Wolff-Parkinson-White syndrome classification scheme

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]

Classification

Classification Based on the Type of Conduction

The accessory pathway in WPW can be classified into:

• Antegrade conduction: also known as manifest, responsible for the "pre-excitation" finding on ECG
• Retrograde conduction: also known as concealed

Most commonly, the accessory pathways conduct in both directions. Isolated retrograde conduction is less common, and isolated antegrade conduction is rare and is usually associated with accessory pathways in the right side of the heart.

Classification Based on the ECG Findings

This classification is based on the side where the accessory pathway is established. The type A preexcitation presents the accessory pathway in the left side of the heart (comunicates the left atrium with the left ventricle). The type B preexcitation presents the accessory pathway in the right side of the heart (comunicates the right atrium with the right ventricle). Each type of preexcitation presents its own electrocardiographyc characteristics.

1. Type A:
   • Prominent R wave in lead V1 and V2.
   • It has been found at EP studies that these patients have early activation of the left ventricle.
   • Generally V1 shows either a notched R wave or RS or Rsr' deflection.
   • Mimics a posterior MI, RVH.
2. Type B:
   • Prominent S wave deflection in the right precordial leads, and upright R waves in the lateral precordial leads.
   • EP studies have showed that this form of WPW syndromes is due to early activation of the lateral aspect of the right ventricle
   • This form is more common.
   • May resemble an abnormal Q wave in the right precordial leads and be mistaken for an anterior MI.
   • In both type A and B there may be abnormal q waves in leads 2, 3 and aVF.

Variants of WPW

Lown-Ganong-Levine Syndrome (LGL)

• There is a short PR interval, but no delta wave
• LGL is due to intranodal bypass tracts (i.e. there is conduction down the James fibers)
• Normal QRS duration
• PR less than 0.12 seconds
• Normal P wave

Mahaim Type Preexcitation

• This form of pre-excitation is due to nodoventricular, nodofascicular or fasciculoventricular connections
• The impulse may travel through the AV node normally and this may then be followed by premature conduction to the basal ventricular myocardium
• There is a delta wave with a normal PR interval
• Rarer than WPW or LGL
• In older patients there can be a prolonged conduction down the accessory pathway resulting in a normal PR interval in the presence of WPW which is tough to distinguish from Mahaim fibers