Unstable Angina: Overview

Acute coronary syndrome (ACS) is a term that encompasses unstable angina (UA), non-ST-segment elevation myocardial infarction (NSTEMI) and ST-segment elevation myocardial infarction (STEMI). All result from an imbalance of supply and demand of oxygen to the myocardium. While all three usually result from atherosclerotic plaque rupture and subsequent thrombus formation in one of the main coronary arteries, there are other possible etiologies of this imbalance such as coronary artery narrowing alone, coronary spasm, or coronary dissection. ACCAHArevref1 UA/NSTEMI and STEMI are distinguished pathophysiologically as to whether or not the thrombus is occlusive (as in the case of STEMI) or non-occlusive (as in the case of UA/NSTEMI). wiviottref1 If an electrocartiogram (EKG) is performed at the time that an occlusive coronary artery thrombus is formed, it will usually show ST-segment elevation in the leads which correspond to the territory of myocardium in which blood supply has been disrupted (see STEMI section). If an EKG is performed at the time that a non-occlusive thrombus is formed, it may or may not show signs of ischemia (see below).

UA and NSTEMI are distinguished based on whether there are elevated serum levels of cardiac biomarkers (i.e., creatine kinase (CK), MB isoenzyme of CK (CK-MB) and Troponins I and T). Elevated cardiac biomarkers are present in NSTEMI but not in UA. (Lee 2004) However, it is important to note that although troponins are fairly sensitive and specific for myocardial necrosis, the diagnosis of NSTEMI should not be made based on laboratory findings alone, as there are other possible etiologies for elevated troponins. ACCAHArevref1