Acute Coronary Syndromes (STEMI/NSTEMI) in the ICU

Overview & definition

Acute coronary syndrome (ACS) encompasses the spectrum of acute myocardial ischaemia: STEMI (ST-elevation — a complete coronary artery occlusion requiring immediate reperfusion), NSTEMI (non-ST-elevation with a troponin rise — a partial or subtotal occlusion), and unstable angina (ischaemia without a troponin rise). The ICU manages the complications — cardiogenic shock, the mechanical complications of MI, the life-threatening arrhythmias, and the post-cardiac-arrest ACS patient.[1][2][1]

STEMI management

Immediate (the MONA-B plus reperfusion):[2][1]

• Aspirin 300 mg loading.
• A P2Y12 inhibitor — ticagrelor 180 mg loading (preferred over clopidogrel per the PLATO trial, NEJM 2009, which showed ticagrelor reduced cardiovascular death and all-cause mortality versus clopidogrel in ACS without an increase in major bleeding)[2] — or prasugrel 60 mg, or clopidogrel 600 mg.
• Anticoagulation — unfractionated heparin or bivalirudin.
• Reperfusion:
  • Primary PCI (preferred) — door-to-balloon within 90 minutes.
  • Thrombolysis (if PCI unavailable within 120 minutes) — tenecteplase or alteplase; then transfer for PCI (pharmacoinvasive).

Post-reperfusion (secondary prevention):[1]

• Dual antiplatelet therapy (DAPT) for 12 months (aspirin plus the P2Y12 inhibitor).
• Beta-blocker (reduces mortality; caution in acute heart failure and hypotension).
• ACE inhibitor / ARB (especially if LV dysfunction, diabetes, or hypertension).
• High-intensity statin (atorvastatin 80 mg).
• Aldosterone antagonist (eplerenone) if LVEF under 40 per cent with heart failure.[1]

NSTEMI management

• Risk stratification with the GRACE score (Global Registry of Acute Coronary Events) — predicts the in-hospital and the 6-month mortality.[1]
• High-risk (refractory ischaemia, haemodynamic instability, dynamic ECG changes, a rising troponin, a GRACE score above 140): early invasive PCI within 24 hours.[1]
• Low-risk: conservative management with a delayed or outpatient angiography.
• Antiplatelet: aspirin plus ticagrelor (PLATO — ticagrelor superior to clopidogrel).[2]
• Anticoagulant: heparin, fondaparinux, or bivalirudin.[1]

ACS with cardiogenic shock — the SHOCK trial

The SHOCK trial (Hochman, NEJM 1999) randomised patients with MI complicated by cardiogenic shock to early revascularisation (PCI or CABG within 24 hours) versus initial medical stabilisation. Early revascularisation reduced the 6-month and the long-term mortality (at 6 months 50 vs 63 per cent; at 6 years 47 vs 56 per cent), even though the 30-day mortality was not significantly different.[1] The principle: in MI with cardiogenic shock, early revascularisation is the standard.[1]

The mechanical complications of MI

These occur at days 2 to 7 post-MI (the necrotic myocardium weakens and ruptures):[1]

• Ventricular septal rupture (VSR/VSD) — a new pansystolic murmur at the lower left sternal border; sudden haemodynamic collapse with a left-to-right shunt; echo diagnostic; surgical or percutaneous closure.
• Papillary muscle rupture — acute severe mitral regurgitation; the murmur may be soft (low forward flow in shock); pulmonary oedema; echo; urgent MV repair or replacement.
• Free wall rupture — cardiac tamponade with sudden death or electromechanical dissociation; echo (a pericardial effusion with RA/RV collapse); surgical repair.[1]

Arrhythmias complicating ACS

• VT/VF — amiodarone, defibrillation; beta-blockade (reduces the arrhythmia); correct the potassium and magnesium.
• Atrial fibrillation — rate control (beta-blocker, amiodarone); anticoagulate.
• Complete heart block — especially in inferior MI (the RCA supplies the AV node); a temporary pacemaker.[1]

[1]

Red flags

The Fourth Universal Definition of Myocardial Infarction (five types)

The 2018 Fourth Universal Definition of MI (Thygesen, Circulation 2018) standardises how an MI is diagnosed and classified worldwide.[9] A diagnosis of acute MI requires a rise and/or fall of cardiac troponin (with at least one value above the 99th percentile upper reference limit) together with at least one of: symptoms of myocardial ischaemia; new ischaemic ECG changes; development of pathological Q waves; imaging evidence of new loss of viable myocardium or new regional wall motion abnormality; or identification of a coronary thrombus by angiography or autopsy.[9][1]

