Localization of A-V conduction defects in man by recording of the his bundle electrogram

His bundle electrograms were recorded in 20 patients. Conduction times from atrium to His bundle (A-H time) and His bundle to ventricle (H-V time) were measured and the sites of delay or block were localized to the proximal or distal A-V junction. On progressively increasing the atrial rate by atrial pacing, the A-H time lengthened, while the H-V time remained constant. Premature atrial beats usually resulted in prolongation of the A-H time only. In some instances, premature atrial beats also resulted in prolongation of the H-V time and aberrant ventricular conduction (change in configuration of the QRS complex). In patients with first degree heart block during sinus rhythm the A-H time was prolonged and the H-V time was either normal or prolonged. In higher degrees of heart block, the block was localized either in the proximal or distal A-V junction.