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Acute coronary syndrome (ACS) is the clinical manifestation of myocardial infarct and commonly the default working diagnosis in patients with new-onset chest pain suspected to be of cardiac ischemic origin. Clinical findings (e.g., onset and characteristics of pain, patient history) in combination with ECG and troponin are the mainstays of diagnosis. Based on ECG findings, patients are categorized into those with ST-elevation (STE-ACS) or non-ST-elevation ACS (NSTE-ACS). Depending on serum levels of cardiac troponin (cTn), NSTE-ACS can be categorized as NSTEMI or unstable angina (UA). STE-ACS patients require immediate with (PCI) or . The timing and necessity of revascularization therapy in NSTE-ACS is determined based on multiple risk factors. All ACS patients receive dual antiplatelet therapy and initially anticoagulation. Adjunctive therapy (e.g., beta blockers, oxygen) helps reduce symptoms and can have a positive impact on mortality.
- Acute coronary syndrome (ACS): the suspicion or confirmed presence of acute myocardial ischemia 
- Acute coronary syndrome may be further classified into the following categories:
- See “Myocardial infarction” for more definitions.
|Overview of acute coronary syndrome (ACS) |
|Unstable angina (UA)||Non-ST-segment elevation myocardial infarction (NSTEMI)||ST-segment elevation myocardial infarction (STEMI)|
|Clinical presentation|| |
|Cardiac troponin|| || |
Subtypes of ACS cannot be differentiated based on clinical presentation alone.
Classic presentation 
Acute retrosternal chest pain
- Typical: dull, squeezing pressure and/or tightness
- Commonly radiates to left chest, arm, shoulder, neck, jaw, and/or epigastrium
- Precipitated by exertion or stress
- Symptom relief after administration of nitrates is not a diagnostic criterion for cardiac ischemia. 
- The peak time of occurrence is usually in the morning.
- See also “ .”
- Dyspnea (especially with exertion)
- Nausea, vomiting
- Diaphoresis, anxiety
- Dizziness, lightheadedness, syncope
- Acute retrosternal chest pain
- Other findings
- Atypical presentations: more likely in elderly, diabetic individuals, and women ; 
- More common in inferior wall infarction
Immediate management 
- Perform a focused clinical evaluation and .
- Obtain 12-lead ECG within 10 minutes of patient arrival.
- Establish IV access and obtain blood samples for laboratory studies.
- Measure cardiac troponin as soon as possible upon clinical presentation.
- Start continuous telemetry and pulse oximetry.
- Initiate supplemental O2 for cyanosis, respiratory distress, or SpO2 < 90%. 
- Give aspirin if there are no contraindications.
- Consider nitroglycerin for chest pain relief. , e.g., sublingual
- If present, and treat , , and/or .
Initial triage based on ECG findings 
- ST elevations present: : Start with immediate revascularization therapy, preferably PCI.
- No ST elevations present
Decision pathway for possible NSTE-ACS 
For patients without ST elevations on ECG, determine the likelihood of NSTE-ACS using serial ECGs and troponin levels. Follow local rapid diagnostic protocols if available and tailor workup and management to individual .
- Dynamic ECG changes consistent with NSTE-ACS: NSTEMI and/or unstable angina likely; begin while waiting for troponin.
No dynamic ECG changes: Check troponin or (hscTn).
- Diagnosis of NSTEMI requires interpretation of both:
- Management based on cardiac biomarkers
- First troponin is detectable PLUS Δtrop is significant: Start
- First troponin is above the PLUS clinical suspicion is significant: Consider starting empiric before second troponin. 
- First ≥ 3 hours from symptom onset PLUS clinical suspicion is low: Consider ruling out NSTEMI.  value is undetectable
- Serial ECG and troponin (or hscTn) inconclusive: Use clinical judgment based on . 
12-lead ECG 
- Indicated for every patient with suspected ACS (best initial test) within 10 minutes of presentation 
- Findings: should always be interpreted in the context of clinical findings and patient history
- If nondiagnostic, consider obtaining V7–V9 and/or V3R–V6R lead tracings (see “Localization of myocardial infarct on ECG”).
- Repeat every 15–30 minutes in the first hour (especially if the first ECG is inconclusive or symptoms recur or change in quality).
