Ventricular tachycardia is characterized as a wide complex (QRS duration greater than 120 milliseconds) tachyarrhythmia at a heart rate greater than 100 beats per minute. It is classified by duration as non-sustained or sustained. Non-sustained ventricular tachycardia is defined as more than 3 beats of ventricular origin at a rate greater than 100 beats per minute that lasts less than 30 seconds in duration. When the rhythm lasts longer than 30 seconds or hemodynamic instability occurs in less than 30 seconds, it is considered sustained ventricular tachycardia. Further classification is made into monomorphic and polymorphic on the basis of QRS morphology. Monomorphic ventricular tachycardia demonstrates a stable QRS morphology from beat to beat while polymorphic ventricular tachycardia has changing or multiform QRS variance from beat to beat. Torsades de pointes is a polymorphic ventricular tachycardia that occurs in the setting of a long QT interval and appears as waxing and waxing QRS amplitude on ECG. The final form of ventricular tachycardia is bidirectional ventricular tachycardia which has a beat-to-beat alternation in the QRS frontal plane axis. It is associated with digitalis toxicity or catecholaminergic polymorphic VT. The most common cause of VT is ischemic heart disease.
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