What is the difference between NSTEMI and STEMI?



Acute coronary syndromes (ACS) are divided into:

1. STEMI - ST Elevation MI - the classical MI
2. NSTEMI - Non-ST Elevation MI.
3. UA - Unstable Angina

STEMI is when there is a transmural infarction of the myocardium - which just means that the entire thickness of the myocardium has undergone necrosis - resulting in ST elevation. Usually due to a complete block of a coronary artery (occlusive thrombus). This requires the use of thrombolytics like Streptokinase to lyse the thrombus. Evidence has proven that it is very effective and not as risky (Benefits > Risk)

UA or NSTEMI is when there is a partial dynamic block to coronary arteries (non-occlusive thrombus). There will be no ST elevation or Q waves on ECG, as transmural infarction is not seen. The main difference between NSTEMI and unstable angina is that in NSTEMI the severity of ischemia is sufficient to cause cardiac enzyme elevation.

Why is streptokinase not used in treating UA/ NSTEMI?

In patients with UA/NSTEMI, plaque stabilization to prevent progression of the disease is required. While fibrinolytics like Streptokinase benefit patients with STEMI, they may increase risk of bleeding complications for those with NSTEMI. This is also based on evidence - no benefit, more risk.

Summary:

1. STEMI - occlusive thrombus - ST elevation (and Q waves) - Cardiac Enzyme elevation - Fibrinolytics beneficial
2. NSTEMI - non-occlusive thrombus - NO ST/Q - Cardiac Enzyme elevation present - Fibrinolytics not beneficial
3. UA - non-occlusive thrombus - NO ST/Q - Cardiac Enzyme elevation absent - Fibrinolytics not beneficial