- Compare with previous ECGs (if available).
Laboratory studies 
- Routine studies: CBC, BMP, coagulation panel
Troponin: all patients at arrival (see also “Cardiac biomarkers”) 
- Repeat interval
- Interpretation alongside clinical findings
- STEMI/NSTEMI: elevation > 99thpercentile PLUS change ≥ 20% on repeat testing
- Unstable angina: no detectable elevation
- Detectable elevation without serial increase or decrease: Consider .
- ≥ 3 hours of symptoms: MI can be ruled out; unstable angina may still be possible depending on clinical suspicion.  undetectable in patients with
In patients with a normal ECG, a single result below the limit of detection using a high-sensitivity troponin assay ≥ 3 hours after symptom onset is considered sufficient to rule out myocardial infarction. 
Transthoracic echocardiography (TTE) 
TTE is generally not necessary and should not delay reperfusion therapy. However, it may be a helpful study in patients with atypical symptoms or if the diagnosis is unclear.
- Indications include:
Do not delay treatment of ACS for imaging.
- Multiple scoring systems are used in patients with NSTE-ACS to:
- Help identify high-risk vs. low-risk patients
- Guide further diagnostic studies
- Guide timing of PCI and disposition
- They are not appropriate for patients with STEMI who require immediate revascularization.
Risk stratification tools are not a substitute for clinical judgment.
GRACE score for risk of mortality in ACS 
- Based on the Global Registry of Acute Coronary Events (GRACE)
- May be used to inform management and disposition (e.g., ICU admission, timing of intervention in NSTE-ACS).
- Incorporates different criteria to estimate risk of mortality in patients with ACS, including:
HEART score 
- The HEART score is an acronym of its components: history, ECG, age, risk factors, and troponin values.
- Risk assessment for major adverse cardiovascular events (MACE) in patients with chest pain presenting to the emergency department
|HEART score for the risk of MACE |
|Nonspecific repolarization changes||1|
|Significant ST depression||2|
|Age||< 45 years||0|
|≥ 65 years||2|
|≥ 3 or history of atherosclerotic disease||2|
|Troponin (initial) ||normal||0|
|1–2 x upper limit||1|
|> 2 x upper limit||2|
TIMI score for NSTE-ACS 
- Estimates the risk of mortality, new or recurrent myocardial infarction, or the need for urgent revascularization in patients with NSTE-ACS
- Can help determine the therapeutic regimen and timing for revascularization.
|TIMI score for NSTE-ACS |
|Age ≥ 65 years||1|
|Known CAD (stenosis > 50%)||1|
|≥ 2 episodes of severe angina in the last 24 hours||1|
|ASA use in the past 7 days||1|
|ST deviation (≥ 0.5 mm)||1|
|Elevated cardiac biomarkers||1|
- Identify patients with STEMI as soon as possible for immediate revascularization.
- Treatment of choice: PCI within 90 minutes of first medical contact (FMC).
- Consider intravenous fibrinolytics if:
- PCI cannot be performed within 120 minutes
- AND there are no
ECG changes in STEMI
ECG changes in STEMI 
- Definition: significant ST elevation in two contiguous leads
- Specific criteria: elevation measured at the J point in reference to the onset of the Q wave
- ECG findings may change over time (see “Timeline of ECG changes in STEMI”)
- Hyperacute T waves can be present without ST elevations in the very early stages of ischemia.
- If inferior myocardial infarction is suspected, investigate for signs of right ventricular involvement (see “Localization of myocardial infarct on ECG”)
Classical timeline of ECG changes in STEMI
- Acute stage: myocardial damage ongoing
- Intermediate stage: myocardial necrosis present
- Chronic stage: permanent scarring
STEMI-equivalent ECG findings 
- Posterior myocardial infarction
- Left main-vessel occlusion or three-vessel disease
- LBBB or RBBB with strong clinical suspicion for MI 
Modified Sgarbossa criteria 
- A set of ECG criteria that can help identify STEMI in patients with LBBB and high clinical suspicion of ACS.
- The criteria can also be used in right-ventricular pacing with LBBB configuration but are less specific in this scenario.
