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Acute Coronary Syndrome - Ischemic Heart Disease

Medical Experts

Contributor

Pearson

Lauren N. Pearson, DO, MPH

Associate Professor of Pathology (Clinical), University of Utah

Chief Medical Officer, ARUP at University of Utah Health

Acute coronary syndrome (ACS, formerly called ischemic heart disease) refers to a large spectrum of clinical conditions including unstable angina, myocardial injury, and myocardial infarction (MI). ACS is caused by a sudden onset of cardiac tissue ischemia secondary to impaired blood flow. The precipitating event is blockage in the coronary arteries or a mismatch between the demand and supply of blood to cardiac tissue. The resulting tissue ischemia can cause changes on an electrocardiogram (ECG), as well as symptoms such as substernal chest pressure and radiation of pain to the left arm, shoulder, or jaw. Patients who present with symptoms of ACS, including chest pain, should be immediately evaluated. The recommended evaluation includes a clinical assessment, ECG, and laboratory testing. Laboratory testing for ACS includes diagnostic testing for markers of damage to heart tissue such as cardiac troponins (cTns), as well as prognostic testing (eg, B-type natriuretic peptide).

Quick Answers for Clinicians

What are the differences between the various types of troponin tests (I, T, conventional, and high sensitivity)?

Although cardiac troponin (cTn) I (cTnI) is more specific to myocardial injury than is cardiac troponin T (cTnT), serial measurements of either cTnI or cTnT can be used in the evaluation of acute coronary syndrome (ACS). Compared with conventional cTn assays, high-sensitivity cTn (hs-cTn) testing can detect elevated levels sooner after symptom onset, which allows for more frequent measurements and increases the likelihood of detecting a rising/falling pattern. It is important to use the same test when performing serial measurements and to ensure the use of the appropriate upper reference limit for the particular test being used.

What is the role of point-of-care cardiac troponin testing in the evaluation of acute coronary syndrome?

Cardiac troponin (cTn) testing is best performed as close to patients as possible in cases of suspected acute coronary syndrome (ACS); however, point-of-care (POC) tests are not currently preferred over automated assays due to the limited availability of high-sensitivity POC tests. As the use of high-sensitivity POC assays is an emerging area of testing, guidance is likely to be reevaluated when more of these assays have been validated.

Indications for Testing

Laboratory testing for ACS is used to:

Screen and assess risk for future ACS in adults
Diagnose ACS in patients with signs, symptoms, and clinical findings consistent with ACS
Determine prognosis in patients diagnosed with or being evaluated for ACS^,

Laboratory Testing

Diagnosis

Cardiac troponin I and T (cTnI and cTnT, respectively) are the preferred biomarkers for the evaluation of myocardial injury and MI^,^,; high-sensitivity cTn (hs-cTn) assays are recommended if available. cTn levels are generally elevated within 2-4 hours of symptom onset but may not become abnormal for up to 12 hours. cTn elevations may persist for >14 days. Although cTns are generally only released in response to cardiac injury, recent evidence suggests that cTnT may be detected in response to skeletal muscle injury. A variety of cardiac conditions besides MI can produce elevated cTns. Therefore, serial measurements that demonstrate a rise or fall in cTn levels are required to distinguish between myocardial injury and MI. Current guidelines recommend a first cTn test on presentation with chest pain, and a second test 3-6 hours later (or sooner if using hs-cTn). Patients who present very early or very late after symptom onset may require additional testing to detect an increase or decrease in cTn values.

Diagnostic Criteria for ACS
	Unstable Angina	Myocardial Injury	MI
cTns	Not elevated	Elevated cTn with at least 1 value above the 99th percentile upper reference limit Acute if rise/fall in serial troponin values Chronic if values are consistently elevated	Acute myocardial injury plus clinical evidence of ischemia plus rise and/or fall of cTn values with at least 1 cTn value above the 99th percentile upper reference limit
Other findings	Chest pain without ST segment elevation on ECG	n/a	One of the following: Symptoms consistent with myocardial ischemia New ECG changes consistent with myocardial ischemia Pathologic Q waves Evidence of new loss of myocardium or new regional wall motion abnormality consistent with myocardial ischemia Coronary thrombus identified by angiography or autopsy
ACC, American College of Cardiology; AHA, American Heart Association; ESC, European Society of Cardiology; n/a, not applicable; WHF, World Heart Federation Sources: Thygesen, 2018; Byrne, 2023

Prognosis

The presence and magnitude of cTn elevations at presentation are useful for prognosis of short- and long-term mortality in ACS. In addition to measurements at presentation, it may be reasonable to remeasure troponin on day 3 or 4 in patients with MI to assess infarct size and the dynamics of necrosis. Several additional biomarkers, including natriuretic peptides, have also been associated with mortality and comorbidities that confer added risk of mortality (such as heart failure) in ACS.

Risk Assessment for Future Events

Multiple organizations recommend laboratory testing, such as high-sensitivity C-reactive protein (hsCRP) screening, to guide risk assessment for and implementation of preventive measures against future ACS.^, Refer to the Atherosclerotic Cardiovascular Disease Risk Markers topic for information on ACS screening and risk assessment.