Cases

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Wolff-Parkinson-White (WPW) syndrome: WPW syndrome is one of the classic preexcitation syndromes that results from an accessory pathway, ie, the Kent bundle, between the atria and the ventricles. Impulses traveling down this pathway bypass all or part of the intrinsic conduction system, resulting in the early depolarization of a portion of the ventricles; this preexcitation produces the classic ECG finding called the delta wave (ie, a slurred upstroke to the QRS complex). This makes the QRS appear wider than expected and the PR interval somewhat shortened. The classic ECG appearance of WPW syndrome is depicted in Figure 2.

WPW syndrome and Lown-Ganong-Levine (LGL) syndrome are 2 major variants of preexcitation and have an estimated prevalence of 0.1-0.3% in the general population. LGL syndrome is similar to WPW syndrome in that preexcitation is secondary to an accessory pathway (the James fibers) that directly connects the atria to the His bundle. In LGL syndrome, the ECG demonstrates a short PR interval (usually less than 0.12 s) without a delta wave and with a normal QRS complex. Both of these syndromes predispose patients to paroxysmal tachydysrhythmias (namely, paroxysmal supraventricular tachycardia and atrial fibrillation). Related aberrant conduction (as in this case) can result in rapid ventricular rates of up to 300 bpm, which may be symptomatic and even lethal.

As many as 80% of patients with WPW syndrome have reentrant tachycardia, 15-30% have atrial fibrillation, and 5% have atrial flutter. Ventricular tachycardia is uncommon, though rapid atrial fibrillation with aberrant conduction can appear as ventricular tachycardia (as in this case in Figure 1) and lead to ventricular fibrillation due to excessive stimulation of the ventricles.

Initial treatment for the acute tachydysrhythmia is as described in the American Heart Association's Advanced Cardiac Life Support (ACLS) protocol. Synchronized cardioversion was performed because of the patient's unstable condition. In general, if patients are stable and have narrow-complex tachydysrhythmias, adenosine can be tried first; however, adenosine can theoretically be harmful to those with antidromic reentrant conduction. Medications such as calcium channel blockers (eg, diltiazem, verapamil) and beta-blockers (eg, metoprolol, esmolol, propranolol) should be avoided in this situation. Stable patients may be treated with intravenous procainamide, and unstable patients, direct cardioversion. Medications that have variable effects on accessory conduction (eg, phenytoin, esmolol, propranolol, verapamil) should be avoided. Digoxin is absolutely contraindicated because it may shorten the refractory period and enhance conduction over the bypass tract and thus cause an even faster tachydysrhythmia or deterioration into ventricular fibrillation.

Some patients with WPW syndrome are at risk for sudden death, namely, those with excessive unstable rhythms with short refractory periods, as in this case. In these patients, cardiac electrophysiologic studies and radiofrequency catheter ablation may be definitive and curative. Catheter ablation can also be used in patients with symptomatic supraventricular tachycardia. Some patients may refuse this somewhat invasive therapy and choose to long-term antiarrhythmic therapy with drugs such as amiodarone, quinidine, or sotalol. Others without worrisome symptoms (ie, syncope, symptomatic tachyarrhythmias, wide-complex tachycardia of uncertain cause, associated structural heart disease, WPW syndrome with a family history of sudden death, recurrent trial fibrillation or atrial flutter) may be treated symptomatically and expectantly.

For more information on WPW syndrome, see the eMedicine articles Wolff-Parkinson-White Syndrome (within the Internal Medicine specialty) and Wolff-Parkinson-White Syndrome (within the Emergency Medicine specialty).