Acute Coronary Syndromes

Acute coronary syndromes (ACS) encompass a spectrum of myocardial ischemia ranging from unstable angina to ST-elevation myocardial infarction (STEMI) and non-ST-elevation myocardial infarction (NSTEMI) ^[1]A1c[6]A1c. The term ACS is used to describe patients presenting with acute chest pain or other symptoms due to reduced blood flow to the heart.

Also Called

• Acute coronary syndrome (ACS)
• Coronary thrombosis (historical term)

Classification

The classification of ACS is based on the initial electrocardiogram (ECG) and cardiac biomarkers. The 2025 ACC/AHA guideline ^[1]A1c and the ROMIAE study ^[20]B2b define the following subtypes:

STEMI indicates transmural ischemia requiring immediate reperfusion. NSTEMI and unstable angina are grouped as non-ST-elevation ACS (NSTE-ACS) ^[14]A1b. The distinction between NSTEMI and unstable angina rests solely on biomarker evidence of myocardial necrosis.

Other Causes of ACS Presentation

Spontaneous coronary artery dissection (SCAD) has emerged as an important cause of ACS, myocardial infarction, and sudden death, particularly among young women and individuals with few conventional atherosclerotic risk factors ^[5]D5. Takotsubo syndrome , characterized by acute transient left ventricular systolic dysfunction, can mimic ACS and is challenging to distinguish from acute myocardial infarction at presentation ^[10]D5. These non-atherosclerotic etiologies require different diagnostic and therapeutic approaches.

Pearl: The initial ECG within 10 minutes of arrival is critical to differentiate STEMI from NSTE-ACS, as the need for emergent reperfusion is time-sensitive and drives the entire management pathway ^[1]A1c.

Building on the classification into STEMI, NSTEMI, and unstable angina, the epidemiology of acute coronary syndromes (ACS) reveals distinct patterns of incidence across populations and a well-defined set of modifiable and non-modifiable risk factors. Although precise global incidence rates for ACS are not reported in the available evidence, the condition remains a leading cause of morbidity and mortality worldwide, with particularly high burden in older adults and those with established atherosclerotic disease.

Demographic Distribution

ACS disproportionately affects men, but women account for a greater proportion of type 2 myocardial infarction (MI), though after adjustment for other risk factors, sex is not an independent predictor (adjusted hazard ratio [aHR] 0.82, 95% CI 0.66-1.01) ^[29]B2b. Spontaneous coronary artery dissection (SCAD), an important cause of ACS, occurs predominantly in young women and individuals with few conventional atherosclerotic risk factors, and is associated with pregnancy, physical and emotional stress triggers, and concurrent systemic arteriopathies such as fibromuscular dysplasia ^[5]D5. Age is a strong predictor: among patients enrolled in lipid-lowering trials, 8.8% of 244 090 participants were aged ≥75 years, and LDL cholesterol lowering reduced major vascular events by 26% per 1 mmol/L reduction in this older group (RR 0.74, 95% CI 0.61-0.89) ^[32]A1a.

Risk Factors for Type 1 and Type 2 Myocardial Infarction

Risk factors for both type 1 (plaque rupture) and type 2 (supply-demand mismatch) MI are similar, with age, hyperlipidaemia, diabetes, abnormal renal function, and known coronary disease predicting both (P < 0.05 for all) ^[29]B2b. The strongest predictor of a future type 2 MI is a prior history of type 2 events (aHR 6.18, 95% CI 4.70-8.12) ^[29]B2b. Beyond traditional risk factors, sex-specific factors are increasingly recognized: hormonal changes, pregnancy-related complications, autoimmune diseases, and treatments for transgender individuals and cancer contribute to the risk profile in women, who also experience higher rates of microvascular disease and endothelial dysfunction ^[13]D5.

Protective Interventions

Influenza vaccination in patients with ischaemic heart disease or heart failure reduces the composite of cardiovascular death, ACS, stent thrombosis, revascularization, stroke, or heart failure hospitalization (random effects HR 0.74, 95% CI 0.63-0.88, p < 0.001; NNT not calculable from reported data) ^[35]A1a. This suggests that infection prevention is a modifiable factor in ACS risk.

Pearl: The risk factors for type 2 MI mirror those for type 1 MI, but a prior history of type 2 events is the strongest predictor, a sixfold increased hazard, highlighting the importance of identifying and managing these patients after an initial episode ^[29]B2b.

The inciting event in acute coronary syndromes is plaque disruption, but the specific mechanism, rupture versus erosion, dictates the subsequent thrombotic and inflammatory response and carries distinct pathophysiological signatures ^[44]B2b.

Plaque Rupture and Erosion: Two Distinct Pathways

Among 170 consecutive ACS patients studied by optical coherence tomography, plaque rupture (RFC-ACS) caused 75.4% of events and intact fibrous cap erosion (IFC-ACS) caused 24.6% ^[44]B2b. Ruptured plaques are typically thin-cap fibroatheromas with a large necrotic core, abundant macrophages, and intraplaque hemorrhage. In contrast, eroded plaques have a thicker overlying fibrous cap, lower lipid content, less calcification, and are most often located near a coronary bifurcation ^[44]B2b.

At the microenvironment level, IFC-ACS culprit lesions show selective enrichment of CD4+ and CD8+ T-lymphocytes (+8.1% and +11.2%, respectively) and increased levels of the cytotoxic effector molecules granzyme A (+22.4%), perforin (+58.8%), and granulysin (+75.4%) compared with RFC plaques ^[44]B2b. These T-cells and their effector molecules cause endothelial cell death, a key mechanism in erosion. Disturbed laminar flow near bifurcations promotes CD8+ T-cell adhesion to endothelial cells, providing a mechanistic link to the predilection site ^[44]B2b.

