Ventricular tachycardia occurs when a rapid and repetitive conduction path exists entirely within the ventricles. Usually a re-entrant arrhythmia, it is often caused as a result of scarred heart tissue. Once the conduction circuit is initiated, the rhythm may stabilise, extinguish and revert to sinus rhythm, or degenerate into ventricular fibrillation.
With ventricular fibrillation, collapse and sudden cardiac death will soon follow unless medical intervention is swiftly provided.
Due to the difficulty in separating ventricular tachycardia from wide QRS complex supraventricular tachycardias (e.g., antedromic atrioventricular reentrant tachycardia), the term wide complex tachycardia is often used.
The first ECG trace below shows five wide QRS complex beats at a rate of 134 bpm, the second shows three wide QRS complex beats at a rate of 300 bpm.