Practice Update: A Proposed Emergency Department Protocol For The Rapid Exclusion of Acute MI
1.0 Introduction and Scope
This protocol provides a systematic, evidence-based framework for the assessment, diagnosis, and initial management of adult patients presenting to the Emergency Department (ED) with symptoms suggestive of Acute Coronary Syndrome (ACS). It is intended for use by all emergency department clinicians within this NHS Trust to ensure a standardised, timely, and effective approach to a common and high-risk clinical presentation.
WARNING: Exclusion of Other Life-Threatening Conditions is Mandatory
Chest pain is a symptom of numerous critical conditions. Before applying this ACS-specific pathway, clinicians must first actively consider and take steps to rule out other life-threatening causes of chest pain. These include, but are not limited to:
- Aortic Dissection
- Pulmonary Embolus
- Pneumothorax
- Oesophageal Rupture
- Significant Pneumonia
- Referred pain from intra-abdominal pathology
This protocol should only be initiated once ACS is deemed a probable diagnosis after careful consideration of alternative pathologies.
The protocol begins with the foundational step of a focused clinical assessment to identify patients who warrant further investigation.
2.0 Step 1: Initial Clinical Assessment (History and Examination)
A focused history and physical examination is the foundational step in identifying patients for whom ACS is a probable diagnosis. The presence of specific clinical features should significantly raise the index of suspicion and trigger progression along this diagnostic pathway.
Key Clinical Indicators Suggestive of ACS
The following features, identified during the initial clinical assessment, warrant the consideration of ACS as a potential cause:
- Chest pain (or pain in the arms, back, or jaw) lasting for longer than 15 minutes.
- Chest pain associated with nausea and vomiting, marked sweating, or breathlessness, particularly when these symptoms occur in combination.
- Chest pain occurring in the context of haemodynamic instability.
- New onset chest pain, or an abrupt deterioration in previously stable angina, with recurrent episodes occurring frequently with minimal or no exertion and lasting longer than 15 minutes.
(National Institute for Health and Care Excellence, 2016)
A strong clinical suspicion of ACS based on these findings mandates immediate diagnostic testing, beginning with a 12-lead electrocardiogram (ECG).
3.0 Step 2: ECG Interpretation and Immediate Actions
The 12-lead ECG is the primary diagnostic tool for rapidly identifying patients with ST-elevation myocardial infarction (STEMI) or significant ongoing ischaemia. These findings require immediate, time-sensitive intervention to restore myocardial perfusion and preserve cardiac function.
Actions must be taken immediately based on the specific ECG findings outlined in the table below.
ECG Finding | Mandatory Action |
STEMI or STEMI Equivalent (See Appendix 1) | Immediately call the Coronary Care Unit (CCU) on extension **** to activate the cardiac catheterisation lab for primary Percutaneous Coronary Intervention (PCI). |
Ongoing Ischemic Chest Pain with ischaemic changes (Territorial ST depression) | Initiate full ACS treatment and consider a Glyceryl Trinitrate (GTN) infusion for ongoing pain. Serial ECGs must be performed if the patient experiences ongoing or recurrent episodes of chest pain to detect evolving changes. |
Following the initial ECG, the diagnostic process proceeds to the use of biochemical markers to detect myocardial injury.
4.0 Step 3: High-Sensitivity Troponin Pathway
After the initial troponin the patient will be either Green, Amber or Red (coloured boxes on algorithm)
The high-sensitivity troponin assay is a critical component of the diagnostic algorithm, used to risk-stratify patients and guide subsequent management or discharge decisions. For the purposes of this pathway, a positive test indicating significant myocardial injury is defined as a second troponin level greater than 120% of the initial value.
Patients will be stratified into one of three pathways (Green, Amber, or Red) based on their initial troponin result.
4.1 Green Pathway
This pathway is for patients with a very low likelihood of ACS.
- Initial Troponin: <5 ng/L
- CAVEAT: If the initial Troponin is <5 ng/L but the chest pain onset was <3 hours from the time of the test, the patient must be managed via the AMBER Pathway.
