An Unusual Ventricular Tachycardia

The techs wanted to know whether to call this a run of ventricular tachycardia or idio-ventricular rhythm.

My first impression was a bizarre run of ventricular couplets with no sinus complex between. I had no idea what that meant!

There is, however, a pattern akin to Wenckebach sequences. Could this be so!

In order to understand these sequences, we need to review Wenckebach AV conduction for the umpteenth time.

With typical Wenckebach AV block, there is a sequence of increasing PR intervals (red highlight) until a dropped beat. The P-P intervals remain constant (assume no sinus arrhythmia), but the R-R intervals may shorten. This is because, the greatest increase in the PR interval is typically between the first and second P waves (R1-R2) with the increment increase of each conducted beat becoming shorter (R2-R3).

Although typical Wenckebach AV block occurs only about 15% of the time, this shortening is an important feature in the recognition of Wenckebach sequences outside AV conduction.

Does our original ECG conform to Wenckebach sequences?

The ventricular tachycardia originates in an ectopic focus and at the junction oft he focus with ventricular myocardium, a 3:2 Wenckebach block occurs (red highlight).

This is: Ventricular tachycardia with Wenckebach block at the ectopic-ventricular myocardial junction.

Here is another example:

Notice the shortening of theR-R interval with the last ventricular complex.

Here is another example I have shown before emphasizing the shortest R-R interval at the end (304 ms).

Remember these examples and particularly the last one, can be explained in a number of other ways. These include a:

•      Triggered focus warming up causing the R-R shortening

•      Circuit with a Wenckebach exit block sequence to the ventricle (thanks Haris)

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I have also shown examples previously in the atrium, where again the shortest P-P interval is the last before the dropped beat.

Remember, it’s all in the timing.