Acute Coronary Syndrome: STEMI vs NSTEMI, DAPT & Reperfusion Protocols

**1. Pathophysiological Spectrum & Triage** Acute Coronary Syndrome (ACS) results from acute disruption of an atherosclerotic plaque (erosion, rupture, or intraplaque hemorrhage) followed by platelet activation, aggregation, and thrombosis: 1. **ST-Elevation Myocardial Infarction (STEMI)**: Complete, occlusive red fibrin-rich thrombus causing transmural myocardial ischemia. Requires immediate emergency reperfusion. 2. **Non-ST-Elevation Myocardial Infarction (NSTEMI)**: Non-occlusive or intermittently occluding white platelet-rich thrombus causing subendocardial ischemia with myocyte necrosis (elevated cardiac troponins). 3. **Unstable Angina (UA)**: Subendocardial ischemia without detectable myocyte necrosis (normal troponins). **2. 🔬 Diagnostic ECG Criteria for STEMI** New ST-segment elevation at the J-point in at least two contiguous leads: * **Leads V2–V3**: - $\ge$ 2.5 mm in men <40 years. - $\ge$ 2.0 mm in men $\ge$ 40 years. - $\ge$ 1.5 mm in women (any age). * **All Other Contiguous Leads**: $\ge$ 1.0 mm (0.1 mV). * **New or Presumed New Left Bundle Branch Block (LBBB)** with clinical ischemia is treated as a STEMI equivalent. * **Sgarbossa Criteria (for STEMI with pre-existing LBBB or Ventricular Paced Rhythm)**: 1. Concordant ST elevation $\ge$ 1 mm in leads with positive QRS (5 pts). 2. Concordant ST depression $\ge$ 1 mm in leads V1, V2, or V3 (3 pts). 3. Excessively discordant ST elevation $\ge$ 5 mm or ST/S ratio $\le$ -0.25 (Modified Sgarbossa, 2 pts). Score $\ge$ 3 is 98% specific for acute myocardial infarction. **3. Reperfusion Strategy in STEMI: Primary PCI vs Fibrinolysis** * **Primary Percutaneous Coronary Intervention (PCI)**: - The undisputed gold standard reperfusion modality. - **FMC-to-Wire Crossing Time Target**: **$\le$ 90 minutes** at a PCI-capable center; or **$\le$ 120 minutes** from First Medical Contact (FMC) if transferred from a non-PCI center. * **Fibrinolytic Therapy**: - Indicated if anticipated time from FMC to PCI wire crossing exceeds **120 minutes**. - **Door-to-Needle Time Target**: **$\le$ 10 minutes** from diagnosis. - Agent of Choice: Fibrin-specific agents (**Tenecteplase [TNK-tPA]** administered as a single weight-based IV bolus, or Alteplase/Reteplase). - Post-Fibrinolysis Triage: Assess reperfusion at 60–90 minutes (>50% ST-segment resolution). If failed: immediate **Rescue PCI**; if successful: routine **Pharmaco-invasive Coronary Angiography within 2 to 24 hours**. **4. Dual Antiplatelet Therapy (DAPT) & Anticoagulation Protocols** * **Aspirin (MANDATORY)**: Non-enteric-coated loading dose of **162–325 mg** chewed immediately, followed by maintenance 75–100 mg daily indefinitely. * **P2Y12 Receptor Antagonists**: - *STEMI & NSTEMI undergoing PCI*: **Ticagrelor** (180 mg loading, then 90 mg BID) OR **Prasugrel** (60 mg loading, then 10 mg daily). Prasugrel is contraindicated in patients with a history of stroke or TIA. - *Fibrinolysis or High Bleeding Risk*: **Clopidogrel** (300 mg loading dose [or 75 mg if age >75], then 75 mg daily). * **Anticoagulation**: - Unfractionated Heparin (UFH, 70–100 units/kg bolus targeting ACT 250–300s during PCI), or Enoxaparin (1 mg/kg SC q12h), or Bivalirudin. * **Secondary Prevention (The 5 Core Drugs)**: DAPT (12 months) + High-Intensity Statin (Atorvastatin 80 mg or Rosuvastatin 40 mg) + Beta-Blocker (Metoprolol succinate) + ACE Inhibitor / ARB (for anterior infarct, EF <40%, or diabetes) + Aldosterone Antagonist (Eplerenone if EF <40% and symptomatic HF). **5. 📖 Standard Textbook Reference** * *Harrison's Principles of Internal Medicine*, 21st Ed., Ch. 275 & 276: ST-Segment Elevation and Non-ST-Segment Elevation Myocardial Infarction, pp. 2011–2038. * *2023 ESC Guidelines for the management of acute coronary syndromes*, European Heart Journal, 44(38):3720–3826.