Plaque Burden and High-Risk Features

Although ACS risk increases with percent diameter stenosis, more than 65% of patients with ACS had nonobstructive coronary artery disease at baseline ^[45]B3b. Among 129 culprit lesion precursors identified by coronary CTA, three-fourths exhibited <50% stenosis ^[45]B3b. Plaque composition matters: per mm³ increase in necrotic core volume, the adjusted hazard ratio for ACS was 1.593 (95% CI 1.219-2.082) ^[45]B3b. High-risk plaque features (positive remodeling, low attenuation, spotty calcification, napkin-ring sign) on CTA identify patients at elevated risk beyond stenosis severity and aggregate plaque burden ^[45]B3b.

Thrombosis and Myocardial Ischemia

Plaque disruption exposes subendothelial collagen and tissue factor, triggering platelet adhesion, activation, and aggregation, followed by the coagulation cascade. The resulting thrombus may cause complete occlusion (typically ST-elevation MI), subtotal occlusion (non-ST-elevation MI), or transient occlusion with spontaneous lysis (unstable angina). The downstream myocardial ischemia-reperfusion injury amplifies inflammation and can lead to microvascular obstruction, further impairing tissue perfusion.

Microvascular Dysfunction

Coronary microvascular dysfunction (CMD) plays a pivotal pathogenic role in ACS, particularly in patients with myocardial infarction with non-obstructive coronary arteries (MINOCA) and Takotsubo syndrome ^[47]D5. Functional and structural mechanisms, including abnormal dilatory responses, microvascular spasm, and extravascular compressive forces, can cause myocardial ischemia even in the absence of obstructive epicardial stenoses ^[47]D5. CMD also contributes to persistent angina after successful revascularization ^[47]D5.

Takotsubo Syndrome: A Catecholamine-Mediated Mimic

Takotsubo syndrome accounts for approximately 2-3% of all and 5-6% of female patients presenting with ACS ^[10]D5. It is precipitated by an endogenous catecholamine surge (epinephrine, norepinephrine) from emotional or physical stress, acting through the hypothalamic-pituitary-adrenal axis and local sympathetic nerve terminals ^[10]D5. The catecholamine excess leads to direct myocardial toxicity, beta-adrenoceptor-mediated damage, epicardial and microvascular vasoconstriction, and increased cardiac workload, resulting in transient apical left ventricular ballooning ^[46]D5. Contraction band necrosis is a histological hallmark, also seen in pheochromocytoma and subarachnoid hemorrhage ^[10]D5. Estrogen deprivation in postmenopausal women may facilitate the syndrome via endothelial dysfunction ^[46]D5.

Inflammatory and Immune Activation

Beyond the acute event, persistent immune activation influences prognosis. Neopterin, a marker of monocyte activation, is an independent predictor of heart failure hospitalization after ACS; per 1-SD increment in log(neopterin), the adjusted risk of HF increased by 34% (HR 1.34, 95% CI 1.10-1.64) ^[38]B2b. In Takotsubo syndrome, both pro-inflammatory (interleukin-2, interleukin-4, interleukin-8, interferon-γ, tumor necrosis factor-α) and anti-inflammatory (interleukin-10) cytokines are elevated at presentation and can remain elevated for months ^[10]D5.

Pearl: The distinct immune signature of plaque erosion (CD8+ T-cell cytotoxicity) versus rupture (macrophage-driven inflammation) may eventually guide tailored antithrombotic therapy; differentiation requires intravascular imaging (OCT) at the time of angiography ^{[37]D5[44]B2b}.

From the pathophysiologic mechanisms of plaque rupture and erosion, the clinical presentation of acute coronary syndromes spans a spectrum of myocardial ischemia from unstable angina to ST-elevation myocardial infarction, each with distinct implications for urgent management ^[1]A1c.

Presenting Symptoms

The 2025 ACC/AHA guideline defines ACS as encompassing ST-elevation myocardial infarction, non-ST-elevation myocardial infarction, and unstable angina ^[1]A1c. The 2021 AHA/ACC chest pain guideline provides an evidence-based approach to risk stratification for patients presenting with chest pain, emphasizing that the initial evaluation must promptly identify those with suspected ACS ^[3]A1c. Spontaneous coronary artery dissection (SCAD) has emerged as an important cause of ACS, particularly among young women and individuals with few conventional atherosclerotic risk factors ^[5]D5. Takotsubo syndrome presents with acute transient left ventricular systolic dysfunction, often triggered by emotional or physical stress, and can be challenging to distinguish from acute myocardial infarction at presentation ^[10]D5.

Phenotypic Variants

The table below summarizes the key phenotypic variants of ACS and their distinguishing features.

Red Flags

In patients with suspected ACS, the presence of hemodynamic instability, pulmonary edema, or cardiogenic shock signals the need for emergent revascularization. The 2025 ACC/AHA guideline provides updated recommendations for the management of these high-risk presentations ^[1]A1c. Additionally, the 2023 AHA/ACC atrial fibrillation guideline notes that atrial fibrillation is a common sustained arrhythmia and may complicate ACS, increasing the risk of thromboembolic events ^[4]A1c.

Atypical Presentations

Atypical presentations are common in certain populations. SCAD should be considered in young women, especially those with few conventional risk factors, pregnancy, or a history of fibromuscular dysplasia ^[5]D5. Takotsubo syndrome often presents with chest pain and dyspnea mimicking STEMI, but with a characteristic emotional or physical stress trigger ^[10]D5. Type 2 myocardial infarction, triggered by acute illness, is more common in women and older patients; its strongest predictor is a prior history of type 2 events (aHR 6.18, 95% CI 4.70-8.12) ^[29]B2b. The 2025 ACC/AHA guideline emphasizes that recognition of these variants is critical for appropriate management ^[1]A1c.

Pearl: In a young woman presenting with chest pain and few atherosclerotic risk factors, consider SCAD as the cause of ACS, especially if there is a history of peripartum or emotional stress ^[5]D5.

The clinical presentation of ACS, chest pain, dyspnea, diaphoresis, triggers a diagnostic pathway that must rapidly differentiate STEMI from NSTEMI and unstable angina, as the need for emergent reperfusion differs fundamentally. The workup hinges on two parallel pillars: the 12-lead ECG and serial cardiac troponin measurement, with coronary angiography serving as the definitive anatomic reference when indicated.

