The electrocardiographic diagnosis of septal infarctions

Abstract

We have analyzed the principal electrocardiographic signs that permit the diagnosis of a necrotic zone in the interventricular septum and have applied this analysis to the cases of septal infarction found in the autopsy files of the Instituto Nacional de Cardiología. Corresponding to the extent of the septal damage found in the autopsy, the cases were studied in the following manner: 1. 1. Massive infarctions of the septum. Where there is no bundle branch block, the electrocardiographic pattern is characterized by the presence of QS complexes in the precordial leads oriented toward the interventricular septum (V 3, V 4; or perhaps from V 1 to V 4). Frequently, this type of infarction is complicated by a complete or incomplete left bundle branch block, and in these conditions the diagnosis is possible because of the presence of a Q wave in leads oriented toward the lateral face of the left ventricle, and, above all, by the presence of QrS complexes in transitional zones (V 3, V 4). In case of right bundle branch block, important destruction of the septum is responsible for the appearance of Q waves in the right precordial leads or in transitional zones. 2. 2. Infarctions of the inferior one-third of the septum. In this group we have noted a high incidence of complete or incomplete left bundle branch block. When there is no bundle branch block, the diagnosis can be very difficult. The presence of QS complexes from V 1 to V 4 or in V 3, V 4, permits a diagnosis of septal damage, although it is practically impossible to differentiate this picture from that of massive infarction. If the infarction of the inferior one-third of the septum is complicated by a left bundle branch block, the diagnosis is made by the presence of qRs complexes in V 3 and V 4 and by the Q wave in the leads oriented to the free wall of the left ventricle. When this type of infarction is complicated by a right bundle branch block, a Q wave is seen in the right precordial leads and its magnitude is accentuated in direct proportion to the extent of septal damage. In those cases in which the infarction extends into the free wall of the right ventricle, it is possible to trace, in the right precordial leads, the morphology found in the high portions of the septum. In cases of left bundle branch block, the morphology may simulate right side alterations of conduction. 3. 3. Infarctions of the superior third of the septum. In all of the cases, there was bundle branch block; nevertheless, electrocardiographic data which would suggest septal damage was not seen. 4. 4. Fibrosis of the septum. Even when on occasion the fibrous zones scattered in the septum were of considerable extent, we did not find an electrocardiographic tracing characteristic of this condition. In some cases, there was a left bundle branch block which may or may not have been the result of the fibrotic zones.