Asynchronous cardioversion is given in-

Occasionally, VT occurs in patients with otherwise healthy heas ('normal hea VT'), usually because of abnormal automaticity in the right ventricular outflow tract or one of the fascicles of the left bundle branch.Ventricular tachycardia Ventricular tachycardia (VT) occurs most commonly in the settings of acute MI, chronic coronary aery disease and cardiomyopathy. It is associated with extensive ventricular disease, impaired left ventricular function and ventricular aneurysm. In these settings, VT may cause haemodynamic compromise or degenerate into ventricular fibrillation . VT is caused by abnormal automaticity or triggered activity in ischaemic tissue, or by re-entry within scarred ventricular tissue. Patients may complain of palpitation or symptoms of low cardiac output, including dyspnoea, lightheadedness and syncope. The ECG shows tachycardia and broad, abnormal QRS complexes with a rate of more than 120/min . It may be difficult to distinguish VT from SVT with bundle branch block or pre-excitation (WPW syndrome) on ECG . A 12-lead ECG or electrophysiology study may help establish the diagnosis. When there is doubt, it is safer to manage the problem as VT. Patients recovering from MI sometimes have periods of idioventricular rhythm ('slow' VT) at a rate only slightly above the preceding sinus rate and below 120/min. These episodes often reflect reperfusion of the infarct territory and may be a good sign. They are usually self-limiting and asymptomatic, and do not require treatment. Other forms of sustained VT require treatment, often as an emergency. Ref Harrison 20th edition pg 1546