This is a prospective observational cohort study of ED patients with acute chest pain or other symptoms suggestive of ACS. Blood samples will be collected from study participants for High-Sensitivity Cardiac Troponin T (hs-cTnT) analysis. Results from hs-cTnT will be used for research purposes only.

Providers will be blinded to results and participants will be treated by their healthcare providers per the standard of care. Participants will have 30 and 90 day phone follow-ups to ascertain study outcomes.

Approximately 8 million - 10 million patients complaining of chest pain present to an Emergency Department (ED) annually in the United States. To avoid missing the diagnosis of acute coronary syndrome (ACS), physicians use a liberal testing strategy. Thus, >50% of ED patients with acute chest pain are hospitalized for a comprehensive cardiac evaluation (serial cardiac biomarkers and stress testing or angiography). However, <10% of these patients are ultimately diagnosed with ACS, and this pervasive over-triage costs an estimated $10 billion - $13 billion annually. Current care patterns for acute chest pain fail to focus health system resources, such as hospitalization and stress testing, on patients most likely to benefit.

It has demonstrated that an accelerated diagnostic protocol (ADP), called the HEART Pathway, which utilizes a clinical decision aid (the HEART score) and serial Cardiac Troponin (cTn) measures are sensitive for ACS (>99%) and can substantially reduce hospitalizations, stress testing, and cost compared to usual care. The HEART Pathway uses contemporary serial cTn measurements at 0 and 3 hours to exclude index myocardial infarction (MI) and relies on clinical features (history, ECG, age, and risk factors) to identify patients likely to have downstream events. However, the HEART Pathway has limitations: a) It identifies only 20 - 40% of patients for early discharge and b) it was developed before high-sensitivity cTn assays became available. Able to detect MI earlier and with greater accuracy than contemporary assays, hs-cTn assays have the potential to be integrated into decision aids to improve chest pain risk stratification. In the near future, hs-cTn assays will replace contemporary assays in the United States.

Inclusion Criteria:

1. Age greater than or equal to 21 years at the time of enrollment in the ED
2. Chest discomfort or other symptoms consistent with possible ACS in which the treating physician plans to obtain an ECG and cTn for the patient's evaluation in the ED

Exclusion Criteria:

1. New ST-segment elevation consistent with myocardial infarction
2. Evidence of shock identified by the provider at the bedside and/or the PI
3. Terminal diagnosis with life expectancy less than 90 days
4. A non-cardiac medical, surgical, or psychiatric illness determined by the provider to require admission
5. Prior enrollment in the STOP CP study
6. Lack of capacity to provide consent and comply with study procedures
7. Inability to be reliably reached after the index visit for follow-up
8. Non-English speaking
9. Pregnant patients
10. Provider does not intend on obtaining serial cTn assays for evaluation of ACS
11. The first study draw (T0) will exceed 1 hour after the site-specific standard of care troponin draw
12. Unable or unwilling to authorize medical records release

All patients 21 years of age or older with possible Acute Coronary Syndrome (ACS) and associated chest pain.