First described in the 1930s, Wolff-Parkinson-White (WPW) syndrome is one of the most common causes of tachyarrhythmic disorders in infants and children. (Am Heart J 1930;5:685.) In the normal heart, electrical impulses generated from specialized pacemaker cells in the sinoatrial (SA) node travel via conduction pathway tissue to the atrioventricular (AV) node. From there the impulse travels into the ventricle along the bundle of HIS to the purkinje fibers. “Preexcitation syndromes” are defined as an accessory (extra) anomalous bundle of conducting tissue directly connecting the atria and ventricle, which bypass the AV node. This conducting tissue — the Bundle of Kent (WPW syndrome), James fibers (Lown-Ganong-Levine syndrome), and Mahaim fibers (atriofascicular tachycardia) are known bypass tracts that cause atrial ventricular reentry tachycardias (AVRT).
Not all patients with the WPW accessory pathway go on to develop symptoms. Asymptomatic patients with ECG abnormalities of WPW are said to have WPW pattern, and those with symptoms secondary to tachycardia have WPW syndrome. Most people with a WPW pattern on ECG never develop symptoms. Those patients who do go on to be symptomatic, however, tend to be younger than those who never develop symptoms.
WPW is a rare congenital condition that may have a familial genetic component. The incidence of WPW pattern is 0.25 percent (Ann Intern Med 1992;116:456) to one percent (Vestn Ross Akad Med Nauk 2009;12:16) in the general population. The incidence of tachyarrhythmia in patients with WPW pattern is reported to be as high as 80 percent (Vestn Ross Akad Med Nauk 2009;12:16) in some populations. Most patients with WPW syndrome do not have structural heart disease, but as many as 20 percent with Ebstein's anomaly of the tricuspid valve have WPW pattern (Circulation 1996;94:376), and a familial form of WPW is associated with hypertrophic cardiomyopathy.
Patients with WPW pattern classically have a short (<0.12 sec) PR interval (because of the abbreviated conduction time between the atria and ventricle) and delta wave (slurred upstroke of the R wave from early depolarization [preexcitation] of the ventricle via the accessory pathway) resulting in a wide QRS (>0.12 sec) caused by a fusion between the delta wave and the QRS complex. In patients with WPW, the Bundle of Kent bypass tract alters the intrinsic atrioventricular conduction system of the heart, allowing premature rapid depolarization of the ventricle (prior to the normal AV node-stimulated impulse) and precipitating a tachyarrhythmia with rates above 200 and as high as 300 beats per minute.
Rhythms vary in WPW syndrome, but the most common are atrioventricular reentry tachycardia (80%), atrial fibrillation (30%), and atrial flutter (5%). ECGs of patients with a WPW pattern can vary (normal vs. WPW pattern), even from one hour to the next as the cardiac impulse is conducted through the normal or aberrant pathway. Interestingly, asymptomatic patients may have complete resolution of the WPW pattern as they age.
A person with WPW syndrome may have dizziness, light-headedness, syncope, or palpitations. Less commonly, patients have chest pain or pressure or shortness of breath. Patients with coronary heart disease may be less able to tolerate WPW-induced tachycardic episodes, which precipitate more serious symptoms. WPW syndrome can rarely result in sudden death; incidence is less than 0.4 percent per year. The diagnosis of WPW initially suspected is based on classic ECG findings and verified by electrophysiologic testing.
Patients with WPW pattern who remain asymptomatic often do not require treatment. Professional athletes with a WPW pattern are advised to get elective electrophysiologic testing to rule out a pathway concerning for sudden cardiac death. Patients with a WPW-associated tachyarrhythmic event require treatment to stop the tachycardia and then definitive treatment to prevent a recurrent event.
Some acute WPW tachycardic events can resolve on their own while others require treatment. Unstable patients require synchronized cardioversion initially with 50 to 100 joules and stabilization using standard resuscitation protocols. The risk of embolic events is three percent or less, but patients with symptoms for longer than 48 hours are at increased risk for embolic events, so anticoagulation should be considered.
For patients with acute tachycardic events and stable blood pressure, it is appropriate to first attempt vagal maneuvers or carotid massage. If unsuccessful, pharmacologic agents are indicated. Patients with orthodromic (anterograde conduction) AVRT will have a narrow complex (if no associated bundle branch block exists) vs. antidromic (retrograde) conduction, which will cause a wide QRS complex. Differentiation of the two can be challenging. Adenosine can be given for orthodromic AVRT (95% of WPW cases), but it can transiently have a lethal proarrhythmic effect (increased vulnerability to developing rapid atrial fibrillation or atrial ectopy that can restart conduction via the aberrant pathway), and is contraindicated in cases of rapid atrial fibrillation. (Ann Intern Med 1995;122:351; Ann Intern Med 1990;113:104.)
AV nodal blocking agents, including beta and calcium-channel blockers, can precipitate conduction via the accessory pathway, leading to a fatal arrhythmia, and should not be used if the direction of conduction is unknown (as is often the case in the emergency department). Treatment with intravenous procainamide is the safest drug to administer for a wide QRS complex tachycardia of unknown etiology. (New Engl J Med 1988;318:358.) Even if procainamide does not resolve the tachycardia, it typically slows the rate and improves hemodynamics.
Treatment to prevent recurrent episodes of WPW syndrome is generally recommended. In the past, surgical ablation was performed to prevent recurrent tachyarrhythmic events. Although it had a 100 percent success rate of preventing future events, it has since been replaced by less invasive electrophysiology ablation techniques. Primarily done with radiofrequency catheter ablation of the accessory pathway by an electrophysiology cardiologist, this procedure is about 90-95 percent successful in preventing recurrent events. (Circulation 2003;108:1871.)
Patients with symptoms related to WPW require emergent consultation with a cardiologist and hospital admission. Patients with incidental findings of WPW pattern on ECG should be told to follow up with a cardiologist.
This patient was given procainamide, which improved his heart rate from around 180 bpm to about 130 bpm. (Photo 2.) Given the patient's persistent wide complex tachycardia, elective cardioversion was performed in consultation with cardiology which converted the rhythm to normal sinus. (Photo 3.) The patient had an electrophysiology evaluation that revealed a left posterior-lateral anterograde accessory pathway that was successfully ablated. The patient completed four weeks of anticoagulation, and has had no recurrence of his symptoms.
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Dr. Wileris an assistant professor of emergency medicine and the medical director of reimbursement at the University of Colorado Denver School of Medicine and an adjunct assistant professor of emergency medicine at the Washington University School of Medicine in St. Louis.© 2011 Lippincott Williams & Wilkins, Inc.