers, digoxin
    • will NOT prevent & may precipitate a rapid ventricular response to atrial fibrillation if anterograde conduction occurs through accessory pathway.
  • use class Ia, Ic & III anti-arrhythmic agents
    • class Ia anti-arrhythmic agents
      • quinidine, procainamide
        • intravenous procainamide (drug of choice); up to 15 mg/kg IV at 25-50 mg/min; monitor BP every 5 min
    • class Ic anti-arrhythmic agents
      • flecainide, propafenone
    • class III anti-arrhythmic agents
      • amiodarone, ibutilide
  • cardioversion if hemodynamic compromise
• chronic therapy
  • class Ia, Ic & III anti-arrhythmic agents (2nd line therapy)
    • slows conduction in accessory pathway
    • procainamide (preferred agent in pregnancy)
    • flecainide
  • if NO atrial fibrillation
    • beta-blocker
    • calcium channel antagonist
• electrophysiologic testing
  • symptomatic patients
  • asymptomatic patients in high-risk occupations
    • pilots
    • bus drivers
• radio frequency catheter ablation of accessory tract for symptomatic AVNRT
  • curative, 1st line therapy
  • indications
    • drug resistant tachycardia
    • patients who do not wish to take long-term drugs
    • 1st line therapy
  • contraindications:
    • avoid during pregnancy, radiation exposure of fluoroscopy

More general terms

• atrioventricular reciprocating tachycardia (AVRT)

Additional terms

• atrial fibrillation (AF)
• AV nodal re-entrant tachycardia (AVNRT)
• Ebstein's anomaly
• paroxysmal supraventricular tachycardia (PSVT)
• pre-excitation

Database

• OMIM: https://mirror.omim.org/entry/194200
• OMIM: https://mirror.omim.org/entry/600858