[Paroxysmal junctional tachycardia with simultaneous supra-nodal and infra-nodal 2/1 block]

It is rare to find 2:1 second degree block in paroxysmal junctional tachycardia. In the case described, atrial stimulation at 200/mn during supra-ventricular tachycardia triggered off simultaneous atrio-ventricular and ventriculo-atrial block. This unusual occurrence was very useful because it localised the re-entry circuit to the junctional region by excluding possible accessory pathways.