Acute Coronary Syndromes

Umbrella term for any acute presentation of coronary artery disease - covers unstable angina, NSTEMI and STEMI

Aetiology

  • Usually the result of a thrombus from an atherosclerotic plaque blocking a coronary artery

Pathophysiology

  • The mechanism that is common to all ACSs is rupture or erosion of the fibrous cap of a coronary artery plaque
  • This leads to platelet aggregation and adhesion, localized thrombosis, vasoconstriction and distal thrombus embolization
  • Thrombus formation and the vasoconstriction produced by platelet release of serotonin and thromboxane A2 result in myocardial ischaemia due to reduction of coronary blood flow
  • Unstable angina: subtotal occlusion, supply led ischaemia without infarction, high (50%) risk of MI in subsequent 30 days
  • NSTEMI: subtotal occlusion
  • STEMI: complete occlusion

Types of MI

  • Type 1: Traditional MI due to an acute coronary event
  • Type 2: Ischaemia secondary to increased demand or reduced supply of oxygen (e.g. secondary to severe anaemia, tachycardia or hypotension)
  • Type 3: Sudden cardiac death or cardiac arrest suggestive of an ischaemic event
  • Type 4: MI associated with PCI / coronary stunting / CABG

Clinical presentation

Symptoms

  • Severe crushing central chest pain at rest
    • Pain radiates to jaw and arms
    • Similar to angina but more prolonged and not relieved by GTN
    • Associated with sweating, nausea, and often vomiting
    • 30 mins or longer
  • Atypical presentation - silent MI
    • Particularly important in women, the elderly and patients with diabetes
    • Milder symptoms (without chest pain) especially in younger women
    • Shortness of breath, fatigue, body aches, overall feeling of illness
    • Unusual feeling/mild discomfort in the back, chest, arm, neck or jaw (without chest pain)
    • Heartburn, nausea/vomiting, abdominal pain
    • Symptoms may occur up to a month before MI: fatigue, sleep disturbance, SOB, anxiety, indigestion, palpitations

Signs

  • Xanthelasma - sign of atherosclerosis
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Investigations

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ECG changes in ACS

  • STEMI:
    • ST segment elevation in leads consistent with an area of ischaemia
    • New Left Bundle Branch Block also diagnoses a 'STEMI'
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  • NSTEMI:
    • May be normal
    • ST segment depression in a region
    • Deep T Wave Inversion
    • Pathological Q Waves (suggesting a deep infarct - a late sign)
  • Unstable angina:
    • May be normal
    • May include non-specfic changes, abnormal T waves or ST depression

Cardiac Biomarkers

  • Troponin I/T
    • Both good to detech myosit damage
    • Troponin I is preferred in renal dysfunction → Troponin T is also elevated during renal dysfunction

Management

Initial management

  • Morphine IV if not relieved by nitroglycerin → 1-5 mg IV, can be repeated every 10-30 min
  • Oxygen if SpO2 < 90%, start at 4 L/min
  • Nitrates if patient hypertensive or in acute LVF → ISDN 5 mg/NTG 0.4-0.5 mg can be repeated 3x/5 min
    • Contraindication : Hypotension, RV infarct, History of Arrythmias, Sildenafil in 24 hours/Tadalafil in 48 hours
  • Aspirin loading dose 160-320 mg (80 mg/tab)
  • Clopidogrel 300 mg (75 mg/tab) / Ticagrelor 180 mg (90 mg/tab)

Definitive management

REVASCULARIZATION
  • Primary PCI → Baloon Catether or Fibrinolysis
    • Fibrinolysis Absolute Contraindications
      • Intracranial Hemorrhage
      • Ischemic stroke < 3 month with > 3 hours duration
      • Intracranial Tumor
      • Cerebral Vascular Anomaly
      • Aortic Dissection suspect
      • Active internal bleeding or coagulation disorders
      • Closed head injury or face injury last 3 months
  • Onset < 12 hours
  • STEMI or NSTEMI with high-risk patient (hemodynamic instability, signs of heart failure)
STEMI
  • PCI (if available within 2 hours of pain onset)
  • Thrombolysis (if PCI not available within 2 hours)
NSTEMI
  • Risk stratification based on ECG changes, troponin and past medical history
  • All receive continuing aspirin and fondaparinux (anticoagulant)
  • Consider IV nitrate
  • High risk - consider PCI, may give tirofiban (antiplatelet)
  • Low risk patients may be discharged after repeat negative troponin and followed up

Secondary prevention

Lifestyle modifications
  • Cardiac rehab program - dietary modification, increase exercise, smoking cessation
  • Good control of BP, cholesterol and diabetes
Medications - DABS
  • Dual antiplatelet – aspirin for life, 6-12 months of a P2Y12 inhibitor (e.g. ticagrelor)
  • ACEi
  • β-blocker should be started within 24 hours of confirmed ACS
  • Statin
  • Others:
    • GTN for angina symptoms
    • Aldosterone antagonists for patients with symptoms and/or signs of heart failure and LV systolic dysfunction

Complications

  • Arrhythmias
    • Brachycardia and heart block
    • Tachyarrhythmias - ventricular fibrillation
  • Heart failure
  • Structural damage
    • VSD
    • Mitral regurgitation
    • Ventricular wall rupture (→ cardiac tamponade) - 5-10 days post MI
    • LV mural thrombus +/- systemic emboli
  • Pericarditis - Dressler’s syndrome
    • Usually occurs around 2-3 weeks after an MI
    • Localised immune response causes pericarditis