Quick Recap
Cardiovascular System, Protocol 6/12.
1. Definition
ACS spectrum: STE-ACS (STEMI) vs NSTE-ACS (encompassing the former unstable angina/NSTEMI distinction, now unified given the recognized continuum). Distinguish myocardial injury (abnormal troponin alone) from myocardial infarction (abnormal troponin + clinical ischemic syndrome) — MI is a subset of injury; other causes of troponin elevation include heart failure, myocarditis, cardiomyopathy, Takotsubo, cardiac contusion, defibrillator shocks.
MI Type classification:
- Type 1: plaque rupture/erosion -> thrombus formation, may (STE-ACS) or may not (NSTE-ACS) fully occlude flow
- Type 2: supply-demand mismatch on a fixed stenosis — triggered by increased demand (tachycardia, surgery, severe HTN) or decreased supply (anemia, hypoxia, hypotension, sepsis) — management differs from Type 1 (treating the precipitant matters more than emergent revascularization)
- Types 3-5 (sudden cardiac death, PCI-related, CABG-related) — less relevant to initial ICU triage but affect biomarker interpretation thresholds
Epidemiology: ~605,000 new + 200,000 recurrent AMI/year in the US; ~3/4 are NSTE-ACS; ~1 in 5 patients admitted with AMI die within the following year despite improved survival trends.
2. Pathophysiology
STE-ACS: sudden COMPLETE coronary occlusion, usually atherosclerotic plaque rupture -> platelet activation/aggregation -> thrombus. "Time is muscle" — infarct size and mortality correlate directly with ischemic time, driving the urgency of reperfusion.
NSTE-ACS: partial/incomplete occlusion or transient occlusion with spontaneous partial lysis; still plaque-rupture-driven but without complete vessel occlusion.
Early STE-ACS mortality is substantially attributable to ventricular arrhythmias, not just pump failure — continuous rhythm monitoring is essential from first contact.
3. Immediate Stabilization (ABCDE)
Airway/Breathing: oxygen only if hypoxemic (SpO2 <90%) — routine supplemental O2 in normoxic ACS patients is not beneficial and may be harmful (not detailed further here, but avoid reflexive O2).
Circulation — STE-ACS pathway ("time is muscle"):
- 12-lead ECG within 10 minutes of first medical contact
- Door-to-balloon time goal: <90 minutes for primary PCI-capable centers; door-to-needle (fibrinolysis) goal: <30 minutes if PCI unavailable within 120 minutes of first medical contact
- TNKase (tenecteplase) weight-based dosing if fibrinolysis chosen: <60kg = 30mg; 60-69kg = 35mg; 70-79kg = 40mg; 80-89kg = 45mg; >=90kg = 50mg
- Sublingual nitroglycerin for pain (caution/avoid if suspected inferior MI, SBP <90, HR <50 or >100, or PDE5-inhibitor use in past 24-48h given risk of profound hypotension); instruct patients to call for help if pain persists >5 min after one dose
- Aspirin 162-325mg PO chewed/loading immediately
- P2Y12 inhibitor loading (clopidogrel 600mg, prasugrel 60mg, or ticagrelor 180mg) per local protocol/PCI plan
- Anticoagulation (heparin) per PCI protocol
- Beta-blocker (caution in acute decompensated HF/cardiogenic shock — do not give in cardiogenic shock)
- Mechanical support (IABP/percutaneous VAD) can be considered for hemodynamic/rhythm instability, severe HF, or cardiogenic shock, but RCT data do not support routine benefit (IABP specifically shown NOT beneficial in SHOCK II trial) — see Cardiogenic Shock protocol for full MCS discussion
NSTE-ACS pathway:
- Risk-stratify with TIMI risk score (validated tool for MACE risk — death, nonfatal MI, stroke); higher score = higher MACE risk and greater benefit from early invasive strategy
- All patients get medical management appropriate to risk level and should be considered for diagnostic angiography with intent to PCI
- Early revascularization especially benefits: high TIMI risk score, hemodynamic instability, electrical instability (ventricular arrhythmias), and chest pain refractory to high-dose nitroglycerin infusion — these findings warrant IMMEDIATE revascularization efforts, not just risk-stratified elective timing
Disability/Exposure: standard assessment; monitor continuously for arrhythmia given early ventricular arrhythmia risk.
