Patient information: Wolff-Parkinson-White syndrome

OVERVIEW

Wolff-Parkinson-White (WPW) syndrome is a condition in which episodes of fast heart rate (called tachycardia) occur because of an extra abnormal electrical pathway in the heart. People with WPW may experience palpitations, dizziness, lightheadedness, fainting, although some people with WPW have no symptoms. Treatments are available for those who do experience symptoms. The long term outcome of people with WPW is excellent, especially when treatments are used to eliminate the abnormal conduction pathway.

This topic review discusses how the heart functions in people with WPW, the signs and symptoms of the condition, how it is diagnosed, and the available treatments.

THE HEART

A brief review of the structure of the heart and the normal electrical conduction system will aid in the understanding of WPW. The heart is made up of four chambers: the right atrium, right ventricle, left atrium, and left ventricle (figure 1). Blood returning to the heart from the body flows into the right atrium, and then the right ventricle. Blood is pumped out of the right ventricle into the lungs (where red blood cells fill with oxygen) and then returns to the heart in the left atrium. Blood in the left atrium flows into the left ventricle, which pumps the blood to the rest of the body through the aorta, the major artery.

Heart muscle cells are stimulated by electrical impulses that cause them to contract in a uniform way at a regular rate (figure 2). This contraction produces the heartbeat, which causes blood to be pumped out of the heart into arteries and then to all parts of the body. The flow of blood into arteries can be measured by feeling the pulse, which corresponds to the heartbeat.

In order to bring the electrical impulse to all parts of the heart in a uniform fashion, the heart has a series of "wires", known as the conduction system. A normal heartbeat is produced when the heart's natural pacemaker, the sinoatrial (or sinus) node, which is an area of specialized cells in the upper part of the right atrium, sends out a series of regular electrical impulses. These impulses travel in an organized way along conduction tissue in the heart, passing first across both atria, then to an area between the atria and the ventricles known as the atrioventricular node (AV node), and finally spreading across the ventricles, which are the heart's main pumping chambers. The normal heart rate is 60 to 100 beats per minute.

CAUSES OF WOLFF-PARKINSON WHITE SYNDROME

Conduction in WPW — Patients with WPW syndrome have an extra electrical pathway between the atria and the ventricles, known as an accessory pathway. The abnormal pathway directly connects the atria and ventricles and bypasses the AV node, which is the slowest conducting part of the heart's electrical system (figure 3). As a result, the normal sinus impulse can travel down the normal pathway through the AV node, as well as the more rapidly conducting accessory pathway. This allows the impulse traveling through the accessory pathway to reach the ventricle earlier, causing what is termed "preexcitation."

The two pathways increase the risk of developing a "short circuit" of the normal electrical pathway, which can result in an abnormally fast heart rate (tachycardia). Patients who have recurring tachycardias because of this abnormality are said to have the WPW syndrome. Some patients have the WPW pathway, but no tachycardia. They do not have WPW syndrome, but may develop it at some point. These patients are said to have a WPW pattern, which can be detected on a routine electrocardiogram (ECG).

Causes of tachycardia — The presence of an accessory pathway alone does not explain tachycardia, since the sinus node rate is only 60 to 100 beats per minute. There are two mechanisms of tachycardia in the WPW syndrome:

Atrial fibrillation — Some patients have an abnormal rhythm called atrial fibrillation. In atrial fibrillation, the atria are beating in an uncoordinated manner at a rate of 350 to 600 beats per minute. The AV node normally blocks most of these impulses so that the ventricular rate (which is felt with the pulse) is usually less than 170 beats per minute. (See "Patient information: Atrial fibrillation".)

With WPW, conduction is much more rapid and more impulses get through the accessory pathway. The ventricles may beat at a rate of 200 or more beats per minute, and there is a risk that the heart can beat up to 300 times per minute. Even higher rates of up to 300 beats per minute can occur with atrial flutter, another type of abnormal atrial rhythm.

Atrioventricular reentrant tachycardia — The second mechanism is called atrioventricular reentrant tachycardia (AVRT). In this tachycardia, an electrical impulse travels down one pathway (either through the AV node or the accessory pathway) and then back up the other, creating a repeating loop. This circular or "reentrant" electrical activity sends impulses to the ventricles at an abnormally high rate, causing the heart to beat from 140 to 220 times per minute.

