What Do You Think 41

This week, I saw more than a dozen examples of ECGs labelled ventricular ectopy and tachycardia.
‍Here are three examples.

What do you think?

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All three cases have been labelled ventricular arrhythmias (yellow oval highlight).

Let us look at each separately.

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Holter ECG labelled 1.

Very irregular rhythm (blue highlight). Occasional sinus beats with a short PR interval (green highlight)and one beat with a Δ wave (purple highlight). Wolff Parkinson White should be considered. The broad complex QRS rhythm labelled ventricular run (red highlight) looks like ventricular tachycardia at a rate of about 200 bpm.However as it slows below 200 bpm, the QRS narrows and confirms atrial fibrillation with a rapid ventricular response and aberrant ventricular conduction.

Holter ECG labelled 2.

Again the rhythm looks like ventricular tachycardia (red highlight) on a background of sinus rhythm. There were very frequent short paroxysms, and all were irregular (blue highlight). When this occurs it is important to look for slower ventricular rates.

With slower ventricular rates, the rhythm becomes narrow (yellow highlight) and identical to the QRS complexes of sinus origin. Once again this is atrial fibrillation with a rapid ventricular response and aberrant ventricular conduction.

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Holter ECG labelled 3.

Sinus bradycardia with what looks like a ventricular couplet, preceded by a premature atrial ectopic (red arrows). However, the broad complexes have P waves (blue arrows). The P wave of the second broad QRS complex is probably concealed in the “peaked” T wave of the previous complex (blue stippled arrows). Following is another premature QRS complex, and it too has a near-concealed P wave in the ST segment of the previous beat (green stippled arrow) and a prolonged PR interval.  PR interval prolongation allows the bundle branches to recover and the QRS is now narrow. You may ask why the bundle branches conduct normally, when earlier ones were in the refractory period.Remember the long cycle/short cycle rule (purple horizontal arrows), which governs the initial relative refractory period length and is not present later.

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Here is another similar example.

This time a 5 beat run of supraventricular tachycardia with aberrant ventricular conduction, labelled as a ventricular run (yellow oval).    

Again sinus bradycardia with along cycle/short cycle sequence (purple horizontal arrows). The broad complexes have preceding P waves (red arrows) and as the cycle length increases the QRS narrows.

Some of you will be over come with all the information on aberrant ventricular conduction. Hence I will summarize it once again.

What is aberrant ventricular conduction?

• Aberrant ventricular conduction results from intermittent uneven physiologic refractoriness in the ventricular conducting system from an early supraventricular beat.
• There is QRS widening usually with a right bundle branch block configuration, consequent to a delay or block in that bundle or a more peripheral branch.

Let us review the action potentials in the bundle branches.

Aberration may occur for a single complex (atrial ectopic) or many.

Here are the classic features with an isolated atrial ectopic:

With atrial ectopy, search for ectopics (red highlight) where the coupling interval is  longer, resulting in normal conduction (follow the yellow highlight). There is no V1.

With atrial fibrillation, there may be a long cycle/short cycle which sets up the aberrant conduction as the relative refractory period depends on the cycle length of the preceding cycle. This is known as the Ashman phenomenon.

One of my observations is that the aberrant beat may have a narrower QRS compared to an ectopic in V6 (red open ring).

Although most cases of aberrant ventricular conduction have a right bundle branch block configuration, a left configuration can occur, even together with right configuration.                                                                                                                          We have already seen examples of left or right bundle branch block configuration.

Here is an example where both occurred in the same tracings.

Left bundle branch block configuration

In other tracings, there was right bundle branch block configuration as well.

How do we differentiate aberrant ventricular conduction from ventricular ectopy or tachyarrhythmias?

V1 is very helpful for right bundle branch block configuration – rabbit’s ears

• Look for P waves (atrial ectopy or runs)
• Irregular rhythm suggests atrial fibrillation
• Long cycle/short cycle
• Search for slower cycle lengths or longer coupling intervals
• Narrow QRS in V6

Its all in the timing.

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Harry Mond