Definitions

Polymorphic ventricular tachycardia (PVT) is a form of ventricular tachycardia in which there are multiple ventricular foci with the resultant QRS complex varying in amplitude, axis, and duration. The most common cause of PVT is myocardial ischaemia/infarction.

Torsades de pointes (TdP) is a specific form of PVT occurring in the context of QT prolongation — it has a characteristic morphology in which the QRS complexes “twist” around the isoelectric line. For TdP to be diagnosed, the patient must have evidence of both PVT and QT prolongation.

Clinical Significance

• TdP is often short lived and self terminating, however can be associated with haemodynamic instability and collapse. TdP may also degenerate into ventricular fibrillation (VF)

• Bidirectional VT is another specific type of of PVT, is a rare ventricular dysrhythmia characterised by a beat-to-beat alternation of the frontal QRS axis. It is most commonly associated with severe digoxin toxicity

Treatment 

Unstable : ABCD Syncronized cardioversion + MgSO4

• 50%MgSO4 2 - 4 mL IV push in 2 – 5 min (1 amp = 2 ml = 1 g)

• 10%MgSO4 10 -20 mL IV push in 2 – 5 min (1 amp = 10 ml = 1 g)

Stable : 

• Adenosine 6 mg IV

• Amiodarone