For patients meeting the Green Pathway criteria, safe discharge from the ED is appropriate if all conditions in Section 4.4 are met.
4.2 Amber Pathway
This pathway is for patients who require further observation and a repeat troponin measurement to rule out ACS.
- Initial Troponin: 5-11 ng/L (or <5 ng/L if pain onset was <3 hours prior to the test).
The mandatory next step is to: Repeat troponin at 1 hour.
- If the change in troponin at 1 hour is >3 ng/L: The patient has "ruled in" for ACS. Refer to Acute Medicine for further assessment and initiate ACS treatment.
- If the change in troponin at 1 hour is <3 ng/L: The patient may be suitable for discharge. This is appropriate only if all conditions in Section 4.4 are met.
4.3 Red Pathway
This pathway is for patients with an elevated initial troponin, indicating a high probability of ACS.
- Initial Troponin: >11 ng/L
The mandatory next step is to: Repeat troponin at 3 hours.
Disposition is determined by the patient's clinical state and ECG findings.
Refer to Acute Medicine (SDEC Suitable)
A referral to the Same Day Emergency Care (SDEC) unit may be appropriate if the patient meets all of the following criteria:
- The ECG is normal or shows only non-specific changes, with no dynamic evolution.
- The patient's pain has fully resolved.
- The initial troponin level is between 12 and 42 ng/L.
Refer to Acute Medicine & Strongly Consider Immediate ACS Treatment
An urgent inpatient referral to the acute medical team is required, and ACS treatment should be strongly considered immediately (before the repeat troponin result is available) if the patient exhibits any of the following high-risk features:
- ECG changes consistent with ischaemia.
- A concerning initial troponin level (e.g., >42 ng/L, >3 times the upper limit of normal, or a >20% rise from a known baseline level).
- Ongoing ischemic chest pain.
4.4 Criteria for Safe ED Discharge
For patients stratified to the Green or Amber pathways who meet the biochemical rule-out criteria, safe discharge from the Emergency Department is appropriate only if all of the following conditions are also met:
- The patient has no other criteria warranting a referral to acute medicine (see Section 5.0).
- The ECG is not concerning for ACS and shows no dynamic ischaemic changes.
- An alternative, non-cardiac cause for the chest pain has been considered and appropriately investigated.
Even with a negative biochemical result, certain clinical presentations require further senior assessment and potential admission.
5.0 Overarching Referral and Disposition Criteria
Clinical judgment remains paramount throughout the patient's journey. A patient may warrant referral to acute medicine irrespective of their position on the troponin algorithm if certain high-risk clinical features are present.
The following scenarios mandate discussion and potential referral to the acute medical team:
- There is a persistent clinical concern regarding unstable angina, following a direct discussion with a senior ED clinician (RED Dr or above).
- The patient has a presentation concerning for crescendo angina (angina pain occurring more frequently with less exertion and/or lasting longer than usual), even if the serial troponin results are negative as per the algorithm.
This document serves as a clinical guideline to standardize care. It does not replace the critical application of sound clinical judgment in the management of individual patients.
6.0 Appendices and References
6.1 Appendix 1: STEMI Equivalents
This appendix contains detailed information on specific ECG patterns of occlusion myocardial infarction that do not meet classic STEMI criteria but carry a similar prognosis and should be managed with the same urgency (i.e., immediate referral for PCI).
Ricci, F., et al. (2025). ECG patterns of occlusion myocardial infarction: A narrative review. Annals of Emergency Medicine, 85(4), 330–340. https://doi.org/10.1016/j.annemergmed.2024.11.019
6.2 References
- National Institute for Health and Care Excellence. (2016). Recent-onset chest pain of suspected cardiac origin: assessment and diagnosis (NICE Clinical Guideline CG95).
- Ricci, F., et al. (2025). ECG patterns of occlusion myocardial infarction: A narrative review. Annals of Emergency Medicine, 85(4), 330–340. https://doi.org/10.1016/j.annemergmed.2024.11.019
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