His bundle electrograms in patients with congestive cardiomyopathy

His bundle electrograms were obtained at rest during atrial pacing in 16 patients with congestive cardiomyopathy. Increments in heart rate during atrial pacing were associated with progressive increases in the A-H interval in all patients. Three patients had abnormal conduction (prolonged P-H) proximal to the His bundle; atrial pacing resulted in second degree A-V block (A-H block) in these three patients at paced rates below 130/min; these three patients were on digitalis at the time of the study. Two patients had left bundle branch block associated with a prolonged H-V interval suggesting a conduction disturbance in the contralateral bundle system either at or distal to the branching portion of the His bundle. Two patients had H-V prolongation in the presence of a normal QRS duration which suggests delay in the bundle of His. Two patients with normal H-V intervals had marked prolongation of the total intraventricular conduction time (H-S prolongation). The His bundle electrogram uncovered abnormalities in atrioventricular conduction not apparent on the standard electrocardiogram and has allowed expansion of our knowledge regarding the electrophysiologic features of congestive cardiomyopathy.