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Acute chest pain for UKMLA AKT: High-Yield Emergency & Acute Care Lessons

Quick Overview

Acute chest pain is a high-stakes emergency presentation requiring rapid risk stratification to identify life-threatening causes (ACS, aortic dissection, PE). NICE NG185 emphasizes troponin timing, validated risk scores (HEART, GRACE), and immediate ECG interpretation to guide management pathways and reduce unnecessary admissions.

Core Facts & Concepts

Troponin Interpretation & Timing

High-sensitivity troponin (hs-Tn): Baseline + repeat at 3 hours (NICE NG185)
Rule-out threshold: <5 ng/L at presentation (if pain >6h) + non-ischemic ECG
Rule-in threshold: >52 ng/L (99th percentile varies by assay)
Delta change: ≥20% rise/fall suggests acute MI vs chronic elevation

Figure 1: ECG showing ST elevation in anterior leads V1-V4

STEMI vs NSTEMI Management

Feature	STEMI	NSTEMI
ECG	ST elevation ≥1mm (≥2mm V2-V3) or new LBBB	ST depression, T-wave inversion, or normal
Reperfusion target	Primary PCI <120 min (symptom onset)	Risk-stratified: PCI <72h if high-risk
Immediate Rx	Aspirin 300mg + Ticagrelor 180mg + morphine + GTN	Aspirin 300mg + Fondaparinux 2.5mg
Troponin	Usually elevated but don't wait for result	Essential for diagnosis + risk stratification

Risk Scores

GRACE score (NICE preferred): Predicts 6-month mortality; >140 = high-risk (invasive strategy <72h)
HEART score: 0-3 = discharge safe; ≥4 = admit for observation/troponin

🚩 Aortic Dissection Red Flags

Tearing/ripping chest/back pain radiating to interscapular region
BP differential >20mmHg between arms
Pulse deficits, new aortic regurgitation murmur
Widened mediastinum on CXR (>8cm)
Investigation: CT aortogram (not troponin)

Problem-Solving Approach

Immediate Assessment (First 10 minutes)

12-lead ECG within 10 minutes of arrival
ABCDE approach: O₂ if SpO₂ <94%, IV access, cardiac monitoring
High-risk features screen: STEMI, haemodynamic instability, arrhythmia
Aspirin 300mg immediately unless clear contraindication

Figure 2: Chest X-ray showing widened mediastinum

Risk Stratification Pathway (NICE NG185)

STEMI identified: Activate primary PCI pathway (door-to-balloon <90 min if presenting hospital)
Non-STEMI pathway:
- Baseline troponin + repeat at 3h
- Calculate GRACE score while awaiting troponin
- High-risk (GRACE >140, ongoing pain, haemodynamic instability): Fondaparinux + invasive strategy <72h
- Low-risk (GRACE <109, negative troponins): Consider discharge with outpatient follow-up

🚩 When to Suspect Non-ACS Causes

PE: Pleuritic pain, dyspnoea, risk factors (use Wells score)
Dissection: Sudden-onset tearing pain, BP asymmetry, neurological signs
Pericarditis: Positional pain (worse lying flat), PR depression on ECG, pericardial rub

Analysis Framework

Discriminating Features: ACS vs Mimics

Cause	Pain Character	ECG	Troponin	Key Discriminator
STEMI	Central crushing, radiation	ST elevation ≥1mm	Elevated	Time-critical: <12h symptom onset
NSTEMI	Similar to STEMI	ST depression/T inversion	Elevated (3h repeat)	GRACE score guides timing
Unstable angina	Crescendo pattern	May be normal	Normal	Clinical diagnosis if troponin negative
Aortic dissection	Sudden tearing, back pain	Usually normal	Normal (unless coronary involvement)	CT aortogram diagnostic
PE	Pleuritic, worse inspiration	Sinus tachycardia, S1Q3T3	May be mildly elevated	D-dimer + CTPA
Pericarditis	Sharp, positional relief	Widespread ST elevation + PR depression	Normal/mildly elevated	Pericardial rub, worse lying flat

⚠️ Warning: Troponin elevation ≠ ACS. Consider PE, myocarditis, renal failure, sepsis, takotsubo in context.

Visual Aid

HEART Score Components

Component	Points
History	Highly suspicious=2, Moderately=1, Slightly=0
ECG	ST deviation=2, Non-specific repolarization=1, Normal=0
Age	≥65y=2, 45-64y=1, <45y=0
Risk factors	≥3 factors=2, 1-2 factors=1, None=0
Troponin	≥3x normal=2, 1-3x normal=1, Normal=0

Key Points Summary

✓ ECG within 10 minutes is non-negotiable; STEMI diagnosis triggers immediate dual antiplatelet (aspirin 300mg + ticagrelor 180mg) + primary PCI pathway

✓ High-sensitivity troponin protocol: Baseline + 3-hour repeat per NICE NG185; <5 ng/L rules out MI if pain >6h and ECG non-ischemic

✓ GRACE score >140 = high-risk NSTEMI requiring invasive coronary angiography within 72 hours; <109 = low-risk suitable for early discharge

✓ Aortic dissection red flags: Tearing pain, BP differential >20mmHg between arms, widened mediastinum on CXR → urgent CT aortogram (troponin misleads)

✓ Don't anchor on troponin: Elevation occurs in PE, myocarditis, sepsis, renal failure; interpret with clinical context and ECG

✓ HEART score 0-3 safely identifies patients for discharge without admission; ≥4 requires observation and serial troponins

📌 Remember: STEMI TIME - S=Symptoms <12h, T=Troponin don't wait, E=ECG <10 min, M=Morphine + antiemetic, I=Immediate dual antiplatelet, T=Transfer for PCI, I=IV access, M=Monitor continuously, E=Exclude dissection if atypical

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Acute chest pain