Combined intra-Hisian block and A-V nodal bypass

A patient with first and second degree atrio-ventricular (A-V) block and left bundle branch block was shown on electrophysiological study to have an intra and infra-His bundle branch block. In addition, this patient also had an A-V nodal bypass tract. The intra-Hisian block was concealed on the resting His bundle electrogram and became evident only during atrial pacing. The A-V nodal bypass was masked on the surface electrocardiogram (ECG) by the associated A-V conduction defect. The clinical significance of A-V bypass and combined block below the A-V node is discussed. The diagnostic value of His bundle electrocardiography in a patient with complex electrophysiological abnormalities is stressed.