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Causes
By Mayo Clinic staff
The extra electrical pathway of Wolff-Parkinson-White syndrome is present at birth. An abnormal gene (gene mutation) is the cause of a small percentage of cases of the disorder. Otherwise, little is known about why this extra pathway develops.
Abnormal electrical circuit
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 natural pacemaker — the sinus node — located in the right atrium. The sinus node produces electrical impulses that initiate each heartbeat.
From the sinus node, electrical impulses travel across the atria, causing the atria muscles to contract and 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 down the electrical signal before sending it to the ventricles. This slight delay allows the ventricles to fill with blood. When electrical impulses reach the muscles of the ventricles, they contract, causing them to pump blood either to the lungs or to the rest of the body.
In Wolff-Parkinson-White syndrome, an extra electrical pathway connects the atria and ventricles. This means that an electrical signal can bypass the AV node. When electrical impulses use this detour through the heart, the ventricles are activated too early — a condition known as preexcitation.
Causing a fast heart beat
The extra electrical pathway in the heart doesn't necessarily cause a fast heartbeat. However, this condition makes it possible for other processes to increase the heartbeat, including:
- Looped electrical impulses. The problem with a fast heartbeat usually occurs in Wolff-Parkinson-White syndrome because electrical impulses travel down one pathway and up the other one, creating a loop of signals. This condition, called AV reentrant tachycardia, sends impulses to the ventricles at a very rapid rate. The ventricles, as a result, pump very quickly.
- 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 them to beat very quickly and out of step with each other. This condition is called atrial fibrillation. These disorganized signals also increase the pumping rate of the ventricles to some extent. If there's an extra electrical pathway, as with Wolff-Parkinson-White syndrome, the ventricles can beat even faster. The ventricles don't have time to fill up with blood and don't pump enough blood to the body. This less common condition can be life-threatening.
- Knight B. Patient information: Wolff-Parkinson-White syndrome. http://www.uptodate.com/home/index.html. Accessed Dec. 14, 2008.
- Mitchell L. Wolff-Parkinson-White syndrome. Merck Manuals Online Medical Dictionary: Home Edition for Patients and Caregivers. http://www.merck.com/mmhe/sec03/ch027/ch027e.html. Accessed Jan. 10, 2009.
- Calkins H. Supraventricular tachycardia: AV nodal reentry and Wolff-Parkinson-White syndrome. In: Fuster V, et al., eds. Hurst's The Heart. 12th ed. New York, N.Y.: McGraw-Hill; 2008. http://www.accessmedicine.com/content.aspx?aID=3050545. Jan. 14, 2009.
- Wolff-Parkinson-White syndrome. National Library of Medicine Genetics Home Reference. http://ghr.nlm.nih.gov/condition=wolffparkinsonwhitesyndrome. Accessed Jan. 10, 2009.
- What are Holter, event and transtelephonic monitors? American Heart Association. http://www.americanheart.org/presenter.jhtml?identifier=3005149. Accessed Jan. 15, 2009.
- Hebbar AK, et al. Management of common arrhythmias: Part I. Supraventricular arrhythmias. American Family Physician. 2002;65:2479-2486.
- Delacretaz E. Supraventricular tachycardia. New England Journal of Medicine. 2006;354:1039-1051.
