Abstract & Commentary
Synopsis: Infarct size and LV function in patients with acute anterior MI are related to ST segment changes in the inferior leads. Those with inferior ST elevation have smaller infarcts with preserved LV function either due to a proximal RCA lesion or a mid to distal LAD lesion.
Source: Sadanandan S, et al. Am Heart J. 2003;146: 653-661.
In patients with acute anterior myocardial infarction (MI) the significance of inferior ECG ST-segment elevation is unclear. Thus, investigators from the GUSTO-I angiographic and the GUSTO-IIb angioplasty substudies evaluated the 1046 patients with anterior ST elevation and divided them into 3 groups: 1) those with inferior ST elevation also (n = 179); 2) those with no inferior ST changes (n = 447); and 3) those with inferior ST-depression (n = 420). Group 1 had more total ST elevation but the lowest peak CK level (1370 vs 1670 vs 2381; P = .0001) and the highest left ventricular ejection fraction (53% vs 48% vs 45%). Angiographically in group 1 patients, the infarct-related artery was either the left anterior descending (36%) or the right coronary artery (59%), whereas in groups 2 and 3 almost all patients had LAD culprit lesions (97%). In the RCA subgroup of group 1, the culprit lesion was usually proximal (67%); in the LAD subgroup, it was mid or distal.
If ST elevation in V1 was > V3 it favored an RCA lesion in group 1. Sadanandan and associates concluded that infarct size and LV function in patients with acute anterior MI is related to ST segment changes in the inferior leads. Those with inferior ST elevation have smaller infarcts with preserved LV function either due to a proximal RCA lesion or a mid to distal LAD lesion.
Comment by Michael H. Crawford, MD
Acute anterior MI with inferior ST elevation suggests the possibility of a large MI involving a dominant wrap around the apex LAD or combined occlusion of the LAD and RCA. In this study it was most likely due to a proximal RCA lesion (59%) or a mid to distal LAD lesion (36%) with limited infarct size. It is obvious in the case of a mid to distal LAD culprit lesion why infarct size would be limited, but why with a proximal RCA lesion? Sadanandan et al speculate that it is because there is a predominant right ventricular infarct and less LV damage, but they do not have ECG or imaging data to substantiate predominant RV involvement. In this study very few patients had multivessel disease, so the possibility of dual artery occlusion (not necessarily simultaneously) is unlikely but could be more common in less carefully selected patients. It is interesting that those with an isolated anterior MI (no ST changes inferiorly) had a larger MI and that those with inferior ST depression had the largest MIs. Presumably, the latter finding is due to the well-known phenomenon that the larger a single-vessel MI is, the more likely reciprocal changes will develop (ST depression). In some cases, the associated ST depression may represent ischemia at a distance due to sudden withdrawal of collateral flow to the adjacent territory of a previously occluded or severely stenosed artery. Finally, no differences in clinical event rates were observed despite the differences in MI size and LV function. This could be the result of a small sample size in this substudy of the GUSTO trials.
Dr. Crawford, Associate Chief of Cardiology for Clinical Programs, University of California, San Francisco, is Editor of Clinical Cardiology Alert.