Implications of inferior ST-segment elevation accompanying anterior wall acute myocardial infarction for the angiographic morphology of the left anterior descending coronary artery morphology and site of occlusion

Abstract

Inferior ST-segment elevation during anterior wall acute myocardial infarction (AMI) due to left anterior descending (LAD) coronary artery occlusion is unusual and was not previously investigated. This study tested the hypothesis that inferior ST-segment elevation during anterior AMI predicts a specific angiographic morphology that satisfies 2 necessary conditions: (1) mass of ischemic anterior wall myocardium is relatively small, resulting in a weaker anterior injury current and less reciprocal inferior ST-segment depression; and (2) there is concomitant inferior wall transmural ischemia that further shifts the inferior ST segments upward. The study group consisted of 42 consecutive patients with anterior AMI undergoing angiography at 4.1 days (range 0 to 14). Coronary angiograms were examined for 3 features: (1) site of LAD artery occlusion (a distal obstruction implying a smaller mass of ischemic anterior wall myocardium), (2) LAD artery extension onto inferior wall of left ventricle (termed a “wrap around” vessel), and (3) collateral flow from LAD artery to inferior wall. The latter 2 features would be expected to contribute to inferior wall transmural ischemia. Acute inferior ST-segment elevation (sum of ST-segment deviation in leads II, III and aVF ≥3.0 mm) was seen in 7 patients (16%). A greater number of LAD artery branches proximal to the site of occlusion was significantly correlated with less inferior ST-segment depression (r = 0.59, p < 0.01). The 33 patients with an LAD artery that “wrapped around” the cardiac apex to the inferior wall had less total inferior ST-segment depression than that of the 9 with a shorter artery (0.2 ± 4.0 vs -3.0 ± 2.8 mm; p < 0.05). Of the 7 patients with inferior ST-segment elevation, 5 had a wrap around artery with the culprit lesion distal to 3 major branches. This combination of angiographic findings occurred in only 2 of the other 35 patients (odds ratio 44, 95% confidence interval 4 to 632; p < 0.001). These results support the hypothesis that inferior ST-segment elevation during anterior AMI results from a smaller mass of ischemic anterior myocardium combined with simultaneous inferior transmural ischemia (i.e., a distal occlusion in a wrap around LAD coronary artery).