Wednesday, April 27, 2011

Ventricular Tachycardia

Ventricular tachycardia is a frequent, post-infarction and perioperative arrhythmia with a fast heart beat that starts in one of the ventricles of the heart. There is a ventricular tachycardia when the pulse rate is more than 100 beats per minute, with at least three irregular heartbeats in a row. It can develop as an early or late complication of a heart infarction. It may also occur in patients with a heart surgery, cardiomyopathy, valvular heart disease, etc. If left untreated, some forms of ventricular tachycardia may get worse and lead to ventricular fibrillation, which can be life-threatening. Recurrent ventricular tachycardia is less common, but it is both physiologically and psychologically incapacitating when it occurs.

According to its morphology ventricular tachycardia is classied in two types: 1) monomorphic ventricular tachycardia, which means that the appearance of all the beats match each other in each lead of a surface electrocardiogram (ECG); 2) polymorphic ventricular tachycardia, which has beat-to-beat variations in morphology, and most commonly appears as a cyclical progressive change in cardiac axis.

n monomorphic ventricular tachycardia, all the beats look the same because the impulse is either being generated from increased automaticity of a single point in either the left or right ventricle, or due to a reentry circuit within the ventricle; the most common cause of monomorphic ventricular tachycardia is myocardial scarring from a previous myocardial infarction. Polymorphic ventricular tachycardia, on the other hand, is most commonly caused by abnormalities of ventricular muscle repolarization; the predisposition to this problem usually manifests on the ECG as a prolongation of the QT interval; QT prolongation may be congenital or acquired. Congenital problems include Long QT syndrome and Catecholaminergic polymorphic ventricular tachycardia. Acquired problems are usually related to drug toxicity or electrolyte abnormalities.