[A-V conduction block at His bundle level; as the cause of syncopal crisis in patients with normal ECG (author's transl)].

The history, clinical evolution and complementary studies used to identify the diagnostic etiology of syncopal crisis in a series of 5 patients are presented. The crisis consisted of advanced disturbances of the A-V conduction at the level of the His bundle. It is pointed out that although the evolution of the disturbance was intermittent, the surface ECG was normal and neither A-V block nor broadening of the QRS complex were seen. The importance of continued monitorization, whether as out-patients (Holter system) or, in some cases in an Intensive Care Unit, as well as the need to practice electrophysiologic studies in all these cases as the only way of establishing a firm diagnosis, are underlined. The fact that these disturbances do not always lead to an advanced blockage of A-V conduction is discussed as being reminiscent of the prospective and retrospective studies in the similar case of bi-fascicle block.