Acute Coronary Syndrome — STEMI and NSTEMI Management

Acute Coronary Syndrome (ACS) encompasses a spectrum of conditions caused by acute myocardial ischemia due to coronary artery occlusion or severe stenosis. ACS includes:

• ST-elevation myocardial infarction (STEMI): Complete coronary occlusion with transmural ischemia • Non-ST-elevation myocardial infarction (NSTEMI): Partial coronary occlusion with subendocardial ischemia and cardiac biomarker elevation • Unstable angina: Partial coronary occlusion without biomarker elevation

[KEY_CONCEPT] The fundamental pathophysiologic mechanism involves atherosclerotic plaque rupture or erosion leading to thrombosis and coronary occlusion. In STEMI, complete occlusion causes transmural infarction, while NSTEMI/unstable angina involve subtotal occlusion.

Epidemiology

• ACS affects >1 million Americans annually
• STEMI accounts for ~30% of ACS cases
• In-hospital mortality: STEMI 5-6%, NSTEMI 3-4%
• Peak incidence: 6-11 AM (circadian variation)

[HIGH_YIELD] The ACC/AHA Guidelines emphasize that time is myocardium — early recognition and intervention are critical for salvaging viable myocardium and improving outcomes.

Risk Factors

Modifiable: • Hypertension, diabetes mellitus, dyslipidemia • Smoking, obesity, sedentary lifestyle • Cocaine use (coronary vasospasm)

Non-modifiable: • Age >65 years, male sex, family history • Prior CAD, peripheral artery disease

Classic Presentation

Typical chest pain characteristics: • Quality: Crushing, squeezing, pressure-like • Location: Substernal, may radiate to left arm, jaw, neck • Duration: >20 minutes (vs. <20 minutes in stable angina) • Associated symptoms: Diaphoresis, nausea, dyspnea, lightheadedness

[CLINICAL_PEARL] Atypical presentations are common in women, elderly, and diabetics: may present with dyspnea, fatigue, nausea, or epigastric pain without chest pain.

Physical Examination Findings

• Often normal in uncomplicated cases • Signs of heart failure: S3 gallop, pulmonary rales, elevated JVP • Mechanical complications: New murmur (papillary muscle rupture, VSD) • Cardiogenic shock: Hypotension, cool extremities, altered mental status

Risk Stratification Tools

[HIGH_YIELD] TIMI Risk Score ≥3 in NSTEMI indicates high-risk patients who benefit from early invasive strategy within 24 hours.

Differential Diagnosis

• Aortic dissection: Tearing pain, pulse deficits • Pulmonary embolism: Dyspnea, pleuritic pain, risk factors • Pericarditis: Positional pain, friction rub • Pneumothorax: Sudden onset, dyspnea • GERD/esophageal spasm: Relationship to meals

ECG Criteria for STEMI

[KEY_CONCEPT] STEMI diagnostic criteria (≥2 contiguous leads):

ST elevation ≥1 mm in limb leads (I, II, III, aVF, aVL) ST elevation ≥2 mm in precordial leads (V1-V6) New or presumably new LBBB Posterior STEMI: ST depression V1-V3 with R/S ratio >1

Coronary Territory Localization

[CLINICAL_PEARL] Reciprocal changes (ST depression) in leads opposite to ST elevation support the diagnosis and help localize the culprit vessel.

Cardiac Biomarkers

Troponin I/T (preferred): • Peak: 12-24 hours • Duration: 7-14 days • High-sensitivity troponin: Detectable within 1-3 hours

Diagnostic Algorithm:

Chest Pain + Suspicious ECG ↓ Serial Troponins (0, 3-6h) ↓ Troponin (+) → STEMI or NSTEMI ↓ Troponin (-) → Unstable Angina vs. Non-cardiac

[HIGH_YIELD] Delta troponin: >20% rise or fall in serial measurements within 6 hours suggests acute MI even with initially normal values.

Additional Diagnostic Tests

• CXR: Rule out complications (pulmonary edema, pneumothorax) • Echocardiogram: Assess wall motion, EF, mechanical complications • Complete metabolic panel: Baseline renal function for contrast procedures • Lipid panel: Initiate statin therapy • PT/INR, aPTT: Baseline before anticoagulation

STEMI Management Algorithm

STEMI Diagnosis ↓ Symptom onset <12 hours? ├─ YES → Primary PCI available within 120 min? │ ├─ YES → PRIMARY PCI (preferred) │ └─ NO → FIBRINOLYSIS → Transfer for PCI └─ NO (>12 hours) → Medical management + PCI if ongoing symptoms

[HIGH_YIELD] Door-to-balloon time goal: ≤90 minutes for primary PCI. Door-to-needle time goal: ≤30 minutes for fibrinolysis.

NSTEMI/UA Management Strategy

Risk Stratification → Early Invasive vs. Conservative

Early Invasive Strategy Indications (<24 hours): • TIMI score ≥3 or GRACE score >140 • Hemodynamic instability • Recurrent ischemia despite medical therapy • Sustained VT/VF • New/worsening heart failure

Pharmacotherapy

Antiplatelet Therapy

[CLINICAL_PEARL] Ticagrelor is preferred over clopidogrel for ACS based on PLATO trial showing reduced cardiovascular mortality.

