Acute coronary syndrome (ACS) is a high-stakes CCS scenario where every minute counts and your diagnostic and therapeutic decisions directly impact patient mortality and your exam score. The distinction between STEMI (ST-elevation myocardial infarction) and NSTEMI (non-ST-elevation MI) or unstable angina determines the urgency of catheterization and interventions. This deep-dive guide equips you with the complete ACS management pathway, from initial ECG interpretation through post-MI risk stratification and secondary prevention.
Acute Coronary Syndrome: Overview and Classification
ACS encompasses three entities along a spectrum of myocardial ischemia and injury:
1. STEMI: Acute transmural myocardial infarction with ST-segment elevation reflecting active ongoing myocardial injury; requires emergent reperfusion (PCI or fibrinolytics)
2. NSTEMI: Myocardial infarction without ST elevation; elevated troponin confirms myocardial necrosis; managed with medical optimization and risk-stratified catheterization
3. Unstable Angina: Acute ischemic symptoms without myocardial necrosis (troponin negative); high-risk ischemia requiring hospitalization and intensive medical management
The clinical presentation often overlaps: chest pain or dyspnea, sometimes radiating to arm/jaw/back, associated with diaphoresis, nausea, or syncope. Atypical presentations are common in women, elderly, diabetics, and post-transplant patients (may present with dyspnea alone).
> Study Tip: The StudyCCS question bank includes STEMI, NSTEMI, and unstable angina cases with real ECGs, troponin trends, and complications—cases where your recognition speed, reperfusion strategy, and medication decisions directly affect your CCS score and patient outcomes.
Initial Stabilization: The MONA Protocol
MONA (Morphine, Oxygen, Nitroglycerin, Aspirin) remains the foundational acute management, though modern practice has refined each component.
Morphine
Dose: 2-4 mg IV push, repeat q5-15 min until pain controlled or SBP <90 mmHg
Benefits: Analgesia, anxiolysis, vasodilation (afterload reduction), decreased myocardial oxygen demand
Caution: Can worsen bradycardia, hypotension; avoid in RV infarction (see special situations below)
Oxygen
Indication: Maintain SpO2 ≥94%. Do not administer supplemental oxygen if SpO2 already adequate (paradoxical hyperoxemia may increase coronary vasoconstriction and worsen outcomes).
Equipment: Nasal cannula or non-rebreather mask as needed
Nitroglycerin
Dose: Sublingual NTG 0.3-0.6 mg, repeat q5 min × 3 doses, then IV drip if needed
Benefits: Relieves angina, reduces preload and afterload, improves coronary flow
Contraindications: RV infarction (relative; NTG will worsen RV afterload), phosphodiesterase inhibitor use within 24-48 hours (sildenafil, tadalafil risk of profound hypotension)
Titration: Maintain SBP >90 mmHg; stop if SBP drops below this
Aspirin
Dose: 325 mg chewed (faster absorption than swallowed), loading dose
Mechanism: Irreversible platelet COX inhibition; reduces thrombotic occlusion
Note: Give even in hemorrhagic stroke concern (initial data suggests benefit outweighs risk); contact neurology if active ICH, but aspirin generally given emergently in ACS
ECG Interpretation: Recognizing STEMI Patterns
A 12-lead ECG should be obtained and interpreted within 10 minutes of presentation. STEMI diagnosis requires ST elevation ≥1 mm in ≥2 contiguous leads (or ≥2 mm in V1-V2 given larger voltages).
