ELECTROCARDIOGRAPHIC DIFFERENTIATION OF THE ST-SEGMENT DEPRESSION OF ACUTE MYOCARDIAL INJURY DUE TO THE LEFT CIRCUMFLEX ARTERY-OCCLUSION FROM THAT OF MYOCARDIAL-ISCHEMIA OF NONOCCLUSIVE ETIOLOGIES

Patients with symptoms of acute myocardial ischemia and ST-segment ele vation can be presumed to have complete occlusion of a coronary artery , which is most often thrombotic in original.(1,2) In contrast to pati ents with ST-segment elevation in whom thrombolytic therapy has been s hown to be beneficial,(3-5) no such benefits have been demonstrated in patients with ST-segment depression. Among patients with acute myocar dial ischemic syndromes presenting with ST-segment depression, some ha ve complete thrombotic occlusion, Many patients with complete acute th rombotic occlusion of the left circumflex (LC) artery have only ST-seg ment depression on their standard 12-lead electrocardiograms.(6,7) The se patients, if accurately distinguished from the remainder of the pop ulation with ST-segment depression, might be as likely to benefit from thrombolytic therapy as those with ST-segment elevation. Complete acu te occlusion of a major coronary artery typically produces a ST-segmen t deviation pattern specific for the location of the occlusion.(8) Con versely, nonocclusive ischemia produces a diffuse ST-segment depressio n pattern that is not specific for the myocardial location of the isch emia.(9.10) To differentiate the ischemia of acute LC occlusion from n onocclusive ischemia we retrospectively studied the pattern of isolate d ST-segment depression in 2 populations: (1) those undergoing percuta neous transluminal coronary angioplasty (PTCA) of the LC coronary arte ry, and (2) those undergoing exercise tolerance testing (ETT).