Wolff-Parkinson-White syndrome

What is Wolff-Parkinson-White syndrome?

Wolff-Parkinson-White syndrome is a congenital heart problem that affects the heart’s electrical system. Although it is present at birth, the onset of symptoms varies and indeed some people never have symptoms. WPW is relatively common, although the exact incidence is not known. About 15% of children with WPW have other heart problems, most often a disease called Ebstein’s anomaly. WPW is not usually hereditary, that is, it is not usually passed from parents to children.

In the normal conduction system, there is only one pathway for electrical signals to pass from the heart’s upper chambers — the atria- to the heart’s lower chambers — the ventricles. This pathway is called the AV node. When a child has WPW, an extra bridge of muscle connects the atria and ventricles of the heart, forming an extra electrical pathway outside the normal conduction system. If there is an early heartbeat, the impulse travels down to the lower chambers using the normal pathway, the AV node, causing the heart to beat, but it may also travel back up the extra pathway to the atria. The impulse continues to travel along this circuit like "a dog chasing its own tail" until it is blocked somewhere along its route. If blocked, the normal heart rhythm can resume.

The type of fast heart rate that occurs is called supraventricular tachycardia (SVT). So, WPW is a sub-group of patients with SVT. Pre-excitation is a finding on the resting electrocardiogram (ECG) that is specific to WPW. Pre-excitation, or the delta wave as it is also known, shows that the ventricles are getting an early electrical signal. The early signal travels very quickly through the extra pathway and reaches the ventricles before the normal signal passing through the AV node.

Another feature of WPW is that a very small percentage of people are at increased risk for sudden cardiac death (see section below).

As stated above, WPW is present at birth. As the heart forms early in fetal life, it is in the shape of a tube. There are muscle fibers throughout the walls of the heart tube. These fibers have the ability to conduct electricity. During early fetal development, the heart tube bends and rotates, a process that ends with the forming of the normal heart- a four-chambered pump with four heart valves. Usually, during this process, the continuity of the muscle fibers between the atria and the ventricles is interrupted. For unknown reasons, sometimes the muscle fibers maintain this connection forming the "accessory pathway", and making the person prone to SVT.

What are the effects of this problem on my child's health?

The information about supraventricular tachycardia applies to children with WPW. In babies, the problem resolves on its own about 50% of the time.

Rarely, WPW can cause sudden cardiac death. This can occur only if 1) the extra pathway can conduct an electrical signal very quickly from the atria to ventricles and 2) the person has an arrhythmia called atrial flutter/fibrillation. In atrial fibrillation/flutter, the upper chambers of the heart beat very fast, from 300 to 600 beats per minute. If the pathway can conduct very rapidly to the lower chambers (and not all can do this), it could result in a life-threatening heart rhythm called ventricular fibrillation. In patients without WPW, the ventricles are protected from the fast atrial rates by the AV-node since is can only conducts a fraction of the signals (see sections on atrial fibrillation and atrial flutter). Sudden cardiac death from WPW is extremely rare in the first few years of life.

How is this problem diagnosed?

Clinical features: See Supraventricular tachycardia.

Physical findings: Most of the time the physical examination is normal when the child is not having an episode. In about 15% of children, the problem is associated with a heart defect. In this case the child has physical findings associated with that defect.

Medical tests: One of the first tests usually done is an electrocardiogram. This is a safe a painless test that involves putting some stickers across the chest. The stickers are connected to a machine that records the heart’s electrical activity. In WPW, the resting ECG shows pre-excitation. This finding is quite specific for WPW and helps to confirm the diagnosis. Sometimes, pre-excitation is found on a routine ECG in a person who has no symptoms.

It may be important to record an ECG at the time of symptoms. This is done by device called a transtelephonic ECG recorder. There are different models of these devices available, but they are all able to record an ECG at the time of symptoms. The tracing can then be sent over the phone to a cardiology center where it can be reviewed. Other tests that may be done include a Holter monitor, echocardiogram, and/or exercise test.

How is the problem treated?

See supraventricular tachycardia. Patients may be treated with heart medicines to prevent episodes of SVT. In general, infants are treated until their first birthday and then the medicines can be stopped. In older children, radiofrequency ablation has become first line treatment as it is safe with high success rates.

Clinics

Care and services for patients with this problem are provided in the Arrhythmia Clinics and Congenital Heart Clinics at the University of Michigan Medical Center in Ann Arbor.

What are the long-term health issues for these children?

Overall, the outlook for children with WPW is excellent. The problem resolves in the majority of infants by 12 months of age although SVT may recur later in childhood.

When the problem persists, radiofrequency ablation has proven to be safe and effective.

Exercise guidelines: Guidelines are best made by a patient’s doctor so that all relevant factors can be included. Participation in vigorous competitive sports (particularly in adolescent boys) may be restricted until the problem is treated by radiofrequency ablation. If the pathway does not conduct rapidly (from the upper to lower chambers), usually no activity restrictions are needed (if the child has an otherwise normal heart).

If an episode of SVT occurs during sports, the child should remove herself/himself from participation until the arrhythmia is converted. Also, activities that involve climbing heights should be avoided since an episode may cause dizziness leading to a fall.