Definition of acute coronary syndrome

Recently, the Fourth Universal Definition of Myocardial Infarction (2018) categorized acute myocardial infarction into various types on the basis of pathological, clinical, and prognostic differences.¹⁴ However, in the TSGH-CHD registry, the patients were classified as having UA, NSTEMI, and STEMI in the spectrum of ACS through conventional practice.^15,16 STEMI was defined as myocardial ischemia in association with persistent ST-segment elevation or new left bundle-branch block on an electrocardiogram, and it was considered to be an indication for immediate reperfusion therapy. Diagnostic ST-segment elevation in the absence of left ventricular hypertrophy was defined as new ST-segment elevation at the J point in at least two contiguous leads as follows: new ST-segment elevation of ≥ 2 mm (0.2 mV) in men or ≥ 1.5 mm (0.15 mV) in women in leads V₂ and V₃ and/or ≥ 1 mm (0.1 mV) in other contiguous chest leads or limb leads. The absence of ST-segment elevation was suggestive of NSTE-ACS, including NSTEMI and UA, depending on whether cardiac biomarkers were elevated. If cardiac biomarkers were elevated and the clinical context was appropriate, NSTEMI was considered. Otherwise, the patients were considered to have UA. Obstructive CAD was defined as a coronary diameter stenosis of ≥ 50%. Cardiogenic shock was defined as systolic blood pressure of < 90 mmHg despite intravenous fluid resuscitation or the administration of inotropic agents on admission.