The unusual finding of 2:1 supra-His block during AVNRT suggests the presence of tissue between the tachycardia circuit and the His bundle, effectively excluding a His-atrial bypass tract.
Alerts electrophysiologists to nodal separation in block patterns; leaves open circuit localization in broader AVNRT cohorts.
A patient with narrow complex supraventricular tachycardia underwent electrophysiological study at which time a tachycardia was initiated which had 2:1 AV conduction, with block occurring above the His bundle. The modes of tachycardia initiation, as well as the responses to atrial and ventricular premature depolarizations during tachycardia, made a diagnosis of atrioventricular nodal reentry as the tachycardia mechanism. The unusual finding of 2:1 supra-His block suggests the presence of tissue situated between the tachycardia circuit and His bundle, and effectively excludes the possibility of a His-atrial bypass tract as the retrograde limb of the tachycardia circuit.
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Schmitt et al. (1988) studied this question.
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