Coronary Territory and ST Elevation Patterns
• Anterior STEMI (LAD): ST elevation in V1-V4, reciprocal ST depression in II, III, aVF
• Inferior STEMI (RCA or LCx): ST elevation in II, III, aVF; reciprocal changes in I, aVL
• Lateral STEMI (LCx or diagonal): ST elevation in I, aVL, V5-V6
• Right Ventricular STEMI (RCA): Inferior STEMI + ST elevation in V4R
• Posterior STEMI (LCx or RCA): Mirrored pattern: ST depression in V1-V3, prominent R wave in V1-V2 (posterior leads not in standard ECG; if suspected, obtain right-sided and posterior leads)
STEMI Equivalents (Treat as STEMI)
• New left bundle branch block (LBBB) with symptoms of ACS (Sgarbossa criteria may aid diagnosis if LBBB pre-existing and new morphologic changes)
• Aortic dissection with STEMI: Dissection extending into RCA → inferior STEMI pattern
• Pulmonary embolism with anterior ST elevation: Rare; consider if no risk factors for ACS but strong PE risk
Pseudoelevations to Recognize
• Early repolarization: Normal variant, diffuse ST elevation especially in precordial and lateral leads; PR depression common; troponin negative
• Pericarditis: Diffuse ST elevation across all territories (not territory-specific); reciprocal PR depression; troponin may be mildly elevated
• Hyperkalemia: Peaked T waves, widened QRS, loss of P wave; different pattern entirely
• LBBB (non-acute): Pre-existing; obtain prior ECG to confirm chronicity
Reperfusion Strategy: PCI vs Fibrinolytics
The goal of STEMI management is myocardial reperfusion—restoring blood flow to the ischemic territory to minimize infarct size and mortality.
Primary Percutaneous Coronary Intervention (PCI)
Preferred strategy for STEMI at centers with catheterization capability.
Door-to-Balloon Time: <90 minutes is the goal; <120 minutes acceptable per guidelines
• This is the time from arrival at the first medical facility (ED door) to balloon inflation in the culprit artery
• Delays >120 min increase mortality; every 30 minutes of delay increases 1-year mortality by ~7.5%
Procedure:
• Emergent cardiac catheterization via femoral or radial approach
• Identification of culprit lesion (usually total or subtotal occlusion)
• Balloon angioplasty and stent placement (drug-eluting stent preferred for STEMI to reduce restenosis)
• Thrombus aspiration if significant thrombus burden
• Assess for complications: cardiogenic shock, mechanical complications (VSD, papillary muscle rupture, free wall rupture), arrhythmias
Outcomes: Superior to fibrinolytics; 30-day mortality ~7% with primary PCI vs ~9% with fibrinolytics
Fibrinolytic Therapy
Reserved for STEMI when PCI is unavailable and presentation is within 12 hours of symptom onset.
Agents:
• Alteplase (tPA): 15 mg IV bolus, then 0.75 mg/kg over 30 min (max 50 mg), then 0.5 mg/kg over 60 min (max 35 mg). Total dose not to exceed 100 mg.
• Reteplase: 10 units IV bolus × 2, given 30 min apart
• Tenecteplase: Weight-based single bolus (30-50 mg depending on weight)
Timing: Administer within 30 minutes of arrival (door-to-needle <30 min) to maximize benefit
Success: TIMI III flow (complete reperfusion) achieved in 50-60% with fibrinolytics vs >90% with PCI
Rescue PCI: If fibrinolytics fail (ongoing chest pain, no ST resolution, hemodynamic instability at 60-90 min), emergent transfer for PCI (rescue PCI or facilitated PCI)
On CCS: PCI vs Fibrinolytic Decision Tree
• PCI available at your facility, door-to-balloon <90 min: Primary PCI is the answer
• PCI >90 min away, or significant transport delay: Consider fibrinolytics if <3-12 hours from symptom onset and no contraindications
• Anterior STEMI (larger territory, higher mortality): PCI preferred; fibrinolytic-ineligible patients are acceptable for fibrinolytic therapy only if no PCI available
> Practice Alert: This is one of the highest-yield CCS topics. Practice it in the StudyCCS question bank to build the reflexes you need on exam day—especially STEMI cases where you must recognize ECG changes, activate the cath lab, and manage hemodynamics.
Dual Antiplatelet Therapy and Anticoagulation
Aspirin (Already Covered Above)
Loading Dose: 325 mg chewed acutely
Maintenance: 81 mg daily indefinitely (lower maintenance dose is equally effective and causes less GI bleeding)
P2Y12 Inhibitors (Loading Doses)
Started immediately upon STEMI diagnosis (ideally before PCI).
• Clopidogrel (Plavix): 600 mg loading dose (faster onset than standard 75 mg daily)
• Prasugrel (Effient): 60 mg loading dose (5 mg if <60 kg) — potent; preferred in STEMI if no contraindications
• Ticagrelor (Brilinta): 180 mg loading dose — potent; preferred in STEMI; given even if prasugrel contraindicated
On CCS: After PCI with stent, dual antiplatelet therapy (aspirin + P2Y12 inhibitor) is continued for 12 months, then aspirin indefinitely.
