IM2.10-13 | ACS Diagnostic Testing — Summary & Reflection

KEY TAKEAWAYS

ECG in ACS (obtain within 10 minutes of first medical contact):
- STEMI criteria: new ST elevation ≥2 mm (precordial V2–V3, men ≥40 yr) or ≥1 mm (other leads) in ≥2 contiguous leads; or new LBBB
- Localisation: inferior (II/III/aVF → RCA), anterior (V1–V4 → LAD), lateral (I/aVL/V5–V6 → LCx), posterior (ST depression V1–V3 → confirm with V7–V9), RV (V4R elevation in inferior STEMI)
- NSTEMI/UA ECG: ST depression, T-wave inversion, de Winter pattern, Wellens pattern
- Mimics: pericarditis (saddle-shaped multi-lead elevation + PR depression), early repolarisation (concave, young patient), LVH strain, Brugada

Troponin: Rise begins 3–6 h post-onset; peaks 12–24 h; remains elevated 7–14 days. ESC 0h/1h rapid protocol: delta ≥5 ng/L = NSTEMI rule-in; both values below threshold = rule-out. CK-MB returns to baseline in 48–72 h — useful for re-infarction detection.

CXR: CTR >0.5 = cardiomegaly; upper lobe diversion = Killip II; Kerley B lines = interstitial oedema; bat-wing haziness = alveolar oedema (Killip III); widened mediastinum = dissection screen.

Lipid targets: Very high risk (prior ACS): LDL-C <55 mg/dL (ESC) or <70 mg/dL (ACC/AHA); add ezetimibe or PCSK9i if statin alone insufficient. Non-HDL target = LDL target + 30 mg/dL.

Echo: LVEF guides pharmacotherapy (ACE-I/ARB + beta-blocker if LVEF ≤40%); RWMA confirms ischaemic territory; mechanical complications (MR, VSD, tamponade) require urgent surgery.

Coronary angiography: Gold standard; indicated for primary PCI in STEMI, early invasive in high-risk NSTE-ACS (GRACE >140), and elective in stable CAD refractory to medical therapy or with high-risk stress test features.

REFLECT

Return to the opening scenario — the ECG handed to you in the emergency department. Now that you have worked through this module, trace your interpretation pathway: (1) rate, rhythm, any arrhythmia requiring immediate intervention; (2) PR interval and QRS — new LBBB present? (3) ST changes — which leads, how many millimetres, contiguous? (4) Territory localisation — which vessel? (5) Reciprocal changes present? (6) STEMI criteria met? If yes — activate the reperfusion pathway immediately; do not wait for troponin. If no — are there ischaemic changes suggesting NSTE-ACS? If the ECG is entirely normal — does that reassure you that the patient has no significant ACS? Remember that up to 50% of NSTEMIs and all early-phase STEMIs (before troponin rise at 3–6 hours) can have non-diagnostic initial investigations. A systematic, time-integrated approach — ECG then serial troponin then CXR then echo — is the diagnostic sequence that saves lives.