I awoke feisty this morning and decided to be controversial.How would you interpret this ECG?

The rhythm is atrial fibrillation with ventricular bigeminy. Or is it?Firstly, let us look at ventricular bigeminy:

The footprints are:

• Unifocal ventricular ectopics
• Fixed coupling intervals (red highlight).

Trigeminy is similar:

Now, let us return to our original ECG.

• The rhythm is atrial fibrillation
• The ventricular ectopics are unifocal
• The coupling intervals differ
• The inter-ectopic intervals are fixed at 1600 ms.
• The blue arrow shows that the next ectopic falls in the refractory period of the intrinsic beat.

So what else could this be?Consider ventricular parasystole. Ventricular parasystole:

• Rare ECG finding
• An independent ventricular ectopic focus
• Sinus impulses cannot enter and reset
• Sinus impulses, however, can create refractoriness of the surrounding myocardium causing an exit block.

ECG features:

• Unifocal ventricular ectopics
• Variable coupling
• Fixed, usually very slow inter-ectopic intervals
• No ventricular ectopics during the refractory periods
• Fusion beats are common depending on the timing.

Our ECG conforms to these features (no fusion beats).To be absolutely sure, we need longer strips and hence the controversy.Here is an example with fusion beats:However, the coupling intervals are fixed.Hence longer tracings are required to confirm the diagnosis.

Here is another confusing tracing:

Interpolated ventricular quadrigeminyIs ventricular parasystole really rare?It is rarely looked for and strips are not long enough.Is there a pseudo-ventricular parasystole?Consider very slow asynchronous ventricular pacing (VOO) and sinus rhythm. What about atrial parasystole?It is said to occur, and I believe I have seen it.One of the arrhythmias of digitalis toxicity and hence not seen today.It’s all in the timingHarry Mond