Acute Coronary Syndrome (ACS)

Details of the Concept

Acute coronary syndromes (ACS) encompass a clinical spectrum of myocardial ischemia caused by disruption (rupture or erosion) of unstable coronary artery atherosclerotic plaque with associated partial or complete coronary thrombosis. This results in reduced myocardial blood flow and ischemia. ACS includes unstable angina (UA), non–ST-segment elevation myocardial infarction (NSTEMI), and ST-segment elevation myocardial infarction (STEMI). In the US, approximately 805,000 AMIs occur annually (605,000 first events; 200,000 recurrent). The total annual economic burden is approximately $84.9 billion.

Key Facts

Definition and Classification

• Three related clinical conditions along a continuum of severity: (1) Unstable angina — transient ischemia without significant myonecrosis (troponin normal); (2) NSTEMI — subendocardial ischemia, partially occluded artery, elevated troponin; (3) STEMI — transmural ischemia, usually completely occluded artery, ST-elevation on ECG with elevated troponin. (sources/ACS-AHA-2025, rating: very high)
• Universal MI Definition Types: Type 1 (atherothrombotic, plaque disruption) — focus of this guideline; Type 2 (supply/demand imbalance); Types 3–5 (procedure-related or cardiac death). (sources/ACS-AHA-2025, rating: very high)
• STEMI ECG criteria: ST-elevation ≥1 mm in ≥2 anatomically contiguous leads (J-point); ≥2 mm in men ≥40 y, ≥2.5 mm in men <40 y, ≥1.5 mm in women in V2–V3. (sources/ACS-AHA-2025, rating: very high)

OMI/NOMI Paradigm — Challenging the STEMI/NSTEMI Model

• An emerging paradigm proposes replacing STEMI/NSTEMI with Occlusion MI (OMI) vs Non-Occlusion MI (NOMI), stratifying by underlying pathophysiology (persistent complete occlusion = OMI) rather than ECG morphology (STE present/absent). (sources/failure-stemi-criteria-lad-omi-ehjacc-2025, rating: high)
• STEMI criteria have only 43% sensitivity for acute coronary occlusion by meta-analysis; 38% of total LAD occlusions (TIMI-0 flow) never meet STEMI criteria on any serial pre-angiography ECG. (sources/failure-stemi-criteria-lad-omi-ehjacc-2025, rating: high)
• Among NSTEMI patients, 25–34% have TIMI-0/1 flow at angiography; this subgroup has nearly twice the mortality of NSTEMI with TIMI ≥2. (sources/failure-stemi-criteria-lad-omi-ehjacc-2025, rating: high)
• OMI ECG features beyond STE that identify occlusion (in decreasing prevalence in subtle LAD OMI): subtle STE <1mm (85%), hyperacute T-waves (85%), pathologic Q-waves (70%), reciprocal STD (50%), terminal QRS distortion (20%). See concepts/OMI-NOMI-Paradigm and concepts/Hyperacute-T-waves.
• Expert ECG interpretation and the PMCardio Queen of Hearts AI model both achieved 100% sensitivity on the first ECG for all total LAD occlusions, compared to 62% for STEMI criteria (P<0.0001). (sources/failure-stemi-criteria-lad-omi-ehjacc-2025, rating: high)
• Patients with LAD occlusion not meeting STEMI criteria had median door-to-balloon time 97 vs 40 min (P<0.001) with equivalent infarct size, demonstrating that STEMI criteria failure translates directly into treatment delays without reducing infarct burden. (sources/failure-stemi-criteria-lad-omi-ehjacc-2025, rating: high)

Epidemiology and Disparities

• Incidence of MI higher in Black males vs non-Hispanic White males — multifactorial (higher CAD risk factors, less guideline-directed medications, socioeconomic factors). (sources/ACS-AHA-2025, rating: very high)
• Women present with ACS ~10 years later than men, with greater CVD risk factor burden; more likely to present with non-chest pain symptoms; less likely to receive guideline-directed medical therapy and revascularization. (sources/ACS-AHA-2025, rating: very high)

Prehospital Assessment

• 12-lead ECG acquisition and interpretation within 10 minutes of FMC — Class I/B-NR. (sources/ACS-AHA-2025, rating: very high)
• STEMI: direct EMS transport to PCI-capable hospital; FMC-to-device goal ≤90 min (acceptable ≤120 min if ≤90 min not achievable). (sources/ACS-AHA-2025, rating: very high)
• Prehospital cath lab activation and advance notification significantly reduce reperfusion time and short/long-term mortality. (sources/ACS-AHA-2025, rating: very high)

