The Electrocardiogram in Myocardial Infarction : PART III. LATERAL INFARCTION

Abstract

In the previous report, the author described the general observation of the electrocardiographic changes in 35 autopsied cases of myocardial infarction. In an attempt to correlate the findings in the electrocardiogram of infarction in each portion of the ventricular wall with the post-mortem findings, the author took up and discussed the anterior infarction in Part II of this serial study. In this communication, the findings in the electrocardiograms have been analyzed and correlated with the pathologic findings in 20 cases with lateral infarction in this series of 35 cases. Of these 20 cases, one had a infarction confined to the lateral wall of the left ventricle. In 12 cases, anterior infarcts extended into the lateral wall of the left ventricle, and in 7 cases, posterior infarcts invaded into the lateral wall of the left ventricle. Of these 20 cases, one had a recent infarction, 19 had healed infarctions, but in 2 of the latter, the infarctions were proved to be of relatively fresh one by microscopic examination, and in at least 8 cases of the latter, the electrocardiograms, were obtained also in the acute stage. The cases were classified into the following three groups, according to the location and extent of the lesion in the lateral wall at autopsy: (A) the infarction involving the apical pne-third or more of the lateral wall, (B) the infarction involving the apical one-fifth or more and less than the apical one-third of the lateral wall, and (C) the infarction involving the middle one-third of the lateral wall. 1. Group A included 13 cases. In 2 cases of 3 transmural infarctions in group A, a QS complex was recorded in one or more of Leads V_5, V_6 and V_7. In 3 of 10 subendocardial infarctions, an abnormal QR(S) complex and a inverted T wave and/or depression of RS-T segment were obtained in one or more of Leads V_5, V_6 and V_7. (in one case in Lead CF_5). An abnormal Q wave could not be found and only depression of the RS-T segment and/or inversion of T wave were present in the left precordial leads in another 7 cases of these subendocardial infarctions, except one case in which the number of the employing leads was insufficient. Consequently, it was shown as difficult to differentiate left ventricular hypertrophy, coronary insufficiency and others by means of the electrocardiographic examination in these cases. 2. Relatively small apical infarction of the lateral wall which was classified into group B was found in 4 cases. One of these cases was a tarnsmural infarct and 3 were subendocardial infarcts. In one case of the latter, a borderline Q wave with a notched upstroke of the succeeding R wave was found in Lead V_5. And the electrocardiogram of these 4 cases displayed a depression of the RS-T segment and an inverted or a frat T wave in one or more (in most cases in two or more) of Leads V_5, V_6 and V_7. 3. In one posterolateral infarction of 3 cases which was classified into group C, the electrocardiogram displayed right bundle branch block and was accompanied by an abnormal Q wave in Lead V_7 and by a depressed RS-T segment in Lead V_5. In another 2 cases of this group, the infarct was patchy and relatively small, and the electrocardiogram recorded only slight depression of RS-T segment in Leads V_4, V_5 and V_6, without an appearance of an abnormal Q wave. 4. Of all 20 cases of the lateral infarction, the abnormal Q wave in the left precordial leads was observed in 5 cases, and the borderline Q wave in only 2 cases. In another 13 cases an abnormal Q waev could not be found. The reason of the absence of an abnormal Q wave was discussed. In respect to this problem, it must be concluded that the infarction was limited to the subendocardial layer in the lateral wall in 15 of these 20 cases. In some cases the displacement of the transitional zone to the left, the presence of other extensive infarction elsewhere in the left ventricule and/or the patchy infarction

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