- Acute STEMI is likely if any of the following are present:
The following recommendations are generally consistent with the 2013 AHA/ACC guidelines for the management of STE-ACS. 
- Patients < 120 minutes away from a PCI-capable facility
- Patients > 120 minutes away from a PCI-capable facility and symptom onset < 12 hours
- All patients with STEMI
Immediate revascularization 
PCI for STEMI 
- Indication: : preferred method of revascularization in patients suspected of having STEMI
- Procedure: coronary angiography with PCI; , i.e., balloon dilatation with stent implantation
First medical contact (FMC) to PCI time
- Ideally ≤ 90 minutes.
- Should not exceed 120 minutes
Fibrinolytic therapy in STEMI 
- Indications (in STEMI and STEMI equivalents, if all of the following apply):
- Timing: within < 30 minutes of patient arrival at the hospital 
- If > 24 hours after symptom onset
- See “Contraindications to fibrinolysis for STEMI.”
- Regimens (one of the following)
- Postfibrinolysis: Evaluate for evidence of reperfusion (i.e., resolution of chest pain and ST-elevations) and transfer to a PCI-capable facility.
|Common contraindications for fibrinolysis in STEMI and STEMI-equivalents |
|Absolute contraindications|| |
|Relative contraindications|| |
- Coronary artery bypass grafting: Not routinely recommended for acute STEMI 
Antiplatelet therapy and anticoagulation in STEMI 
- Timing: Initiate therapy without delaying revascularization.
|Dual antiplatelet therapy (DAPT) and anticoagulation in STEMI |
|Class||Regimen if undergoing PCI||Regimen if undergoing fibrinolysis|
|Dual antiplatelet therapy (DAPT) |
Glycoprotein IIb/IIIa inhibitor (GPI) 
For patients < 120 min away from a PCI-capable facility
- Immediate cardiology consult and evaluation for emergency revascularization (code STEMI)
- Transfer to cath lab for angiography.
- Start antiplatelets and anticoagulation (see “Antiplatelet therapy and anticoagulation in STEMI”).
For patients > 120 min away from a PCI-capable facility and symptom onset < 12 hours
- Immediate cardiology consult (code STEMI), even if no PCI is available
- Check for contraindications to fibrinolysis (see “Contraindications for fibrinolysis in STEMI and STEMI-equivalents”).
- If no absolute contraindications present: Administer fibrinolytic (see “Fibrinolytic therapy in STEMI”).
- Start antiplatelets and anticoagulation (see “Antiplatelet therapy and anticoagulation in STEMI”).
- Postfibrinolysis: Evaluate for evidence of reperfusion (i.e., resolution of chest pain and ST-segment elevations).
- Transfer to a PCI-capable facility.
For all patients with STEMI
Adjunctive medical therapy for ACS
- Supplemental oxygen as needed: target SpO2 > 90%
- Nitroglycerin for patients with ongoing chest pain or hypertension
- Analgesia with morphine only for patients with very strong pain.
- High-intensity statin
- Consider a beta blocker if there are no contraindications.
- Consider an ACE inhibitor if there are no contraindications.
- Order continuous telemetry, serial ECG, and serum troponins every 4–6 hours.
- Consider ICU level of care
- Patients with NSTE-ACS are classified based on the presence (NSTEMI) or absence (UA) of significantly elevated cardiac troponin (cTn) levels.
- A key element of management is to assess the necessity for and timing of PCI (fibrinolytics are not indicated in NSTE-ACS).
- Hemodynamically unstable patients and those with intractable angina require immediate PCI (i.e., they are managed like STEMI patients).
- Multiple risk scores (e.g., HEART, TIMI, GRACE) can help to determine an adequate strategy but are no substitute for individual clinical judgment.
- Dual antiplatelet therapy and anticoagulation is indicated initially and the preferred regimens vary based on patient risk factors and timing of revascularization.
- Some low-risk NSTE-ACS patients can be managed conservatively.
- Findings 
- Additional considerations
The following recommendations are generally consistent with the 2014 AHA/ACC guidelines for the management of NSTE-ACS. 
Risk-dependent timing of revascularization 
- Management of NSTE-ACS depends on a patient's mortality risk (e.g., TIMI score), clinical findings, and the availability of resources.
