LBBB-Like VT in Patient with RBBB

Report:

Ventricular tachycardia 178/min

LBBB morphology with right axis deviation

Comment:

This is, morphologically, right ventricular outflow tract (RVOT) tachycardia, with LBBB and marked right axis deviation (not seen in aberrant conduction8). The morphology is important to recognise as this VT is relatively easily treatable29. RVOT VT is not entirely unexpected in a patient with ASD repair. Lead V1 is in fact more helpful than it looks – one can draw a perpendicular from the QRS onset in lead V3 to see at once that V1 complex starts with a sizeable isoelectric segment. Therefore, the S wave nadir is reached late.

And another thing: this patient has a broad right bundle branch block in sinus rhythm (Fig 24a). The aberrancy would then be expected to follow or exaggerate the original conduction defect2, 3.

Like in most clinical instances of VT, one cannot discern the pattern of atrial activity. There may well exist A-V dissociation, but it cannot be seen. Slower VTs are more amenable to this kind of analysis.

This was reported as SVT with aberrancy by a Cardiology Registrar. Another episode of VT in this patient had left axis deviation (Case 92), and was also reported as aberrant SVT.

24a. RBBB in sinus rhythm.

25. 45 year old man with known ischæmic heart disease, ventilated in ICU for an unrelated condition.