The tachycardia of WPW syndrome begins suddenly and may stop just as suddenly on its own. Sometimes, however, treatment is necessary to end the tachycardia and reinstate a normal rhythm. Patients with WPW syndrome typically have recurrent episodes of the tachycardia.

WOLFF-PARKINSON WHITE SYMPTOMS

As mentioned earlier, patients can have the WPW pathway but never experience tachycardia or any other symptoms (WPW pattern). If symptoms do occur (WPW syndrome), they are related to the development of an irregular heart rhythm and a rapid heart rate.

During tachycardia, patients may experience palpitations, dizziness, lightheadedness, fainting, or rarely, sudden death. Sudden death is usually a result of the very rapid ventricular response seen in WPW syndrome as well as atrial fibrillation or atrial flutter. A very rapid heart rate means that the ventricles cannot pump blood effectively to other vital organs. Fortunately, the incidence of sudden death in patients with the WPW syndrome is quite low, ranging from 0 to 0.39 percent per year. People with WPW but who have no symptoms have the lowest risk of sudden death.

Most patients with WPW syndrome have no other underlying heart disease. When other heart disease is present, the heart may be less able to tolerate the rapid heart rate. In this case, the likelihood of serious symptoms, including chest pain and difficulty breathing due to poor heart function, increases.

WOLFF-PARKINSON WHITE DIAGNOSIS

WPW is usually diagnosed with a standard electrocardiogram (ECG), but specialized testing is required in some patients.

The electrocardiogram — The WPW pattern can be detected by an ECG, even while the patient is in a normal rhythm. Conduction through the accessory pathway produces a characteristic ECG pattern. A classic finding is a short PR interval (the time for conduction between atria and ventricles) and a delta wave, which reflects early conduction (preexcitation) to the ventricles through the accessory pathway (figure 4).

If, however, most of the impulses traveling from the atria to the ventricles go through the AV node, then a short PR interval, a delta wave, and other findings associated with the WPW pattern will not be seen.

In some people with WPW, the ECG can vary from day to day or even from hour to hour, depending upon other factors (such as adrenaline released during periods of stress or the intake of caffeine). These factors can alter the relative proportion of impulses that are conducted the accessory pathway; it is only these impulses that produce the WPW pattern.

Diagnosis of the WPW syndrome is based upon ECG evidence of the accessory pathway and the presence of a related tachycardia.

Electrophysiologic testing — In some patients, a specialized procedure called electrophysiologic testing may be performed. This test can:

• Determine the reason for tachycardia
• Identify the location of the accessory pathway
• Determine if the accessory pathway has dangerous properties

The test is performed in an area of a hospital or clinic called an electrophysiology lab, and the patient is given a sedative medication before the procedure. The patient's oxygen levels, heart rate and rhythm, and blood pressure are monitored throughout testing.

To perform the test, a specially trained cardiologist threads small wires (called electrode catheters), usually through a vein in the inner thigh. A vein in another area of the body may be preferred in some situations. The catheters are threaded into the heart, where they are positioned at various locations. The catheters are used to precisely monitor, or map, the heart's electrical pathways.

WOLFF-PARKINSON WHITE TREATMENT

Most people with the WPW pattern on ECG who do not experience tachycardia do not need treatment. These patients may never develop symptoms and, in many cases, conduction via the accessory pathway spontaneously disappears as the patient grows older.

However, some asymptomatic patients with a WPW ECG pattern (such as people with a high risk occupation or professional athletes) are advised to undergo additional testing, including electrophysiologic testing, to determine if the accessory pathway is associated with a high risk of sudden cardiac arrest.

Patients with WPW syndrome require treatment when or if they have an episode of tachycardia due to the serious potential risks. Treatment focuses on stopping the tachycardia and preventing its from recurring.

Stopping the tachycardia — When the tachycardia is an AVRT, the tachycardia can often be stopped by interfering with the circular loop described above (see 'Atrioventricular reentrant tachycardia' above.

