What is an NSTEMI (Non-ST-Elevation Myocardial Infarction)?

Non-ST-Elevation Myocardial Infarction (NSTEMI)

NSTEMI is an acute coronary syndrome characterized by myocardial necrosis with elevated cardiac biomarkers (particularly troponin) in the absence of ST-segment elevation on ECG, resulting from a partial or subtotal occlusion of a coronary artery. 1

Definition and Pathophysiology

NSTEMI represents part of the acute coronary syndrome (ACS) spectrum that includes:

• Unstable Angina (UA): Ischemic chest discomfort without myocardial necrosis (normal biomarkers)
• NSTEMI: Ischemic chest discomfort with evidence of myocardial necrosis (elevated biomarkers)
• STEMI: ST-segment elevation with myocardial necrosis (elevated biomarkers)

The most common cause of NSTEMI is reduced myocardial perfusion from a non-occlusive thrombus that develops on a disrupted atherosclerotic plaque 2. Other mechanisms include:

• Microembolization of platelet aggregates and plaque components
• Dynamic obstruction (coronary spasm)
• Progressive mechanical obstruction
• Coronary artery inflammation
• Secondary causes (increased oxygen demand with fixed supply)
• Coronary artery dissection (rare)

Diagnostic Features

Feature	NSTEMI	Unstable Angina
Chest Pain	Ischemic-type discomfort, often >20 minutes	Ischemic-type discomfort
Cardiac Biomarkers	Elevated (particularly troponin)	Normal
Myocardial Necrosis	Present	Absent
ECG Changes	ST depression, T-wave inversion, or normal	May show ischemic changes or be normal
Coronary Occlusion	Partial/subtotal	Partial/transient

Diagnostic Criteria

1. Biomarkers: Detection of a rise and/or fall of cardiac troponin with at least one value above the 99th percentile upper reference limit 1
2. Clinical presentation: Symptoms of myocardial ischemia (chest pain, pressure, discomfort radiating to jaw/arms/back)
3. ECG findings: ST-segment depression, T-wave inversion, or non-specific changes (normal ECG does not exclude NSTEMI)

Risk Stratification

Risk assessment is crucial for determining management strategy. Common risk assessment tools include:

• TIMI risk score
• GRACE risk score
• PURSUIT risk score
• NCDR-ACTION registry 2

Management

Immediate Management

1. Antiplatelet therapy:

   • Aspirin (162-325 mg loading dose, then 81-325 mg daily)
   • P2Y12 inhibitor (ticagrelor or clopidogrel) for intermediate to high-risk patients 1

2. Anticoagulation:

   • Unfractionated heparin, enoxaparin, or bivalirudin 1

3. Anti-ischemic therapy:

   • Oxygen (if hypoxemic)
   • Nitrates for ongoing chest pain
   • Beta-blockers (if no contraindications)
   • Morphine for pain relief if needed 2

Invasive vs. Conservative Strategy

• Early invasive strategy (coronary angiography within 24 hours) for:

  • High-risk features (elevated troponin, dynamic ECG changes)
  • Recurrent symptoms
  • Heart failure or hemodynamic instability
  • Ventricular arrhythmias

• Conservative strategy (medical therapy with selective invasive approach) for:

  • Low-risk patients
  • Significant comorbidities
  • Patient preference

Secondary Prevention

• Dual antiplatelet therapy (DAPT)
• Statin therapy (high-intensity)
• Beta-blockers
• ACE inhibitors/ARBs (especially if reduced ejection fraction or diabetes)
• Lifestyle modifications (smoking cessation, diet, exercise) 1

Important Clinical Considerations

1. Atypical presentations are more common in:

   • Older adults
   • Women
   • Patients with diabetes
   • Chronic renal failure
   • Dementia 1

2. Type 1 vs. Type 2 NSTEMI:

   • Type 1: Primary coronary event (plaque rupture/erosion)
   • Type 2: Supply-demand mismatch (anemia, hypotension, tachycardia)
   • Treatment differs based on type (Type 2 focuses on underlying cause) 1

3. Prognosis:

   • Long-term outcomes are often worse in NSTEMI than STEMI due to higher burden of comorbidities, older age, and more extensive CAD 1
   • Approximately 30% of NSTEMI patients have a totally occluded coronary artery and may benefit from immediate invasive strategy 3

Pitfalls to Avoid

1. Delayed diagnosis: A normal ECG does not exclude NSTEMI; serial ECGs and troponin measurements are essential when clinical suspicion is high 1

2. Overlooking Type 2 NSTEMI: Always identify and treat underlying causes (anemia, hypoxemia, tachyarrhythmias)

3. Missing high-risk features: Patients with NSTEMI without chest pain often have worse outcomes 1

4. Inadequate secondary prevention: Long-term medication adherence and risk factor modification are critical to prevent recurrent events

By understanding the pathophysiology, diagnosis, and management of NSTEMI, clinicians can provide optimal care for patients with this common and potentially life-threatening condition.