Acute coronary syndrome: initial assessment and management

Overview

•AV node supplied by posterior interventricular artery - branch of the right coronary artery (RCA) in ~85% (right-dominant circulation)

•RCA occlusion → infarction of AV node → complete heart block - classic complication of inferior STEMI

Presentation

•Central crushing chest pain ± radiation to jaw/left arm; diaphoresis, nausea, dyspnoea

•Complete heart block (inferior MI/RCA) - chest pain + bradycardia (~40 bpm) + haemodynamic compromise (hypotension)

•Unstable presentation - signs of shock (hypotension, tachycardia), reduced consciousness, heart failure → requires immediate electrical intervention

Investigations

🥇 First-line

•12-lead ECG - ST elevation, new LBBB, ST depression, T-wave changes, heart block

•High-sensitivity troponin - serial at 0 h and 1-3 h; rise/fall confirms necrosis (NSTEMI); normal in unstable angina

•Continuous cardiac monitoring - detects VF, complete heart block

🏆 Gold standard

•Coronary angiography - defines occlusion, guides PCI/CABG

Management

•Oxygen only if SpO2 <94% (target 94-98%; 88-92% in COPD) - routine O2 in normoxic patients not beneficial

•Aspirin 300 mg orally (loading dose) unless allergy

•Sublingual GTN for pain - withhold if SBP <90 mmHg

🧠

BATMAN mnemonic for NSTEMI immediate management: Base angiography on GRACE score | Aspirin 300 mg | Ticagrelor 180 mg (or clopidogrel if high bleeding risk) | Morphine titrated IV | Antithrombin: fondaparinux (unless immediate angiography) | Nitrate (sublingual GTN)

Complications

•Complete heart block - inferior MI (RCA occlusion); bradycardia + haemodynamic compromise

•VF - most common cause of early death post-MI

•New pan-systolic murmur 2-5 days post-MI:

•Papillary muscle rupture → acute mitral regurgitation (posterior wall MI, RCA)

•Ventricular septal rupture → left-to-right shunt (anterior MI, LAD)

•Both cause acute haemodynamic collapse - require urgent surgical/catheter intervention

🎯

RCA occlusion = inferior STEMI = complete heart block. The AV node is supplied by the RCA in ~85% of people - tested directly in exam questions linking coronary anatomy to conduction block.

Unstable tachycardia / cardiac arrest management

•Unstable tachycardia (shock, heart failure, syncope, reduced consciousness) → synchronised DC cardioversion - can be repeated up to 3 times

•Non-shockable cardiac arrest (asystole/PEA) → CPR 30:2 + IV adrenaline 1 mg = 10 ml of 1 in 10,000 solution IV

•Shockable arrest (pulseless VT/VF) → unsynchronised defibrillation

⚠️

Synchronised cardioversion requires a clear QRS complex to synchronise to - it cannot be used in pulseless rhythms (use unsynchronised defibrillation instead). Digoxin and oral bisoprolol are too slow for haemodynamically unstable patients.

Follow-up / secondary prevention

•Aspirin 75 mg once daily indefinitely

•Second antiplatelet - ticagrelor 90 mg twice daily or clopidogrel 75 mg once daily for 12 months (DAPT)

•Atorvastatin 80 mg once daily - high-intensity statin

•ACE inhibitor (e.g. ramipril) - reduces afterload, attenuates LV remodelling

•Beta-blocker (e.g. bisoprolol) - for at least 12 months post-MI

•Second-line: Aldosterone antagonist (e.g. eplerenone 50 mg once daily) - if heart failure or LVEF ≤40%; monitor potassium