Electrocardiogram

A 12-lead ECG should be obtained and interpreted within 10 minutes of first medical contact. ST-segment elevation at the J point in two contiguous leads (≥1 mm in limb leads, ≥2 mm in precordial leads V2-V3) defines STEMI and mandates immediate reperfusion. The absence of ST-elevation does not exclude ischemia; dynamic ST-depression or T-wave inversion may signal NSTEMI or unstable angina. The 2025 ACC/AHA guideline emphasizes that ECG interpretation must be integrated with clinical context and serial tracings ^[1]A1c[6]A1c.

Cardiac Troponin

Cardiac troponin (I or T) is the gold-standard biomarker for myocardial injury. The diagnosis of acute myocardial infarction requires a rise and/or fall of troponin with at least one value above the 99th percentile upper reference limit, accompanied by evidence of myocardial ischemia (symptoms, ECG changes, imaging, or pathology). High-sensitivity troponin (hs-cTn) assays enable rapid rule-out algorithms (0/1-hour or 0/2-hour). In low-risk patients (HEAR score ≤3), a single pre-hospital point-of-care troponin measurement can safely rule out NSTE-ACS, reducing healthcare costs without increasing 30-day major adverse cardiac events (MACE: 0.5% vs 1.0% in the pre-hospital vs ED strategy; risk difference -0.5%, 95% CI -1.6% to 0.7%) ^[14]A1b.

Diagnostic Test Performance

Imaging

Coronary CT angiography (CCTA) is recommended for low-to-intermediate-risk patients (TIMI risk score 0-2) presenting with possible ACS. In the ROMICAT II trial, a CCTA-based strategy allowed safe discharge from the emergency department in 49.6% of patients vs 22.7% with traditional care (difference 26.8 percentage points), with a shorter median length of stay (18.0 vs 24.8 hours) and higher detection of coronary disease (9.0% vs 3.5%) ^[19]A1b. A negative CCTA (no coronary stenosis ≥50%) carries a 30-day MACE rate of 0% (95% CI 0-0.57), supporting expedited discharge ^[19]A1b.

Diagnostic Algorithm

Step 1: Obtain ECG within 10 minutes. If ST-elevation, proceed to STEMI pathway. Step 2: Measure serial hs-cTn. If elevated, diagnose NSTEMI and risk-stratify ( GRACE , TIMI). Step 3: If troponin negative, assess clinical risk. Low-risk patients (HEAR ≤3) may be ruled out with a single pre-hospital POC troponin ^[14]A1b. Low-to-intermediate-risk patients (TIMI 0-2) benefit from CCTA; a negative study permits safe discharge ^[19]A1b. High-risk features (hemodynamic instability, recurrent pain, GRACE >140) warrant invasive angiography.

Differential Diagnosis

Several conditions mimic ACS and must be distinguished, particularly when troponin is elevated or ECG is abnormal:

• Spontaneous coronary artery dissection (SCAD): An important cause of ACS in young women and those without traditional risk factors; requires conservative management rather than aggressive revascularization ^[5]D5.
• Takotsubo syndrome : Acute transient left ventricular systolic dysfunction triggered by emotional or physical stress, often with apical ballooning; catecholamine-induced myocardial injury is the leading hypothesis ^[10]D5.
• Myocarditis : Diffuse or focal myocardial inflammation, often viral, with troponin elevation and ECG changes that may simulate infarction.
• Pulmonary embolism: Can cause chest pain, dyspnea, and troponin elevation due to right ventricular strain.
• Aortic dissection: Severe tearing chest pain radiating to the back, with possible coronary ostial involvement causing secondary ACS.
• Pericarditis: Pleuritic chest pain, diffuse ST-elevation (concave upward), PR depression, and often a pericardial rub.

Pearl: A normal hs-cTn at presentation does not exclude unstable angina or NSTEMI if symptoms are ongoing, repeat troponin at 1-3 hours is essential, and the ECG must be scrutinized for dynamic changes that may precede biomarker elevation.

Following diagnosis, the next critical step is to stratify the patient's risk to guide the intensity and timing of therapy. The GRACE risk score , with a threshold >140, identifies patients who derive mortality benefit from an early invasive strategy (HR 0.70, 95% CI 0.52-0.95) ^[34]A1a. Low-risk patients ( TIMI risk score 0-2) can be safely managed with coronary computed tomographic angiography; a negative study yields 0% major adverse cardiac events at 30 days ^[19]A1b. The HEART score|HEAR score ≤3 identifies low-risk patients suitable for pre-hospital rule-out, with major adverse cardiac events of only 0.5% ^[14]A1b. However, an electrocardiogram-based machine learning model outperforms the HEART score, with a negative predictive value of 93.4% and sensitivity of 85.9% vs 89.0% and 75.0%, respectively ^[59]B2b.

Novel biomarkers refine risk prediction. The ceramide ratio Cer(d18:1/16:0)/Cer(d18:1/24:0) improves the GRACE score (net reclassification improvement 0.17, ΔAUC 0.09) ^[57]B2b. The KID-ACS score, integrating proenkephalin , predicts in-hospital acute kidney injury (AUC 0.72) and 30-day mortality (AUC 0.91) ^[58]B2b. The ABC-ACS ischemia score, incorporating growth differentiation factor 15 and N-terminal pro-B-type natriuretic peptide , has a C-index of 0.71-0.72 for 1-year cardiovascular death or myocardial infarction ^[56]B2b.

Familial hypercholesterolemia confers a >2-fold adjusted risk of coronary event recurrence within 1 year ^[55]B2b. A prior type 2 myocardial infarction is the strongest predictor of future type 2 events (adjusted HR 6.18) ^[29]B2b. The Thrombolysis In Myocardial Infarction Risk Score for Secondary Prevention and DAPT score stratify risk for antiplatelet monotherapy, but clopidogrel 's benefit over aspirin is consistent across risk groups ^[52]B2b.

Pearl: The KID-ACS score, with just six variables, simultaneously predicts in-hospital acute kidney injury and 30-day mortality, outperforming established scores.

