Wolff-Parkinson-White Syndrome (WPW)

ECG
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Wolff-Parkinson-White syndrome (WPW) is a congenital cardiac condition affecting the heart’s electrical system. WPW can cause supraventricular tachycardia (SVT), as well as changes on the ECG. Sometimes WPW produces an increased risk for other more dangerous cardiac arrhythmias.

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.

Why Accessory Pathways Are Important

Accessory pathways are important because they provide the setting needed to develop the type of SVT known as atrioventricular reciprocating tachycardia (AVRT). AVNRT is a type of reentrant tachycardia.

An accessory pathway (which, again, is an abnormal electrical connection between the atria and the ventricles) completes a potential electrical circuit. This abnormal circuit allows AVNRT to develop.

With “typical” AVNRT, during the SVT the electrical impulse travels from the atria to the ventricle using the normal pathway (that is, the AV node), and then returns to the atria through the accessory pathway. The circuit travels in this direction because, with typical AVNRT, the accessory pathway is only capable of conducting electrical impulses in one direction - from the ventricle to the atrium.

Why Is WPW Different From Typical AVNRT?

The difference between typical AVNRT and the AVNRT seen with WPW is that, in WPW, the accessory pathway is capable of conducting electrical impulses in both directions - including from the atrium to the ventricle.

This means that, during reentrant tachycardia in WPW, the electrical impulse travels down the accessory pathway into the ventricles, then returns to the atria through the AV node, then goes back down the accessory pathway to the ventricles again - and keeps repeating the same circuit.

This is the opposite direction of travel than in patients with typical AVRT.

Why WPW Is Important

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." By recognizing the presence of a delta wave, the doctor can make the diagnosis of WPW.

Second, during the reentrant tachycardia caused by WPW, the electrical impulse is stimulating the ventricles solely through the accessory pathway (instead of 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 rhythm 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 travel down the accessory pathway and stimulate the ventricles at an also extremely rapid rate, leading to a dangerously fast heart beat. (Normally, the AV node protects the ventricles from being stimulated too rapidly during atrial fibrillation.) So in patients with WPW, atrial fibrillation can become a life-threatening problem.

Symptoms With WPW

The symptoms of the SVT seen with WPW are the same as with any SVT. They include palpitations, lightheadedness, and/or dizziness. 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.

Treating 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 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.

Using antiarrhythmic drugs to prevent recurrent arrhythmias in WPW is often only somewhat effective. However, the accessory pathway in WPW can usually (more than 95% of the time) be eliminated entirely with ablation therapy, in which the accessory pathway is carefully mapped and ablated.

Because the onset of atrial fibrillation in WPW can lead to dangerously rapid heart rates, and because atrial fibrillation is common (and may be more common in people with WPW than in the general population), most specialists encourage patients with WPW to consider ablation therapy.

Sources:

Pediatric and Congenital Electrophysiology Society (PACES), Heart Rhythm Society (HRS), American College of Cardiology Foundation (ACCF), et al. PACES/HRS expert consensus statement on the management of the asymptomatic young patient with a Wolff-Parkinson-White (WPW, ventricular preexcitation) electrocardiographic pattern: developed in partnership between the Pediatric and Congenital Electrophysiology Society (PACES) and the Heart Rhythm Society (HRS). Endorsed by the governing bodies of PACES, HRS, the American College of Cardiology Foundation (ACCF), the American Heart Association (AHA), the American Academy of Pediatrics (AAP), and the Canadian Heart Rhythm Society (CHRS). Heart Rhythm 2012; 9:1006.

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