Left Bundle Branch Block-Like Ventricular Tachycardia

Report:

Ventricular tachycardia 196/min[! XE !]

Comment:

This is a rapid VT with morphology quite similar to LBBB. The QRS duration is about 0.16”, best measured in the inferior leads. However, in V1, normally the most important diagnostic lead, it looks shorter; further, the S wave downstroke appears as brisk as the upstroke – more in keeping with LBBB than ectopic ventricular rhythm. This is an illusion, brought about by the initial QRS segment in V1 being isoelectric.

The left axis deviation in the frontal plane is of no diagnostic significance.

Below (Fig 3a) is further evidence for the ectopic ventricular provenance of the tachycardia: (i) VEBs looking like the VT complexes, with, furthermore, the second and the last complexes being fusion beats, (ii) evidence of previous myocardial infarction and (iii) presence of RBBB in sinus rhythm À propos the last, an SVT would be expected to retain RBBB morphology, probably with even wider QRS complex, while LBBB aberrancy would be most unexpected2, 3.

The marked ST segment depression suggests ischæmia or infarction as the underlying cause of the VT.

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