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Acute Coronary Syndromes: NSTE-ACS (Unstable Angina and NSTEMI)

BASICS

Description

  • Unstable angina (UA) and non-ST-segment elevation myocardial infarction (NSTEMI) are acute coronary syndromes without ST-segment elevation (NSTE-ACS).
  • Differentiated by myocardial necrosis: no troponin elevation in UA, but elevated troponin in NSTEMI.
  • Early differentiation challenging; troponin elevation may be delayed.
  • Initial management is similar for both.
  • Diagnosis requires combination of history, ECG, and biomarkers.

Epidemiology

  • Estimated annual incidence: 605,000 new MIs, 200,000 recurrent MIs.
  • US average age at first MI: 65.6 years (males), 72.0 years (females).
  • Male:female ratio approximately 3:2.

ETIOLOGY AND PATHOPHYSIOLOGY

  • Sudden decrease in myocardial blood flow β†’ imbalance of oxygen supply/demand.
  • Caused by acute plaque rupture or erosion β†’ partially occlusive thrombus (vs total occlusion in STEMI).
  • Other mechanisms:
  • Prinzmetal angina/coronary vasospasm (tobacco, hyperventilation, Mg deficiency, cocaine, methamphetamines).
  • Type 2 NSTEMI: supply-demand mismatch (PE, sepsis, shock, arrhythmias).
  • Coronary microvascular/endothelial dysfunction without epicardial obstruction.
  • Rare: aneurysm, spontaneous dissection, thromboembolism.
  • Genetics: MMP-3 5A/6A and ACE I/D polymorphisms increase STEMI risk but not NSTEMI/UA.

RISK FACTORS

  • Classic: age, male sex, prior MI, HTN, tobacco, diabetes, dyslipidemia, family history premature CAD.
  • Emerging: sedentary lifestyle, obesity/metabolic syndrome, inflammation (psoriasis, RA), smoking, psychosocial factors, CKD, OSA, pollutants.

GENERAL PREVENTION

  • Smoking cessation.
  • Maintain normal BMI.
  • Stress management.
  • Regular exercise.
  • Glycemic and BP control.
  • Risk-based statins.
  • Aspirin in documented CAD.

DIAGNOSIS

History

  • Chest heaviness/tightness β‰₯10 minutes; retrosternal, may radiate to neck, jaw, back, arms, epigastrium.
  • Descriptions: pressure, tightness, heaviness, squeezing, fullness.
  • Associated symptoms: palpitations, dyspnea, nausea/vomiting, diaphoresis, light-headedness, syncope.
  • Atypical presentations (esp. >75 years, women, diabetes, renal insufficiency): stabbing, pleuritic pain, epigastric discomfort, indigestion, isolated dyspnea, "anginal equivalents."

Physical Exam

  • Vital signs: tachy/bradycardia, HTN/hypotension, widened pulse pressure, tachypnea, fever.
  • Signs: poor dental hygiene, dysrhythmias, JVD, new murmurs (S3/S4), rub, gallop, diminished pulses, carotid bruits.
  • Respiratory: crackles, increased work of breathing.
  • Pain reproducible with palpation unlikely cardiac.
  • Cool skin, pallor, diaphoresis, xanthomas/xanthelasma.

Differential Diagnosis

  • Cardiac: aortic dissection, myocarditis, pericarditis, tamponade, HF, hypertensive emergency, takotsubo, dysrhythmias, mitral valve disease.
  • Pulmonary: PE, pneumothorax, pneumonia, pleuritis, bronchitis.
  • Psychiatric: panic, anxiety.
  • Musculoskeletal: costochondritis, rib fracture.
  • GI: GERD, esophageal spasm/esophagitis, rupture, hiatal hernia, PUD, biliary/pancreatic pain.

DIAGNOSTIC TESTS & INTERPRETATION

Initial Tests

  • 12-lead ECG within 10 minutes; applicable for UA and NSTEMI.
  • CBC, BMP (electrolytes), troponin biomarkers (negative in UA).
  • Chest X-ray, CT with contrast if indicated.
  • Transthoracic echocardiography recommended.

Follow-up Tests

  • Fasting lipid profile, aPTT, TSH, HbA1c, urine drug screen (selected patients).

Diagnostic Procedures

  • Low/intermediate-risk with symptom resolution and negative tests: consider exercise treadmill, stress echo, myocardial perfusion scan, or coronary CT angiography.