Checklist:
4. Focused History
Chest discomfort >20 minutes (typical), atypical presentations more common in women/diabetics/older adults (dyspnea, epigastric discomfort, fatigue, syncope without classic chest pain), radiation pattern, associated diaphoresis/nausea, cardiac risk factors (DM, smoking, HTN, low HDL, family history of premature CAD, age), prior CAD/PCI/CABG, medication use (PDE5 inhibitors affecting nitrate safety), bleeding risk factors (affecting antiplatelet/anticoagulant/fibrinolytic decisions), recent surgery/trauma/active bleeding (fibrinolysis contraindications).
5. Examination + POCUS
Vitals (bradycardia/hypotension in inferior MI, signs of heart failure), new murmur (acute MR from papillary muscle dysfunction/rupture), JVD (RV involvement in inferior MI), rales (LV failure).
POCUS: regional wall motion abnormality, EF estimation, mechanical complications (acute MR, VSD, free wall rupture/tamponade), RV involvement assessment in inferior MI.
6. Syndrome Identification
Distinguish STE-ACS (emergent reperfusion pathway) from NSTE-ACS (risk-stratified pathway) from non-ACS troponin elevation (Type 2 MI or non-ischemic myocardial injury) — this triage decision drives the entire subsequent pathway.
7. Differential Diagnosis
Tier | Examples |
Must exclude (mimics with different management) | Aortic dissection ("Think Aorta" — do NOT give thrombolytics if dissection possible), PE, pericarditis/myocarditis, Takotsubo cardiomyopathy |
Type 2 MI triggers | Sepsis, severe anemia, hypoxia, tachyarrhythmia, severe hypertension, surgery |
Non-ischemic troponin elevation | Heart failure, myocarditis, cardiac contusion, defibrillator shock, renal failure (reduced clearance), PE with RV strain |
8. Severity Assessment
TIMI risk score for NSTE-ACS (age>=65, >=3 CAD risk factors, known CAD >=50% stenosis, ST deviation on presenting ECG, >=2 anginal events in 24h, aspirin use in prior 7 days, elevated cardiac markers — 1 point each, 0-7 total): higher score predicts higher MACE risk and identifies patients benefiting most from early invasive strategy.
CAD risk factors (for calculating TIMI and general risk): DM, smoking, HTN, low HDL (<40), family history premature CAD (male first-degree relative <=55, female <=65), age (men >=45, women >=55).
9. Investigations
- Bedside: 12-lead ECG (repeat serially if initial non-diagnostic and suspicion remains high), continuous rhythm monitoring
- Labs: troponin I or T (serial, per local assay-specific protocol), BMP, CBC, coagulation panel (baseline before anticoagulation/fibrinolysis), lipid panel
- Imaging: echo (wall motion, EF, mechanical complications), coronary angiography (diagnostic + therapeutic for STE-ACS and high-risk NSTE-ACS)
- Stress testing accuracy (for lower-risk NSTE-ACS/risk stratification when angiography deferred): exercise treadmill (men 68% sens/77% spec; women 61%/70%); exercise/adenosine thallium (88%/77%); exercise/dobutamine echo (76%/88%)
10. Evidence-Based Management — Antiplatelet/Anticoagulant Dosing
Agent | Dosing | Key toxicity |
Aspirin | 162-325mg PO daily | Bleeding, dyspepsia |
Clopidogrel | 600mg PO load, then 75mg daily | Bleeding, rare TTP |
Prasugrel | 60mg PO load, then 10mg daily | Bleeding, HTN, headache; avoid if prior stroke/TIA |
Ticagrelor | 180mg PO load, then 90mg BID | Bleeding, dyspnea, bradyarrhythmia |
Cangrelor | 30 mcg/kg IV bolus pre-PCI, then 4 mcg/kg/min during procedure | Bleeding |
