ST segment depression in lateral limb leads in inferior wall acute myocardial infarction: Implications regarding the culprit artery and the site of obstruction

We examined whether the pattern of ST segment depression inlateral leads (I, aVL, V5, V6) in the initial electrocardiogramof patients (n=88) with inferior wall acute myocardial infarction(ST segment elevation of 1 mm in 2 inferior leads) correlateswith the site of obstruction, as determined angiographicallyduring acute hospitalization. Of the 62 patients in which the culprit artery could be determinedunequivocally, in 46 the culprit artery was the right coronaryartery (20 proximal to the first right ventricular branch and26 distal), and in 16 the left circumflex coronary artery (sevenproximal to the first marginal branch or involving a high firstmarginal branch, and nine with distal obstruction). SignificantST segment depression (ST1 mm) in leads I and aVL was more commonin right coronary artery obstruction (P<0.05 and P<0.0001,respectively). The absence of significant ST segment depressionin lead a VL was most common in proximal circumflex obstruction(P<0.0001), with a similar trend for lead I (P<0.11).ST segment depression patterns in leads V₅ and V₆ were not indicativeof the infarct-related artery or the site of obstruction. Thus,significant ST segment depression in leads I and aVL indicatesright coronary artery-associated inferior wall acute myocardialinfarction with a sensitivity of 70% and 100%, and a specificityof 63% and 38%, respectively, whereas the lack of ST segmentdepression in these leads indicates proximal circumflex obstructionwith a sensitivity of 71% and 86%, and a specificity of 65%and 100%, respectively.