V. Correlation of electrocardiographic and pathologic findings in posterior infarction

Abstract The findings in Lead aV F have been analyzed and correlated with cardiac position and with the pathologic findings in 110 patients with infarction of the posterior wall of the left ventricle. The infarct was recent in forty-three cases and healed in the other sixty-seven. Determination of the electrical position of the heart was essential to the interpretation of the findings in Lead aV F , since the direction of the initial phase of the QRS complex was dependent upon the surface of the septum that faced downward, whereas the potential variations of the left leg throughout the remainder of the cycle were governed principally by those of the epicardial surface that rested upon the diaphragm. Findings in Lead aV F in Thirty-Five Cases of Posterior Infarction With Electrocardiographic Evidence of Horizontal to Semihorizontal position of the Heart .—In twenty-two of the group, Lead aV F displayed a small R and deep S wave, representative of the customary findings due to transmission of the potential variations of the right side of the septum and epicardial surface of the posterior wall of the right ventricle to the left leg and in no way suggestive of the posterior infarct found at autopsy. In nine others, a continuation of the infarct into the septum was manifested by one of the following three diagnostic patterns in Lead aV F : a small Q, small R, and deep S wave; a small Q and tall late R wave similar to the pattern in Lead V 1 and referable to septal infarction with right bundle branch block; and a QS comple: attributable to septal infarction after establishment of the presence of transverse position and exclusion of the QS complex that occurs as a normal variant under these circumstances. The latter was present in two of the thirty-five cases. Lead aV F in the two remaining cases displayed a broad, slurred QS and QR complex, regarded as a manifestation of left bundle branch block in a horizontal and semihorizontal heart, respectively, and considered independent of the posterior and and septal infarcts found at autopsy. Criteria for the Diagnosis of Posterior Infarction in the Presence of Intermediate, Semivertical, or Vertical Position of the Heart .—Under these conditions, the potential variations of the epicardial surface of the posterior wall of the left ventricle had the predominant effect upon the QRS-T pattern in Lead aV F . The abnormal QR pattern due to posterior infarction was differentiated from the normal QR complex in Lead aV F by the time interval from onset to nadir of the Q wave, the ratio of the amplitude of the Q to that of the R wave, and the duration and contour of the ascending limb of the R wave. QR complexes of 0.5 millivolt or more, with a Q wave measuring 0.03 second or more from onset to nadir and a Q R ratio over 25 per cent were considered diagnostic of posterior infarction. QR complexes that met part, but not all, of the foregoing requirements were generally classed as borderline to strongly suggestive, but were also considered diagnostic, provided that (a) the time interval from onset to nadir of the Q wave was 0.04 second or more; (b) the Q wave was followed by an abnormally prolonged, notched, or coarsely slurred upstroke; (c) the tracing was obtained within twenty-four hours of the onset of symptoms and showed classical displacement of the RS-T segment; or (d) previous tracings were available, showing perfectly normal patterns prior to the development of the borderline QR complex. QS deflections of 0.5 millivolt or more, which consumed 0.03 second or more from onset to nadir, were considered diagnostic of extensive transmural posterior infarction, provided it could be established that the heart was in intermediate to vertical position and not in horizontal or semihorizontal position. Findings in Lead aV F in Seventy-Five Cases of Posterior Infarction With Electrocardiographic Evidence of Intermediate to Vertical Position of the Heart .—On the basis of the criteria described, the findings in Lead aV F were classed as diagnostic of posterior infarction in forty-two cases, borderline to strongly suggestive in seventeen cases, and negative in sixteen cases. The findings in Lead aV F , as classified into the foregoing three categories, were correlated with the size and position of the infarct in reference to the long axis of the left ventricle. Of thirty-one patients with infarction extending two-thirds or more of the length of the posterior wall, Lead aV F was negative in only one. The normal QRS pattern in this case was probably due to the fact that the lesion was posterolateral in position and spared the septal half of the posterior wall. The incidence of diagnostic failures in patients with smaller posterior infarcts varied with the size and location of the lesion and was lowest when the infarct involved the middle third of the posterior wall, as shown by the following observations. Lead aV F was negative in only one of five patients with infarction confined to the middle third of the posterior wall. On the other hand, the findings in Lead aV F were negative in eight of fourteen patients with infarction confined to the apical third, but in only two of fourteen other patients in whom the posteroapical infarct continued into the middle third. Both of these failures were explained by the presence of left bundle branch block. The findings in Lead aV F were negative in all three patients with infarction confined to the basal third of the posterior wall, but in only one of eight patients in whom the posterobasal lesion continued into the middle third. The latter failure occurred despite the fact that serial tracings were available before and after the development of the infarct. A QRS-T pattern that was considered diagnostic of posterior infarction was found terminally in Lead aV F of one patient with hemopericardium due to dissecting aneurysm. Esophageal leads were obtained in five patients and were considered diagnostic of the posterior infarct found at autopsy. Recent posterior infarction was generally manifested by reciprocal changes in the RS-T segment of precordial leads when the anterior wall was intact, but not when the anterior wall was infarcted. Standard Leads II and III failed to provide diagnostic evidence of posterior infarction in cases where Lead aV F was negative. Furthermore, the application of the Pardee criteria to the interpretation of the findings in the standard leads led to errors in a number of cases where correct diagnoses could be made from the findings in Lead aV F .