<P> If an MI is presented with ECG evidence of an ST elevation known as STEMI, or if a bundle branch block is similarly presented, then reperfusion therapy is necessary . In the absence of an ST elevation, a non-ST elevation MI, known as an NSTEMI, or an unstable angina may be presumed (both of these are indistinguishable on initial evaluation of symptoms). ST elevations indicate a completely blocked artery needing immediate reperfusion . In NSTEMI the blood flow is present but limited by stenosis . In NSTEMI the same thrombolytics are used as for STEMI, but they are also often stabilised with antiplatelets and anticoagulants . If the condition stays stable a cardiac stress test may be offered, and if needed subsequent revascularization will be carried out to restore a normal blood flow . If the blood flow becomes unstable an urgent angioplasty may be required . In these unstable cases the use of thrombolytics is contraindicated . </P> <P> At least 10% of treated cases of STEMI do not develop necrosis of the heart muscle . A successful restoration of blood flow is known as aborting the heart attack . About 25% of STEMIs can be aborted if treated within the hour of symptoms onset . </P> <P> Thrombolytic therapy is indicated for the treatment of STEMI--if it can begin within 12 hours of the onset of symptoms, and the person is eligible based on exclusion criteria, and a coronary angioplasty is not immediately available . Thrombolysis is most effective in the first 2 hours . After 12 hours, the risk of intracranial bleeding associated with thrombolytic therapy outweighs any benefit . Because irreversible injury occurs within 2--4 hours of the infarction, there is a limited window of time available for reperfusion to work . </P> <P> Thrombolytic drugs are contraindicated for the treatment of unstable angina and NSTEMI and for the treatment of individuals with evidence of cardiogenic shock . </P>

The maximum window of time a fibrinolytic can be administered​ is