Anticoagulation

STEMI with PCI: • Unfractionated heparin: 60-70 U/kg IV bolus • Bivalirudin: Alternative if high bleeding risk

NSTEMI: • Enoxaparin: 1 mg/kg SQ BID (preferred if conservative management) • Fondaparinux: 2.5mg SQ daily (lowest bleeding risk)

Additional Acute Therapies

• Beta-blockers: Metoprolol 25mg BID (start within 24h if stable) • ACE inhibitors: Lisinopril 5-10mg daily (start within 24h if EF <40%) • Statins: High-intensity (atorvastatin 80mg or rosuvastatin 40mg)

Fibrinolytic Therapy (when PCI unavailable)

Contraindications: • Prior intracranial hemorrhage • Active bleeding or bleeding diathesis • Recent surgery (<3 weeks) • Uncontrolled hypertension (SBP >180 or DBP >110)

Mechanical Complications (2-7 days post-MI)

[HIGH_YIELD] Mechanical complications are rare but life-threatening, typically occurring 2-7 days post-MI:

Papillary Muscle Rupture

• Presentation: Acute severe MR, pulmonary edema • Murmur: Holosystolic at apex, radiating to axilla • Management: Emergent surgical repair

Ventricular Septal Defect (VSD)

• Presentation: New harsh holosystolic murmur, CHF • Location: Anterior MI → apical VSD; inferior MI → basal VSD • Diagnosis: Echo with color Doppler • Management: Surgical repair (delayed if possible for scar formation)

Free Wall Rupture

• Presentation: Sudden cardiovascular collapse, PEA arrest • Risk factors: First MI, elderly women, hypertension • Management: Emergent pericardiocentesis + surgical repair

Electrical Complications

[CLINICAL_PEARL] Inferior STEMI commonly causes transient bradycardia/AV block due to increased vagal tone. Anterior STEMI causing complete heart block indicates extensive damage and poor prognosis.

Cardiogenic Shock

Definition: CI <1.8 L/min/m² + SBP <90 mmHg despite adequate filling

Management approach:

Cardiogenic Shock ↓ Emergent revascularization (PCI/CABG) + Vasopressor support (norepinephrine preferred) + Mechanical circulatory support if refractory

Mechanical support options: • IABP: Contraindicated in severe AS, aortic dissection • Impella: Higher flow rates than IABP • ECMO: For refractory cases

Post-MI Monitoring

Hospital monitoring: • Continuous telemetry × 24-48 hours • Serial troponins until peak/plateau • Daily ECGs × 3 days • Echo within 24 hours to assess EF

Complications to watch: • Pericarditis: Friction rub, diffuse ST elevation • Dressler syndrome: Late pericarditis (weeks to months) • LV aneurysm: Persistent ST elevation, dyskinesis on echo

Secondary Prevention (Guideline-Directed Medical Therapy)

[KEY_CONCEPT] GDMT is the cornerstone of long-term ACS management and includes:

Antiplatelet Therapy

• Aspirin: 81mg daily indefinitely • P2Y12 inhibitor: 12 months minimum (clopidogrel, ticagrelor, or prasugrel) • Extended DAPT: Consider beyond 12 months if high ischemic/low bleeding risk

ACE Inhibitors/ARBs

Indications: All patients with EF ≤40%, diabetes, hypertension, or CKD • Target: Maximum tolerated dose • PARADIGM-HF: Sacubitril/valsartan superior to enalapril in HFrEF post-MI

Beta-Blockers

• All patients unless contraindicated (asthma, decompensated HF) • Target: Resting HR 50-60 bpm • Duration: Minimum 3 years, indefinite if EF ≤40%

Statins

High-intensity statin therapy for all patients: • Atorvastatin 80mg or rosuvastatin 40mg • Target: LDL <70 mg/dL (consider <55 mg/dL for very high risk)

[CLINICAL_PEARL] The ISCHEMIA trial showed that in stable CAD, optimal medical therapy is as effective as invasive strategy for preventing cardiovascular events, emphasizing the importance of GDMT.

Emerging Therapies

SGLT2 Inhibitors (DAPA-HF trial): • Dapagliflozin: Reduces HF hospitalization and CV death in HFrEF • Consider in diabetic patients with HFrEF post-MI

Anticoagulation (COMPASS trial): • Rivaroxaban 2.5mg BID + aspirin: Reduces MACE in stable CAD • Consider if high ischemic risk and low bleeding risk

Lifestyle Modifications

• Smoking cessation: Most important modifiable risk factor • Cardiac rehabilitation: Class I recommendation, improves outcomes • Diet: Mediterranean diet, limit sodium <2g/day • Exercise: 150 minutes moderate activity weekly • Weight management: BMI <25 kg/m²

Follow-up Schedule

Hospital discharge: • 1-2 weeks: Assess symptoms, medication tolerance • 1-3 months: Echo to reassess EF, lipid panel • 3-6 months: Stress testing if incomplete revascularization • Annually: Comprehensive risk factor assessment

Prognosis

STEMI outcomes (with primary PCI): • 30-day mortality: 5-6% • 1-year mortality: 7-8% • Major determinants: Age, EF, comorbidities, door-to-balloon time

NSTEMI outcomes: • 30-day mortality: 3-4% • Paradox: Higher long-term mortality than STEMI due to older age, more comorbidities

[HIGH_YIELD] Ejection fraction is the strongest predictor of long-term prognosis. EF <40% warrants ICD evaluation at 40 days post-MI if optimal medical therapy established.