Abciximab | 0.25mg/kg bolus at PCI, then 0.125 mcg/kg/min | Bleeding, thrombocytopenia, hypotension |
Eptifibatide | 180 mcg/kg bolus, then 2 mcg/kg/min | Bleeding, thrombocytopenia |
Tirofiban | 25 mcg/kg over 5min, then 0.15 mcg/kg/min | Bleeding, thrombocytopenia, bradycardia |
Metoprolol | 5mg IV q5min x3, then 25-50mg PO q6-12h | Bradycardia, hypotension, heart block, bronchospasm |
Esmolol | 500 mcg/kg bolus, then 50-300 mcg/kg/min | Same class effects, short-acting/titratable |
Nitroglycerin | 5-200 mcg/min IV | Hypotension, headache, tachyphylaxis |
11. Post-ACS Inpatient/Discharge Bundle — "ABCDE" Checklist
A — Antiplatelet/Anticoagulation: Aspirin indefinitely + P2Y12 inhibitor for at least 1 year; PPI prophylaxis if PUD/GI bleed risk factors; heparin/enoxaparin during hospitalization; ACE-I if EF<=40%/DM/CKD/HTN (ARB if ACE-I intolerant); aldosterone antagonist if EF<40% + DM/HF already on ACE-I + beta-blocker (caution with hyperkalemia/CKD).
B — Beta-blocker (all patients unless contraindicated) + Blood pressure (goal <140/90; <130/80 if CKD/DM — maximize beta-blocker/ACE-I before adding other agents).
C — Cigarette cessation (complete, with pharmacotherapy/counseling) + Cholesterol (high-intensity statin regardless of baseline LDL).
D — Diet (10% weight reduction goal if BMI>25) + Diabetes (HbA1c goal <7.0%).
E — Exercise (30 min aerobic activity >=5 days/week, cardiac rehab referral) + Ejection fraction (measure before discharge).
12. Organ Support
Mechanical circulatory support (IABP/Impella) for cardiogenic shock complicating ACS per Cardiogenic Shock protocol (evidence for routine benefit is weak/absent per SHOCK II for IABP specifically); mechanical ventilation for pulmonary edema/respiratory failure; standard post-MI ICU supportive care.
13. Consultation Matrix
Consultation | Trigger | Timing |
Interventional Cardiology | Any STE-ACS, high-risk/unstable NSTE-ACS | Immediate |
Cardiothoracic Surgery | Mechanical complication (VSD, papillary muscle rupture, free wall rupture), left main/multivessel disease requiring CABG | Immediate if mechanical complication |
Cardiac Rehabilitation | All post-ACS patients | Pre-discharge referral |
14. Monitoring Framework
Continuous rhythm monitoring (arrhythmia risk highest in first 24-48h), serial troponin trend, serial ECG if evolving picture, echo for mechanical complication surveillance if new murmur/hemodynamic change, watch for post-thrombolysis bleeding/angioedema if fibrinolysis given (see Section 15).
15. Complications (mnemonic: "FEAR AMI")
F — Failure: LV dysfunction is the strongest predictor of post-MI survival; ranges from mild (rales/S3) to cardiogenic shock; treat per severity — O2, afterload reduction (nitroglycerin/nitroprusside), RAAS inhibition, diuretics; cardiogenic shock warrants PAC consideration and inotrope/vasopressor/MCS per Cardiogenic Shock protocol. RV dysfunction occurs in ~10% of inferior/posterior MI — suspect if hypotension + elevated JVP without pulmonary edema; manage with judicious fluids for preload + dobutamine; avoid nitrates/diuretics which drop preload further.
E — Embolism/Effusion/pericarditis: mural thrombus in up to 20% overall (60% of large anterior MI) — consider anticoagulation if severely depressed EF or visualized LV thrombus.
A — Arrhythmia: most common early complication; ventricular arrhythmias drive much of early STE-ACS mortality.