This can be achieved by two simple maneuvers:

• Coughing or bearing down as if having a bowel movement (called the Valsalva maneuver)
• Firmly massaging the main artery in the patient's neck (called carotid sinus pressure)

If these measures are not effective, medications may be used to stop the tachycardia. The best medication depends upon the mechanism that is responsible. A cardiologist (heart specialist) with experience in the treatment of rhythm disturbances usually assists with treatment in this case.

If a patient is unstable due to low blood pressure (due to the rapid heart rate) or if the medication is not immediately effective, cardioversion can be used to stop the arrhythmia. In cardioversion, electricity is discharged into the patient's heart from pads or paddles placed on the chest. The current affects the electrical charge of the heart muscle cells to restart a normal rhythm. (See "Patient information: Cardioversion".)

Preventing recurrence of the tachycardia — There are three major options for preventing recurrence of the tachycardia: radiofrequency ablation, medications, and surgery. The choice is best made with a cardiologist who has experience in treating the WPW syndrome.

Radiofrequency ablation — Radiofrequency ablation of the accessory pathway is the treatment of choice for patients with WPW syndrome. Radiofrequency ablation is performed in a hospital or clinic electrophysiology lab, similar to electrophysiology testing. The patient is given a sedative medication to reduce discomfort.

A wire (electrode catheter) is threaded into the heart and positioned within the chambers of the heart using fluoroscopy (low energy x-rays). Radiofrequency energy (low-voltage, high frequency electricity) is targeted toward the area, damaging the pathway and preventing it from conducting impulses. (See "Patient information: Radiofrequency catheter ablation".)

Ablation cures the WPW syndrome roughly 90 percent of the time. However, some patients have multiple accessory pathways. In these patients, one of the pathways may not be detected and ablated during the initial procedure, and the arrhythmia may reoccur. When this happens, the ablation procedure is repeated, generally with very good results.

Surgery — Surgery is another method to ablate the WPW pathway. The success rate for surgical ablation is close to 100 percent and the complication rate is low. However, radiofrequency ablation is a less invasive option; as a result, surgery is now rarely performed. Surgical ablation may be preferred if the patient is undergoing cardiac surgery for other reasons (such as coronary artery bypass surgery or valve surgery) and is recommended when radiofrequency ablation and medications are not effective. (See "Patient information: Coronary artery bypass graft surgery".)

Medications — Medications can prevent recurrences of the tachycardia in some patients. Patients who have tachycardia infrequently may be given medications to use during an episode. They may also be taught to perform maneuvers (eg, Valsalva) that can stop the tachycardia. Other patients need to take medication all the time to prevent the arrhythmia.

WHERE TO GET MORE INFORMATION

Your healthcare provider is the best source of information for questions and concerns related to your medical problem. Because no two people are exactly alike and recommendations can vary from one person to another, it is important to seek guidance from a provider who is familiar with your individual situation.

This discussion will be updated as needed every four months on our web site (www.uptodate.com/patients). Additional topics as well as selected discussions written for healthcare professionals are also available for those who would like more detailed information.

Some of the most pertinent include:

Patient Level Information:
Patient information: Radiofrequency catheter ablation
Patient information: Atrial fibrillation
Patient information: Cardioversion
Patient information: Coronary artery bypass graft surgery

Professional Level Information:
Anatomy, pathophysiology and localization of accessory pathways in the preexcitation syndrome
Electrocardiographic features of the Wolff-Parkinson-White pattern
Electrophysiologic evaluation of arrhythmias associated with the Wolff-Parkinson-White syndrome
Epidemiology of the Wolff-Parkinson-White syndrome
Nonpharmacologic therapy of arrhythmias associated with the Wolff-Parkinson-White syndrome
Pharmacologic therapy of arrhythmias associated with the Wolff-Parkinson-White syndrome
Tachyarrhythmias associated with accessory pathways

A number of web sites have information about medical problems and treatments, although it can be difficult to know which sites are reputable. Information provided by the National Institutes of Health, national medical societies and some other well-established organizations are often reliable sources of information, although the frequency with which they are updated is variable.

• National Library of Medicine

      (www.nlm.nih.gov/medlineplus/healthtopics.html)

• National Heart, Lung, and Blood Institute

      (www.nhlbi.nih.gov/)

• American Heart Association

      (www.americanheart.org)

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