What is it?
Normally, there is just one electrical pathway connecting the upper and lower chambers (atria and ventricles, respectively) of the heart. This is the AV node. Impulses may pass in only one direction and this ensures normal, sequential contraction of the cardiac chambers. Patients with the Wolff-Parkinson-White syndrome (commonly known by its acronym, WPW syndrome) have an extra conduction pathway, called an accessory pathway, bridging the divide between the atria and ventricles. This may permit the normal electrical signal to arrive at the ventricles more quickly than usual, causing "pre-excitation" and producing characteristic changes on the electrocardiogram. The same pathway may at times function as a "short-circuit", allowing impulses to circulate rapidly down the normal AV nodal pathway and back up the accessory pathway causing one form of supraventricular tachycardia. Patients in whom this occurs will complain of rapid heart beating and may experience dizziness, chest tightness and may even faint. The most serious situation which is fortunately very rare is when patients with WPW develop atrial fibrillation (very rapid, chaotic electrical activity within the atria, see above) which may conduct very rapidly down the accessory pathway to the ventricles. This may then cause ventricular tachycardia or fibrillation and cardiac arrest. Other people with WPW never have tachycardia or other symptoms. About 80 percent of people with symptoms first experience them between the ages of 11 and 50.

How is it treated?
Once the diagnosis is made, patients are nowadays usually referred to a specialist who will try to assess the conduction properties of the accessory pathway in order to assess the risk it might pose. Patients without symptoms will not require treatment unless the pathway poses a risk to them or if they have special occupations such as airline pilot. People who have episodes of tachycardia can be treated with long term medication or can undergo radiofrequency catheter ablation (discussed in separate section) which is curative in 95 to 98% of cases. Whether an individual will be treated with medication or by an ablation procedure depends on several factors such as the severity and frequency of symptoms, risk for future arrhythmias and patient preference.