RESUMO
Objective The purpose of this study was to clarify the mechanism of 2:1 atrioventricular block (AVB) during AV node reentrant tachycardia (AVNRT) induced during electrophysioloic study.Methods In consecutive patients with AVNRT referred for electrophysiologic study, the data of 2 : 1 AVB during induced AVNRT was retrospectively analysed. Results The data of 4 patients was excluded from analyzing because of the unsatisfactory recording of His bundle potential during AVNRT. A His bundle deflection was present in the blocked beats in three of the remaining 5 patients and absent in the other two. At the beginning of AVNRT induced in those patients whose His bundle deflection was present in the blocked beats, H-V Wenckebach sequence with a QRS pattern of RBBB or LBBB was seen preceding and following the 2 : 1 AVB. A pattern of H-V Wenckebach phenomenon occurred once during AVNRT with 2:1 AVB in one of the two patients whose His bundle deflection was absent in the blocked beats.Conclusion The induced 2:1 AVB during AVNRT is due to functional block in the His-Purkinje system regardless of the presence or absence of a His bundle deflection in blocked beats.