Heart attack medication, clinical diagnosis
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Heart Attack (Myocardial Infarction): Clinical Diagnosis & Medications
Overview
A heart attack (myocardial infarction, MI) results from sustained ischemia causing irreversible myocardial cell death, most commonly due to acute plaque rupture with superimposed thrombosis in a coronary artery. The clinical spectrum is divided into:
- STEMI (ST-Elevation MI) - complete occlusion, immediate reperfusion required
- NSTEMI (Non-ST-Elevation MI) - partial occlusion, elevated troponin without ST elevation
- Unstable Angina (UA) - partial occlusion, no troponin rise
Together these are called Acute Coronary Syndromes (ACS).
Part 1: Clinical Diagnosis
Symptoms
| Symptom | Notes |
|---|---|
| Chest pain/pressure | Often described as "crushing," "heavy," or "squeezing" - may radiate to jaw, left arm, or back |
| Diaphoresis | Cold, clammy sweat - an autonomic response |
| Dyspnea | Especially in anterior MI or LV dysfunction |
| Nausea/vomiting | Common, especially in inferior MI (vagal response) |
| Syncope/presyncope | May indicate serious arrhythmia or cardiogenic shock |
Atypical presentations are common in women, diabetics, and the elderly - they may present with fatigue, epigastric discomfort, or absence of chest pain entirely.
ECG Findings
STEMI criteria:
- ST elevation ≥1 mm in ≥2 contiguous limb leads
- ST elevation ≥2 mm in ≥2 contiguous precordial leads (V1-V6)
- New left bundle branch block (LBBB) is treated as STEMI equivalent
- Posterior MI: ST depression in V1-V3 + tall R waves (mirror image)
Localization by ECG:
| Territory | Leads Affected | Artery |
|---|---|---|
| Anterior | V1-V4 | LAD |
| Lateral | I, aVL, V5-V6 | LCx |
| Inferior | II, III, aVF | RCA |
| Posterior | V1-V3 (reciprocal changes) | RCA/LCx |
NSTEMI/UA shows ST depression, T-wave inversions, or may have a normal ECG.
Serum Biomarkers
Cardiac Troponin (I or T) is the gold standard:
- Rises within 2-4 hours of onset
- Peaks at 12-24 hours
- Returns to baseline in 7-14 days (troponin I) or up to 14 days (troponin T)
- High-sensitivity troponin (hs-Tn) allows earlier rule-in/rule-out (within 1-3 hours)
- Serial measurements (0h, 1h or 0h, 3h) are used in modern accelerated diagnostic protocols
CK-MB:
- Less specific than troponin
- Rises at 4-6 hours, peaks at 12-24h, returns to normal in 36-72h
- Still useful for detecting reinfarction (as troponin remains elevated)
Myoglobin:
- Earliest marker (rises in 1-2h) but highly non-specific
Clinical Decision Rules for Risk Stratification
- HEART Score (History, ECG, Age, Risk factors, Troponin) - widely used in ED
- EDACS-ADP - Emergency Department Assessment of Chest pain Score
- TIMI Risk Score - for NSTEMI/UA prognosis
- GRACE Score - predicts in-hospital and 6-month mortality in ACS
Imaging
- Echo (TTE/TEE): Detects wall motion abnormalities, LV function, mechanical complications
- Coronary CTA: Useful for ruling out ACS in low-intermediate risk patients
- Nuclear scintigraphy / stress testing: For stable intermediate-risk patients after rule-out
Part 2: Medications
Emergency/Acute Phase (ED Management)
The classic mnemonic: MONA (Morphine, Oxygen, Nitrates, Aspirin) - though oxygen is now reserved for hypoxia (SpO₂ <90%).
1. Antiplatelets
| Drug | Dose | Notes |
|---|---|---|
| Aspirin | 162-325 mg chewed immediately | First-line for all ACS; irreversibly inhibits COX-1, blocks TXA₂-mediated platelet aggregation |
| Clopidogrel (P2Y12 blocker) | 600 mg loading dose for PCI; 300 mg for fibrinolysis | Prodrug, requires CYP2C19 activation; delayed onset |
| Ticagrelor | 180 mg loading dose | Preferred over clopidogrel for STEMI/NSTEMI; reversible, faster onset; do NOT use with fibrinolytics |
| Prasugrel | 60 mg loading dose | Potent P2Y12 blocker; avoid in prior stroke/TIA, age >75, weight <60 kg |
Dual antiplatelet therapy (DAPT = aspirin + P2Y12 inhibitor) is standard for all ACS.
