Why Fibrinolysis is Contraindicated in NSTEMI
Fibrinolytic therapy is absolutely contraindicated in NSTEMI because these patients have partial or intermittent coronary artery occlusion rather than complete occlusion, and fibrinolysis has been shown to be harmful rather than beneficial in this population. 1
Pathophysiologic Rationale
The fundamental difference between STEMI and NSTEMI explains why fibrinolysis works in one but not the other:
STEMI involves complete coronary artery occlusion with an organized thrombus that responds to fibrinolytic agents, creating the opportunity for rapid reperfusion and myocardial salvage 2
NSTEMI involves partial or intermittent occlusion with dynamic thrombus formation and degradation, resulting in waxing and waning symptoms rather than persistent complete occlusion 1
The partially occluding thrombus in NSTEMI is often platelet-rich and less responsive to fibrinolytic therapy, while the risk of destabilizing the plaque and causing complete occlusion or distal embolization remains 1
Evidence of Harm
The evidence demonstrates that fibrinolysis may actually be harmful in NSTEMI patients: 1
Fibrinolytic therapy activates platelets and promotes thrombin activity, which can paradoxically worsen the thrombotic process in the setting of an unstable, partially occluding plaque 3
The heterogeneous nature of NSTEMI presentations means that some patients have minimal thrombus burden or even non-atherosclerotic causes (Type 2 MI), making fibrinolysis both ineffective and unnecessarily risky 4
Clinical guidelines explicitly state that fibrinolysis is contraindicated in this heterogeneous group of patients and may be harmful 1
Appropriate Management Strategy
Instead of fibrinolysis, NSTEMI management focuses on:
Risk stratification using validated scores (GRACE, TIMI) to identify high-risk patients who benefit from early invasive strategy 4
Antiplatelet therapy (aspirin plus P2Y12 inhibitor) and anticoagulation to stabilize the partially occluding thrombus without the bleeding risks of fibrinolysis 1, 4
Early invasive coronary angiography within 24-48 hours for high-risk patients with positive biomarkers or unstable features, which reduces mortality from 6.5% to 4.9% 2
Medical management with anti-ischemic therapy for lower-risk patients or those with contraindications to invasive procedures 4
Critical Distinction on ECG
Fibrinolytic therapy should not be administered to patients with ST depression except when a true posterior (inferobasal) MI is suspected or when associated with ST elevation in lead aVR 1
This guideline reinforces that the ECG pattern matters: ST depression typically indicates NSTEMI or unstable angina, where fibrinolysis is contraindicated, while ST elevation indicates complete occlusion requiring immediate reperfusion 1
Common Pitfall to Avoid
The most dangerous error is administering fibrinolysis based solely on elevated troponins and chest pain without carefully examining the ECG for ST elevation. NSTEMI patients may have ST-segment depressions (31%), T-wave inversions (12%), both (16%), or neither (41%), but none of these patterns warrant fibrinolytic therapy 2. Only persistent ST elevation or new left bundle branch block in the appropriate clinical context justifies fibrinolysis 1.