Second Degree Atrioventricular Block

Abstract
Mechanisms of clinically known varieties of second degree A-V block were studied in isolated rabbit hearts, utilizing ultramicroelectrode techniques. Progressive A-V conduction delay in Wenckebach phenomenon was due mainly to depressed conduction within the A-V node, while Mobitz type 2 block was due to either block in or below His bundle or concealed re-excitation in the A-V junction. Two levels of block were demonstrated both in forward and retrograde A-V transmission.