Abstract
Five patients with tricuspid atresia underwent His bundle studies with the recording catheter placed close to the mitral valve ring. Right atrial pacing and measurement of the refractory periods were performed in three. The prolonged intraatrial conduction time found in all patients is thought to be caused by a hypertrophied and dilated right atrium with increased internodal distance due to stretching of internodal pathways. The A-H interval was normal in all; the H-V interval was short in three and normal in two. The pattern of left axis deviation in the group with a short H-V interval is thought to be due to early origin of the posterior branches of the left bundle branch from the bundle of His and early activation of the posteroinferior parts of the left ventricle. The pattern of left axis deviation in the group with a normal H-V interval may be related to the previously reported anomalous course of the left bundle. Atrial pacing produced a normal response. The refractory periods were within normal range, suggesting functional integrity of conduction through the atrioventricular node and bundle branches.
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