Wolff-Parkinson-White syndrome
Overview
Wolff-Parkinson-White syndrome (WPW) is a syndrome of pre-excitation of the ventricles of the heart due to an accessory pathway known as the bundle of Kent. This accessory pathway is an abnormal electrical communication from the atria to the ventricles. The incidence of WPW syndrome is between 0.9 and 3% of the general population. While the vast majority of individuals with a bundle of Kent remain asymptomatic throughout their entire lives, there is a risk of sudden death associated with the syndrome. Sudden death due to WPW syndrome is rare (incidence of less than 0.6%), and is due to the effect of the accessory pathway on tachyarrhythmias in these individuals.
Diagnosis
WPW syndrome is commonly diagnosed on the basis of the surface ECG in an asymptomatic individual. In this case it is manifested as a delta wave, which is a slurred upstroke in the QRS complex that is associated with a short PR interval. The short PR interval and slurring of the QRS complex is actually the impulse making it through to the ventricles prematurely (across the accessory pathway) without the usual delay experienced in the AV node. If the patient experiences episodes of atrial fibrillation, the ECG will show a rapid polymorphic wide-complex tachycardia (without torsades de pointes). This combination of atrial fibrillation and WPW is considered dangerous, and most antiarrhythmic drugs are contraindicated. When an individual is in normal sinus rhythm, the ECG characteristics of WPW syndrome are a short PR interval, widened QRS complex (greater than 120ms in length) with slurred upstroke of the QRS complex, and secondary repolarization changes reflected in ST segment-T wave changes. In individuals with WPW syndrome, electrical activity that is initiated in the SA node travels through the accessory pathway as well as through the AV node to activate the ventricles via both pathways. Since the accessory pathway does not have the impulse slowing properties of the AV node, the electrical impulse first activates the ventricles via the accessory pathway, and immediately afterwards via the AV node. This gives the short PR interval and slurred upstroke to the QRS complex known as the delta wave. Patients with WPW often exhibit more than one accessory pathway, and in some patients as many as eight additional abnormal pathways can be found. This has been seen in individuals with Ebstein's anomaly. Wolff-Parkinson-White syndrome is sometimes associated with Leber's hereditary optic neuropathy (LHON), a form of mitochondrial disease.
Treatment
Acutely, people with WPW who are experiencing tachyarrhythmias may require electrical cardioversion if their condition is critical, or, if more stable, medical treatment may be used. Patients with atrial fibrillation and rapid ventricular response are often treated with amiodarone or procainamide to stabilize their heart rate. Adenosine and other AV node blockers should be avoided in atrial fibrillation and atrial flutter with WPW or history of it; this includes adenosine, diltiazem, verapamil, other calcium channel blockers and beta-blockers. Patients with a rapid heart beat with narrow QRS complexes (circus movement tachycardias) may also be cardioverted, alternatively, adenosine may be administered if equipment for cardioversion is immediately available as a backup. The definitive treatment of WPW syndrome is a destruction of the abnormal electrical pathway by radiofrequency catheter ablation. This procedure is performed almost exclusively by cardiac electrophysiologists. Radiofrequency catheter ablation is not performed in all individuals with WPW syndrome because there are inherent risks involved in the procedure. When performed by an experienced electrophysiologist, radiofrequency ablation has a high success rate.If radiofrequency catheter ablation is successfully performed, the patient is generally considered cured. Recurrence rates are typically less than 5% after a successful ablation.The one caveat is that individuals with underlying Ebstein's anomaly may develop additional accessory pathways during progression of their disease