The electrocardiographic features of high posterolateral myocardial infarction.

The cardiographic features of anterior and posterior myocardial infarction are well recognized. The occurrence of high lateral infarction has also been established, but infarction confined to the posterolateral aspect of the heart has in contrast received little attention. It is the purpose of this paper to stress the diagnostic cardiographic features of infarction in this area. Anatomically the heart is an irregular and slightly flattened cone, with a base, an apex, and three surfaces, described anatomically as the sterno-costal, the diaphragmatic, and the left. Cardiographically, lesions of the sterno-costal and diaphragmatic surfaces are classified respectively as anterior and posterior. The left surface faces backwards, upwards, and to the left. It is not in close relationship to any of the six routine precordial leads, but does in part face towards the left shoulder. Infarction confined to this left surface is posterolateral in position. As there is no lesion of the diaphragmatic surface, the infarct should be classed cardiographically as a " high" posterolateral infarct. In 1944 Wilson pointed out that the combination of diagnostic changes of infarction in the left leg lead, unusual prominence of the R and T waves in leads to the right of the prncordium, and significant abnormalities in leads V5 and V6, was associated with infarction of the posterolateral aspect of the heart. Myers et al. (1949) have reported on 33 cases which at autopsy showed infarction of the posterolateral aspect, and have correlated the cardiographic and post-mortem findings. Changes in the left leg lead were taken as an index of the posterior aspect of the lesion, while the lateral extension was evidenced by precordial leads V5 and V6 and the left arm lead. Less than one-third of the cases showed diagnostic changes in both limb leads. In the majority of cases changes of infarction were confined to one or other limb lead, depending on the exact size and position of the infarcted area, and on the position of the heart, particularly the degree of rotation around the long axis. Two cases showed no evidence of infarction in either limb lead. Sixteen cases were observed during the acute stage, and in eleven, pricordial leads from VI to V4 showed reciprocal depression of the S-T segment, or exaggeration of the height of the R and T waves or of the T waves alone, sufficient to arouse suspicion of posterolateral infarction. Both Wilson and Myers have illustrated their writings, but in no record does the R wave exceed the S wave in VI. Sears and Myers (1950) now record additional leads from the back of the chest in these cases, but have not as yet published their results. Recently Levy (1950) has stressed the occurrence of a prominent R wave and shallow S wave in lead VI in lateral infarction; in eightof his twelve cases, the infarct was localized to the posterolateral aspect, but autopsy confirmation was apparently not available.