Risk stratification immediately directs the next decision: the need for and timing of invasive coronary angiography. The 2025 ACC/AHA/ACEP/NAEMSP/SCAI guideline on ACS provides the contemporary framework for this pathway ^[1]A1c[6]A1c. The following algorithm outlines the acute management sequence from the moment of diagnosis.

Step 1: Immediate Pharmacotherapy

All patients with suspected ACS receive aspirin 162-325 mg chewed immediately, followed by a P2Y12 inhibitor. The 2025 guideline recommends ticagrelor 180 mg oral loading dose or prasugrel 60 mg oral loading dose (for those undergoing PCI) as first-line agents ^[1]A1c[6]A1c. The STOPDAPT-3 trial (N=6002) compared an aspirin-free strategy using low-dose prasugrel (loading 20 mg, maintenance 3.75 mg/day) versus DAPT (aspirin 81-100 mg + prasugrel 3.75 mg/day) in patients with ACS or high bleeding risk undergoing PCI. At 1 month, the no-aspirin group was not superior for major bleeding (4.47% vs 4.71%; HR 0.95, 95% CI 0.75-1.20; P=0.66) and was noninferior for cardiovascular events (4.12% vs 3.69%; HR 1.12, 95% CI 0.87-1.45; Pnoninferiority=0.01), but showed an excess of subacute stent thrombosis (0.58% vs 0.17%; HR 3.40, 95% CI 1.26-9.23) ^[22]A1b. Therefore, DAPT with aspirin plus a P2Y12 inhibitor remains the standard of care; an aspirin-free strategy is not recommended in the acute phase.

Anticoagulation is added to DAPT in the acute setting. Choose either:

• Unfractionated heparin (UFH) 60 IU/kg bolus (max 4000 IU) then 12 IU/kg/h infusion (max 1000 IU/h), titrated to aPTT 1.5-2.0 times control, or
• Enoxaparin 1 mg/kg subcutaneous every 12 h (preferred for NSTEMI), or
• Bivalirudin 0.75 mg/kg bolus then 1.75 mg/kg/h for the duration of PCI (alternative for patients at high bleeding risk).

Step 2: Revascularization Strategy

For STEMI, primary PCI is the definitive therapy and should be performed within 90 minutes of first medical contact ^[1]A1c[6]A1c. For NSTEMI, the decision for early invasive versus selective invasive management is guided by risk stratification. The pre-hospital rule-out strategy using a point-of-care troponin measurement in low-risk patients (HEAR score ≤3) was shown to reduce healthcare costs (€1349 vs €1960; mean difference €611, 95% CI 353-869) with very low MACE in the ruled-out group (0.5% vs 1.0%; risk difference -0.5%, 95% CI -1.6%-0.7%) ^[14]A1b. This supports a risk-based approach to avoid unnecessary ED evaluation in low-risk patients.

Step 3: Lipid-Lowering Therapy Initiation

High-intensity statin therapy (e.g., atorvastatin 80 mg daily) should be started as soon as possible after ACS, regardless of baseline LDL-C. The ES-BempedACS trial (N=206) evaluated triple lipid-lowering therapy (high-intensity statin + ezetimibe + bempedoic acid) versus dual therapy (statin + ezetimibe) initiated within 72 hours of ACS. At 8 weeks, the proportion achieving LDL-C <55 mg/dL was 59.4% in the triple group vs 53.1% in the dual group (P=0.376); adding bempedoic acid did not improve LDL-C goal attainment ^[60]A1b. Therefore, initiation of high-intensity statin plus ezetimibe is recommended; bempedoic acid is not indicated in the acute phase.

Step 4: What NOT to Do in the Acute Phase

Colchicine should not be started for acute ACS. The COPS trial (N=795) randomized patients with ACS to colchicine 0.5 mg twice daily for 1 month then 0.5 mg daily for 11 months versus placebo. The primary composite outcome (all-cause mortality, ACS, urgent revascularization, stroke) occurred in 24 colchicine vs 38 placebo patients (P=0.09). Notably, all-cause death was higher in the colchicine group (8 vs 1; P=0.017), driven by noncardiovascular deaths (5 vs 0; P=0.024) ^[11]A1b. The 2025 guideline does not recommend colchicine for acute management.

Drug Comparison Table: Antiplatelet Options for ACS

Controversies and Guideline Disagreement

Pearl: For every patient with ACS, start aspirin and a P2Y12 inhibitor (ticagrelor or prasugrel) immediately, proceed to revascularization based on ECG and risk score, and initiate high-intensity statin plus ezetimibe; do not use colchicine in the acute phase ^{[1]A1c[6]A1c[11]A1b[22]A1b[60]A1b}.

After the acute phase is stabilized, the focus shifts to long-term secondary prevention with guideline-directed medical therapy to reduce recurrent ischemic events and mortality. The 2025 ACC/AHA/ACEP/NAEMSP/SCAI Guideline for the Management of Patients With Acute Coronary Syndromes provides the framework for this chronic phase ^[1]A1c[6]A1c. The following steps outline the evidence-based ladder for antiplatelet, lipid-lowering, and anti-inflammatory therapy.

Step 1: Antiplatelet Therapy, DAPT Duration and Monotherapy Choice

Dual antiplatelet therapy (DAPT) with aspirin and a P2Y12 inhibitor is standard for the first 12 months after ACS, unless bleeding risk is prohibitive. After DAPT, single antiplatelet therapy is continued indefinitely. The 2025 guideline updates recommendations on DAPT duration ^[1]A1c[6]A1c.

• Clopidogrel monotherapy after DAPT is an attractive alternative to aspirin. In the STOPDAPT-2 trial, clopidogrel monotherapy following 1 month of DAPT was noninferior to aspirin monotherapy following 12 months of DAPT for the primary composite endpoint (11.75% vs 13.57%; HR 0.85, 95% CI 0.70-1.05; Pnoninferiority<0.001) and superior for cardiovascular outcomes (8.61% vs 11.05%; HR 0.77, 95% CI 0.61-0.97; P=0.03) ^[62]A1b.
• Aspirin-free strategy with prasugrel monotherapy early after PCI failed to show superiority for bleeding and was associated with excess subacute stent thrombosis (0.58% vs 0.17%; HR 3.40, 95% CI 1.26-9.23) in the STOPDAPT-3 trial ^[22]A1b. Therefore, initial DAPT remains mandatory.

