Ventricular tachycardia (VT) is broad-complex tachycardia originating from a ventricular ectopic focus. It has the potential to precipitate ventricular fibrillation and hence requires urgent treatment.

An SVT can cause a broad spectrum tachycardia - in a peri-arrest situation it is assumed to be ventricular in origin

Pathophysiology

1. The more common cause is re-entrant - the electrical signal essentially looping around the ventricular myocardium causing persistent contractions. This can be influenced by ischaemia or presence of scar tissue causing changes in the conducting properties and refractory periods of different myocardial tissue.

2. Another cause: In VT the pulse originates in ventricular myocardium, normally ventricular myocardium does not control the HR as they are overpowered by the faster SA node, however if the ventricular myocardium becomes irritated or stressed it can beat faster essentially overtaking the speed of firing at the SA node and thus overtaking its job as the primary pacemaker

Causes of stress to ventricular myocardium-

• medications
• drugs e.g. cocaine
• electrolyte imbalance
• ischaemia

Investigations

• Originates in ventricular myocardium (e.g. after MI/ ischaemia) or His/Purkinje system - no P waves!
• Shape of QRS complexes is usually monomorphic (all QRS complexes in one ECG look the same), but can be polymorphic (vary in axis, amplitude and duration)
• QRS are always BROAD, rate > 120 beats/minute

A patient with VT may have a cardiac output (a pulse).

OR they may have PULSELESS VT - needing immediate resuscitation