- Invasive strategy for NSTE-ACS (very high- to intermediate-risk patients): coronary angiography within 2–72 hours
- Ischemia-guided strategy for NSTE-ACS (in stable, low-risk patients): noninvasive (e.g., exercise ECG, stress echocardiography) to evaluate the need for coronary angiography
|Risk-dependent timing of revascularization in NSTE-ACS |
|Revascularization strategy||Risk group||Criteria|
|Urgent revascularization (< 2 hours)|| || |
|Early invasive strategy (< 24 hours)|| |
|Delayed invasive (24–72 hours)|| |
Selection of an ischemia-guided strategy via may be appropriate in intermediate-risk patients without serious comorbidities or contraindications. 
Antiplatelet therapy and anticoagulation in NSTE-ACS 
|Dual antiplatelet therapy (DAPT) and anticoagulation in NSTEMI |
|Dual antiplatelet therapy (DAPT) |
Glycoprotein IIb/IIIa inhibitor (GPI) 
- Start DAPT as soon as possible; duration depends on whether PCI is performed or not.
- Start anticoagulation as soon as possible; continue for the duration of hospitalization or until PCI is performed.
- GPI should only be started in high-risk patients undergoing PCI and in consultation with a cardiologist.
- Evaluate for very-high risk factors requiring urgent coronary angiography : If present, follow STEMI checklist. 
- Start antiplatelet therapy and anticoagulation.
- Calculate TIMI score and GRACE score.
- Cardiology consult for discussion of strategy (see “Risk-dependent timing of revascularization in NSTE-ACS”)
- Adjunctive medical therapy for ACS
- Order continuous telemetry, serial ECG, and serum troponins every 3–6 hours.
- Transfer to cardiac telemetry floor or (cardiac) ICU.
Monitoring and adjunctive medical therapy
- Continuous cardiac monitoring
- Serial 12-lead ECG every 15–30 minutes for the first hour
- Serial serum troponin measurement (every 1–6 hours)
|Adjunct medical therapy in ACS |
|Class||Options||Indications||Contraindications and additional considerations|
| || |
Aldosterone antagonists 
Options for initial MI treatment include “MONA-BASH”: Morphine, Oxygen, Nitroglycerin, Antiplatelet drugs (aspirin + ADP receptor inhibitor), Beta blockers, ACE inhibitors, Statins, and Heparin. The scope of interventions depends on the patient's risk profile (see “Indications”).
- Oxygen therapy for patients with:
- Fluid management: see “Management of acute heart failure.”
- Intravenous fluids (e.g., normal saline)
- Loop diuretic (e.g., furosemide ): consider for patients with pulmonary edema, acute heart failure
- See “Prevention of myocardial infarction.”
- See “.”
Provide ICU-level care to all patients.
- At PCI-capable site: Consult cardiology immediately and transfer to as soon as possible for .
- < 120 minutes from nearest PCI-capable site: Arrange immediate interfacility transfer for primary PCI at referral center.
- > 120 minutes from nearest PCI-capable site
NSTEMI and unstable angina 
- Cardiology consult
- Hospital admission
- Assess PCI-capable site. and consider the need for transfer to the nearest
Negative initial workup for ACS 
- Rule out other potential .
- Use HEART score) to determine the short-term risk of a . (e.g., the
- Consider the need for observation or admission for further diagnostics based on the risk.
Risk-based management 
High-risk (e.g., HEART score ≥ 7)
- Inpatient admission
- Obtain invasive coronary angiography during admission.
Intermediate-risk (e.g., HEART score 4–6)
- Noninvasive testing (i.e., or ) is usually required prior to discharge.
- In patients with a recent negative workup for CAD , no further testing is indicated prior to discharge.
Low-risk (e.g., HEART score ≤ 3)
- No further testing is indicated prior to discharge from the ED.
- Ensure outpatient follow-up.
- Outpatient coronary artery calcium scoring may be considered for .
Differential diagnoses of increased troponin 
- Cardiovascular causes
- Noncardiovascular causes
Differential diagnoses of ST elevations on ECG 
- Early repolarization
- Brugada syndrome
- Pulmonary embolism
- Tricyclic antidepressant use
- Poor ECG lead placement
The differential diagnoses listed here are not exhaustive.
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