Evidence of concealed atrioventricular conduction in man.

THE TERM "concealed conduction" was introduced by Langendorfl to describe the phenomenon of entry of an electrical impulse into the A-V node without complete transmission but with modification of conduction of a subsequent impulse. This concept unified diverse observations of earlier years concerning disturbances of A-V transmission2-4 and clarified the mechanisms of many arrhythmias.5 6 Subsequent studies in animals have proved the occurrence of concealed conduction in the form of impulses which only partially penetrate the A-V nodal system.7 Most recently, Langendorf and his co-workers8 have conducted experiments in man which conclusively prove the occurrence of concealed conduction in patients with disease of the A-V conduction system. The present study became possible because 2:1 A-V conduction occurs in many healthy persons with normal A-V nodes when the right atrium is paced at rates only moderately above the intrinsic sinus nodal rate. This phenomenon permits observations of A-V nodal conduction time with and without an interposed atrial depolarization at comparable ventricular rates. The present experimental approach, which is a variant of that originally used by Lewis and Master,2 is applied here to the study of normal human A-V conduction.