The American Heart Association/American College of Cardiology guidelines recommend that patients who present to the emergency department (ED) with chest pain and who are at low risk for acute coronary syndrome (ACS) based on their history, electrocardiogram (ECG) findings, and cardiac biomarkers should undergo diagnostic cardiac testing.^1,2 Such testing is deemed useful to diagnose occult coronary disease and identify patients who are at risk for short- to long-term cardiac events.

The practice of obligatory objective testing for all patients with negative results on cardiac biomarker testing is questionable. With the improved analytical performance of troponin assays, many patients with normal serial biomarkers and ECGs have a near zero risk of ACS, meaning the yield of objective testing is very low.³ It has been suggested that patients with a pretest probability for ACS below 2% should not undergo objective testing because the benefits of conducting testing on this cohort do not outweigh the potential risks associated with false positive testing. However, it is unlikely that clinicians would support miss-rates for ACS as high as this.⁴ Identifying the particular groups of patients who can be safely discharged without further investigation remains a challenge; no randomized trials exist, and those observational studies that do are based on different health systems and may incorporate different cohorts of patients.

Despite the limitations of the existing literature, a number of studies have highlighted groups of patients who may not benefit from objective testing. This group of patients who are less than 40 years old with a low risk history, normal serial troponin, and normal ECG results is one such cohort investigated; such patients have a very low probability of ACS. An analysis of 1,027 patients under 40 found that only 4 (0.4%) of these had a positive exercise stress test. Three of these patients underwent subsequent testing that yielded a negative result, and one declined further testing. Even if this patient were presumed to be a true positive, the incidence of true positive stress testing would be 0.097%.⁵ Patients meeting such criteria could be safely discharged without further testing; however, this cohort is likely to be small.

More recently, we reported a clinical decision tool (the "no objective testing" rule) that identified patients whose probability of ACS is <1%. The rule was developed using 2,396 individuals with normal serial troponin and ECG results at 2 hours after presentation. It utilized age, history of myocardial infarction, and risk factors and proposed that approximately one third of patients could be safely discharged without further testing.⁶ The no objective testing rule requires prospective validation, but if its utility is supported, it may enable safe reduction in testing for a significant proportion of ED chest pain patients.

A number of alternative ACS risk stratification tools may also be useful for identifying a low-risk cohort for discharge. The Vancouver Chest Pain Rule identifies ACS with a high degree of accuracy based on the ECG, troponin, history of ACS, age, and pain characteristics.⁷ The HEART (history, ECG, age, risk factors, and troponin) score utilizes history, ECG, age, risk factors, and troponin to identify a group of patients with a very low major adverse cardiac event (MACE) rate (acute myocardial infarction or death, 0.6%).⁸ Finally, the Manchester Acute Coronary Syndromes rule uses a slightly more complex computation to determine risk based on the ECG, high-sensitivity troponin, heart fatty acid binding protein, worsening of angina, pain radiation, vomiting, sweating, and hypotension. Very low-risk patients had a MACE rate <2% and may be able to be discharged home without further testing.⁹ Some of these scores have not specified whether outpatient investigation for coronary artery disease is required, and all require further validation, ideally in randomized trials. The latter two scores also have assessed MACE as the outcome rather than all ACS events (which includes unstable angina). Objective testing can be beneficial for the detection of patients with symptomatic coronary artery disease and unstable angina because it may lead to risk factor modification and other medical management. As such, unstable angina is a key outcome variable in assessing the requirement for objective testing. Nonetheless, the combined research into risk scores suggests that younger patients with normal serial troponins, normal ECGs, no prior history of ACS, and low risk factor burden make up a group that is unlikely to require objective testing.

With the increasing number of chest pain presentations to EDs and the recognition of potential harm from unnecessary investigations, efforts to define patients who present to the ED with symptoms of possible ACS who need no further testing for coronary artery disease are urgently needed. Based on the minimal evidence currently available, a small portion of such patients may be safely discharged without testing after assessment in the ED that includes risk stratification, ECG, and biomarker evaluation.

References

1. Amsterdam EA, Kirk JD, Bluemke DA, et al. Testing of low-risk patients presenting to the emergency department with chest pain: A scientific statement from the American Heart Association. Circulation 2010;122:1756-76.
2. Rybicki FJ, Udelson JE, Peacock WF, et al. 2015 ACR/ACC/AHA/AATS/ACEP/ASNC/NASCI/SAEM/SCCT/SCMR/SCPC/SNMMI/STR/STS Appropriate Utilization of Cardiovascular Imaging in Emergency Department Patients With Chest Pain: A Joint Document of the American College of Radiology Appropriateness Criteria Committee and the American College of Cardiology Appropriate Use Criteria Task Force. J Am Coll Cardiol 2016;67:853-79.
3. Greenslade JH, Parsonage W, Ho A, et al. Utility of Routine Exercise Stress Testing among Intermediate Risk Chest Pain Patients Attending an Emergency Department. Heart Lung Circ 2015;24:879-84.
4. Than M, Herbert M, Flaws D, et al. What is an acceptable risk of major adverse cardiac event in chest pain patients soon after discharge from the Emergency Department?: a clinical survey. Int J Cardiol 2013;166:752-4.
5. Scott AC, Bilesky J, Lamanna A, et al. Limited utility of exercise stress testing in the evaluation of suspected acute coronary syndrome in patients aged less than 40 years with intermediate risk features. Emerg Med Australas 2014;26:170-6.
6. Greenslade JH, Parsonage W, Than M, et al. A Clinical Decision Rule to Identify Emergency Department Patients at Low Risk for Acute Coronary Syndrome Who Do Not Need Objective Coronary Artery Disease Testing: The No Objective Testing Rule. Ann Emerg Med 2015 Sept 10 [Epub ahead of print].
7. Scheuermeyer FX, Wong H, Yu E, et al. Development and validation of a prediction rule for early discharge of low-risk emergency department patients with potential ischemic chest pain. CJEM 2014;16:106-19.
8. Mahler SA, Hiestand BC, Goff DC Jr, Hoekstra JW, Miller CD. Can the HEART score safely reduce stress testing and cardiac imaging in patients at low risk for major adverse cardiac events? Crit Pathw Cardiol 2011;10:128-133.
9. Body R, Carley S, McDowell G, et al. The Manchester Acute Coronary Syndromes (MACS) decision rule for suspected cardiac chest pain: derivation and external validation. Heart 2014;100:1462-8.

Clinical Topics: Acute Coronary Syndromes, Cardiovascular Care Team, Dyslipidemia, Atherosclerotic Disease (CAD/PAD), ACS and Cardiac Biomarkers, Lipid Metabolism

Keywords: Acute Coronary Syndrome, Angina Pectoris, Angina, Unstable, Biomarkers, Chest Pain, Coronary Artery Disease, Electrocardiography, Emergency Service, Hospital, Exercise Test, Fatty Acid-Binding Proteins, Hypotension, Myocardial Infarction, Outpatients, Prospective Studies, Randomized Controlled Trials as Topic, Risk Factors, Sweating, Troponin, Vomiting

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