What Do You Think 57

I was asked this week for an opinion on a Holter monitor recording.

I have selected short strips which summarize the study.

What do you think?

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The top series show sinus rhythm, pre-excitation (red highlight) and atrial ectopy (yellow highlight).

From above: bigeminy, trigeminy, couplet and triplet. The ectopy QRS complex is near identical to the sinus beat with both showing a Δ wave confirming that the ectopics conduct via the accessory pathway.

Here is an example of an atrial couplet conducted via the accessory pathway and demonstrating an inverted P wave (red arrows).

The other tracings show a tachycardia.

Let us revisit the tachyarrhythmias of Wolff-Parkinson-White (WPW).

The WPW syndrome is the ECG appearance of the accessory pathway, together with associated re-entry tachyarrhythmias. The most frequently encountered tachyarrhythmia in the WPW syndrome is an atrioventricular re-entrant tachycardia (AVRT).It involves the accessory pathway and AV node to form a re-entry circuit with the arrhythmia being triggered by an appropriately timed ectopic. The circuits may be orthodromic or antidromic.

• ‍Orthodromic AVRTs represent about 70%of the tachyarrhythmias and conduct anterograde down the AV node and retrograde up the accessory pathways. The result is a normal QRS morphology tachycardia without a Δ wave as the accessory pathway is the retrograde limb. The tachycardia rates are about 160 to 260 bpm. There may beinverted P waves within the QRS/T complex but unlike AVNRT the P wave is further away from the QRS complex (blue arrows).  

• Antidromic AVRT is less common. The pathway conducts anterograde using the accessory pathway and retrograde via the AV node. The Δ wave is seen in the wide QRS complex, mimicking ventricular tachycardia.

Pre-excitation with short PR interval and Δ wave (red highlight).There is a short run of a rapid broad QRS tachycardia with a Δ wave (yellow highlight), consistentwith, but not diagnostic of an antidromic AVRT.

Now let us return to our tracings.

There is a tachycardia with aQRS similar to pre-excited sinus QRS (red highlight) and thus the initial thought that this was an antidromic AVRT (yellow highlight). However, there is a second tachycardia configuration with anon-pre-excited QRS (blue highlight) suggesting normal AV conduction. Both tachycardias were frequent, short-lived and combined with each other. They usually commenced with pre-excited atrial ectopy and short pre-excited runs before reverting to normal conduction. This is unlikely to be two tachyarrhythmias but rather one with differing conduction pathways, depending on refractory period of the accessory pathway.

I suggest that this is an atrial tachycardia in a patient with pre-excitation. Remember that atrial tachycardias are very common and therefore would be expected in apatient with an accessory pathway with or without AVRT.

Here is another example of a probable atrial tachycardia (yellow highlight) conducted via an accessory pathway.

Because of concern that such arrhythmias can degenerate into atrial fibrillation such pathways should be ablated, even if asymptomatic.

In regard to atrial fibrillation, not surprisingly it is the most important non-re-entrant atrial tachyarrhythmia conducted via the accessory pathway. Because of the short refractory period in the accessory pathway, anterograde conduction may be very fast and lead to ventricular fibrillation. The combination of a very rapid rhythm and a Δ wave results in a broad QRS, mimicking ventricular tachycardia, albeit very irregular.

Atrial fibrillation with accessory pathway conduction. Note the block in accessory pathway conduction (red highlight), resulting in a single conducted beat via the AV node and thus the absence of a Δ wave. This is a very important clue to differentiate the rhythm from ventricular tachycardia.

When intermittent AV conduction is not present, the irregularity in the rhythm should at least alert the ECG reporter as to possible pre-excitation.

Pseudo WPW.

Pre-excitation rhythms are great mimickers of ECG abnormalities. The presence of a Δ wave, broad QRS, tall voltages and T wave abnormalities result in a plethora of misdiagnoses including bundle branch blocks, cardiac hypertrophy, previous myocardial infarction, myocardial ischaemia, and even ventricular pacing. These false Δ waves with a short PR interval are referred to as “pseudo WPW”.        

Junctional escape beats with embedded sinus P wave.

Sinus rhythm with late junctional escape bigeminy. The sinus P wave is embedded in the upstroke of theQRS resulting in a pseudo-Δwave (red highlight).

Idioventricular rhythm.

Two examples of idioventricular rhythm with a ventricular fusion beat having a short PR interval and a pseudo-Δ wave (red highlight).

Non-selective His-bundle pacing.

To the untrained eye, this is the perfect mimicker of pre-excitation. Both the Hisbundle and para-Hisian tissues (red highlight) are stimulated simultaneously with para-Hisian conduction creating a Δ wave.

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Harry Mond