Differentiating wide complex tachycardias.

Wide complex tachycardias are cardiac rhythm disorders with three or more consecutive beats, rates exceeding 100 beats per minute and a QRS duration of 120 msec (0.12 second) or greater. The width of the QRS complex should be verified in a number of leads, since the QRS complex often appears mistakenly narrower (i.e., a QRS duration of less than 120 msec) in one or two of the 12 leads. Most wide complex tachycardias are ventricular tachycardia, and they are managed with antiarrhythmic drugs and correction of serum potassium and magnesium levels. Electrical cardioversion/defibrillation may be used in patients with serious cardiac compromise. Supraventricular tachycardias occur with or without ventricular conduction abnormalities. The management of supraventricular tachycardia requires careful evaluation for aberrant ventricular conduction or preexcitation. The cause of a wide complex tachycardia must be identified, because certain therapies can result in potentially fatal arrhythmias. If the cause cannot be determined, a test dose of intravenous adenosine can be used. Another approach is intravenous administration of procainamide and a beta-adrenergic blocker.