Acute Coronary Syndrome - Excluding STEMI

Objectives

To outline the management of patients presenting to deployed medical facilities with chest pain due to acute coronary syndrome, excluding those presenting with ST elevation Myocardial Infarction (STEMI).  

Scope

This guideline intends to cover the initial investigations and management of patients presenting to the deployed medical treatment facilities with cardiac sounding chest pain and later diagnosed and acute coronary syndrome. It confirms the definition of ACS/NSTEMI/Unstable angina . It does not include management of STEMI, for which another dedicated guideline is available.   

Audience

This guideline is intended for the use of healthcare professionals delivering deployed healthcare in roles 1-3. 

Initial Assessment & Management

Background:

Acute Coronary Syndromes are broadly categorised into ST elevation Myocardial infarction and those which present similarly, but do not have appearances of ST elevation on 12 lead ECG (Non-ST-Elevation Acute Coronary Syndrome - NSTE-ACS). ST elevation suggests a specific pathology known as plaque rupture, where a pre-existing atherosclerotic plaque ruptures, leading to rapid platelet aggregation and subsequent occlusion of a coronary artery. This leads to hyperacute ischaemia of myocardium supplied by that artery, and treatments are focussed on rapid clearance of the artery by breaking down the newly formed clot (thrombolysis) or in current practice in the UK, angioplasty and stent insertion.

This guideline focusses on NSTE-ACS. Cardiogenic chest pain in NSTE-ACS still comes from ischaemia. This may be from a plaque rupture that leads to an only partially occluded coronary artery, or one that occluded briefly and spontaneously cleared. A significant minority reflect a supply/demand mismatch in situations such as tachyarrhythmia, severe anaemia or profound hypoxia, where the myocardium becomes ischaemic due to the oxygen requirement of the heart muscle temporarily exceeding the ability of the coronary arteries to deliver it (a type 2 Myocardial infarction).

This distinction is important. The risk of thrombolysis is relatively high, and studies suggest the benefit only outweighs the risk in acute occlusive plaque rupture (STEMI). Studies suggest the risk of thrombolysis is higher than the benefit derived when thrombolysis is used in sub-total occlusions, or any pathology that leads to classical cardiac chest pain without STEMI appearances on ECG (NSTE-ACS), so this is not typically recommended.

Troponin assays are available at role 2 and are qualitative, giving a positive/negative result. Some modules also contain a quantitative assay; check with the deployed biochemist which assay is available and for the cut-off values that apply. 

Initial presentation 

Chest Pain:

• Character: A heavy, pressure-like or squeezing discomfort.
• Site: Typically retrosternal (behind the sternum).
• Radiation: May radiate to the left arm, neck, jaw, or back.
• Intensity: Moderate to severe, often described as distressing and persistent.
  Time: 

Onset:

• Sudden onset, often occurring at rest or with minimal exertion. Pain at rest or with minimal exertion indicates plaque instability or rupture and reduced coronary perfusion.
• In contrast stable angina is usually precipitated by a consistent amount of exertion or emotional stress and relieved by rest or nitrates within 5–10 minutes, reflecting a fixed coronary obstruction rather than an acute event.

Duration: Typically lasts more than 20 minutes and does not fully resolve with rest or nitrates.

Symptoms: SOB, sweating, nausea, palpitations 

Observations: Pulse, BP, Resp rate, Saturations

Initial investigations 

12L ECG 

POC troponin if available  

Place on continuous cardiac monitoring 

All ACS should be transferred IMMEDIATELY to R2/3/HNF as able and Admit to critical care area for monitoring 

if STEMI confirmed on 12L ECG AND expected transfer delay consider thrombolysis – see thrombolysis pathway  

If NSTE-ACS confirmed with very high-risk features (i.e. haemodynamic instability, ongoing chest pain refractory to medications, acute heart failure, cardiac arrest or recurrent and dynamic ECG changes) consider treating as STEMI 

Management  

Immediately 

12L ECG – repeat if already done prior to arrival and continuous cardiac monitoring

Repeat GTN S/L if ongoing pain 

Ensure aspirin 300mg PO has been given (± PPI only if at high bleeding risk) 

Oxygen if saturations <92%

IV morphine if in pain  

Advanced Assessment & Management

ROLE 2 & 3 

Further Medication 

If coronary angiography +/- PCI planned within 24 hours: 

Give unfractionated heparin / enoxaparin (1mg/Kg/BD S/C route) 

If coronary anatomy not known, pre-treatment with P2Y12 receptor inhibitor is not recommended in the immediate setting 

If coronary angiography +/- PCI not planned within 24 hours: 

Give unfractionated heparin / enoxaparin (1mg/Kg/BD S/C route) OR Fondaparinux 

Give P2Y12 receptor inhibitor (Ticagrelor 180mg LD or prasugrel 60mg LD). Clopidogrel 300-600mg LD also an option if ticagrelor/prasugrel unavailable / contraindicated 

Concurrent Investigations *as available - availability will depend on deployed role, host or allied nation capability. 

Bloods – FBC, U&Es, LFTs, Glucose, Blood sugars, Cardiac enzymes 

Chest X-ray – any signs of congestion or mediastinal enlargement suggesting alternative diagnoses.

Bedside transthoracic echocardiogram / V scan - dependent on skillset of deployed physician

Evacuation 

ALL cases of ACS (STEMI and NSTEMI) require evac to a cardiac centre ASAP 

Calculate GRACE score: (see drop down)

>140 high risk 

>180 may require transfer to ICU  

In those with NSTE-ACS, there should be an early inpatient invasive strategy (<24 hours from onset) if high risk features are present: dynamic ECG changes, GRACE score >140, transient ST elevation)  

Prolonged Casualty Care

• Observe in critical care area with continuous ECG monitoring 

• Ensure daily dual anti-platelet therapy (DAPT) 

• Additional medication to institute when available and haemodynamically unsupported, typically between days 3-14 post event: 

• • High Dose Statin 

• • ACEi 

• • Beta-blocker 

• • Mineralocorticoid receptor antagonist like spironolactone/eplerenone if LVEF <40%, evidence of heart failure or diabetes 

PRIOR TO EVACUATION 

• Ensure repeat ECG prior to emplaning: to identify evidence of dynamic ischaemia, arrhythmias or other changes e.g. post-MI pericarditis 

• Optimise analgesia to ensure patient remains pain free 

• consider beta-blocker for tachycardia with SBP >120 to reduce myocardial oxygen demand 

• If patient has had PCI in country of deployment, check access site (radial or femoral) for bruising, bleeding or haematoma.