Step 2: Lipid-Lowering Therapy, Intensive LDL-C Reduction

High-intensity statin therapy is the cornerstone. The EVOPACS trial demonstrated that adding evolocumab 420 mg SC to atorvastatin 40 mg in-hospital after ACS reduced LDL-C from 3.61 to 0.79 mmol/L at 8 weeks, with 95.7% of patients achieving LDL-C <1.8 mmol/L ^[63]A1b.

• First-line: High-intensity statin (e.g., atorvastatin 40 mg) ^[63]A1b.
• Second-line: Add ezetimibe if LDL-C remains ≥55 mg/dL.
• Third-line: Add a PCSK9 inhibitor (evolocumab or alirocumab). In ODYSSEY Outcomes, alirocumab reduced MACE (HR 0.85, 95% CI 0.78-0.93) and lowering lipoprotein(a) independently contributed to risk reduction (HR 0.994 per 1 mg/dL reduction; P=0.0081) ^[26]A1b. Alirocumab also reduced oxidized phospholipids on apolipoprotein B-100 (OxPL-apoB) by 13.0% and Lp(a) by 26.2%, abrogating the risk associated with elevated OxPL-apoB ^[12]B2b.
• Bempedoic acid: Adding bempedoic acid to statin+ezetimibe early after ACS did not improve the proportion achieving LDL-C <55 mg/dL at 8 weeks (59.4% vs 53.1%; P=0.376) ^[60]A1b. Its role may be reserved for later intensification.

Figure 1: Stepwise lipid-lowering algorithm after ACS (adapted from ^[1]A1c[6]A1c).

Step 3: Anti-Inflammatory Therapy, Colchicine

Colchicine 0.5 mg/day reduces cardiovascular events in patients with stable coronary disease. In the LoDoCo trial, colchicine reduced the primary composite outcome (ACS, out-of-hospital cardiac arrest, or noncardioembolic ischemic stroke) from 16.0% to 5.3% (HR 0.33, 95% CI 0.18-0.59; NNT=11) ^[25]A1b. A meta-analysis of >11,000 patients reported a >30% reduction in CV death, MI, ischemic stroke, and ischemia-driven revascularization (RR 0.63, 95% CI 0.49-0.81) ^[61]D5. Initiate after the acute phase once the patient is stable. Gastrointestinal intolerance occurs in ~10% of patients but is usually transient ^[61]D5.

Step 4: Other Risk Factor Management

• Sex-specific care: Women are less likely to receive guideline-directed therapy and have higher risk of adverse outcomes after ACS ^[13]D5. Ensure equitable treatment and consider microvascular disease.
• Special populations: Spontaneous coronary artery dissection (SCAD) requires different management, avoid aggressive antiplatelet therapy and revascularization unless necessary ^[5]D5. Takotsubo syndrome lacks evidence-based interventions; supportive care and trigger avoidance are mainstays ^[10]D5.

What NOT to Do

• Do not use an aspirin-free strategy with prasugrel monotherapy early after PCI; it increases stent thrombosis without reducing bleeding ^[22]A1b.
• Do not start colchicine in patients with advanced renal or liver disease without dose adjustment ^[61]D5.
• Do not routinely add bempedoic acid early after ACS; it did not improve LDL-C goal attainment ^[60]A1b.

Controversies and Guideline Disagreement

No major guideline disagreements were identified in the reviewed evidence. The 2025 ACC/AHA guideline ^[1]A1c[6]A1c provides updated recommendations that supersede prior guidelines.

Dosing Table

Pearl: After ACS, initiate high-intensity statin and DAPT, then step down to clopidogrel monotherapy after 12 months; add colchicine 0.5 mg/day for anti-inflammatory benefit, and escalate to PCSK9 inhibitor if LDL-C remains above 55 mg/dL despite statin+ezetimibe.

While guideline-directed medical therapy provides the long-term foundation, the management of ACS is defined by procedural decisions on revascularization, who, when, and how.

Step 1: Revascularization Decision

The 2025 ACC/AHA/ACEP/NAEMSP/SCAI guideline recommends immediate primary PCI for STEMI with a goal of ≤120 minutes from first medical contact ^[1]A1c. For NSTE-ACS, an early invasive strategy (≤24 hours) is indicated for high-risk patients (refractory ischemia, hemodynamic instability, GRACE score >140). A meta-analysis of 17 RCTs (n=10,209) found that early invasive strategy did not reduce all-cause mortality (RR 0.90, 95% CI 0.78-1.04) or MI, but reduced recurrent ischemia (RR 0.57, 95% CI 0.40-0.81) and length of stay (median difference -22 hours) ^[68]A1a.

In patients with prior CABG , a meta-analysis of 11 RCTs (n=897) found no benefit of routine invasive over conservative strategy for all-cause mortality (RR 1.12, 95% CI 0.97-1.29) or cardiac mortality (RR 1.05, 95% CI 0.70-1.58) ^[67]A1a. A conservative approach is reasonable in this subgroup unless high-risk features are present.

Step 2: Percutaneous Coronary Intervention (PCI), Technique and Timing

For intermediate coronary lesions, fractional flow reserve (FFR)-guided PCI reduces the composite of cardiac death or MI compared to medical therapy (HR 0.72, 95% CI 0.54-0.96; driven by MI reduction; NNT not calculable from reported data) ^[69]A1a. In selected patients undergoing elective PCI, same-day discharge is safe: a meta-analysis of 37 studies (n=12,803) showed no difference in death/MI/TLR (OR 0.90, 95% CI 0.43-1.87) or major bleeding (OR 1.69, 95% CI 0.84-3.40) compared to overnight observation ^[65]B2a.

