Ventricular Tachycardia - Classification

Classification

Ventricular tachycardia can be classified based on its morphology:

• Monomorphic ventricular tachycardia means that the appearance of all the beats match each other in each lead of a surface electrocardiogram (ECG).
  • RVOT tachycardia is a type of monomorphic ventricular tachycardia originating in the right ventricular outflow tract. RVOT morphology refers to the characteristic pattern of this type of tachycardia on an ECG.
• Polymorphic ventricular tachycardia, on the other hand, has beat-to-beat variations in morphology. This most commonly appears as a cyclical progressive change in cardiac axis, previously referred to by its French name torsades de pointes ("twisting of the points"). However, currently the term torsades is reserved for polymorphic VT occurring in the context of a prolonged resting QT interval.

Another way to classify ventricular tachycardias is the duration of the episodes: Three or more beats in a row on an ECG that originate from the ventricle at a rate of more than 100 beats per minute constitute a ventricular tachycardia.

• If the fast rhythm self-terminates within 30 seconds, it is considered a non-sustained ventricular tachycardia.
• If the rhythm lasts more than 30 seconds, it is known as a sustained ventricular tachycardia (even if it terminates on its own after 30 seconds).

A third way to classify ventricular tachycardia is on the basis of its symptoms: Pulseless VT is associated with no effective cardiac output, hence, no effective pulse, and is a cause of cardiac arrest. In this circumstance, it is best treated the same way as ventricular fibrillation (VF), and is recognized as one of the shockable rhythms on the cardiac arrest protocol. Some VT is associated with reasonable cardiac output and may even be asymptomatic. The heart usually tolerates this rhythm poorly in the medium to long term, and patients may certainly deteriorate to pulseless VT or to VF.

Less common is ventricular tachycardia which occurs in individuals with structurally normal hearts. This is known as idiopathic ventricular tachycardia and in the Monomorphic form appears with little or no incidence of increased risk of sudden cardiac death. In general, idiopathic ventricular tachycardia occurs in younger individuals diagnosed with VT. While the causes of idiopathic VT are not known, it is generally presumed to be congenital, and can be brought on by any number of diverse factors.