Anticoagulation
Unfractionated Heparin (UFH):
• Bolus: 60-70 units/kg IV (typically 5000 units)
• Infusion: 12-15 units/kg/hour (typically 1000-1200 units/hour) to achieve aPTT 1.5-2× control or 50-70 seconds
• Preferred during PCI because easily reversible (stop infusion, effect wears off in minutes)
Enoxaparin (LMWH):
• Bolus: 0.3 mg/kg IV (if PCI planned) or 1 mg/kg SC BID (if medical management only)
• Can be used; slightly inferior to UFH in PCI setting due to longer half-life
Fondaparinux:
• Dose: 2.5 mg IV, then 2.5 mg daily
• Lower bleeding risk than heparin; less favorable for STEMI with PCI; avoid if serum creatinine >3 mg/dL
On CCS: UFH is typical first choice for STEMI undergoing PCI; continue throughout procedure, then continue post-PCI for 24-48 hours depending on comorbidities.
Risk Stratification and Catheterization Timing in NSTEMI
NSTEMI lacks ST elevation but has elevated troponin (or dynamic ECG changes with ischemic symptoms).
NSTEMI Risk Stratification (TIMI Risk Score)
Calculate at admission; each variable = 1 point:
1. Age ≥65 years
2. ≥3 coronary risk factors
3. Prior CAD
4. ST deviation on ECG
5. ≥2 anginal episodes in prior 24 hours
6. Use of aspirin in prior 7 days
7. Elevated cardiac markers (troponin, BNP)
Risk Categories:
• 0-1: Low risk; consider outpatient catheterization or stress test
• 2-3: Intermediate risk; inpatient catheterization within 24 hours
• 4-6: High risk; early invasive strategy with catheterization within 12-24 hours
• 7: Very high risk; catheterization emergently (same as STEMI urgency)
NSTEMI Management Pathway
1. Dual antiplatelet therapy: Aspirin 325 mg + P2Y12 inhibitor loading (prasugrel 60 mg or ticagrelor 180 mg preferred)
2. Anticoagulation: UFH bolus + infusion or LMWH
3. Beta-blocker: Metoprolol, atenolol, or carvedilol (target HR 50-60 bpm if tolerated)
4. ACE inhibitor or ARB: Ramipril, lisinopril, losartan (start after hemodynamic stability)
5. Statin: Atorvastatin 80 mg daily (high-intensity statin)
6. Serial troponins: At admission, 3 hours, 6 hours to assess for myocardial infarction (rise and fall pattern)
7. Cardiac catheterization timing based on risk (see TIMI score above)
Special Situations in ACS
Right Ventricular Infarction (RV-MI)
Usually complicates inferior STEMI (60% of inferior STEMIs have RV involvement).
Key Findings:
• Inferior STEMI (II, III, aVF ST elevation) + ST elevation in V4R or posterior leads
• Hemodynamically: RV afterload-dependent; hypotension exacerbated by RV dysfunction
Management (CRITICAL DIFFERENCES):
• Avoid nitrates and morphine (further reduce RV preload → cardiovascular collapse)
• Maintain RV preload: IV fluids (500-1000 mL bolus of normal saline), check for hypovolemia
• Maintain systemic pressure: Avoid vasodilators; use vasopressors (dopamine, dobutamine) if needed
• Avoid bradycardia: Maintain AV synchrony; pacing if high-grade AV block develops
• PCI is essential: Restore RCA flow quickly; inferior STEMI with RV involvement has higher mortality with fibrinolytics
On CCS: If you recognize RV-MI, explicitly avoid nitrates/morphine and order IV fluids instead.
Cardiogenic Shock Complicating STEMI
Occurs in 5-10% of STEMI cases; mortality ~50% even with PCI.
Mechanisms:
• Extensive myocardial necrosis (>40% LV territory)
• Mechanical complication: acute VSD, papillary muscle rupture, free wall rupture
• RV infarction with RV dysfunction
• Severe mitral regurgitation (post-ischemic)
Management:
• Emergent PCI (same catheterization + revascularization as STEMI)
• Hemodynamic support: IV fluids if hypotensive and RV involvement (see above); consider inotropes (dobutamine, milrinone, levosimendan) or vasopressors (dopamine, norepinephrine) to maintain MAP >60-65 mmHg
• Mechanical support: Intra-aortic balloon pump (IABP) improves coronary perfusion pressure and reduces afterload; bridge to PCI or mechanical circulatory support
• Left ventricular assist device (LVAD) or extracorporeal membrane oxygenation (ECMO) if PCI fails and irreversible shock persists
• Assess for mechanical complication on echo (see below)
Acute Mechanical Complications
Occur in 1-2% of STEMI; devastating mortality if missed.
