Not what it seems – Pseudo WPW - CardioScan Australia
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Not what it seems – Pseudo WPW

April 7, 2020

A Holter monitor report from an overseas customer was recently returned with a note pointing out that we had missed the diagnosis of intermittent pre-excitation – the Wolff-Parkinson-White Syndrome.

On inspection of the tracings, sure enough there were frequent complexes that had a short PR interval and a delta wave (highlighted).

Did we actually miss this diagnosis?

On careful inspection, each of these complexes occurs when the rhythm transitions from a narrow sinus rhythm with a normal P wave and PR interval to a broad QRS rhythm with no P wave. This is an idioventricular rhythm, rate 60-70 bpm and the complexes with a short PR interval and delta wave are fusion beats.

Remember fusion causes confusion.

This can be called pseudo-WPW.

With Wolff-Parkinson-White syndrome, pre-excitation can be intermittent


And alternating!


Sometimes the delta wave is unusual.

What other situations can cause pseudo-WPW?

Late ventricular ectopics (VE) and fusion (F1, F2), all highlighted.

This is an example of isorhythmic AV dissociation with the alternating junctional escape beats fused with the sinus P waves resulting in a pseudo-WPW appearance (highlighted).


About Assoc Prof Harry Mond

In 49+ years as a practicing cardiologist, Dr Harry Mond has published 260+ published manuscripts & books. A co-founder of CardioScan, he remains Medical Director and oversees 500K+ heart studies each year.

See Dr Mond’s full profile here


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