[Left bundle of His branch block in stages 3 and 4 with conduction in the right branch only in a super-normal period].

The authors report a case of chronic second degree atrio-ventricular block with permanent right bundle branch block. Intracavitary electrophysiological recordings allowed them to delimit the refractory period of the left branch, which was affected by a block during phase 3 but also during phase 4. They showed that there was possible conduction by the right branch during the extremely fine time limits of a supernormal period; using an atrial stimulation rate of 150/mn, it is therefore possible to obtain 1/1 conduction in the presence of a left bundle branch block.