1. Acute Ventricular Septal Defect (VSD)
• Presents as new holosystolic murmur at left lower sternal border + acute cardiogenic shock
• CXR shows pulmonary edema; echo shows septal rupture with left-to-right shunt
• Mortality >50% without surgery; surgery ideally performed at 1-2 weeks after infarction (allow scar formation for better suture hold)
• Management: IABP to reduce afterload, diuretics for pulmonary edema, emergent surgical consultation for timing
2. Acute Papillary Muscle Rupture
• Posterior papillary muscle (RCA territory) rupture more common than anterior
• Presents with acute severe mitral regurgitation, new pansystolic murmur at apex, acute pulmonary edema/shock
• Echo shows flail leaflet ± ruptured papillary muscle
• Mortality high even with surgery; emergent surgical consultation
• IABP reduces afterload; diuretics for pulmonary edema
3. Free Wall Rupture
• Catastrophic; leads to pericardial tamponade and cardiogenic shock
• Presents with chest pain, hypotension, muffled heart sounds, elevated JVP (Beck's triad)
• Diagnosis: Echo shows pericardial effusion; pericardiocentesis yields blood
• Management: Emergency surgery; without intervention, death within minutes
On CCS: Recognize acute mechanical complications by clinical presentation + echo findings; involve cardiothoracic surgery immediately.
Post-MI Medications (ABCDE Protocol)
After STEMI with successful PCI, implement:
A - Aspirin: 81 mg daily indefinitely (started acutely)
B - Beta-blocker: Metoprolol 25-50 mg BID, atenolol 25-50 mg daily, or carvedilol 3.125-6.25 mg daily titrated to HR 50-60 bpm. Hold if bradycardic, hypotensive, or in cardiogenic shock.
C - Calcium channel blocker or ACE inhibitor: ACE inhibitor preferred (ramipril, lisinopril 2.5-10 mg daily); calcium channel blocker (diltiazem, verapamil) only if beta-blocker contraindicated or insufficient symptom control. Do NOT start both.
D - Diuretics: If heart failure or volume overload; furosemide or torsemide dosed to euvolemia
E - Eplerenone or spironolactone: If EF <40% and heart failure; eplerenone 25 mg daily preferred (fewer gynecomastia than spironolactone). Monitor K+ and creatinine closely.
Additional Post-MI Medications
• High-intensity statin: Atorvastatin 80 mg daily or rosuvastatin 20-40 mg daily
• P2Y12 inhibitor: Continue for 12 months (ticagrelor or prasugrel preferred over clopidogrel for STEMI)
• Aldosterone antagonist: As above if EF <40%
• Ezetimibe: Consider if LDL not at goal on statin monotherapy
• PCSK9 inhibitor: Evolocumab or alirocumab if LDL >70 mg/dL on high-intensity statin + ezetimibe
Cardiac Rehabilitation and Secondary Prevention
Before discharge:
• Referral to cardiac rehabilitation program (structured exercise, risk factor modification, education)
• Activity restrictions initially: Avoid heavy lifting, strenuous exercise for 4-6 weeks; gradual return to activity
• Risk factor modification: Smoking cessation, blood pressure control (target <130/80 mmHg), diabetes control (target A1C <7%), lipid lowering (LDL goal <70 mg/dL)
• Return to work: Typically 4-8 weeks for desk jobs; longer for strenuous occupations
• Sexual activity: Generally safe to resume at 4-6 weeks if hemodynamically stable
Risk Stratification Before Discharge
Assess left ventricular ejection fraction (LVEF) post-MI:
• LVEF >40%: Low-risk, standard medical management, standard activity
• LVEF 30-40%: Moderate risk, consider ICD evaluation at 40 days post-MI if EF remains <35%
• LVEF <30%: High-risk, consider ICD, optimize medical therapy, close cardiology follow-up
Arrhythmia Risk: Obtain Holter monitor or event monitor if symptoms suggest arrhythmia; consider ICD if sustained VT documented.
