His Bundle Refractoriness.

Multiple points of instruction discussed practically in the context of a challenging case make for a memorable learning experience. In this installment of Teaching Rounds in Cardiac Electrophysiology, Nayyar et al elucidate the unique findings and analysis in such a manner and take us through to diagnosis and a treatment plan that eliminated arrhythmia without having to ablate all of the abnormal structures identified in their patient. Their case in which 2 unusual arrhythmogenic substrates coexist and interact to result in what appears to be a random and inexplicable series of electrophysiological findings is broken down in logical steps defining each aspect of the arrhythmia. These steps include defining the antegrade and retrograde limbs of the putative tachycardia circuit, defining the mechanism of tachycardia, and coming to a conclusion keeping in mind certain difficult differential diagnostic situations and the importance of interpreting His bundle refractory extrastimuli maneuvers.