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A complete study of the electrical effects of the atrial repolarization is made, since it seems that such effects are often inadequately considered in the routine daily interpretation of electrocardiograms. The alterations of the atrial repolarization are classified as follows: (1) primary, related to ischemia or injury of the atria, and hypersympathetic activity, (2) secondary, when appearing with modifications of the atrial activation, in cases of dilatation, hypertrophy, or intra-atrial block. The electrocardiographic changes produced by hypersympathetic activity are characterized by a P-PR junction (Ja) in the isoelectric line, descending P-R segment, depressed J point, and ascending S-T segment. The P-R and S-T segments have concordant deviations, which means that they behave as "arcs of a same circumference." The record of these electrical events is made in such a manner that the tracing can be morphologically compared to an anchor. An S-T depression has no pathologic significance whenever it is preceded by a concordant and symmetric P-R depression. A myocardial injury is diagnosed only when the P-R and S-T segments are discordant, that is, when they correspond to "arcs of different circumference." An electrocardiographic exercise test is considered as negative, even in the presence of S-T depression, as long as this segment is inscribed with the same radius as that of the preceding P-R segment. Other processes that act upon the atrial repolarization, such as atrial infarction, wounds, dilatation, hypertrophy, and pericarditis, are also analyzed, and their influence on the inscription of the ventricular repolarization is stressed. Exact knowledge of the phenomena of atrial repolarization allows a more accurate interpretation of S-T displacements, and therefore is a safer diagnosis of the pathologic changes acting upon the ventricular repolarization.

Atrial Repolarization—Its Importance in Clinical Electrocardiography