The diagnosis of infarction of the interventricular septum

Abstract

Thirty-five cases of myocardial infarction have been studied with particular emphasis on the pathologic and electrocardiographic correlations in those with septal involvement. The hearts were examined by the Schlesinger method of injection plus dissection supplemented by multiple microscopic sections of the myocardium. Septal involvement was present in thirty-two, and was considerable in twenty-two of the cases. Septal lesions were always associated with infarction of the free wall anteriorly or posteriorly. In twenty-five of the thirty-two cases with septal involvement, infarction of both anterior and posterior walls was present. The left ventricular side of the septum was invariably affected; extension to the right ventricular side (that is, transmural septal infarction) was present in five cases. It is probable that massive septal infarction is usually fatal, since no healed case of this type was encountered. Conduction defects were the most common electrocardiographic findings in cases with septal infarction. The development of bundle branch block or high-grade auriculoventricular block during the course of myocardial infarction was always correlated with acute septal infarction. Complete left bundle branch block was associated with moderate or massive septal infarction in five cases. Low voltage in the limb and left precordial leads was observed in three of these; at autopsy extensive infarction of the left ventricle was present. Q waves were present in the left precordial leads of one case of left bundle branch block associated with massive septal infarction. Incomplete left bundle branch block occurred in two cases with moderate septal infarction, and in one with minimal septal involvement. Low voltage was present in one of the former, and was associated with extensive infarction of the left ventricle. Complete right bundle branch block and septal infarction were observed in three cases. It is worthy of note that extensive and transmural septal infarction was present in all three, and all showed prominent Q waves in the right precordial leads. Incomplete right bundle branch block with Q waves in the right precordial leads was encountered in one case with moderate infarction limited to the left side of the septum and massive anterior wall infarction. Another case showed incomplete right bundle branch block with Q waves in Leads III and aV F associated with posterior wall infarction and minimal septal involvement. An unidentified type of intraventricular block, probably representing right bundle branch block complicated by right ventricular infarction, preceded the development of complete auriculoventricular block in one case with moderate septal infarction. In another case with minimal septal involvement the electrocardiogram displayed the features described as characteristic of arborization peri-infarction block. High-grade auriculoventricular block was observed in four cases with acute infarction of the posterobasal region of the septum. This defect was transient, or was a terminal event. P-R interval prolongation was present in three cases. It was felt that the observed septal lesions could reasonably account for the disturbed conduction in the cases of complete bundle branch block and high-grade auriculoventricular block. No clear relationship could be discerned, however, in the cases of incomplete right bundle branch block, arborization block, and P-R interval prolongation, and in one of the cases of incomplete left bundle branch block. Electrocardiographic evidence of simultaneous acute anteroseptal and posterior infarction was present in two cases with septal involvement. Three others exhibited diagnostic signs and six showed suggestive signs of anterior and posterior infarctions of varying ages. Thus, electrocardiograms disclosed evidence of both anterior and posterior infarction in less than half of the cases with such lesions. QS deflections with elevated S-T segments in right precordial leads were present in eight cases, seven of which had septal infarction.