Step 3: Antiplatelet Therapy After PCI

Post-PCI antiplatelet strategy is integral to the interventional plan. The Academic Research Consortium defines modulation strategies, de-escalation, escalation, and monotherapy ^[64]D5. An individual patient meta-analysis of 4 RCTs (n=10,133) showed that de-escalation of potent P2Y12 inhibitor reduced ischemic (2.3% vs 3.0%, HR 0.761, 95% CI 0.597-0.972) and bleeding events (6.5% vs 9.1%, HR 0.701, 95% CI 0.606-0.811) ^[66]A1a.

Early aspirin cessation is supported by the T-PASS trial (n=2850), which demonstrated that stopping aspirin within 1 month (median 16 days) for ticagrelor 90 mg twice daily monotherapy was superior to 12-month DAPT for net clinical benefit (2.8% vs 5.2%, HR 0.54, 95% CI 0.37-0.80; NNT = 42), primarily due to reduced major bleeding (1.2% vs 3.4%, HR 0.35, 95% CI 0.20-0.61; NNT = 46) ^[70]A1b.

For long-term monotherapy, the HOST-EXAM Extended study (n=5438) showed that clopidogrel 75 mg daily was superior to aspirin 100 mg daily for the composite of death, MI, stroke, ACS readmission, and major bleeding (12.8% vs 16.9%, HR 0.74, 95% CI 0.63-0.86; NNT = 24) over 5.8 years ^[24]A1b. This benefit was consistent across risk subgroups ^[52]B2b. However, the STOPDAPT-3 trial (n=6002) found that an aspirin-free strategy with prasugrel 3.75 mg/day followed by clopidogrel monotherapy was associated with excess stent thrombosis (0.58% vs 0.17%, HR 3.40, 95% CI 1.26-9.23) compared to DAPT ^[22]A1b. At 1 year, aspirin vs clopidogrel monotherapy after 1-month DAPT showed similar outcomes (HR 1.00 for cardiovascular, 1.02 for bleeding) ^[31]A1b.

Step 4: Coronary Artery Bypass Grafting (CABG)

For multivessel disease, especially with left main or proximal LAD involvement, CABG may be preferred over PCI. Hybrid revascularization (culprit PCI followed by CABG for non-culprit vessels) is an option but requires careful management of DAPT interruption ^[71]D5.

Special Populations: Spontaneous Coronary Artery Dissection (SCAD)

SCAD accounts for up to 4% of ACS, particularly in young women. Conservative management is preferred; PCI carries risk of propagation. Revascularization is reserved for ongoing ischemia or hemodynamic instability ^[5]D5.

What NOT to Do

Do not routinely use colchicine in ACS; the COPS trial (n=795) showed no significant benefit and higher all-cause mortality (8 vs 1 death, P=0.017) ^[11]A1b. Do not use an aspirin-free strategy with prasugrel alone due to increased stent thrombosis ^[22]A1b.

No major guideline disagreements identified in the reviewed evidence.

Pearl: For NSTE-ACS, early invasive strategy reduces recurrent ischemia but not mortality; in patients with prior CABG, a conservative approach is reasonable. After PCI, consider de-escalation or early aspirin cessation to reduce bleeding, the T-PASS trial supports ticagrelor monotherapy after 1 month, and HOST-EXAM supports clopidogrel monotherapy long-term.

The evolution of pharmacotherapy for ACS has paralleled advances in revascularization, with landmark trials progressively refining antiplatelet, lipid-lowering, and anti-inflammatory strategies. The 2025 ACC/AHA/ACEP/NAEMSP/SCAI Guideline for the Management of Patients With Acute Coronary Syndromes incorporates new evidence since the 2013 STEMI guideline, the 2014 NSTE-ACS guideline, and the 2015 focused update on primary PCI, and retires the 2016 focused update on dual antiplatelet therapy (DAPT) duration ^[1]A1c[6]A1c. This section traces the evidentiary origin of current standards and highlights therapies that were abandoned or refined.

Antiplatelet Therapy: From Aspirin to DAPT and Beyond

Aspirin was the historical cornerstone. The addition of a P2Y12 inhibitor ( clopidogrel , prasugrel , ticagrelor ) became standard after trials showing reduced ischemic events. The optimal duration and composition of DAPT have been intensely studied. The STOPDAPT-3 trial tested an aspirin-free strategy using low-dose prasugrel (3.75 mg/day) monotherapy versus DAPT with aspirin plus prasugrel in 6002 patients with ACS or high bleeding risk. At 1 month, the no-aspirin group was not superior for major bleeding (4.47% vs 4.71%; HR 0.95, 95% CI 0.75-1.20; P=0.66) and was noninferior for cardiovascular events (4.12% vs 3.69%; HR 1.12, 95% CI 0.87-1.45; Pnoninferiority=0.01). However, there was an excess of subacute stent thrombosis (0.58% vs 0.17%; HR 3.40, 95% CI 1.26-9.23) and unplanned revascularization ^[22]A1b. This safety signal prevented adoption of an aspirin-free strategy early after PCI.

Long-term monotherapy choices have shifted. The HOST-EXAM Extended study followed 5438 patients who had completed 12±6 months of DAPT without events and were randomized to clopidogrel 75 mg once daily or aspirin 100 mg once daily. Over a median 5.8 years, the primary composite endpoint occurred in 12.8% of the clopidogrel group vs 16.9% of the aspirin group (HR 0.74, 95% CI 0.63-0.86; P<0.001; NNT=24). Clopidogrel also reduced thrombotic events (7.9% vs 11.9%; HR 0.66, 95% CI 0.55-0.79) and bleeding (4.5% vs 6.1%; HR 0.74, 95% CI 0.57-0.94) ^[24]A1b. Similarly, STOPDAPT-2 compared clopidogrel monotherapy after 1 month of DAPT versus aspirin monotherapy after 12 months of DAPT; over 5 years, clopidogrel was noninferior and superior for cardiovascular outcomes (8.61% vs 11.05%; HR 0.77, 95% CI 0.61-0.97; P=0.03) ^[62]A1b. These trials support clopidogrel as the preferred long-term monotherapy over aspirin.