Diagnosis

• hs-cTn preferred over conventional cTn; serial sampling at 0 and 1–2 h (hs-cTn) or 0 and 3–6 h (conventional); rising/falling pattern + ≥1 value >99th percentile = AMI. (sources/ACS-AHA-2025, rating: very high)
• Evidence-based clinical decision pathways (CDPs) incorporating delta hs-cTn achieve NPV >99.5% and reduce unnecessary testing in 21–43% of patients. (sources/ACS-AHA-2025, rating: very high)
• Risk scores: GRACE 2.0 (superior to physician assessment for predicting death/MI in STEMI/NSTE-ACS) and TIMI Risk Score are validated tools for risk stratification and guiding invasive strategy timing. (sources/ACS-AHA-2025, rating: very high)

Standard Medical Therapies

• Aspirin: Loading dose 162–325 mg → maintenance 75–100 mg daily — Class I/A. Non-enteric coated, chewed for faster onset. (sources/ACS-AHA-2025, rating: very high)
• P2Y12 inhibitors: Ticagrelor (180 mg load → 90 mg BID) or prasugrel (60 mg load → 10 mg daily) preferred over clopidogrel for PCI — Class I/B-R. Clopidogrel (300–600 mg load → 75 mg daily) is appropriate alternative (Class I). (sources/ACS-AHA-2025, rating: very high)
  • Prasugrel contraindicated with prior stroke/TIA (Class III: Harm)
  • Ticagrelor: 10–15% transient dyspnoea; always use with aspirin ≤100 mg daily
• Anticoagulation: UFH standard; bivalirudin COR 1 for STEMI-PCI (BRIGHT-4: post-PCI full-dose infusion 2–4 h reduces death + bleeding vs UFH); fondaparinux must NOT be used alone to support PCI (catheter thrombosis). (sources/ACS-AHA-2025, rating: very high)
• Lipid management: High-intensity statin — Class I/A; add nonstatin agent (ezetimibe, PCSK9 inhibitor, inclisiran, bempedoic acid) if LDL-C ≥70 mg/dL on maximal statin — Class I/A; reasonable if LDL-C 55–69 mg/dL — Class IIa. (sources/ACS-AHA-2025, rating: very high)
• Supplemental oxygen: Only if SpO₂ <90%; routine oxygen in SpO₂ ≥90% NOT recommended — Class III: No Benefit/A (DETO2X-AMI, AVOID trials). (sources/ACS-AHA-2025, rating: very high)

Reperfusion for STEMI

• PPCI preferred over fibrinolysis; radial approach preferred over femoral — reduces bleeding (51% RRR), vascular complications (62%), all-cause death (24%). (sources/ACS-AHA-2025, rating: very high)
• FMC-to-device ≤90 min system goal; each 30-minute delay → 7.5% relative increase in 1-year mortality. (sources/ACS-AHA-2025, rating: very high)
• Fibrinolysis if PCI not available within time window → transfer to PCI centre for angiography within 3–24 h post-fibrinolysis. (sources/ACS-AHA-2025, rating: very high)

NSTE-ACS Invasive Strategy

• Intermediate/high-risk: routine invasive approach with intent to revascularize during hospitalization — Class I/A (18% reduction in death/MI, 25% reduction in MI vs selective invasive, collaborative meta-analysis). (sources/ACS-AHA-2025, rating: very high)
• Immediate invasive (<2 h): refractory angina, hemodynamic/electrical instability — Class I/C-LD. (sources/ACS-AHA-2025, rating: very high)
• Low-risk: routine or selective invasive approach + noninvasive testing (stress test or CCTA) before discharge — Class I/A. (sources/ACS-AHA-2025, rating: very high)
• Comatose, stable, no ST-elevation after cardiac arrest: immediate angiography NOT recommended — Class III: No Benefit/A (6 contemporary RCTs). (sources/ACS-AHA-2025, rating: very high)

Multivessel CAD

• Complete revascularization in STEMI: Recommended — Class I/A; single-procedure multivessel PCI may be preferred over staged — Class IIb/B-R (BIOVASC, MULTISTARS AMI). (sources/ACS-AHA-2025, rating: very high)
• STEMI + cardiogenic shock: Culprit-only PCI; routine non-culprit PCI NOT recommended — Class III: Harm/B-R (CULPRIT-SHOCK: higher 30-day death/renal failure with multivessel PCI). (sources/ACS-AHA-2025, rating: very high)
• NSTE-ACS + multivessel disease: Complete revascularization — Class I/B-R (FIRE trial in elderly; BIOVASC); CABG preferred for complex left main/LAD disease, diabetes with multivessel LAD involvement. (sources/ACS-AHA-2025, rating: very high)

