Wolff-Parkinson-White syndrome
Several syndromes involve an abnormal electrical connection (or bypass tract) between the atria and ventricles of the heart, of which Wolff-Parkinson-White (WPW) is the most common. The bypass tract allows electricity in the heart to travel abnormally fast and results in a very rapid heart rate.
The AV node normally serves as the only electrical connection between the atria and the ventricles. In WPW and other similar syndromes, an abnormal connection exists between the atria and ventricles that allows the electrical impulses that start in the atrium to bypass the AV node, travel directly to the ventricles, and electrically activate or excite the ventricles earlier than normal. Thus, these syndromes are often referred to as preexcitation syndromes.
The abnormal connection usually consists of a small collection of heart muscle fibres and is known as a bypass tract or an accessory pathway. Most people with this syndrome can be identified by looking at their electrocardiogram (EKG or ECG). The electrical abnormality in WPW produces a particular abnormal pattern on an EKG and is usually recognized by a physician. On EKG in WPW, the electrical preexcitation of the ventricles can be seen as an abnormality on the EKG known as a delta wave. In about 30% of people with WPW, the accessory pathway is "concealed" and cannot be seen on an EKG.
The bypass tract allows for a continuous electrical loop to form, with one side being the bypass tract and the other being the AV node. The electrical impulse can continuously cycle in this circuit, stimulating the heart to beat at rates of 160 to 220 times per minute. This type of arrhythmia is known as an atrioventricular re-entrant tachycardia and is the most common arrhythmia in people with bypass tracts. Additionally, people with bypass tracts are more likely to develop atrial fibrillation or atrial flutter. When they do, the electrical impulses can travel down the bypass tract and cause the heart to beat at rates in excess of 250 to 300 times per minute. This may result in fainting (syncope), cardiac arrest, or sudden death.
| Author: | Douglas Dana Monica Rhodes | Last Updated: February 7, 2007 |
| Medical Review: | Anne C. Poinier, MD - Internal Medicine Caroline S. Rhoads, MD - Internal Medicine Laurence Epstein, MD - Cardiac Electrophysiologist Stephen Fort, MD, MRCP, FRCPC - Interventional Cardiology | |
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