VT or SVT in a Patient with Known LBBB?

Report:

Ventricular tachycardia 174/min.

Comment:

The QR morphology in lead V1, however, is that of VT, unless there was a previous anteroseptal infarction. The marked LAD -90o is neither here or there, diagnostically. Interestingly, a recent study using the Brugada algorithm in a Californian Casualty (Emergency Room) found disagreement between the physicians 22% of the time143!

The decisive factor is the presence of LBBB in sinus rhythm: aberration preserves the original conduction defect2, or adds to it.

There are, admittedly, cases of identical QRS morphology in VT (or VEBs) and sinus rhythm144, but this is obviously not the case here.

This VT should logically originate from the left posterior fascicle of the blocked left bundle branch.

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