The Electrocardiogram in Myocardial Infarction : PART V. INFARCTION OF THE INTERVENTRICULAR SEPTUM

Abstract

In this study, infarction of the interventricular septum was demonstrated pathologically in 24 of all 35 cases. The author had studied the correlation between electrocardiographic and post-mortem findings concerning the septal infarction in these 24 cases. Of 24 cases, 8 were men and 16 were women and their age ranged from 52 to 86, except in 2 cases. Among these 24 cases, 3 had recent and 21 had healed infarctions at autopsy, but it was considered that in at least 5 cases with healed infarctions, the electrocardiogram was obtained when the infarction was in the acute stage. These cases were classified into four groups, according to the distribution of the lesion at autopsy: (1) coexistent septal extension of anterior infarction in 5 cases; (2) septal extension of anteroposterior infarction in 13 cases; (3) extension of posterior infarction into the posterior portion of the interventricular septum in 5 cases; (4) infarction limited to the interventricular septum in 1 case. On the other hand, the cases were classified into three groups, according to the extent of the lesion in the interventricular septum at autopsy: (〓) large, massive infarction involving at least half or more of the inverventricular septum in 7 cases; (〓) minimal infarction confined to only small portion of the interventricular septum or distributed in patchy fashion in the septum in 10 cases; (〓) moderate infarction corresponded to the middle of both above-mentioned groups in 7 cases. The electrocardiographic patterns in these septal infarction were summarized as follows: 1. Interventricular conduction defects, in which QRS interval was 0.12 second or more, were obtained in 3 cases with right bundle branch block, in one case with the so-called arborization block in the form of left bundle branch block, and in one case with prolonged QRS interval, uncomplicated by a bundle branch block. a) In 2 of 3 cases with right bundle branch block, autopsy revealed the anteroposterior infarction accompanied by a three-plus or two-plus infarction in the interventricular septum, and the electrocardiogram showed an abnormal Q wave and a late (delayed) R wave from Lead V_1 to V_4. In a remaining case of right bundle branch block, in which posterior infarct extended into the posterior portion of the interventricular septum, the electrocardiogram showed an abnormal Q wave in Leads _aV_F III and II, but the right precordial leads showed the similar pattern of uncomplicated right bundle branch block. b) In a case with left bundle branch block, an acute infarction limited to the basal portion of the interventricular septum was found at autopsy, and the electrocardiogram showed the pattern of arborization block characterized by the high grade prolongation of QRS interval and low voltage in the standard and unipolar limb leads, without appearance of an abnormal Q wave in any lead. c) In another case of intraventricular conduction defect, which showed QRS interval of 0.12 second, the damage in the free wall of the left ventricle was extensive, but the septal involvement was very small at autopsy, and a diagnostic pattern of septal infarction could not be found in the electrocardiogram. 2. Auriculoventricular block was observed in only one case of incomplete auriculoventricular block which was probably caused by digitalis intoxication in the course of infarction. 3. The cases without intraventricular conduction defect. a) The cases with septal extension of anterior or anteroposterior infarction: When the extent of infarct in the interventricular septum was moderate (〓) or massive (〓), in 10 of 12 cases, an abnormal Q wave was observed in Leads V_1 and V_2 or Lead V_2, and most of them were accompanied by RS-T variations. In the remaining 2 cases, the amplitude of the initial R wave in the right precordial leads decreased abnormally as the electrode was moved from right to left, and finally an abnormal Q wave was recorded in Lead