Wolff-Parkinson-White Syndrome

Wolff-Parkinson-White (WPW) syndrome is a congenital cardiac preexcitation syndrome that arises from abnormal cardiac electrical conduction through an accessory pathway that can result in symptomatic and life-threatening arrhythmias. The hallmark electrocardiographic (ECG) finding of WPW pattern or preexcitation consists of a short PR interval and prolonged QRS with an initial slurring upstroke (“delta” wave) in the presence of sinus rhythm. The term WPW syndrome is reserved for an ECG pattern consistent with the above-described findings along with the coexistence of a tachyarrhythmia and clinical symptoms of tachycardia such as palpitations, episodic lightheadedness, presyncope, syncope, or even cardiac arrest.  The normal heart consists of two electrically insulated units, the atria and the ventricles. These units are connected by a conduction system that allows for normal cardiac synchrony and function. The cardiac electrical potential originates from the sinoatrial node of the right atrium and propagates through the atria to the atrioventricular (AV) node. The action potential is delayed in the AV node and is then quickly transmitted through the His-Purkinje system to the ventricular myocytes allowing for rapid ventricular depolarization and synchronized contraction.  Patients with WPW syndrome have an accessory pathway that violates the electrical isolation of the atria and ventricles, which can allow electrical impulses to bypass the AV node. In some settings, this pathway can result in the transmission of abnormal electrical impulses leading to malignant tachyarrhythmias. The ECG findings of the WPW pattern are caused by the fusion of ventricular preexcitation through the accessory pathway and normal electrical conduction. Most patients with WPW pattern will never develop arrhythmia and will remain asymptomatic. Some accessory pathways will not manifest the described typical ECG findings, and as a result, some patients can develop a tachyarrhythmia with no prior ECG evidence that the pathway exists.  These are referred to as concealed bypass tracts. In the early 1900s, Frank Wilson and Alfred Wedd are thought to have first described ECG patterns that would later be recognized as a WPW pattern. In 1930, Louis Wolff, Sir John Parkinson, and Dr. Paul Dudley White published a case series consisting of 11 patients who experienced paroxysmal tachycardia associated with an underlying ECG pattern of sinus rhythm with short PR and bundle branch block/wide QRS. This phenomenon was subsequently named as Wolff-Parkinson-White (WPW) syndrome. The electrocardiographic features of preexcitation were first correlated with anatomic evidence of anomalous conducting tissue or bypass tracts in 1943.