Lipid-Lowering Therapy: Statins , Ezetimibe , and PCSK9 Inhibitors

High-intensity statin therapy became standard after ACS. The 2025 guideline recommends an LDL-C target <55 mg/dL ^[1]A1c[6]A1c. The EVOPACS trial randomized 308 patients hospitalized for ACS to evolocumab 420 mg subcutaneously or placebo, on top of atorvastatin 40 mg. At 8 weeks, mean LDL-C fell from 3.61 to 0.79 mmol/L in the evolocumab group vs 3.42 to 2.06 mmol/L in placebo (difference -; 95% CI -45.2 to -36.2; P<0.001). 95.7% of evolocumab-treated patients achieved LDL-C <1.8 mmol/L vs 37.6% with placebo ^[63]A1b. This established the feasibility and safety of early PCSK9 inhibition.

The ODYSSEY OUTCOMES trial (18,924 patients) showed that alirocumab reduced major adverse cardiovascular events (MACE) by 15% (HR 0.85, 95% CI 0.78-0.93) over a median 2.8 years ^[26]A1b. Alirocumab also lowered lipoprotein(a) by 5.0 mg/dL (IQR 0-13.5), and each 1 mg/dL reduction in Lp(a) independently predicted lower MACE risk (HR 0.994, 95% CI 0.990-0.999; P=0.0081) ^[26]A1b. Furthermore, achieved apolipoprotein B levels ≤35 mg/dL were associated with lower residual risk, even after adjusting for LDL-C ^[23]B2b.

In contrast, the ES-BempedACS trial tested triple lipid-lowering therapy (high-intensity statin + ezetimibe + bempedoic acid) versus dual therapy (statin + ezetimibe) in 206 patients within 72 hours of ACS. At 8 weeks, the proportion achieving LDL-C <55 mg/dL was 59.4% vs 53.1% (P=0.376), and the percentage change in LDL-C was similar (57.5% vs 56.9%; P=0.823) ^[60]A1b. Adding bempedoic acid did not improve goal attainment, though it was safe.

Anti-Inflammatory Therapy: Colchicine

Colchicine emerged from the observation that neutrophil activation contributes to plaque instability. In stable coronary disease, the LoDoCo trial (532 patients) showed that colchicine 0.5 mg/day reduced the composite of ACS, cardiac arrest, or stroke from 16.0% to 5.3% (HR 0.33, 95% CI 0.18-0.59; P<0.001; NNT=11) ^[25]A1b. However, in the acute setting, the COPS trial (795 patients with ACS) found no significant reduction in the primary composite endpoint (24 events vs 38; P=0.09) and a higher rate of total death (8 vs 1; P=0.017) and noncardiovascular death (5 vs 0; P=0.024) with colchicine 0.5 mg twice daily for 1 month then 0.5 mg daily ^[11]A1b. This safety concern tempered enthusiasm for routine use in ACS. Mechanistically, the COLOCT trial (128 patients) demonstrated that colchicine 0.5 mg daily for 12 months increased minimal fibrous cap thickness by 34.2 μm (95% CI 9.7-58.6; P=0.006) and reduced lipid arc and macrophage extension on optical coherence tomography ^[48]A1b, providing a plausible plaque-stabilizing effect.

Controversies and Guideline Disagreement

Pearl: The evolution of ACS pharmacotherapy is marked by the shift from aspirin monotherapy to clopidogrel monotherapy for long-term prevention (NNT=24 over 5.8 years) ^[24]A1b, the early use of PCSK9 inhibitors to achieve LDL-C <55 mg/dL ^[63]A1b, and the abandonment of routine aspirin-free strategies early after PCI due to excess stent thrombosis ^[22]A1b.

Advances in antithrombotic and revascularization strategies have shifted the complication profile of ACS from exclusive focus on ischemic events to a dual burden of ischemia and iatrogenic harm, particularly bleeding and contrast-associated kidney injury.

Bleeding Complications

Major bleeding remains the most common iatrogenic complication after ACS revascularization. In the T-PASS trial, ticagrelor monotherapy after <1 month of dual antiplatelet therapy (DAPT) reduced major bleeding from 3.4% to 1.2% (HR 0.35, 95% CI 0.20-0.61; P<0.001; NNT ≈ 45) ^[70]A1b. Conversely, an aspirin -free strategy with prasugrel monotherapy in STOPDAPT-3 failed to reduce major bleeding (4.47% vs 4.71%; P=0.66) and was associated with excess subacute stent thrombosis (0.58% vs 0.17%; HR 3.40, 95% CI 1.26-9.23) ^[22]A1b. Twice-daily aspirin dosing in patients with diabetes or high-risk aspirin resistance did not lower MACE (7.7% vs 8.8%; HR 0.90, 95% CI 0.69-1.19) and did not increase major bleeding (1.9% vs 2.1%) ^[74]A1b.

Contrast-Induced Nephropathy

Contrast-induced nephropathy (CIN) complicates 30.5% of coronary angiograms in at-risk ACS patients (mean age 71 years, 56% with CKD). In the NITRATE-CIN trial, a 5-day course of inorganic nitrate 12 mmol daily reduced CIN to 9.1% (OR 0.21, 95% CI 0.13-0.34; P<0.001; NNT ≈ 5) and also lowered procedural myocardial infarction (2.7% vs 12.5%) and 1-year MACE (9.1% vs 18.1%) ^[73]A1b.

Pharmacotherapy Adverse Effects

Colchicine 0.5 mg twice daily then 0.5 mg daily in ACS was associated with a higher rate of total death (8 vs 1; P=0.017) and noncardiovascular death (5 vs 0; P=0.024) compared with placebo ^[11]A1b. In stable CAD, colchicine 0.5 mg/day reduced cardiovascular events (5.3% vs 16.0%; HR 0.33, 95% CI 0.18-0.59; NNT = 11) but 11% of patients withdrew within 30 days due to intestinal intolerance ^[25]A1b. These data underscore that colchicine should not be used in the acute phase of ACS.