Test Interpretation

  • ECG in NSTE-ACS:
  • New ST depression β‰₯0.5 mm or T-wave inversions β‰₯1 mm in β‰₯2 contiguous leads.
  • ST depression/tall R wave in V1/V2 may indicate posterior STEMI β†’ add posterior leads (V7–V9).
  • Serial ECGs every 15–30 min if initial ECG nondiagnostic.
  • Troponin rises 3–6 hrs post symptoms; can be delayed to 8–12 hrs.
  • NSTEMI diagnosed with troponin >52 ng/L or β‰₯10 ng/L rise in 2 hrs.
  • Negative troponin at 6 hrs effectively rules out MI.
  • CK-MB useful post-PCI; rises faster, normalizes faster than troponin.
  • Repeat biomarkers at 8–12 hrs to assess peak.

TREATMENT

General Measures

  • Initial ABCDs; assess clinical stability.
  • Risk stratify using TIMI or GRACE scores for invasive vs ischemia-guided therapy.
  • Urgent invasive for very high risk (hemodynamic instability, cardiogenic shock, refractory chest pain, life-threatening arrhythmias).
  • Continuous ECG monitoring; maintain O2 >90%; tight BP control; discontinue NSAIDs.
  • Smoking cessation and electrolyte correction (K ~4 mEq/L, Mg ~2 mg/dL).

Medication

First Line

  • Dual antiplatelet therapy (DAPT)
  • Aspirin: 162–325 mg chewed initially; maintenance 75–100 mg daily indefinitely.
  • P2Y12 inhibitors:
    • Ticagrelor 180 mg loading β†’ 90 mg BID (avoid in 2nd/3rd degree AV block; can cause dyspnea; contraindicated in severe liver disease).
    • Prasugrel 60 mg loading β†’ 10 mg daily (post-PCI stents; contraindicated age β‰₯75, prior CVA/TIA).
    • Clopidogrel 300–600 mg loading β†’ 75 mg daily (caution in thrombocytopenia, CKD).
  • Nitroglycerin sublingual 0.4 mg q5 min Γ—3 doses; IV nitro as needed.
  • Morphine sulfate 2–4 mg, titrated q5-15 min for persistent pain.
  • Oral Ξ²-blocker within 24 hrs if no HF, shock, or contraindications.
  • High-intensity statins: atorvastatin 80 mg or rosuvastatin 20–40 mg daily.
  • ACE inhibitors if LVEF <40%, diabetes, or HTN.
  • Aldosterone antagonists if LVEF ≀40%, DM, or HF and on ACEi/ARB + Ξ²-blocker, with no renal dysfunction/hyperkalemia.
  • Anticoagulation: unfractionated heparin, enoxaparin, bivalirudin, fondaparinux. Stop after PCI or continue minimum 48 hrs if conservative.

Second Line

  • Non-dihydropyridine CCBs (verapamil, diltiazem) if Ξ²-blockers contraindicated with normal LVEF.
  • Long-acting CCBs for coronary vasospasm.
  • Avoid in heart block.

ISSUES FOR REFERRAL

  • Cardiology consultation.
  • Referral for cardiac rehabilitation pre-discharge to reduce morbidity and mortality.

SURGERY/OTHER PROCEDURES

  • Exercise stress testing weeks post-discharge as part of rehab for activity counseling.

ONGOING CARE

Follow-Up

  • Low-risk patients with normal serial ECG/troponin: treadmill ECG, stress myocardial perfusion, or stress echo within 72 hrs.
  • Repeat LVEF 1–3 months post discharge if initial LVEF <40%.

Diet

  • Mediterranean diet reduces CVD mortality.
  • DASH diet reduces CAD risk.
  • Sodium reduction not proven to reduce CVD risk.

Patient Education

  • Resume exercise and sexual activity within 2 weeks if asymptomatic and after outpatient reevaluation.
  • Adults: β‰₯150 minutes moderate aerobic activity per week reduces CVD risk.

PROGNOSIS

  • 50% with UA progress to MI within 30 days untreated.
  • 9–19% mortality within 6 months post-ACS diagnosis; half occur within first 30 days.

REFERENCES

  1. Amsterdam EA, Wenger NK, Brindis RG, et al. 2014 AHA/ACC guidelines for management of NSTE-ACS. J Am Coll Cardiol. 2014;64(24):e139-e228.

Codes

Code Description
I24.9 Acute ischemic heart disease, unspecified
I20.0 Unstable angina
I21.4 Non-ST elevation (NSTEMI) MI

Clinical Pearls

  • NSTEMI diagnosis: symptoms + elevated troponin without STEMI ECG changes.
  • UA mimics NSTEMI but no troponin elevation.
  • Initial management of UA and NSTEMI is identical. ```