Ventricular tachycardia is defined as three or more consecutive premature ventricular ectopics in a series, at a rate above 100 per minute.
Mechanisms of VT
Reentrant – scar related, bundle branch reentry, fascicular tachycardia
Automatic – acute ischemia, electrolyte imbalance, increased sympathetic tone
Triggered activity – early and delayed after depolarisation, idiopathic right ventricular outflow tract VT
Sustained ventricular tachycardia
Ventricular tachycardia lasting more than 30 seconds or requiring termination before that due to hemodynamic compromise is termed sustained ventricular tachycardia. Unsustained ventricular tachycardia is one which lasts less than 30 seconds.
Idiopathic right ventricular outflow tract VT
Mechanism of idiopathic RVOT VT is triggered activity. It responds to beta-blockers and verapamil, but the current therapy of choice is radiofrequency catheter ablation. Usually there is no structural heart disease associated with this VT.
Bundle branch reentrant tachycardia
Circuit is confined to the left and right bundle branches. Most often the tachycardia has an left bundle branch block (LBBB) pattern and rarely a right bundle branch block (RBBB). Either case, the treatment is ablation of the right bundle. The sinus rhythm ECG can manifest an LBBB pattern.