Cardiogenic Shock

• Emergency culprit vessel revascularization (PCI or CABG) regardless of time from onset — Class I/B-R. (sources/ACS-AHA-2025, rating: very high)
• Microaxial flow pump (Impella): Class IIa/B-R for selected STEMI + severe/refractory cardiogenic shock — DanGer-SHOCK (26% mortality reduction at 180 days, HR 0.74, NNT=8); selection: SCAI Stage C/D/E, noncomatose, LVEF <45%, adequate peripheral vasculature. (sources/ACS-AHA-2025, rating: very high)
• IABP + VA-ECMO: Routine use NOT recommended — Class III: No Benefit/B-R (IABP-SHOCK II; ECLS-SHOCK; ECMO-CS). (sources/ACS-AHA-2025, rating: very high)
• See also entities/Heart-Failure for detailed cardiogenic shock hemodynamics. (sources/ACS-AHA-2025, rating: very high)

Post-ACS Complications

• Mechanical complications (VSR, papillary muscle rupture, free wall rupture): manage at surgical centre; MCS as bridge to surgery; definitive surgical repair preferred; percutaneous options for prohibitive surgical risk. (sources/ACS-AHA-2025, rating: very high)
• ICD: LVEF ≤40% at ≥40 days post-MI + ≥90 days post-revascularization — Class I/A; clinically relevant VA >48 h within 40 days — Class IIa/C-EO; wearable cardioverter-defibrillator (VEST trial) — Class IIb/B-R (missed primary endpoint). (sources/ACS-AHA-2025, rating: very high)
• Post-MI pericarditis: High-dose aspirin + colchicine; glucocorticoids potentially harmful (impaired myocardial healing). (sources/ACS-AHA-2025, rating: very high)
• LV thrombus: Anticoagulation 3 months; DOACs non-inferior to VKA; highest risk with anterior STEMI + LVEF <30%. (sources/ACS-AHA-2025, rating: very high)

Long-Term Secondary Prevention (Discharge)

• DAPT default: Aspirin + oral P2Y12 inhibitor ≥12 months in patients not at high bleeding risk — Class I/A. See concepts/DAPT-Strategies for de-escalation strategies. (sources/ACS-AHA-2025, rating: very high)
• ACS + oral anticoagulant: Aspirin discontinuation 1–4 weeks post-PCI + P2Y12 (preferably clopidogrel) + OAC to reduce bleeding — Class I/B-R. See entities/Atrial-Fibrillation for triple therapy strategy. (sources/ACS-AHA-2025, rating: very high)
• Lipid reassessment: Fasting lipid panel 4–8 weeks after LLT initiation/adjustment — Class I/C-LD. (sources/ACS-AHA-2025, rating: very high)
• Colchicine 0.5 mg daily: Class IIb/B-R — COLCOT (32% composite MACE reduction at 22 months); noncardiovascular death signal under surveillance. (sources/ACS-AHA-2025, rating: very high)
• Influenza vaccination: Annual — Class I/A (IAMI trial: reduced CV death/MI/stent thrombosis vs placebo). (sources/ACS-AHA-2025, rating: very high)
• Cardiac rehabilitation: Referral before discharge — Class I/A; home-based CR equivalent for QOL and safety. (sources/ACS-AHA-2025, rating: very high)
• LVEF assessment before discharge — Class I/C-LD; repeat at 6–12 weeks if reduced. (sources/ACS-AHA-2025, rating: very high)