2. Anticoagulants
| Drug | Notes |
|---|---|
| UFH (Unfractionated Heparin) | Preferred for STEMI going to PCI (faster onset, easily reversible with protamine); 60 units/kg IV bolus (max 4000 units) + infusion |
| Enoxaparin (LMWH) | 1 mg/kg SC twice daily; preferred for conservative NSTEMI management; reduce to 1 mg/kg daily if GFR <30 mL/min; UFH preferred for immediate PCI |
| Bivalirudin | Direct thrombin inhibitor; used as alternative to heparin during PCI; reduces bleeding risk |
| Fondaparinux | Factor Xa inhibitor; preferred for medically managed NSTEMI when PCI not planned; NOT for primary PCI (risk of catheter thrombus) |
3. Nitrates
- Nitroglycerin (sublingual or IV): Vasodilation reduces preload and ischemic pain; contraindicated if SBP <90 mmHg, severe bradycardia, right ventricular infarction, or recent PDE5 inhibitor use (sildenafil within 24h, tadalafil within 48h)
4. Beta-Blockers
- Metoprolol, atenolol, carvedilol
- Reduce HR, contractility, and O₂ demand; reduce arrhythmias; decrease mortality post-MI
- Contraindicated in: acute decompensated HF, cardiogenic shock, severe bradycardia (HR <60), high-degree AV block, active bronchospasm
- Oral beta-blocker should be initiated within 24 hours if no contraindications; IV form only for refractory hypertension or tachyarrhythmia
5. GP IIb/IIIa Inhibitors
- Abciximab, eptifibatide, tirofiban
- Block fibrinogen binding to GP IIb/IIIa receptor on platelets
- Used adjunctively during PCI, especially with large thrombus burden
- Eptifibatide/tirofiban: small-molecule; abciximab: monoclonal antibody fragment
6. Oxygen
- Only for hypoxic patients (SpO₂ <90%); routine supplemental O₂ in normoxic patients is no longer recommended and may be harmful
7. Opioid Analgesia
- Morphine (2-4 mg IV): For refractory pain; associated with delayed clopidogrel absorption - use with caution
Post-MI / Long-Term Medications
| Drug Class | Drugs | Indication |
|---|---|---|
| ACE inhibitor / ARB | Lisinopril, ramipril, valsartan | Start within 24h in STEMI, especially with LV dysfunction (EF <40%), anterior MI, or HF; reduce remodeling and mortality |
| Statin (high-intensity) | Atorvastatin 80 mg, rosuvastatin 40 mg | Start immediately in all ACS patients regardless of baseline LDL; pleiotropic effects beyond LDL lowering |
| Beta-blocker | Metoprolol succinate, carvedilol | Long-term therapy for LV dysfunction; continue for at least 1-3 years post-MI |
| Aldosterone antagonist | Eplerenone, spironolactone | Post-MI with EF ≤40% and either HF or diabetes; avoid if K⁺ >5.0 or GFR <30 |
| DAPT | Aspirin + P2Y12 inhibitor | Continue for 12 months post-ACS (both stent and non-stent); duration may be modified based on bleeding vs. ischemic risk |
Reperfusion Therapy
This is the cornerstone of STEMI management:
- Primary PCI (percutaneous coronary intervention): Gold standard - balloon/stent across the culprit lesion; target door-to-balloon time ≤90 minutes; every 30-minute delay increases 12-month mortality by 7.5%
- Fibrinolysis (thrombolytics): If PCI not available within 120 min of first medical contact; give within 30 minutes of arrival; agents include alteplase (tPA), tenecteplase (TNK), reteplase (rPA)
- Fibrinolysis contraindications: Prior intracranial hemorrhage, ischemic stroke <3 months, active internal bleeding, aortic dissection, severe uncontrolled hypertension
Summary Table: ACS Drug Overview (from Rosen's Emergency Medicine)
| Medication Class | Examples | Indication | Key Risks |
|---|---|---|---|
| Antiplatelet | Aspirin, clopidogrel, ticagrelor, prasugrel | All ACS | Bleeding, GI upset |
| Anticoagulant | UFH, enoxaparin, bivalirudin, fondaparinux | All ACS | Bleeding, HIT (UFH) |
| Nitrate | Nitroglycerin | Ischemic pain, HF | Hypotension; CI in RV infarct, PDE5 use |
| Beta-blocker | Metoprolol, atenolol | Rate control, arrhythmia, anti-ischemic | Bradycardia, bronchospasm, cardiogenic shock |
| GP IIb/IIIa inhibitor | Abciximab, eptifibatide, tirofiban | High-risk PCI | Bleeding, thrombocytopenia |
| ACE-I / ARB | Lisinopril, valsartan | Post-MI, LV dysfunction | Hypotension, hyperkalemia, renal impairment |
| Statin | Atorvastatin 80 mg | All ACS, long-term | Myopathy, hepatotoxicity (rare) |
| Aldosterone antagonist | Eplerenone | Post-MI with EF ≤40% | Hyperkalemia |
Sources: Rosen's Emergency Medicine, 10th Ed. - Chapter 64 (ACS); Goldman-Cecil Medicine, 26th Ed.; Braunwald's Heart Disease, 12th Ed.
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