Types of Ventricular Tachycardia

Three or more ventricular beats in a row at a rate above 100 per minute is termed ventricular tachycardia. Ventricular tachycardia lasting more 30 seconds or requiring termination earlier due to hemodynamic compromise is called sustained ventricular tachycardia. Non sustained ventricular tachycardia is one which lasts less than 30 seconds without hemodynamic compromise.

Based on the morphology, ventricular tachycardia can be classifed into monomorphic in which all beats have same morphology on ECG in a given lead and polymorphic in which there is beat to beat variation.

Polymorphic ventricular tachycardia with QT interval prolongation is known as torsades des pointes. Another variety is bidirectional ventricular tachycardia in which alternate beats will be positive and negative. It is typically seen in digoxing toxicity, catecholaminergic polymorphic ventricular tachycardia and in Andersen syndrome or congenital long QT syndrome 7.

Ventricular tachycardia can be classified according to the mechanism of genesis into reentrant, automatic and triggered activity. Reentrant VT can be scar related as after a myocardial infarction, bundle branch reentry and fascicular tachycardia. Automatic ventricular tachycardia can occur in acute ischemia, electrolyte imbalance and with increased sympathetic tone. Triggered activity can be early and delayed afterdepolarization.

Idiopathic left ventricular tachycardias are verapamil-sensitive intrafascicular tachycardias. Three types have been described: RBBB, left-axis pattern – originating from left posterior fascicle also known as Belhassen VT which comprises 90 – 95% ; RBBB, right-axis pattern – originating from left anterior fascicle and left septal fascicular tachycardia with normal axis. ILVT is seen in 2nd – 4th decade and more in men (60%-80%). Radiofrequency catheter ablation is highly effective (85%-90%) in those with severe symptoms.

Circuit in bundle branch reentry is confined to the left and right bundle branches. Most often the tachycardia has a left bundle branch block pattern and rarely a right bundle branch block pattern. Either case, the treatment is ablation of the right bundle. The sinus rhythm ECG can manifest an LBBB pattern.

Idiopathic right ventricular outflow tract VT can occur due to triggered activity. RVOT VT has LBBB pattern with inferior axis. Idiopathic right ventricular outflow tract VT 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.

Left ventricular outflow tract VT is characterized by S waves in lead I, and R-wave transition in V1/ V2 and constitutes about 10% of outflow VT. There are two varieties of LVOT VT -supravalvular and infravalvular. Absence of S wave in V5/V6 is suggestive of supravalvular origin, while the presence of S wave in V5/V6 indicates infravalvular origin. There is a risk of left main coronary artery occlusion while ablating LVOT VT. Hence coronary angiography before, during and after ablation is recommended. The ablation catheter tip has to be kept 1 cm away from the ostia of the coronary arteries.