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Acute Coronary Syndrome

Practice Essentials

Acute coronary syndrome (ACS) refers to a spectrum of clinical presentations ranging from those for ST-segment elevation myocardial infarction (STEMI) to presentations found in non–ST-segment elevation myocardial infarction (NSTEMI) or in unstable angina. It is almost always associated with rupture of an atherosclerotic plaque and partial or complete thrombosis of the infarct-related artery.

The image below illustrates an algorithm for triaging patients with chest pain.

Suggested algorithm for triaging patients with che

Suggested algorithm for triaging patients with chest pain. ACS = ACS; ASA = aspirin; EKG = ECG; MI = myocardial infarction; Rx = treat; STEMI = ST-elevation myocardial infarction. Courtesy of Wu et al (1999).

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See Are You Missing Subtle MI Clues on ECGs? Test Your Skills, a Critical Images slideshow, to help identify a variety of electrocardiographic abnormalities.

Signs and symptoms

Atherosclerosis is the primary cause of ACS, with most cases occurring from the disruption of a previously nonsevere lesion. Complaints reported by patients with ACS include the following:


Pain, which is usually described as pressure, squeezing, or a burning sensation across the precordium and may radiate to the neck, shoulder, jaw, back, upper abdomen, or either arm

Exertional dyspnea that resolves with pain or rest

Diaphoresis from sympathetic discharge

Nausea from vagal stimulation

Decreased exercise tolerance

Physical findings can range from normal to any of the following:

Hypotension: Indicates ventricular dysfunction due to myocardial ischemia, myocardial infarction (MI), or acute valvular dysfunction

Hypertension: May precipitate angina or reflect elevated catecholamine levels due to anxiety or to exogenous sympathomimetic stimulation


Pulmonary edema and other signs of left heart failure

Extracardiac vascular disease

Jugular venous distention

Cool, clammy skin and diaphoresis in patients with cardiogenic shock

A third heart sound (S3) and, frequently, a fourth heart sound (S4)

A systolic murmur related to dynamic obstruction of the left ventricular outflow tract

Rales on pulmonary examination (suggestive of left ventricular dysfunction or mitral regurgitation)

Potential complications include the following:

Ischemia: Pulmonary edema

Myocardial infarction: Rupture of the papillary muscle, left ventricular free wall, and ventricular septum

See Presentation for more detail.


Updated guidelines for the management of non-ST-segment elevation ACS were released in 2020 by the European Society of Cardiology (ESC).
The updates place increased reliance on high-sensitivity cardiac troponin testing (hs-cTn) for diagnosis. The guidelines include the use of the CRUSADE risk score (Can Rapid risk stratification of Unstable angina patients Suppress ADverse outcomes with Early implementation) of the ACC/AHA guidelines.

In the emergency setting, electrocardiography (ECG) is the most important diagnostic test for angina. ECG changes that may be seen during anginal episodes include the following:

Transient ST-segment elevations

Dynamic T-wave changes: Inversions, normalizations, or hyperacute changes

ST depressions: These may be junctional, downsloping, or horizontal

Laboratory studies that may be helpful include the following:

Creatine kinase isoenzyme MB (CK-MB) levels

Cardiac troponin levels

Myoglobin levels

Complete blood count

Basic metabolic panel

Diagnostic imaging modalities that may be useful include the following:

Chest radiography


Myocardial perfusion imaging

Cardiac angiography

Computed tomography, including CT coronary angiography and CT coronary artery calcium scoring

See Workup for more detail.


Initial therapy focuses on the following:

Stabilizing the patient’s condition

Relieving ischemic pain

Providing antithrombotic therapy

Pharmacologic anti-ischemic therapy includes the following:

Nitrates (for symptomatic relief)

Beta blockers (eg, metoprolol): These are indicated in all patients unless contraindicated

Pharmacologic antithrombotic therapy includes the following:





Glycoprotein IIb/IIIa receptor antagonists (abciximab, eptifibatide, tirofiban)

Pharmacologic anticoagulant therapy includes the following:

Unfractionated heparin (UFH)

Low-molecular-weight heparin (LMWH; dalteparin, nadroparin, enoxaparin)

Factor Xa inhibitors (rivaroxaban, fondaparinux)

Additional therapeutic measures that may be indicated include the following:


Percutaneous coronary intervention (preferred treatment for ST-elevation MI)

Current guidelines for patients with moderate- or high-risk ACS include the following:

Early invasive approach

Concomitant antithrombotic therapy, including aspirin and clopidogrel, as well as UFH or LMWH

See Treatment and Medication for more detail.

The image below depicts a 62-year-old woman with a history of chronic stable angina and a “valve problem.”

A 62-year-old woman with a history of chronic stab

A 62-year-old woman with a history of chronic stable angina and a “valve problem” presents with new chest pain. She is symptomatic on arrival, complaining of shortness of breath and precordial chest tightness. Her initial vital signs are blood pressure = 140/90 mm Hg and heart rate = 98. Her electrocardiogram (ECG) is as shown. She is given nitroglycerin sublingually, and her pressure decreases to 80/palpation. Right ventricular ischemia should be considered in this patient.

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