VT or VF?

Report:

Supraventricular rhythm, probably sinus with SVEBs

R-on-T VEBs

Ventricular fibrillation

Comment:

It is sometimes quite difficult to determine if a very fast ventricular rhythm is multiform VT, perhaps torsades de pointes, of VF. This trace was sent to me by a Casualty sister asking that very question.

It is also difficult to decide whether the paroxysm starts as VT and “degenerates” into VF, or whether it’s VF ab initio. The beginning certainly looks like formed complexes – but there are similar parts further along the strip, separated by what anyone would call VF without hesitation! It is not ventricular flutter, at least: it’s too irregular for that. Tachycardie préfibrillatoire?40 Fibrillatoire, more likely!

My approach to this is not very scientific, but may be of value to someone: if there is no output, I call it VF. If it stops spontaneously, I call it VT! A good discussion of the nosological conundrum can be found in a recent issue of the Lancet42.

The VEBs – all three of them – appear precipitated by a long preceding pause. This is the basis of the so-called rule of bigeminy, although no bigeminy results in this case. The pause makes the QT interval longer, propitiating the R-on-T phenomenon.

Below (Fig 114a) is the patient’s 12-lead ECG with global, but symmetric, T wave inversion.

114a. T waves are less deeply inverted for the shorter SVEB cycles. This is an observation of no consequence. 115. 7 month old baby with osteogenesis imperfecta and episodes of tachycardia.