What Do You Think 46

I was shown this ECG this week.

There are two ectopic beat configurations labelled “S” for supraventricular  and “V” for ventricular. The issue with the referring doctor was that they were mislabelled because the broad QRS is labelled supraventricular and the narrow QRS, ventricular.

What do you think?

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A conundrum exists when in the same tracing, an atrial ectopic is broader than a ventricular ectopic.

Sinus rhythm with a bundle branch block (red highlight). An atrial couplet has the same broad configuration (yellow highlight, “S”).However, an ectopic with a narrow configuration is most likely a ventricular ectopic. The focus may be in or very close to a fascicle and the wave of depolarization avoids the block in the bundle branch, which is probably very proximal.

The labelling is correct.

A fascicular ectopic  as its name implies has its focus in left bundle branches of the His-Purkinje system. The QRS therefore, has aRBBB-like morphology with either a superior or inferior axis, depending on whether the focus is in the posterior or anterior fascicles. These ectopics have a relatively narrow QRS and the initial forces are abrupt and not slurred asthe early conduction is within the conducting system.  Ventricular ectopics arising from the right bundle branch and bundle of His also occur.

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Harry Mond