The 2025 ACC/AHA guideline provides comprehensive recommendations for respiratory monitoring, autonomic complications, DVT/PE prophylaxis, pain management, rehabilitation, and hospital-acquired complications (pneumonia, pressure injury, UTI) ^[1]A1c[6]A1c; the evidence available here focuses on the most common iatrogenic complications.

Pearl: The most impactful modifiable complication is contrast-induced nephropathy, a 5-day course of inorganic nitrate cuts risk by two-thirds, with an NNT of 5 ^[73]A1b.

Despite advances in acute management, the long-term prognosis after ACS remains shaped by residual ischaemic and bleeding risks, as well as the effectiveness of secondary prevention. Without treatment, ACS carries high mortality, but contemporary data focus on risk reduction with guideline-directed therapy.

Long-Term Outcomes After Guideline-Directed Therapy

With optimal medical therapy, event rates are substantially reduced but residual risk persists. The absolute risk reduction depends on the agent and patient profile:

Antiplatelet de-escalation (guided or unguided) reduced both ischaemic (2.3% vs 3.0%, HR 0.76) and bleeding events (6.5% vs 9.1%, HR 0.70) at 1 year ^[66]A1a. Early invasive strategy in NSTE-ACS reduced recurrent ischaemia (RR 0.57) but not mortality or MI ^[68]A1a.

Predictors of Outcomes

• Apolipoprotein B: Baseline and achieved apoB levels predict MACE independently of LDL-C. Achieving apoB ≤35 mg/dL is associated with lowest risk ^[23]B2b.
• Lipoprotein(a): Baseline Lp(a) and on-treatment reductions independently predict MACE; a 1 mg/dL reduction with alirocumab gave HR 0.994 (95% CI 0.990-0.999) ^[26]A1b.
• GRACE score: High-risk patients (≥140) may benefit from early invasive strategy, though data remain limited ^[68]A1a.
• OSA phenotype: High-risk OSA (heart rate acceleration >9.4 bpm or hypoxic burden >87.1% min/h) identifies patients who benefit from CPAP for cardiovascular prevention ^[30]A1a.
• Sex: Women, especially young women, have worse prognosis due to underdiagnosis, less guideline-directed therapy, and differences in pathophysiology ^[13]D5.
• SCAD: High rates of recurrent SCAD, associated with fibromuscular dysplasia , pregnancy, and emotional stress ^[5]D5.

Bleeding Risk and Net Clinical Benefit

De-escalation strategies consistently reduce bleeding without increasing ischaemic events ^{[66]A1a[70]A1b}. Twice-daily aspirin did not reduce MACE in patients with diabetes or high risk of aspirin resistance (7.7% vs 8.8%, HR 0.90) ^[74]A1b. Colchicine 0.5 mg/day for secondary prevention in stable CAD reduced events (HR 0.33) ^[25]A1b but was associated with higher mortality in acute ACS ^[11]A1b.

Pearl: The strongest modifiable predictors of long-term outcome after ACS are achieved apoB ≤35 mg/dL, sustained intensive BP control (SBP <130 mm Hg) ^[28]A1b, and an antiplatelet regimen that balances ischaemic and bleeding risk, guided de-escalation or early ticagrelor monotherapy can achieve this.

Following the natural history of ACS, management must be tailored in populations where presentation, risk-benefit calculus, and treatment thresholds differ. The 2023 AHA/ACC Guideline for Chronic Coronary Disease provides recommendations for special populations ^[2]A1c[8]A1c.

Elderly Patients

The STEP trial of 8511 hypertensive patients demonstrated that intensive SBP lowering to 110-<130 mm Hg reduced the primary composite outcome (stroke, ACS, heart failure, revascularization, atrial fibrillation , or CV death) compared with standard target 130-<150 mm Hg, with an incidence of 1.12% vs 1.33% per year (HR 0.82, 95% CI 0.71-0.96) over 6.1 years ^[28]A1b. Hypotension occurred more frequently with intensive treatment ^[28]A1b.

For antiplatelet therapy, the Elderly ACS 2 trial compared prasugrel 5 mg daily with clopidogrel 75 mg daily in 1443 patients >74 years (mean age 80) undergoing PCI after ACS. The primary composite (mortality, MI, disabling stroke, rehospitalization for CV causes or bleeding) occurred in 17% vs 16.6% (HR 1.007, P=0.955), but stent thrombosis trended lower with prasugrel (0.7% vs 1.9%, OR 0.36, P=0.06) ^[79]A1b. Bleeding (BARC ≥2) was numerically higher with prasugrel (4.1% vs 2.7%, P=0.18) ^[79]A1b. Thus, prasugrel 5 mg offers no net benefit over clopidogrel in this age group.

Pregnancy and Postpartum

Spontaneous coronary artery dissection (SCAD) is a leading cause of ACS in young women, particularly during pregnancy and the postpartum period ^[5]D5. SCAD is associated with fibromuscular dysplasia and emotional stress triggers ^[5]D5. Management differs from atherosclerotic ACS: conservative therapy is preferred in stable patients, as PCI carries high risk of propagation ^[5]D5. Women with SCAD have high rates of recurrent dissection ^[5]D5. Sex-specific differences in ACS presentation are well documented: women are more prone to microvascular disease and endothelial dysfunction, receive less guideline-directed therapy, and have worse outcomes at young age ^[13]D5.

Immunocompromised Patients

Data on ACS management in immunocompromised patients are limited. Autoimmune diseases contribute to sex-specific risk ^[13]D5. Standard guideline-directed therapy should be applied, with attention to drug interactions and atypical presentations.

Secondary Prevention

Text message-based programs (TEXTMEDS) did not improve medication adherence (RR 0.93, P=0.15) but had small effects on lifestyle factors ^[77]A1b.

Pearl: In elderly patients, intensive BP control to <130 mm Hg systolic improves outcomes, but prasugrel 5 mg offers no advantage over clopidogrel; for secondary prevention, influenza vaccination, colchicine 0.5 mg/day, and extended DAPT with ticagrelor or rivaroxaban reduce events at the cost of increased bleeding.