Question 5#

Which one of the following features is least suggestive that a broad complex tachycardia is ventricular in origin (VT)?

A) P waves seen ‘walking through the tachycardia’
B) The QRS duration shortens as the patient goes from sinus rhythm to tachycardia
C) Capture beats
D) A right bundle branch block pattern with a small R wave and a large R' wave (i.e. rsR') in V1
E) Negative concordance in the chest leads

Correct Answer is D


P waves walking through the tachycardia and capture beats are evidence of independent P-wave activity and ‘prove’ that the rhythm is VT. If the QRS is broad in sinus rhythm, it indicates pre-existing conduction tissue disease which will not shorten if the tachycardia is an SVT. Therefore shortening of the QRS proves that the rhythm is VT, probably originating from the septum to give a relatively narrow QRS. Negative concordance shows that the rhythm is originating from the apex of the heart and is therefore VT. The rsR' pattern is seen in typical RBBB and is suggestive of aberrancy rather than VT, although this is not diagnostic.