Wolff-Parkinson-White Syndrome (WPW) : Causes, Mechanism, ECG Findings and diagnosis, Treatment

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Wolff-Parkinson-White Syndrome : Causes, Mechanism, ECG Findings and diagnosis, Treatment

Wolff-Parkinson-White Syndrome (Pre-Excitation/Accessory Pathway)
The Wolff-Parkinson-White (WPW) syndrome is seen mostly in children who have bursts of symptomatic tachycardia. This is a congenital condition leading to abnormal cardiac conduction tissue, leading to an accessory atrioventricular (AV) pathway that results in ventricular “pre-excitation”. This pre-excitation can sometimes produce sudden tachycardic episodes.

Mechanism.
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Ventricular pre-excitation is exactly what it sounds like: a ventricle that gets excited (depolarized) before (pre) the normal timing through the AV node. Think of the accessory pathway as a highway where there is no speed limit; instead of being slowed down by the speed limit of the AV node, the electrical conduction between atria and ventricles can go as fast as it wants to. Now each accessory pathway has a different inherent speed limit, but the very fast pathways are the ones that cause problems. At baseline sinus rhythm in WPW, the impulse travels from the SA node to both the accessory pathway and the AV node and then to the ventricles. This shows up as a delta wave on ECG, described below.

Like AVNRT, the genesis of re-entrant SVT in WPW involves the presence of dual conducting pathways between the atria and the ventricles, usually the normal pathway plus one or more AV accessory pathways. Pre-excitation from an accessory pathway causes problems because it is not subject to autonomic control like the AV nodal pathway; therefore, there is no AV pause. As a result, the impulse from the accessory path arrives at the ventricles too early, making them contract sooner than expected. With this accessory pathway, the atrial impulses are not slowed down but can be conducted directly to the ventricle.

Secondary Causes.
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WPW is a congenital disorder.

Symptoms. The symptoms that come from the tachycardia include palpitations, lightheadedness, presyncope or syncope, chest pain, and even sudden cardiac death.

ECG and diagnosis. Findings while in sinus rhythm show a shortened PR interval (often less than120 ms) and characteristic delta wave at the initiation of each QRS complex due to pre-excitation. When tachycardic episodes occur, there is a regular rhythm but a ventricular rate of 150-250/min. Unlike the similar-appearing AVNRT, the QRS complexes during tachycardia episodes are slightly prolonged (greater than120 ms) due to this delta wave, but they terminate normally.

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