What is the diagnosis and treatment flow for Non-ST-Elevation Myocardial Infarction (NSTEMI)?

NSTEMI Diagnosis and Treatment Flow

Initial Evaluation and Triage (Within 10 Minutes)

All patients with suspected NSTEMI must be immediately placed in an environment with continuous ECG monitoring and defibrillation capability, with a 12-lead ECG obtained and interpreted within 10 minutes of first medical contact. 1

Step 1: Immediate Assessment Components

• Chest pain characteristics: Assess quality, duration, persistence, and radiation of symptoms 1
• Vital signs: Document systolic blood pressure, heart rate, respiratory rate, and oxygen saturation 1
• Physical examination: Perform cardiopulmonary auscultation and assess for signs of heart failure (Killip classification) 1
• 12-lead ECG: Look specifically for ST-segment depression ≥0.5 mm, T-wave inversions ≥2 mm, transient ST changes, or non-diagnostic patterns 2, 3
• CAD probability assessment: Consider age, gender, cardiovascular risk factors, known CAD, prior MI, prior revascularization 1

Step 2: Working Diagnosis Assignment

Based on initial findings, assign patients to one of four categories 1:

1. STEMI → Transfer immediately for reperfusion therapy (excluded from NSTEMI pathway)
2. NSTE-ACS with ongoing ischemia or hemodynamic instability → Immediate invasive strategy
3. NSTE-ACS without ongoing ischemia or hemodynamic instability → Risk stratification pathway
4. NSTE-ACS unlikely → Consider alternative diagnoses (assign with extreme caution)

Diagnostic Confirmation

Biomarker Testing

NSTEMI is definitively diagnosed by elevated cardiac troponin (preferably high-sensitivity troponin T or I) above the 99th percentile upper reference limit with a rise and/or fall pattern, in the appropriate clinical context of acute myocardial ischemia. 2

• Initial blood draw on arrival: Troponin T or I, creatinine, hemoglobin, hematocrit, platelet count, blood glucose, INR (if on anticoagulation) 1
• Troponin results available within 60 minutes 1
• Repeat troponin at 1-3 hours if high-sensitivity assays are used 1
• Repeat troponin at 6-12 hours if standard assays are used or if high-sensitivity results are equivocal 1

Critical distinction: The sole difference between NSTEMI and unstable angina is the presence of detectable cardiac biomarkers of necrosis—both conditions share identical pathogenesis and clinical presentations but differ only in severity. 1, 2

Additional Diagnostic Considerations

• Lipid profile: Assess in early phase of admission if NSTE-ACS is confirmed 1
• Echocardiography: Consider immediately in patients with ongoing chest pain and inconclusive ECG to identify regional wall motion abnormalities and exclude alternative diagnoses (aortic dissection, pulmonary embolism, pericarditis) 1
• Serial ECGs: Obtain at 15-30 minute intervals during first hour if initial ECG is non-diagnostic but clinical suspicion remains high, especially if symptoms recur 3

Immediate Medical Management

Symptom Relief and Stabilization

• Oxygen therapy: Only if oxygen saturation <90% or respiratory distress (routine oxygen is not beneficial) 1, 4
• Nitroglycerin: 0.4 mg sublingual every 5 minutes × 3 doses, or IV infusion starting at 10 mcg/min, titrating to relieve symptoms and reduce BP by 10-20% (contraindicated if systolic BP <90 mmHg or suspected right ventricular infarction) 4
• Morphine: 2-4 mg IV with increments of 2-8 mg IV at 5-15 minute intervals, reserved for patients with persisting severe chest pain refractory to nitrates 1, 4

Antiplatelet Therapy

Dual antiplatelet therapy must be initiated immediately upon diagnosis. 4

• Aspirin: 162-325 mg loading dose (chewed for faster absorption), then 75-100 mg daily indefinitely 4
• P2Y12 inhibitor: 4
  • Ticagrelor or prasugrel preferred over clopidogrel for higher-risk patients not requiring urgent CABG
  • Prasugrel: 60 mg loading dose, then 10 mg daily (contraindicated in patients with prior TIA/stroke, age ≥75 years unless high-risk with diabetes/prior MI, weight <60 kg consider 5 mg maintenance dose) 5
  • Timing: In UA/NSTEMI patients, loading dose should be administered after coronary anatomy is established, not routinely before diagnostic angiography 5

Anticoagulation

• Unfractionated heparin: 60 U/kg IV bolus (maximum 4000 units), then 12 U/kg/hr infusion (maximum 1000 units/hr), adjusted to aPTT 1.5-2.5 times control 4
• Alternative anticoagulants: Choice depends on selected management strategy (invasive vs. conservative) and revascularization approach 1

Additional Pharmacotherapy

• Beta-blockers: Initiate orally within 24 hours unless contraindicated (heart failure signs, low-output state, heart rate <60, systolic BP <100 mmHg)—avoid IV administration in patients with risk factors for cardiogenic shock 4
• Avoid: NSAIDs (both COX-2 selective and nonselective increase mortality, reinfarction, and myocardial rupture risk), fibrinolytic therapy (no benefit and potential harm in NSTEMI), routine upstream GP IIb/IIIa inhibitors (reserve for high-risk patients undergoing PCI) 4

Risk Stratification and Invasive Strategy Timing

Immediate Invasive Strategy (<2 Hours)

Patients with any of the following high-risk features require immediate coronary angiography regardless of ECG or biomarker findings: 1, 4

• Refractory angina despite maximal medical therapy
• Hemodynamic instability or cardiogenic shock
• Life-threatening ventricular arrhythmias
• Mechanical complications of MI
• Recurrent angina with ST-segment depression ≥0.05 mV or new bundle branch block
• Ongoing myocardial ischemia with echocardiographic regional wall motion abnormality

Early Invasive Strategy (12-24 Hours)

High-risk patients without immediate indications should undergo early invasive strategy within 12-24 hours: 1, 4

• GRACE score >140
• Elevated troponin levels
• Dynamic ST-segment or T-wave changes
• LVEF <40%
• Diabetes mellitus
• Prior PCI or CABG

Selective Invasive Strategy (Within 72 Hours)

• Intermediate-risk patients without high-risk features may undergo selective invasive approach within 72 hours 1

Critical pitfall: Do not delay angiography for "cooling off" period—the ISAR-COOL trial demonstrated that prolonged medical stabilization (median 86 hours) before angiography increased death/MI compared to early approach (median 2.4 hours). 4

Monitoring During Initial Phase

• Continuous ECG monitoring with defibrillator capacity 4
• Defibrillator patches should be placed in case of ongoing ischemia until urgent revascularization is performed 1
• Serial troponin measurements at presentation, 3-6 hours, and if clinically indicated 4
• Repeat ECG if symptoms recur or worsen 4
• Vital signs assessed on regular basis 1

Common Diagnostic Pitfalls

• Normal ECG does not exclude ACS: 1-6% of patients with normal ECG will have MI, and at least 4% will have unstable angina 3
• Context is critical: Abnormal ECG and elevated troponins in isolation are insufficient—they must be interpreted within appropriate clinical context 2
• 5-10% of NSTEMI cases may have non-obstructive coronary atherosclerosis or no angiographic CAD, particularly in women 2
• Elderly, diabetics, and women are more likely to present with atypical symptoms and non-diagnostic ECGs 3
• Alternative causes of troponin elevation must be considered (Type 2 MI from supply-demand mismatch, myocarditis, pulmonary embolism, renal failure) 2