Ventricular tachycardia

What it is

Ventricular tachycardia is 3 or more consecutive ventricular complexes, wide QRS complex, at a frequency of 100 per minute or more.

It is classified twice over, and both classifications decide a later step:

• By duration: VT that is not sustained lasts under 30 seconds; sustained VT lasts 30 seconds or more.
• By morphology: monomorphic VT, and polymorphic VT, which is torsades de pointes and is treated by magnesium sulfate.

The morphology is not a label only. Polymorphic VT is defibrillated and monomorphic VT is cardioverted, so the form of the complexes decides which shock the patient gets.

Where it sits among the tachycardias

The tachycardias are split first by the width of the QRS and then by regularity, and ventricular tachycardia is one of the four boxes that come out of that:

• Wide QRS, ventricular: regular is ventricular tachycardia, irregular is ventricular fibrillation
• Narrow QRS, atrial: regular is SVT, sinus tachycardia or atrial flutter; irregular is atrial fibrillation or MAT

So a wide and regular tachycardia is the one being asked about, and a wide and irregular one is not VT.