Don't-Miss Diagnoses and Complications
• Acute pericarditis post-MI (Dressler's syndrome): Chest pain, pericardial friction rub, can occur weeks after MI; NSAIDs or colchicine for treatment
• Ventricular free wall rupture: Hypotension, muffled heart sounds, pericardial effusion; surgical emergency
• Acute mitral regurgitation: New systolic murmur ± pulmonary edema; echo and surgical consultation
• Thrombosis in situ post-stent: Recurrent chest pain, ST re-elevation; return to cath lab
• Aortic dissection: Can present as inferior STEMI; look for pulse deficits, aortic regurgitation, widened mediastinum
• Pulmonary embolism: Can mimic ACS; consider if hypoxia out of proportion, tachycardia, elevated JVP; CT angiography if high suspicion
Complete Order Set: STEMI Presentation
STAT/IMMEDIATE
• 12-lead ECG (interpret within 10 min; identify territory)
• Aspirin 325 mg chewed + P2Y12 inhibitor (prasugrel 60 mg or ticagrelor 180 mg) + UFH 60-70 units/kg IV
• Nitroglycerin SL 0.3-0.6 mg; repeat q5 min × 3
• Morphine 2-4 mg IV PRN for chest pain
• Supplemental O2 if SpO2 <94%
• Chest X-ray
• Troponin, CBC, BMP, coagulation studies
• Blood cultures if fever
URGENT (<10 min)
• STEMI alert activation / Cath lab activation (door-to-balloon <90 min)
• Continuous cardiac monitoring and pulse oximetry
• Establish IV access (large bore for PCI sheath)
• NPO (in case emergent anesthesia needed)
DURING CATHETERIZATION
• Continue UFH infusion (aPTT 50-70 sec)
• Prepare for PCI with stent placement
• Plan for post-PCI dual antiplatelet therapy (aspirin + prasugrel or ticagrelor)
POST-CATHETERIZATION/PCI
• Continue UFH × 24 hours (or switch to LMWH if uncomplicated)
• Start beta-blocker (metoprolol, atenolol, carvedilol)
• Start ACE inhibitor or ARB (ramipril, lisinopril) when hemodynamically stable
• High-intensity statin (atorvastatin 80 mg daily)
• Continue aspirin 81 mg daily + P2Y12 inhibitor × 12 months
• Echocardiography within 24 hours to assess LVEF and mechanical complications
• Serial troponins if NSTEMI diagnosis uncertain
• Consider Holter monitor or event monitor for arrhythmia detection
BEFORE DISCHARGE
• Verify LVEF; consider ICD referral if EF ≤35%
• Cardiac rehabilitation referral
• Arrange cardiology follow-up within 2-4 weeks
• Counsel on activity, diet, medications, risk factor modification
• Verify dual antiplatelet therapy (12 months total)
Key Takeaways for CCS Success
1. Recognize STEMI on ECG: ST elevation ≥1 mm in ≥2 contiguous leads (or ≥2 mm in V1-V2)
2. Activate cath lab emergently: Door-to-balloon <90 min is critical
3. MONA protocol: Morphine, Oxygen (if SpO2 low), Nitroglycerin, Aspirin — avoid in RV infarction
4. Dual antiplatelet therapy: Aspirin + prasugrel or ticagrelor loading before PCI
5. Anticoagulation: UFH bolus + infusion for PCI
6. PCI is preferred over fibrinolytics if available within 90 min
7. Recognize complications: RV infarction (avoid nitrates/morphine), cardiogenic shock (IABP, inotropes), mechanical complications (VSD, papillary muscle rupture, free wall rupture)
8. Post-MI medications (ABCDE): Aspirin, Beta-blocker, ACE inhibitor, Diuretics, Eplerenone/spironolactone
9. Risk stratify post-MI: LVEF <35% at 40 days → ICD evaluation
10. Cardiac rehabilitation: Essential for secondary prevention and recovery
Ready to practice? The StudyCCS question bank includes STEMI, NSTEMI, unstable angina, mechanical complications, and cardiogenic shock cases with real ECGs and troponin trends. Practice real-time decision-making on exam-like cases. Try a case today.
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• CCS Antiplatelet Agents: Aspirin, Clopidogrel, Prasugrel, Ticagrelor
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