2.1 Acute Coronary Syndromes & Stable Angina

2.1 Acute Coronary Syndromes & Stable Angina

Ischaemic Heart Disease (IHD) remains the leading single cause of mortality worldwide. For the MRCPI Part I examination, a rigorous understanding of the spectrum of coronary artery disease—ranging from chronic stable angina to non-ST-elevation acute coronary syndromes (NSTE-ACS) and ST-elevation myocardial infarction (STEMI)—is mandatory. Candidates must master diagnostic algorithms, risk stratification tools, antiplatelet and antithrombotic regimens, invasive timelines, and guideline-directed secondary prevention strategies.

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Pathophysiology & Classification

Ischemic heart disease results from an imbalance between myocardial oxygen supply and demand. The primary underlying etiology in over 95% of cases is coronary artery atherosclerosis. Acute coronary syndromes arise when an atherosclerotic plaque undergoes sudden disruption:

• Plaque Rupture (60–70% of ACS): Fibrous cap disruption exposing a lipid-rich core to circulating blood, precipitating intense platelet activation, aggregation, and thrombosis.
• Plaque Erosion (25–30% of ACS): Endothelial denudation over a hyalinized stroma, frequently seen in female patients and smokers, generating a platelet-rich thrombus.
• Myocardial Infarction Classification:
  • Type 1 MI: Spontaneous MI related to acute atherothrombotic plaque disruption.
  • Type 2 MI: Myocardial injury secondary to oxygen supply-demand mismatch without acute plaque disruption (e.g., severe anemia, tachyarrhythmias, septic shock, coronary vasospasm).
  • Type 3 MI: Cardiac death suggestive of myocardial ischemia prior to troponin sampling.
  • Type 4a/4b MI: Peri-procedural PCI-related MI / Stent thrombosis.
  • Type 5 MI: CABG-related myocardial infarction.

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Clinical Presentation & Diagnostic Workup

Symptoms

Typical anginal chest pain is described as retrosternal pressure, heaviness, or squeezing radiating to the left arm, neck, or jaw. Stable angina is predictably precipitated by exertion or emotional stress and relieved within 5 minutes by rest or sublingual glyceryl trinitrate (GTN). ACS presents with rest angina lasting >20 minutes, new-onset severe angina (Canadian Cardiovascular Society Class III/IV), or crescendo angina.

Exam Pearl: Atypical presentations (dyspnea, diaphoresis, epigastric distress, or unexplained fatigue) are disproportionately common in elderly patients, females, and individuals with long-standing diabetes mellitus secondary to autonomic neuropathy.

High-Sensitivity Cardiac Troponin (hs-cTn)

High-sensitivity assays measure cardiac troponin T or I with high analytical precision. The European Society of Cardiology (ESC) recommends rapid rule-out and rule-in protocols based on 0h/1h or 0h/2h blood sampling.

• Rule-out Criteria: Baseline hs-cTn below the very low threshold OR low baseline value without a significant 1-hour or 2-hour delta.
• Rule-in Criteria: Baseline hs-cTn above the upper reference limit (99th percentile) OR a significant 1-hour/2-hour absolute delta change (e.g., delta >5 ng/L for hs-cTnT).

ECG Localization in Acute Myocardial Infarction

Recognizing anatomical territory and culprit vessel involvement from the 12-lead ECG is a core MRCPI testing point:

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ST-Elevation Myocardial Infarction (STEMI)

STEMI is defined by persistent chest pain accompanied by ST-segment elevation measured at the J-point in at least two contiguous leads:

• Leads V2–V3: >=2.5 mm in men <40 years, >=2.0 mm in men >=40 years, or >=1.5 mm in women.
• Other Leads: >=1.0 mm ST elevation.
• New Left Bundle Branch Block (LBBB) or Right Bundle Branch Block (RBBB) with concordant ST elevation (Sgarbossa criteria) must be managed as STEMI equivalent.

