Causes

The extra electrical pathway that causes a rapid heartbeat is present at birth. An abnormal gene is the cause in a small percentage of people with WPW. The syndrome also is associated with some forms of congenital heart disease, such as Ebstein anomaly.

Otherwise, little is known about why the extra pathway develops.

Normal heart electrical system

Your heart is made up of four chambers — two upper chambers (atria) and two lower chambers (ventricles). The rhythm of your heart is normally controlled by a mass of tissue in the right atrium (sinus node). The sinus node produces electrical impulses, or signals, that cause each heartbeat.

These electrical signals travel across the atria, causing muscle contractions that pump blood into the ventricles. The signals then arrive at a cluster of cells called the atrioventricular (AV) node — usually the only pathway for signals to travel from the atria to the ventricles. The AV node slows the electrical signal before sending it to the ventricles.

This slight delay allows the ventricles to fill with blood. When the electrical signals reach the ventricles, muscle contractions pump blood to the lungs and the rest of the body.

Abnormal electrical system in WPW

In WPW syndrome, an extra electrical pathway connects the atria and ventricles, allowing electrical impulses to bypass the AV node. This detour activates the ventricles too early.

The extra pathway can also transmit electrical impulses from the ventricles back to the atria, disrupting the coordinated movement of the electrical signals through the heart, leading to changes in the heart rhythm.

The most common arrhythmia associated with WPW syndrome is called paroxysmal supraventricular tachycardia. Some people with WPW syndrome have a type of irregular heartbeat known as atrial fibrillation.