Key Facts

Wolff-Parkinson-White (WPW) syndrome is a pre-excitation condition caused by an accessory electrical pathway (bundle of Kent) connecting the atria and ventricles, bypassing the AV node. This allows early ventricular activation producing the characteristic delta wave and predisposes to re-entrant tachycardias.

Epidemiology

• Prevalence: 1-3 per 1,000 population
• More common in males (~60-70%)
• Usually presents in adolescence or young adulthood (20-40 years)
• 50-60% of patients with WPW pattern experience symptomatic tachycardia
• Risk of sudden cardiac death: ~0.1-0.5% per year

Aetiology

• Congenital accessory pathway persisting from embryological development
• Most cases sporadic; rarely familial (associated with PRKAG2 mutations)
• Associated conditions: Ebstein anomaly, hypertrophic cardiomyopathy, mitral valve prolapse

Pathophysiology

• Accessory pathway conducts impulses faster than AV node (no physiological delay)
• Pre-excitation: early ventricular depolarisation via accessory pathway produces delta wave
• Re-entrant circuits form between AV node and accessory pathway:
  • Orthodromic AVRT: anterograde via AV node, retrograde via accessory pathway (narrow complex, ~95%)
  • Antidromic AVRT: anterograde via accessory pathway, retrograde via AV node (wide complex, ~5%)
• In AF: accessory pathway may conduct rapidly (no AV nodal rate-limiting), potentially causing VF

Typical Presentation

• Paroxysmal palpitations: sudden onset and termination
• Dizziness, presyncope, or syncope during tachycardia
• Chest discomfort during episodes
• Polyuria post-episode (ANP release from atrial distension)

ECG Findings (Sinus Rhythm)

• Short PR interval (<120 ms)
• Delta wave (slurred upstroke of QRS)
• Wide QRS (>120 ms)
• Secondary ST-T wave changes

During Tachycardia

• Orthodromic AVRT: narrow complex regular SVT (rate 150-250 bpm), P waves may be visible after QRS
• Antidromic AVRT: wide complex regular tachycardia
• AF with WPW: irregularly irregular wide complex tachycardia (extremely dangerous)

Red Flags

• AF with rapid ventricular rate and wide bizarre QRS complexes
• Syncope or cardiac arrest
• Very short RR intervals during AF (<250 ms)
• Haemodynamic instability during tachycardia

Bedside

• 12-lead ECG: delta wave pattern during sinus rhythm; rhythm strip during tachycardia
• Continuous monitoring: capture tachycardia episodes

Bloods

• U&Es: electrolytes
• TFTs: hyperthyroidism may precipitate tachycardia

Imaging

• Echocardiography: exclude structural heart disease (Ebstein anomaly, HCM)

Special Tests

• Electrophysiology study: localise accessory pathway, assess conduction properties, risk stratification
  • Measure shortest pre-excited RR interval during AF (SPERRI)
  • SPERRI <250 ms indicates high-risk pathway
• Ambulatory monitoring: capture intermittent tachycardia episodes
• Exercise testing: intermittent pre-excitation that disappears with exercise suggests lower-risk pathway

Non-pharmacological

• Vagal manoeuvres: Valsalva, carotid sinus massage for acute orthodromic AVRT
• Avoid precipitants: caffeine, alcohol, stimulants

Pharmacological

Acute orthodromic AVRT (narrow complex):

• Adenosine 6mg rapid IV push (can escalate to 12mg, then 12mg); safe as blocks AV node
• Verapamil 5-10mg IV (alternative if adenosine ineffective)
• DC cardioversion if haemodynamically unstable

AF with pre-excitation (wide complex irregular):

• DO NOT give adenosine, verapamil, digoxin, or beta-blockers — will enhance conduction via accessory pathway and may precipitate VF
• IV flecainide 2mg/kg (max 150mg over 10 min)
• IV procainamide: alternative (slows accessory pathway conduction)
• DC cardioversion: if haemodynamically unstable or in doubt

Surgical/Interventional

• Catheter ablation of accessory pathway: definitive treatment
  • Success rate >95%, recurrence ~5%
  • Low complication rate (~1-2%)
  • Recommended for: symptomatic patients, high-risk pathways, high-risk occupations (pilots, athletes)
  • NICE and ESC recommend ablation as first-line for symptomatic WPW

Referral Criteria

• All symptomatic WPW: referral to electrophysiology for EP study and ablation
• Incidental WPW pattern on ECG: risk stratification with EP study, especially if <35 years or high-risk occupation
• AF with WPW: urgent specialist input

• Post-ablation: cure rate >95%, normal life expectancy
• Untreated symptomatic WPW: risk of sudden death 0.1-0.5% per year
• Asymptomatic WPW pattern: risk of sudden death ~0.1% per year
• Sudden death risk higher if: short SPERRI (<250 ms), multiple accessory pathways, Ebstein anomaly
• Some accessory pathways lose conduction with age (fibrous degeneration)
• Intermittent pre-excitation (comes and goes on ECG) suggests lower-risk pathway

Key Dangerous Drug Interactions in WPW + AF

Accessory Pathway Location by Delta Wave Axis