[Interatrial block with retrograde activation of the left atrium (author's transl)]

Six cases with P wave abnormalities compatible, according to the criteria of Castillo and Vernant, with the diagnosis of block of the Bachmann's bundle, have been studied by means of intra-atrial and esophageal electrography. In two cases the P wave abnormalities were intermittent. In agreement with the results of Castillo and Vernant right atrial activation appears to be normal and coincides with the initial positive deflection of the P wave in leads II, III, and aVF. Left atrial activation starts at the end of the right atrial activation, coinciding with the terminal negative deflection of the P wave in leads II, III, and aVF and shows an abnormal progression from the lower part to the upper part of the atrium. This pattern of atrial depolarisation can only be explained by a block of the superior interatrial pathways. On the basis of the present findings it is supposed that the block occurs in a specialized type of atrial tissue rather than in the common atrial myocardium. From the clinical point of view it is of some interest to point out that this abnormal pattern of atrial depolarisation does not necessarily prolong the atrial deloparisation and may not determine a terminal negative deflection of the P wave in lead II.