Here’s an EKG you may never have seen before. Only slightly frightening, right? The rate is tachycardic and the width of the QRS tells you that it is coming from below the AV node. The defining feature here is that the QRS complex alternates from left to right axis between beats. This EKG is a rare rhythm that is nearly pathognomonic for digitalis poisoning and is termed bidirectional ventricular tachycardia. Very rare alternative causes of this rhythm include aconite poisoning and a rare in-born syndrome characterized called chatecholaminergic polymorphic ventricular tachycardia. The rhythm itself is provoked by increased automaticity of cells in the his-purkinje system mediated by increased intracellular calcium and extracellular potassium concentrations. The left and right sides of the his-purkinje fire in an alternating fashion producing the alternating electrical axis.