Acute Coronary Syndromes (ACS)

Understanding Acute Coronary Syndromes (ACS)

• ACS is a broad term encompassing three primary conditions.
• Unstable Angina (UA) involves chest pain at rest or with minimal exertion due to partial coronary artery occlusion without myocardial necrosis.
• NSTEMI (Non-ST Elevation Myocardial Infarction) involves partial coronary artery occlusion causing myocardial injury, but without ST-segment elevation on ECG.
• STEMI (ST-Elevation Myocardial Infarction) involves complete coronary artery occlusion leading to myocardial necrosis and ST-segment elevation on ECG.

Pathophysiology of ACS

• Coronary Artery Disease (CAD) is the primary cause of ACS.
• Atherosclerotic plaque rupture causes platelet aggregation and thrombus formation, leading to partial or complete coronary artery occlusion.
• Ischemia (lack of oxygen to the heart muscle) occurs, leading to myocardial injury or infarction.
• The degree of occlusion determines if the patient has UA, NSTEMI, or STEMI.

Clinical Assessment of ACS - Signs & Symptoms

• Chest pain (angina) is often described as pressure, squeezing, or burning.
• Pain may radiate to the jaw, left arm, back, or epigastric region.
• Dyspnea is experienced due to decreased cardiac output.
• Diaphoresis presents as cold, clammy sweating.
• Nausea and vomiting are more common in inferior MI.
• Syncope or dizziness occur due to hypotension or reduced cardiac output.

Atypical Presentations

• Atypical symptoms are more common in women, diabetics, and older adults.
• Atypical presentations may include epigastric pain, fatigue, nausea, or dyspnea instead of classic chest pain.

Prehospital Assessment

• A 12-Lead ECG identifies STEMI (ST-elevation) and helps differentiate from NSTEMI.
• Vital signs to monitor include BP, heart rate, respiratory rate, and oxygen saturation.
• The OPQRST mnemonic helps characterize chest pain.
• Focused history should inquire about risk factors such as hypertension, diabetes, smoking, hyperlipidemia, and family history.
• Cardiac biomarkers like troponins and CK-MB are only available in hospital settings.

Pharmacologic Management of ACS

• Prehospital providers use medications to relieve ischemia, reduce myocardial workload, and prevent further clot formation.

Oxygen (O₂)

• Administer only if SpO₂ is < 94% or signs of respiratory distress are present.
• Rationale: Prevents hypoxia; excessive O₂ can cause vasoconstriction and worsen outcomes.
• Dosage: 2-4 L/min via nasal cannula, with higher flow if severe hypoxia is present.

Aspirin (ASA)

• Administer to every ACS patient unless contraindicated.
• Dosage: 160-325 mg chewed for rapid absorption.
• Mechanism: Inhibits platelet aggregation, reducing clot formation.
• Contraindications: Active GI bleeding, allergy to aspirin, recent hemorrhagic stroke.

Nitroglycerin (NTG)

• Used for chest pain due to suspected ischemia.
• Dosage: 0.3-0.6 mg sublingually every 5 minutes, up to 3 doses.
• Mechanism: Vasodilator that reduces myocardial oxygen demand.
• Contraindications: Systolic BP < 90 mmHg, use of PDE-5 inhibitors (Viagra, Cialis) within 24-48 hours, right ventricular infarction.

Morphine Sulfate

• Use for persistent severe chest pain despite NTG.
• Dosage: 2-4 mg IV, repeated as needed.
• Mechanism: Opioid analgesic that reduces pain and myocardial oxygen demand.
• Contraindications: Hypotension, respiratory depression.

Anticoagulants (Hospital Use)

• Heparin (Unfractionated or LMWH) prevents thrombus propagation.
• Fibrinolytics (tPA, Tenecteplase) are used in STEMI when PCI is unavailable within 90 minutes.
• P2Y12 Inhibitors (Clopidogrel, Ticagrelor) are used in STEMI/NSTEMI before PCI.

STEMI Identification & Prehospital Protocols

• STEMI Recognition on ECG: ST-segment elevation ≥ 1 mm in two contiguous leads, new left bundle branch block (LBBB) with ACS symptoms.
• Prehospital STEMI Activation: Rapid 12-lead ECG acquisition and transmission to hospital; Immediate transport to PCI-capable facility; Consider fibrinolytics if transport delay > 90 minutes.

Summary Table: ACS Medication Guide

Key Points

• ACS is a time-sensitive emergency requiring early recognition and treatment.
• Prehospital treatment focuses on reducing myocardial oxygen demand, improving perfusion, and preparing for definitive reperfusion therapy.
• STEMI requires rapid PCI or fibrinolytic therapy for optimal outcomes. Aspirin and nitroglycerin are first-line medications unless contraindicated.