Diagnosis
WPW is commonly diagnosed on the basis of the electrocardiogram in an asymptomatic individual. In this case it is manifested as a delta wave, which is a slurred upstroke in the QRS complex that is associated with a short PR interval. The short PR interval and slurring of the QRS complex is actually the impulse making it through to the ventricles prematurely (across the accessory pathway) without the usual delay experienced in the AV node.
If a person with WPW experiences episodes of atrial fibrillation, the ECG will show a rapid polymorphic wide-complex tachycardia (without torsades de pointes). This combination of atrial fibrillation and WPW is considered dangerous, and most antiarrhythmic drugs are contraindicated.
When an individual is in normal sinus rhythm, the ECG characteristics of WPW are a short PR interval (less than 120 milliseconds in duration), widened QRS complex (greater than 120 milliseconds in duration) with slurred upstroke of the QRS complex, and secondary repolarization changes (reflected in ST segment-T wave changes).
In individuals with WPW, electrical activity that is initiated in the SA node travels through the accessory pathway as well as through the AV node to activate the ventricles via both pathways. Since the accessory pathway does not have the impulse slowing properties of the AV node, the electrical impulse first activates the ventricles via the accessory pathway, and immediately afterwards via the AV node. This gives the short PR interval and slurred upstroke of the QRS complex known as the delta wave.
In case of type A pre-excitation (left atrioventricular connections), a positive R wave will be seen in V1 ("positive delta") on the precordial leads of the electrocardiogram, while in type B pre-excitation (right atrioventricular connections), a predominantly negative delta wave will be seen in lead V1 ("negative delta").
People with WPW may have more than one accessory pathway—in some cases, as many as eight abnormal pathways have been found. This has been seen in individuals with Ebstein's anomaly.
Wolff–Parkinson–White syndrome is sometimes associated with Leber's hereditary optic neuropathy (LHON), a form of mitochondrial disease.
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