Physicians frequently report ECGs with their eyes closed and may miss subtle abnormalities.Look at this ECG: Is there something abnormal apart from the bundle branch block?

Lead I looks unusual, although most people would call this extreme axis deviation.However, it is most likely reversed arm leads.To summarize:

The left arm lead is on the right arm and the right lead on the left arm.The major footprint: Lead I is flipped (red highlight). The big clue!Minor footprints: Leads aVR/aVL reversed (yellow highlight).Can be confusing. Leads II/III reversed. Usually no help.So let us return to our ECG:

Flip lead I (red highlight) and it appears normal apart from the bundle branch block.Leads aVR/aVL (yellow highlight) are of little help, but this is often the appearance with bifascicular block.Look at this example of normal arm lead attachment:

Bifascicular block and probable right ventricular hypertrophy.aVR/aVL in the correct position (yellow highlight) are very similar to our example.Here are a couple of reversed arm leads: Note flipped P waves in lead I.

We have now seen the confusion with right bundle branch block.What about left bundle branch block?

You can see how easy it is to miss reversed arm leads, if your eyes are closed.Some may ask “is it important to recognise” ?Envisage the patient presenting with chest pain and the ECG last year was correctly performed. Then surely this is infarction and the next step is urgent coronary angiography.You can also miss reversed arm leads with ventricular pacing.

There are large atrial and subtle ventricular stimulus artefacts (red straight arrow). The best lead to confirm the bipolar ventricular stimulus artefact is V2 or any chest lead close to the lead in the ventricle. In this example, atrial depolarisation is hard to confirm.Once again, it is difficult to diagnose reversed arm leads with your eyes closed, but the signs are there even if the T wave is inverted in lead I.Atrial fibrillation is another situation where you may miss reversed arm leads because sinus P waves are absent, but the other features are present.

Add artefact, right bundle branch block and ventricular ectopy to the atrial fibrillation and you really need to keep your eyes open, but the signs are all there.

You can get confused with right axis deviation!Here are two examples:

Remember with right axis deviation, only the QRS is negative and the P and T waves are normal.However, aVR/aVL can be confusing, because the larger the S wave in lead I, the more positive aVR and the more negative aVL (yellow highlight).Another confusing appearance is dextrocardia, but that’s another story and will have to wait until next time.Remember, keep your eyes open when you report ECGs!Harry Mond