Unstable angina and non-ST elevation (non-Q wave) myocardial infarction (NSTEMI) are part of the continuum of acute coronary syndrome (ACS) that also includes ST elevation MI. (See "Criteria for the diagnosis of acute myocardial infarction", section on 'Third Universal Definition of MI'.)
Two observations constitute the rationale for consideration of the use of fibrinolytic agents in the treatment of unstable angina or acute NSTEMI:
- The important role of intraarterial thrombus formation in this disorder
- The efficacy of fibrinolysis in the management of acute ST elevation (Q wave) MI (STEMI).
In STEMI, fibrinolytic agents offer a trade-off between reduced mortality and increased incidence of intracerebral bleeding. In this setting, the net benefit is expressed as a difference between these two events. The choice of dose and the means of administration (eg, rapid bolus loading and concomitant intravenous heparin) is influenced by the need to achieve rapid reperfusion to preserve as much myocardium as possible. (See "Fibrinolytic therapy in acute ST elevation myocardial infarction: Initiation of therapy".)
There are a number of important differences in unstable angina/NSTEMI: