How is Wolff-Parkinson-White (WPW) syndrome diagnosed?

Diagnosis of Wolff-Parkinson-White Syndrome

The diagnosis of Wolff-Parkinson-White (WPW) syndrome is primarily based on electrocardiographic findings of a short PR interval, delta wave, and widened QRS complex, along with a history of tachyarrhythmias. 1

ECG Diagnostic Criteria

The definitive diagnosis of WPW relies on the following electrocardiographic features:

• Short PR interval (<0.12 seconds)
• Delta wave (slurring of the initial segment of the QRS complex)
• Widened QRS complex (total duration >0.12 seconds)
• Secondary repolarization changes (ST segment-T wave changes generally directed opposite to the major delta wave and QRS complex) 2

In newborns and infants, WPW can be diagnosed when two of the following four characteristics are present:

• PR interval <100 ms
• QRS complex duration <80 ms
• Lack of a Q wave in V6
• Left axis deviation 1

Additional Diagnostic Evaluation

After identifying WPW pattern on ECG, further evaluation is necessary to:

1. Confirm the diagnosis
2. Assess risk of sudden cardiac death
3. Evaluate for associated structural heart disease

Risk Assessment

Several tests are recommended for risk stratification:

• 24-hour Holter monitoring: To detect intermittent pre-excitation (loss of delta wave), which suggests a longer refractory period of the accessory pathway and lower risk of sudden death 1

• Exercise testing: Disappearance of the delta wave during exercise indicates a longer refractory period of the accessory pathway and lower risk of sudden cardiac death 1

• Electrophysiological study: The gold standard for risk assessment, measuring:

  • Shortest pre-excited R-R interval during atrial fibrillation (high risk if <250 ms)
  • Presence of multiple accessory pathways
  • Inducibility of atrioventricular re-entrant tachycardia 1

• Pharmacological testing: Administration of adenosine/verapamil to assess the refractory period of the accessory pathway 1

Structural Heart Disease Assessment

• Echocardiography: To rule out associated structural heart disease, such as:
  • Ebstein's anomaly
  • Hypertrophic cardiomyopathy
  • Glycogen storage cardiomyopathy 1

Clinical Context

WPW syndrome affects approximately 0.1-0.3% of the general population and is the second most common cause of paroxysmal supraventricular tachycardia 3. The diagnosis of WPW syndrome is reserved for patients who have both pre-excitation on ECG and tachyarrhythmias 1.

Special Considerations

• Intermittent pre-excitation: The detection of intermittent pre-excitation (abrupt loss of delta wave) indicates a relatively long refractory period of the accessory pathway and lower risk of ventricular fibrillation 1

• Concealed pathways: Some accessory pathways conduct only in the retrograde direction and do not cause pre-excitation on the standard ECG 1

• Asymptomatic WPW: Even asymptomatic patients with WPW pattern on ECG should undergo risk stratification, as sudden cardiac death can be the first manifestation in some cases 4

Common Pitfalls to Avoid

1. Misdiagnosis as myocardial infarction: WPW can mimic inferior myocardial infarction due to deep Q waves in leads II, III, aVF 1, 5

2. Inappropriate medication use: Avoid digoxin and verapamil in patients with WPW and atrial fibrillation as they can shorten the refractory period of the accessory pathway and increase the risk of ventricular fibrillation 1

3. Missing associated conditions: Failure to screen for associated structural heart diseases like Ebstein's anomaly, which increases the risk of sudden death 1

4. Relying solely on non-invasive tests: Non-invasive tests are considered inferior to invasive electrophysiological assessment for risk stratification 1

By following these diagnostic criteria and evaluation steps, WPW syndrome can be accurately diagnosed and risk-stratified to guide appropriate management decisions.