1. Bidirectional Ventricular Tachycardia
Bidirectional ventricular tachycardia is quite rare, but pathognomonic for digoxin toxicity. This ECG has two distinct QRS morphologies alternating every other beat. The QRS complex duration is prolonged (wide). Both morphologies meet criteria for a ventricular origin. They are both in a right bundle branch block pattern since they are upright in lead V1. One of the QRS complexes is upward concordant in the precordial leads (all upward) indicating a ventricular origin. The other morphology has an R larger than the R' in lead V1 indicating a ventricular origin. Note the pause, one sinus beat, then the resumption of the bidirectional ventricular tachycardia.