R — Rupture: free wall rupture (tamponade, often catastrophic), papillary muscle rupture (acute severe MR), VSD — all are surgical emergencies, suspect with new murmur/sudden hemodynamic collapse.
AMI completes the mnemonic as the overarching context.
Post-thrombolysis intracranial hemorrhage (if fibrinolysis given): stop infusion, emergent CT head, CBC/PT/PTT/fibrinogen/type & crossmatch, BP and glucose control, consider reversal (cryoprecipitate 10U over 1h, repeat if fibrinogen <150; or TXA 1000mg IV over 1h, or epsilon-aminocaproic acid 4-5g over 20min), neurosurgery consult.
Post-thrombolysis angioedema: stop infusion, monitor airway, IV diphenhydramine 50mg + ranitidine 50mg + methylprednisolone 125mg; if worsening, epinephrine 0.3mL SC or 0.5mL nebulized; avoid ACE inhibitors going forward.
16. Escalation & De-escalation
Escalate: hemodynamic/electrical instability, refractory ischemic pain, mechanical complication suspected -> immediate invasive strategy/surgical consult.
De-escalate: stable post-revascularization, no arrhythmia, EF assessed, medical therapy optimized -> transition to step-down/ward, initiate ABCDE discharge bundle.
17. ICU Discharge Criteria
Hemodynamically stable, no ongoing ischemia/arrhythmia, revascularization completed or medical management optimized, EF measured, ABCDE bundle initiated, cardiac rehab referral placed.
18. Documentation & Medicolegal Checklist
19. Key Guidelines
2013 ACCF/AHA STEMI guideline (O'Gara et al.); 2014 AHA/ACC NSTE-ACS guideline (Amsterdam et al.); Third Universal Definition of Myocardial Infarction (Thygesen et al., 2012) — note newer (Fourth) universal definition exists and should be checked for updates given rapid evolution in this field.
20. Landmark Trials
- TIMI risk score validation (Antman et al., JAMA 2000) — foundational NSTE-ACS risk stratification tool.
- SHOCK II trial: IABP in AMI-cardiogenic shock — no 30-day mortality benefit; led to downgrade from Class I to IIb (AHA)/III (ESC) recommendation.
21. Controversies
Role of routine mechanical circulatory support (IABP, percutaneous VAD) in ACS-complicated cardiogenic shock remains contested given SHOCK II's neutral result, despite continued widespread real-world use based on observed hemodynamic/organ-perfusion benefits not captured by the trial's mortality endpoint. Optimal P2Y12 inhibitor choice (clopidogrel vs prasugrel vs ticagrelor) involves genuine trade-offs (potency vs bleeding risk vs cost) without a single universally preferred agent across all patients. Type 2 MI management (extent of ischemic workup/revascularization vs treating the precipitant alone) remains an evolving, individualized area without firm consensus.
22. References
- Martz C, Sintek MA. Acute Myocardial Infarction. Washington Manual of Critical Care, 4th ed, 2025 (Ch. 20).
- O'Gara PT, Kushner FG, Ascheim DD, et al. 2013 ACCF/AHA guideline for the management of ST-elevation myocardial infarction. Circulation. 2013;127(4):e362-e425.
- Amsterdam EA, Wenger NK, Brindis RG, et al. 2014 AHA/ACC guideline for the management of patients with non-ST-elevation acute coronary syndromes. Circulation. 2014;130(25):e344-e426.
- Antman EM, Cohen M, Bernink PJ, et al. The TIMI risk score for unstable angina/non-ST elevation MI. JAMA. 2000;284(7):835-842.
- Thygesen K, Alpert JS, Jaffe AS, et al. Third universal definition of myocardial infarction. Circulation. 2012;126(16):2020-2035.
- Thiele H, Zeymer U, Neumann FJ, et al. Intraaortic balloon support for myocardial infarction with cardiogenic shock (IABP-SHOCK II). N Engl J Med. 2012;367(14):1287-1296.