EKG changes with Wolff-Parkinson-White syndrome.

12 lead EKG of individual with Wolff-Parkinson-White syndrome.

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Wolff-Parkinson-White syndrome

Wolff-Parkinson-White syndrome (WPW) is a syndrome of pre-excitation of the ventricles due to an accessory pathway known as the Bundle of Kent. This accessory pathway is an abnormal electrical communication from the atria to the ventricles. more...

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The incidence of WPW syndrome is between 0.1 and 3 percent of the general population.^,^, While the vast majority of individuals with WPW syndrome remain asymptomatic throughout their entire lives, there is a risk of sudden death associate with WPW syndrome. Sudden death due to WPW syndrome is rare (incidence of ≤0.6%^,), and is due to the effect of the accessory pathway on tachyarrhythmias in these individuals.

Pathophysiology

In normal individuals, electrical activity in the heart is initiated in the sinoatrial (SA) node (located in the right atrium), propagates to the atrioventricular (AV) node, and then through the bundle of His to the ventricles of the heart. (See electrical conduction system of the heart).

The AV node acts as a gatekeeper, limiting the electrical activity that reaches the ventricles of the heart. This is an important function of the AV node, because if the signals generated in the atria of the heart were to increase in rate (such as during atrial fibrillation or atrial flutter), the AV node will limit the electrical activity that conducts to the ventricles. For instance, if the atria are electrically activated at 300 beats per minute, half those electrical impulses are blocked by the AV node, so that the ventricles are activated at 150 beats per minute (giving a pulse of 150 beats per minute). Another important property of the AV node is that it slows down individual electrical impulses. This is manifest on the EKG as the PR interval, the time from activation of the atria (manifest as the P wave) and activation of the ventricles (manifest as the QRS complex).

Individuals with WPW syndrome have an accessory pathway that connects the atria and the ventricles, in addition to the AV node. This accessory pathway is known as the bundle of Kent. This accessory pathway does not share the rate-slowing properties of the AV node, and may conduct electrical activity at a significantly higher rate than the AV node. For instance, in the example above, if an individual had an atrial rate of 300 beats per minute, the accessory bundle may conduct all the electrical impulses from the atria to the ventricles, causing the ventricles to activate at 300 beats per minute. The ventricles are not capable of activating in a uniform manner at rates that fast and will fibrillate instead (ventricular fibrillation). If not corrected rapidly, ventricular fibrillation leads to sudden cardiac death (SCD).

Definition

Wolff-Parkinson-White syndrome is an abnormality in the electrical functioning of the heart which may cause rapid heart rates. The abnormality affects the electrical signal between the atria and ventricles.

Description

Blood is circulated through the heart and body by a muscular pump and valve system involving the atria and ventricles. The right atrium receives oxygen-lacking blood returning to the heart from the body. The blood is passed from the right atrium into the right ventricle, which contracts and sends blood out to the pulmonary artery. The pulmonary artery sends the blood into the lungs, where carbon dioxide is removed, and fresh oxygen is added. The left atrium receives blood with oxygen from the lungs and passes this arterial blood to the left ventricle, where it is emptied into the aorta, the main artery of the heart.

These functions are directed by electrical signals within the heart. In patients afflicted with Wolff-Parkinson-White syndrome, an abnormal pathway exists that causes additional electrical signals to pass between the atria and ventricles, possibly causing rapid heart rate.

Causes & symptoms

Congenital heart disease may contribute to this and other arrhythmias. Ebstein's anomaly, a congenital heart defect that involves displacement of the tricuspid valve, located on the right side of the heart, is one known cause of Wolff-Parkinson-White syndrome. This anomaly allows blood to flow via the small hole to the other side of the heart. Often, there is no known cause for Wolff-Parkinson-White syndrome. Many people with the syndrome have no symptoms. On the other hand, some people experience temporary rapid heartbeat due to certain drugs, smoking, and anxiety.

Diagnosis

Electrocardiography (ECG) is used to diagnose Wolff-Parkinson-White syndrome, and other cardiac arrhythmias. A trained physician, normally a cardiologist, can recognize patterns of electrical conduction. With this syndrome, the extra pathway will show a pattern different from those of normal conduction. If no irregular patterns show on the ECG, the patient may be sent home with a 24-hour heart monitor, called a Holter monitor, which will help detect intermittent occurrences. Other studies, such as the cardiac electrophysiologic study (EPS), may be ordered to pinpoint the location of the accessory pathway, and to determine a course of treatment.

Treatment

Various drugs may be used to treat Wolff-Parkinson-White syndrome, as well as other cardiac arrhythmias. The purpose of these drugs is to slow the electrical signals and excitation of heart muscles. As some of these drugs may have side effects, including the rare production of new or more frequent arrhythmias, the patient should be carefully observed. Ablative therapies may be accomplished with radiofrequency or cardiac catheters to cut through the tissue which is causing the abnormal electrical signals.

At one time, only open heart surgery was used, but the procedure can be done now with local anesthesia in a special cardiac laboratory. In some cases, surgery may still be recommended to treat Wolff-Parkinson-White syndrome.Young people with this syndrome may be treated more successfully with surgery, rather than enduring a lifetime of drug treatments, or the possible threat of sudden cardiac death.

Alternative treatment

A provider may teach patients methods to help control heart rate. Relaxation techniques, acupuncture, botanical medicine, and homeopathy can all be helpful supportive therapies.

Prognosis

Most patients with this syndrome can lead normal lives, even with episodes of tachycardia. In many cases, the syndrome is secondary to the underlying congenital heart defect. However, Wolff-Parkinson-White syndrome can cause sudden cardiac arrest in certain instances.

Prevention

If the syndrome is not due to congenital heart disease, the patient may try avoiding behaviors which lead to arrhythmia, such as elimination of caffeine, alcohol, cocaine, and smoking.

Key Terms

Ablative: Used to describe a procedure involving removal of a tissue or body part, or destruction of its funtion.
Arrhythmia: Irregular heart beat.
Electrocardiograph (ECG): A test of a patient's heartbeat that involves placing leads, or detectors, on the patient's chest to record electrical impulses in the heart. The test will produce a strip, or picture record of the heart's electrical function.
Tachycardia: Rapid heart rate, defined as more than 100 beats per minute.

For Your Information

Books

Conn, Howard F., Robert J. Clohecy, and Rex B. Conn. Current Diagnosis. Philadelphia: W.B. Saunders, 1997.
Organizations
American Heart Association. 7320 Greenville Ave. Dallas, TX 75231. (214) 373-6300. http://www.amhrt.org.
National Institutes of Health. National Heart, Lung and Blood Institute. Building 31, Room 4A21, Bethesda, MD 20892. (301) 496-4236. http://www.nhlbi.nih.gov.

Gale Encyclopedia of Medicine. Gale Research, 1999.

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