Revascularization Timelines

Primary Percutaneous Coronary Intervention (pPCI) is the gold-standard reperfusion modality.

• First Medical Contact (FMC) to ECG: <=10 minutes.
• FMC to Wire Cross (at pPCI Center): <=90 minutes.
• FMC to Wire Cross (Transfer from Non-pPCI Center): <=120 minutes.
• Fibrinolysis Threshold: If pPCI cannot be delivered within 120 minutes of STEMI diagnosis, intravenous fibrinolysis (Weight-adjusted Tenecteplase) must be administered within 10 minutes of diagnosis, followed immediately by transfer to a pPCI-capable facility for routine angiography (rescue PCI if failure of lysis at 60–90 minutes defined by <50% ST resolution).

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Risk Stratification in NSTE-ACS

Unlike STEMI, patients with NSTE-ACS undergo emergency risk stratification to determine the timing of invasive coronary angiography:

• TIMI Risk Score (0–7 points): 1 point each for Age >=65, >=3 CAD risk factors, Known CAD (stenosis >=50%), Aspirin use in last 7 days, Severe angina (>=2 episodes in 24h), ST-segment deviation >=0.5 mm, Elevated cardiac markers. High risk (score >=3) indicates benefit from early invasive management.
• GRACE Risk Score: Incorporates age, heart rate, systolic BP, serum creatinine, Killip class, cardiac arrest at presentation, ST-segment deviation, and elevated troponin.

ESC Triage Categories for Invasive Angiography:

1. Immediate Invasive (<2 hours): Hemodynamic instability, cardiogenic shock, recurrent/refractory angina despite medical therapy, life-threatening ventricular arrhythmias, or acute heart failure.
2. Early Invasive (<24 hours): Confirmed NSTEMI (troponin elevation), dynamic ST-T segment changes, or GRACE score >140.
3. Selective Invasive: Low-risk patients without recurrent symptoms; non-invasive testing (CT coronary angiography or stress imaging) recommended prior to discharge.

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Pharmacotherapy & Secondary Prevention

Acute Medical Management

• Antiplatelet Therapy: Aspirin 300 mg loading dose, followed by 75 mg once daily indefinitely. Combined with a potent P2Y12 inhibitor: Prasugrel (60 mg load, 10 mg daily; preferred in PCI) or Ticagrelor (180 mg load, 90 mg twice daily). Clopidogrel (600 mg load, 75 mg daily) is reserved for cases where potent P2Y12 inhibitors are contraindicated or high bleeding risk is present.
• Parenteral Anticoagulation: Unfractionated heparin (UFH) bolus (70–100 IU/kg) during PCI; Enoxaparin (1 mg/kg bd) or Fondaparinux (2.5 mg subcutaneous daily) for conservative NSTE-ACS management.
• Anti-ischemic Agents: Sublingual or IV GTN for ongoing chest pain (contraindicated if RV infarction or recent phosphodiesterase-5 inhibitor use). Oral Beta-blockers (Bisoprolol 2.5–10 mg daily) initiated within 24 hours if hemodynamically stable.

Long-Term Secondary Prevention Guidelines

• High-Intensity Statin: Atorvastatin 80 mg daily targeting LDL-C <1.4 mmol/L (<55 mg/dL) and a >=50% reduction from baseline. If target not achieved, add Ezetimibe 10 mg; if still above target, add PCSK9 inhibitor (Evolocumab or Alirocumab).
• ACE Inhibitors / ARBs: Ramipril or Perindopril indicated for LVEF <=40%, hypertension, diabetes, or CKD.
• SGLT2 Inhibitors: Empagliflozin 10 mg or Dapagliflozin 10 mg recommended for patients with heart failure or type 2 diabetes post-MI.
• Dual Antiplatelet Duration: Standard duration is 12 months. In patients with High Bleeding Risk (HBR, PRECISE-DAPT >=25), monotherapy (Aspirin or P2Y12 inhibitor alone) can be considered after 1 to 3 months.