How do you diagnose Wolff-Parkinson-White (WPW) syndrome in a patient?

Diagnosing Wolff-Parkinson-White (WPW) Syndrome

WPW syndrome is diagnosed by identifying the classic triad on a 12-lead ECG: PR interval <0.12 seconds, delta wave (slurred upstroke of the QRS), and QRS duration >0.12 seconds, combined with clinical symptoms of tachyarrhythmias. 1

Essential ECG Diagnostic Criteria

The diagnosis relies on specific electrocardiographic features that must all be present 1:

• PR interval <0.12 seconds (shortened due to bypass of the AV node) 1
• Delta wave - a slurred, slow upstroke at the initial segment of the QRS complex representing early ventricular activation 1
• Widened QRS complex >0.12 seconds (total duration) 1
• Secondary ST-T wave changes that are discordant (opposite direction) to the major delta wave and QRS vector 1

The degree of pre-excitation varies based on relative conduction through the AV node versus the accessory pathway, which explains why some patients show intermittent patterns 2.

Distinguishing Pattern from Syndrome

A critical distinction exists between WPW pattern (ECG findings alone) and WPW syndrome 3:

• WPW pattern: Pre-excitation visible on ECG in an asymptomatic patient 3
• WPW syndrome: Pre-excitation plus documented symptomatic tachyarrhythmias 3, 4

Approximately half of patients with the ECG pattern remain asymptomatic throughout their lives 1, 4.

Key Clinical Symptoms to Assess

When symptoms occur, they indicate WPW syndrome and include 4:

• Palpitations - the most common symptom, representing tachyarrhythmia episodes 3
• Syncope or near-syncope - particularly concerning as it may indicate rapid accessory pathway conduction and sudden death risk 3
• Dizziness during tachyarrhythmia episodes 3
• Dyspnea suggesting hemodynamic compromise 3, 4
• Chest pain during arrhythmic episodes 3

Diagnostic Testing Beyond Baseline ECG

Ambulatory Monitoring

• 24-hour Holter monitoring to detect paroxysmal arrhythmias and assess for intermittent pre-excitation 5
• Intermittent loss of pre-excitation indicates a longer accessory pathway refractory period and lower risk (90% positive predictive value for low risk) 2, 3

Exercise Testing

• Exercise ECG to evaluate if pre-excitation disappears with exercise 5
• Sudden disappearance of the WPW pattern during exercise suggests a long anterograde refractory period and low risk of sudden death 5

Provocative Testing

• Adenosine or verapamil administration can unmask latent pre-excitation when the diagnosis is uncertain 5
• In pediatric patients, blocked accessory pathway conduction with adenosine has 100% specificity and positive predictive value for non-rapid baseline conduction 6
• Adenosine typically increases pre-excitation in WPW patients, which can be diagnostic when the baseline ECG is questionable 6

Electrophysiological Study

• EPS is the gold standard for definitive diagnosis and risk stratification in both symptomatic and asymptomatic patients 3
• EPS determines the shortest pre-excited R-R interval during induced atrial fibrillation (high risk if <250 ms) 3
• EPS measures accessory pathway refractory period (high risk if <240 ms) 3

Associated Structural Heart Disease to Exclude

Further investigation with echocardiography is essential to rule out 5:

• Ebstein anomaly - the most common associated congenital defect 5, 3
• Hypertrophic cardiomyopathy 5
• Glycogen storage cardiomyopathy (PRKAG2-related familial WPW) 5

Family History Assessment

Obtain detailed family history focusing on 5:

• Pre-excitation in first-degree relatives (prevalence 0.55% vs 0.15-0.25% in general population) 2
• Sudden cardiac death in young family members 5
• Cardiomyopathy 5

An ECG should be obtained in siblings of young athletes with bifascicular block patterns 5.

Common Diagnostic Pitfalls

Beware of misdiagnosing pre-excited atrial fibrillation as ventricular tachycardia - the wide, irregular QRS complexes in pre-excited AF can mimic VT, but incorrect treatment with AV nodal blockers can precipitate ventricular fibrillation 7. Pre-excited AF shows irregular wide QRS complexes with varying morphology and extremely rapid rates (often >200 bpm) 7.

Short PR interval (<0.12 seconds) without a delta wave requires careful evaluation, as it may represent Lown-Ganong-Levine syndrome or underlying structural disease like HCM or Fabry disease 5.