In Wolff-Parkinson-White (WPW) syndrome, an extra electrical pathway between your heart's upper chambers (atria) and lower chambers (ventricles) causes a rapid heartbeat (tachycardia). This pathway of Wolff-Parkinson-White syndrome is present at birth. An abnormal gene (gene mutation) is the cause in a small percentage of people with the syndrome. WPW also is associated with some forms of congenital heart disease, such as Ebstein's anomaly. Otherwise, little is known about why this 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 the sinus node, a mass of tissue in the right atrium. The sinus node produces electrical impulses that generate each heartbeat.

These electrical impulses travel across the atria, causing muscle contractions that pump blood into the ventricles. The electrical impulses then arrive at a cluster of cells called the atrioventricular node (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 electrical impulses reach the ventricles, muscle contractions pump blood to the lungs and the rest of the body.

Abnormal electrical system in WPW

In Wolff-Parkinson-White syndrome, an extra electrical pathway connects the atria and ventricles, allowing electrical impulses to bypass the AV node. When the electrical impulses use this detour through the heart, the ventricles are activated too early (pre-excitation).

The extra electrical pathway can cause two major types of rhythm disturbances:

  • Looped electrical impulses. In WPW, the heart's electrical impulses travel down either the normal or the extra pathway and up the other one, creating a complete electrical loop of signals. This condition, called AV reentrant tachycardia, sends impulses to the ventricles at a very rapid rate. As a result, the ventricles pump very quickly, causing rapid heartbeat.
  • Disorganized electrical impulses. If electrical impulses don't begin correctly in the right atrium, they may travel across the atria in a disorganized way, causing the atria to beat very quickly and out of step with each other (atrial fibrillation). The disorganized signals and the extra pathway of WPW also can cause the ventricles to beat faster. As a result, the ventricles don't have time to fill with blood and don't pump enough blood to the body.
Mar. 19, 2014