Acute Coronary Syndrome — Diagnosis & Management
Acute Coronary Syndrome (ACS) is the term encompassing three clinical entities: STEMI (ST-elevation myocardial infarction), NSTEMI (non-ST-elevation MI), and unstable angina (UA). ACS is the leading cause of cardiovascular death in India, with an estimated 30 lakh ACS events annually. Time-to-reperfusion is the single most important determinant of survival in STEMI — every 30-minute delay reduces 1-year survival by 7.5%.
ACS occurs when an atherosclerotic coronary plaque ruptures or erodes, triggering platelet aggregation and thrombus formation. Partial occlusion causes NSTEMI/UA; complete occlusion causes STEMI. Risk factors include age, male sex, smoking, hypertension, diabetes, dyslipidaemia, family history, obesity, and sedentary lifestyle. Indians develop CAD 5-10 years earlier than Western populations and have higher mortality at younger ages.
The diagnosis rests on three pillars: (1) clinical features (typical chest pain > 20 minutes), (2) ECG changes (ST elevation, depression, T-wave inversion), and (3) cardiac biomarkers (troponin I or T). The 12-lead ECG is the single most important initial investigation — it should be obtained within 10 minutes of arrival and interpreted immediately.
Clinical features: Crushing/pressure chest pain, radiating to left arm/jaw/epigastrium, lasting > 20 minutes, not relieved by rest or nitrates. Associated symptoms: sweating, dyspnoea, nausea, vomiting, palpitations. Atypical presentations common in diabetics, women, elderly — may present with dyspnoea alone, syncope, or epigastric pain.
ECG findings:
- STEMI: ST elevation ≥ 1 mm in limb leads or ≥ 2 mm in precordial leads, in 2 contiguous leads. New LBBB is treated as STEMI equivalent. Localise: anterior = V1-V4, inferior = II/III/aVF, lateral = I/aVL/V5/V6, posterior = V1-V2 ST depression with tall R waves.
- NSTEMI: ST depression, T wave inversion, or non-specific changes. May also be normal.
- UA: Ischemic changes without biomarker elevation.
Troponin: Cardiac troponin I or T rises 3-4 hours after MI, peaks at 18-24 hours, remains elevated for 7-10 days. High-sensitivity troponin (hs-cTn) allows earlier detection — measure at presentation and 1 hour later (ESC 0/1-hour algorithm). Troponin is also elevated in myocarditis, PE, sepsis, renal failure — interpret in clinical context.
| Feature | STEMI | NSTEMI | UA |
|---|---|---|---|
| ECG | ST elevation or new LBBB | ST depression, T inversion, or normal | ST depression, T inversion, or normal |
| Troponin | Elevated | Elevated | Normal |
| Pathology | Complete coronary occlusion | Partial occlusion | Partial occlusion, no necrosis |
| Immediate management | Reperfusion (PCI or thrombolysis) | Antithrombotic + angiography within 24-72 hr | Antithrombotic + angiography within 24-72 hr |
| Mortality (in-hospital) | 5-10% | 3-5% | < 2% |
Immediate (MONA-B): Morphine 2-4 mg IV for pain; Oxygen if SpO2 < 90%; Nitrates (sublingual GTN 0.4 mg, repeat every 5 min x 3, then IV); Aspirin 300-325 mg chewed; Beta-blocker (Metoprolol 5 mg IV slow) if no contraindication (heart failure, bradycardia, AV block, severe asthma).
STEMI Reperfusion: Time targets:
- Primary PCI: Door-to-balloon time < 90 minutes. Preferred over thrombolysis if available within 120 minutes of first medical contact.
- Thrombolysis: Door-to-needle time < 30 minutes if PCI not available within 120 min. Use Tenecteplase (single bolus weight-adjusted), Streptokinase (1.5 MU over 60 min), or Reteplase. Tenecteplase preferred due to ease of administration and lower bleeding risk.
- Fibrinolysis window: Within 12 hours of symptom onset. Beyond 12 hours, reperfusion only if ongoing ischaemia or cardiogenic shock.
Antithrombotic therapy: Dual antiplatelet therapy (DAPT) — Aspirin 75 mg OD lifelong + P2Y12 inhibitor (Clopidogrel 75 mg OD, Prasugrel 10 mg OD, Ticagrelor 90 mg BD) for 12 months. Anticoagulation: Heparin (UFH or LMWH — Enoxaparin 1 mg/kg SC BD) or Bivalirudin during PCI.
High-intensity statin: Atorvastatin 80 mg or Rosuvastatin 40 mg started immediately, continued lifelong.
ACE inhibitor / ARB: Started within 24 hours if no contraindication. Particularly beneficial in anterior MI, LV dysfunction, heart failure, diabetes.
- Secondary prevention: Smoking cessation (critical), BP < 130/80, LDL < 70 mg/dL (or < 55 in very high risk), HbA1c < 7%, weight loss, regular exercise (150 min/week), cardiac rehabilitation
- Drugs (4 pillars): Aspirin 75 mg OD lifelong + P2Y12 inhibitor for 12 months + Beta-blocker lifelong (or at least 3 years if LV function preserved) + ACE inhibitor/ARB lifelong + High-intensity statin lifelong
- Echocardiography: Before discharge to assess LV function (ejection fraction). If EF < 35-40%, consider ICD for primary prevention of sudden cardiac death
- Cardiac rehabilitation: Structured exercise programme, psychosocial support, dietary counselling, smoking cessation support
- Return to work: Usually 4-6 weeks for low-intensity jobs, 3 months for heavy physical work. Driving: 4 weeks off. Sexual activity: resume after 4-6 weeks if can climb 2 flights without symptoms.
Reference: ESC ACS Guidelines 2023, ACC/AHA 2022 guidelines, and the Cardiological Society of India (CSI) 2024 update.
ACS management is one of the highest-stakes clinical scenarios — minutes determine outcomes. For UPSC CMS aspirants, ECG interpretation in STEMI, troponin kinetics, the MONA protocol, and the door-to-balloon/needle times are extremely high-yield clinical topics.