Unstable angina (UA) and non–ST-elevation myocardial infarction (NSTEMI) are part of the acute coronary syndrome (ACS) spectrum. Both involve acute myocardial ischemia caused by reduced coronary blood flow—typically from plaque rupture and thrombosis.

The key difference:

• Unstable angina: ischemia WITHOUT myocardial cell death → normal cardiac biomarkers
• NSTEMI: ischemia WITH myocardial necrosis → elevated cardiac biomarkers

Because neither condition presents with persistent ST elevation, diagnosis relies heavily on clinical symptoms, ECG changes, and troponin trends.

Primary References:

• AHA/ACC NSTEMI Guideline (2014)
• ESC ACS Guidelines
• StatPearls – Unstable Angina

Classic ischemic symptoms include:

• Chest pressure, tightness, or burning
• Radiation to jaw, arm, or back
• Shortness of breath
• Nausea, diaphoresis, anxiety
• Occurs at rest, with minimal exertion, or is worsening compared to baseline

UA is defined by:

• Increasing frequency, duration, or severity of angina
• New-onset angina (<2 months)
• Angina at rest

NSTEMI typically presents similarly but includes measurable troponin elevation.

The ECG may be normal or show subtle ischemic changes. This makes serial ECGs essential.

• ST-segment depression (horizontal or downsloping)
• T-wave inversion (often symmetric and deep)
• Transient ST-segment elevation (<20 min)
• Pseudonormalization of T waves during pain
• Normal ECG does NOT exclude UA/NSTEMI

High-risk features:

• ST depression ≥ 1 mm
• T inversion ≥ 2 mm in V2–V6
• Widespread ST depression with STE in aVR (suggesting left main or triple-vessel disease)

Both UA and NSTEMI are usually caused by:

• Rupture or erosion of an atherosclerotic plaque
• Partial coronary artery occlusion
• Dynamic thrombus formation
• Distal microembolization
• Vasoconstriction
• Endothelial dysfunction

Whether an event becomes UA or NSTEMI depends on the extent of microvascular obstruction and duration of ischemia.

Common scoring systems:

• TIMI Score (Thrombolysis in Myocardial Infarction)
• GRACE Score (Global Registry of Acute Coronary Events)

High-risk criteria prompting early invasive strategy:

• Recurrent chest pain
• Dynamic ST/T wave changes
• Troponin elevation (NSTEMI)
• Hemodynamic instability
• Ventricular arrhythmias
• CHF symptoms / new MR
• Diabetes, renal failure, older age

Reference: Murphy SP, McCarthy CP, Cohen JA, Rehman S, Jones-O’Connor M, Olshan DS, Singh A, Vaduganathan M, Cui J, Januzzi JL Jr, Wasfy JH. Application of the GRACE, TIMI, and TARRACO Risk Scores in Type 2 Myocardial Infarction. J Am Coll Cardiol. 2025;75(3).

• Aspirin
• P2Y12 inhibitor (e.g., clopidogrel, ticagrelor)
• Anticoagulation (heparin, enoxaparin)
• Nitrates (for pain)
• Beta blockers (unless contraindicated)
• High-intensity statin
• Oxygen if needed (SpO2 < 90%)
• Treat hypertension or tachycardia contributing to ischemia

• Coronary angiography within 24 hours
• Possible PCI or CABG
• Echocardiography to assess ventricular function

NSTEMI patients with shock or ongoing ischemia may require immediate angiography.

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• UA and NSTEMI are caused by partial occlusion of a coronary artery.
• NSTEMI is distinguished by troponin elevation, while UA has normal biomarkers.
• ECG changes can be subtle or absent—serial ECGs are essential.
• High-risk patterns (e.g., widespread ST depression with STE in aVR) require urgent cardiology evaluation.
• Treatment focuses on antiplatelet therapy, anticoagulation, beta blockers, statins, and early invasive evaluation.
• UA and NSTEMI require rapid recognition to prevent progression to full-thickness MI.