Alternating Ventricular Tachycardia

Report :

Ventricular tachycardia 136/min

Alternating QRS morphology throughout

Comment :

This is a good example of how alternating and bidirectional tachycardia are basically the same. This one would be called bidirectional if only the negative axis in the frontal plane were more pronounced; nobody would be penalised for calling it bidirectional anyway. It has the alternating frontal plane axis and the basic RBBB morphology in V1 – like the classical bidirectional VT.

The rate is relatively slow due to antiarrhythmic drug therapy (not digitalis). Being slow, it facilitates the recognition of AV dissociation – there are at least four “bumps” at regular intervals in the rhythm strip. This patient eventually required a permanent pacemaker in order to remain on those drugs once the VT was controlled.

The patient had many runs of VT, most of them uniform (121a). The volcano-like QRS in V1 in the trace below is as suggestive as the dominant left rabbit ear for the diagnosis of VT, but is much less common.

Sinus rhythm ECG is shown in 121b.