Wolff-Parkinson-White syndrome

What it is

Wolff-Parkinson-White syndrome is a congenital condition characterized by intermittent tachycardias and signs of ventricular preexcitation on ECG, both of which arise from an accessory pathway known as the bundle of Kent.

The congenital accessory pathway connects the atria and ventricles, bypassing the AV node, and that is what leads to ventricular preexcitation. Put the other way, WPW is caused by an accessory electrical pathway between the atria and ventricles, and its primary significance is that it predisposes the individual to the development of reentry tachycardias.

How it presents

It may be asymptomatic, which is the WPW pattern, or associated with arrhythmias, which is the WPW syndrome. The arrhythmias named are two, and their order matters: AVRT is the most common, at 80%, and atrial fibrillation follows at 15-35%, with an incidence that increases with age.

The ECG

The ECG findings in WPW are:

• Short PR interval, given as < 120 msec
• A delta wave, a slurred upstroke at the start of the QRS complex, secondary to preexcitation
• Widened QRS

The width of the QRS is written two ways in the same book: > 100 msec in one place and > 120 msec in another. Hold the delta wave and the short PR as the fixed findings and do not hang an answer on the QRS number alone.

Which way the impulse runs decides what the ECG shows during the tachycardia. When conduction occurs anterograde down the AV node and then retrograde up the accessory pathway, which is orthodromic, the ECG will appear normal. When the impulse occurs anterograde down the accessory pathway and retrograde up the AV node, which is antidromic, the QRS complex will be wide.