Overview of Wolff-Parkinson-White Syndrome (WPW)

Wolff-Parkinson-White syndrome (WPW) is a congenital cardiac condition that can cause cardiac arrhythmias. People born with WPW have characteristic changes on their electrocardiogram (ECG), and they frequently develop supraventricular tachycardia (SVT), a type of rapid arrhythmia that often produces severe palpitations, lightheadedness, and fatigue. In addition, sometimes people with WPW can have other, more dangerous types of cardiac arrhythmias.

Stethoscope arranged as an EKG
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What Is WPW?

People with WPW are born with an abnormal electrical connection that joins one of the atria (the upper chambers of the heart) with one of the ventricles (the lower chambers of the heart). These abnormal electrical connections are called accessory pathways. The accessory pathways create the electrical conditions in which abnormal cardiac rhythms can occur.

Why Accessory Pathways Are Important

The accessory pathway creates an “extra” electrical connection between an atrium and a ventricle, and by doing so it completes a potential electrical circuit. This abnormal circuit allows unusual heart rhythms, or arrythmias, to develop.

Accessory pathways provide the setting for a particular type of arrhythmia — the SVT known as atrioventricular reciprocating tachycardia (AVRT). AVRT is a type of reentrant tachycardia.

During AVRT the electrical impulse travels from the atrium to the ventricle using the normal pathway (that is, the AV node) and then returns to the atrium (that is, it “reenters” the atrium) through the accessory pathway. The electrical impulse can then spin around the circuit continuously, creating the arrhythmia. The impulse travels across the accessory pathway from ventricle to the atrium because, in the most common type of AVRT, that’s the only direction in which the accessory pathway is capable of conducting electricity. 

How Is WPW Different From Typical AVRT?

The difference between this typical AVRT and the AVRT seen with WPW is that, in WPW, the accessory pathway is capable of conducting electrical impulses in both directions — from the atrium to the ventricle as well as from the ventricle to the atrium.

As a result, during reentrant tachycardia in WPW, the electrical impulse is able to travel down the accessory pathway into the ventricles, then return to the atria through the AV node, then back down the accessory pathway to the ventricles again — and it can keep repeating the same circuit. This is the opposite direction of travel than in patients with typical AVRT.

Why WPW Is A Particular Problem

The ability of the accessory pathway in WPW to conduct electrical impulses from the atria into the ventricles is important for three reasons.

First, during normal sinus rhythm, the electrical impulse spreading across the atria reaches the ventricles both through the AV node and through the accessory pathway. This "dual" stimulation of the ventricles creates a distinguishing pattern on the ECG — specifically, a "slurring" of the QRS complex which is referred to as a "delta wave." Recognizing the presence of a delta wave on the ECG can help a doctor can make the diagnosis of WPW.

Second, during the AVRT seen with WPW, the electrical impulse is stimulating the ventricles solely through the accessory pathway (instead of going through the normal, AV nodal pathway). As a result, the QRS complex during tachycardia takes on an extremely abnormal shape, which is suggestive of ventricular tachycardia (VT) instead of SVT. Mistaking the AVRT caused by WPW for VT can create great confusion and unnecessary alarm on the part of medical personnel, and may lead to inappropriate therapy.

Third, if a patient with WPW should develop atrial fibrillation — an arrhythmia in which the atria are generating electrical impulses at an extremely rapid rate — those impulses can also travel down the accessory pathway and stimulate the ventricles at an also extremely rapid rate, leading to a dangerously fast heartbeat. (Normally, the AV node protects the ventricles from being stimulated too rapidly during atrial fibrillation. This protection is lost if the ventricles are being stimulated via the accessory pathway.) So in patients with WPW, atrial fibrillation can become a life-threatening problem.

Symptoms With WPW

The symptoms of the SVT caused by WPW are the same as with any SVT. They include palpitations, lightheadedness or dizziness, and extreme fatigue. Episodes usually last from a few minutes to several hours.

If atrial fibrillation should occur, however, the extremely rapid heart rate may lead to loss of consciousness, or even cardiac arrest.

Treatment of WPW

The reentrant circuit which produces SVT in WPW incorporates the AV node, a structure that is richly supplied by the vagus nerve. So patients with WPW can often stop their episodes of SVT by taking steps to increase the tone of their vagus nerve, such as the Valsalva maneuver, or immersing their face in ice water for a few seconds. For some people who have only rare episodes of SVT, this treatment may be sufficient.

Using antiarrhythmic drugs to prevent recurrent arrhythmias in WPW is only somewhat effective, and this approach is not used very often today.

However, the accessory pathway in WPW can usually (95% of the time) be eliminated entirely with ablation therapy, in which the accessory pathway is carefully mapped and ablated. Ablation therapy is almost always the best option in somebody with WPW who has had arrhythmias.

Furthermore, because the onset of atrial fibrillation in WPW can lead to dangerously rapid heart rates, and because atrial fibrillation is common (and maybe more common in people with WPW than in the general population), even asymptomatic people with WPW may want to consider ablation.

A Word From Verywell

WPW, a congenital abnormality involving the cardiac electrical system, is associated with cardiac arrhythmias that can produce severe symptoms. People found to have WPW should be evaluated by a cardiologist, and will often benefit from definitive treatment to eliminate the condition.

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