Contradictions / Open Questions

• STEMI criteria vs OMI — the paradigm gap: Standard STEMI STE criteria miss 38% of total LAD occlusions on all serial ECGs, yet remain the primary gatekeeper for emergent cath lab activation. NSTEMI patients with TIMI-0/1 flow (occluded artery) have nearly twice the mortality of NSTEMI with open arteries — a patient group currently denied immediate reperfusion under the STEMI model. Expert ECG interpretation and AI (PMCardio Queen of Hearts) both achieve 100% sensitivity where STEMI criteria fail, but widespread implementation requires validated quantitative criteria and prospective outcome data for OMI-based activation strategies. (sources/failure-stemi-criteria-lad-omi-ehjacc-2025, rating: high)
• Discharge diagnosis paradox: In patients with confirmed LAD occlusion not meeting STEMI criteria, the discharge diagnosis of STEMI vs NSTEMI correlated with door-to-balloon time rather than actual ECG findings — those treated quickly were labelled STEMI, those treated late were labelled NSTEMI. This suggests diagnostic labels may sometimes be retrospectively influenced by quality metric considerations rather than clinical reality. (sources/failure-stemi-criteria-lad-omi-ehjacc-2025, rating: high)
• Ticagrelor monotherapy vs aspirin monotherapy: Prasugrel monotherapy safety not established post-ACS; aspirin monotherapy after P2Y12 discontinuation carries excess thrombotic risk in STEMI subgroup. Optimal single antiplatelet after DAPT phase in ACS remains debated. (sources/ACS-AHA-2025, rating: very high)
• Routine pre-loading of P2Y12 inhibitors in NSTE-ACS: No RCT benefit for ticagrelor pre-loading before early (<24 h) invasive strategy; prasugrel pre-loading increases bleeding without ischemic benefit. Yet pharmacodynamic delay in STEMI context supports earlier loading — evidence gap for optimal timing. (sources/ACS-AHA-2025, rating: very high)
• Colchicine noncardiovascular death signal: COPS trial showed 8 vs 1 noncardiovascular deaths in colchicine vs placebo arm. COLCOT (larger, longer) did not confirm this. No definitive mechanistic explanation. Ongoing trials (post-MI specific) are needed before routine use can be unconditionally recommended. (sources/ACS-AHA-2025, rating: very high)
• Microaxial flow pump (Impella) generalizability: DanGer-SHOCK was conducted at 14 specialised European centres with strict selection criteria; optimal insertion timing, duration of support, and weaning strategy are not defined; real-world limb ischemia and bleeding rates may be higher. (sources/ACS-AHA-2025, rating: very high)
• Beta-blocker benefit in NSTE-ACS: Evidence supporting routine beta-blocker use in NSTE-ACS (as opposed to HFrEF post-ACS) is limited — identified as a future research gap. (sources/ACS-AHA-2025, rating: very high)
• Transition from ACS to chronic coronary syndrome: The exact timing of this transition is not defined; management implications for de-escalating antithrombotic therapy are individualized and lack RCT data. (sources/ACS-AHA-2025, rating: very high)

Transition to Chronic Coronary Disease

• Once ACS has been stabilised and the patient is discharged, management transitions to the chronic phase governed by the 2023 AHA/ACC CCD guideline. (sources/CCS-AHA-2023, rating: very high)
• Key chronic phase considerations not covered by the ACS 2025 guideline: beta-blocker de-escalation (COR 3 No Benefit if no prior LV dysfunction or ongoing indication), extended DAPT vs rivaroxaban low-dose strategy, INOCA if anatomy nonobstructive, CABG benefit for ischaemic cardiomyopathy, SGLT2i/GLP-1 RA integration.
• See entities/Chronic-Coronary-Disease for the full chronic phase management framework. (sources/CCS-AHA-2023, rating: very high)

Connections

• Related to entities/Chronic-Coronary-Disease — ACS stabilises into CCD; chronic phase management
• Related to concepts/DAPT-Strategies — DAPT duration and bleeding risk management post-ACS and CCD
• Related to entities/Heart-Failure — cardiogenic shock, post-MI LV dysfunction, MCS devices
• Related to entities/Atrial-Fibrillation — ACS + AF anticoagulation (triple therapy strategy)
• Related to concepts/Dyslipidemia-Management — LDL-C targets and statin/nonstatin use in ACS
• Related to concepts/ASCVD-Risk-Assessment — secondary prevention context
• Related to concepts/Right-Heart-Catheterization — cardiogenic shock hemodynamic assessment
• Related to concepts/OMI-NOMI-Paradigm — paradigm shift challenging STEMI/NSTEMI classification
• Related to concepts/Hyperacute-T-waves — most common OMI ECG finding missed by STEMI criteria
• Related to concepts/ST-T-Changes — mechanism and measurement of ischemia-related ECG changes
• Related to entities/PMCardio-Queen-of-Hearts — AI ECG model achieving 100% sensitivity for LAD OMI

Sources

• sources/ACS-AHA-2025
• sources/CCS-AHA-2023
• sources/failure-stemi-criteria-lad-omi-ehjacc-2025