The definition then stratifies MI into five pathophysiological types, each with fundamentally different management implications — the type determines whether the patient needs a catheter or whether the underlying trigger is the real target:[9]

ACS classification — STEMI vs NSTEMI vs unstable angina

The three clinical phenotypes of ACS share a common pathology (an unstable ruptured or eroded atherosclerotic plaque with varying degrees of overlying thrombus) and are separated by the ECG and the troponin:[1][15]

Pathophysiology — the unstable plaque

ACS begins with atherosclerotic plaque disruption (rupture of a thin-cap fibroatheroma, or superficial erosion). Circulating platelets adhere to exposed collagen and von Willebrand factor, become activated (via the ADP/P2Y12 and thromboxane A2 pathways), and aggregate. The coagulation cascade is simultaneously activated (tissue factor → extrinsic pathway), generating thrombin that converts fibrinogen to fibrin and further amplifies platelet activation. The result is a thrombus that partially (NSTEMI/UA) or completely (STEMI) occludes the lumen.[1] This dual pathway — platelets (white clot) and coagulation (red clot) — is the rationale for the two pillars of ACS pharmacotherapy: antiplatelets (aspirin + P2Y12 inhibitor) and anticoagulants (heparin or bivalirudin).

Antiplatelet therapy in ACS

Antiplatelet therapy targets the platelet arm of the thrombus. Dual antiplatelet therapy (DAPT) — aspirin plus a P2Y12 inhibitor — is the foundation of ACS management and is given to every patient unless contraindicated.[2][14]

Aspirin

• Mechanism: irreversibly acetylates and inhibits cyclo-oxygenase-1 (COX-1), blocking thromboxane A2 production for the lifespan of the platelet (7-10 days).
• Dose: 150-300 mg loading (chewed for fastest absorption), then 75-100 mg daily lifelong.
• Adverse: gastrointestinal bleeding, hypersensitivity, allergy. [1]

P2Y12 inhibitors

The P2Y12 (ADP) receptor is the dominant amplifier of platelet activation — its blockade is the key second antiplatelet. Three oral agents are available:[2][6][8]

[1]

Glycoprotein IIb/IIIa inhibitors (GPI)

The GPIs (abciximab, tirofiban, eptifibatide) block the final common pathway of platelet aggregation (fibrinogen cross-linking via GPIIb/IIIa). They are not used routinely in the era of potent oral P2Y12 inhibitors — reserve for bailout during PCI (large thrombus burden, slow/no reflow, massive thrombus) or in patients not yet loaded with a P2Y12 inhibitor.[1]

Duration of DAPT

• Default: 12 months for all ACS (the index ischaemic risk is highest in the first year).
• Ticagrelor beyond 12 months: the PEGASUS-TIMI 54 trial showed that extending ticagrelor (60 mg BD) beyond 12 months in patients with prior MI and additional high-risk features reduced MACE (but increased major bleeding).[13] Consider in patients with high ischaemic and low bleeding risk.
• Dual pathway inhibition: low-dose rivaroxaban 2.5 mg BD + aspirin (ATLAS ACS 2-TIMI 51, then COMPASS) reduces CV events post-ACS / in stable CAD, at a cost of more bleeding.[12] Useful in selected stable post-MI patients.
• Patients on oral anticoagulation (AF): OAC + aspirin (≤1 week) + clopidogrel then OAC + clopidogrel (triple→dual therapy) to minimise bleeding — NOT ticagrelor/prasugrel routinely.

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Anticoagulation in ACS

Anticoagulation targets the thrombin/fibrin arm of the thrombus. Parenteral anticoagulation is given at presentation and continued through PCI (then stopped after successful stenting, as DAPT takes over long-term).[1][7]

[1]

Reperfusion strategy

STEMI — the time-critical reperfusion

In STEMI, every minute of coronary occlusion means more myocardium lost ("time is muscle"). The two reperfusion strategies are primary PCI (preferred) and fibrinolysis (when PCI cannot be delivered in time).[15]

[1]

Complete vs culprit-only revascularisation

~50% of STEMI patients have multivessel disease. The strategy for the non-culprit lesions has evolved:[4][10][11]

• In stable STEMI (no shock): complete revascularisation (staging the non-culprit lesions, either during the index procedure or a staged PCI) reduces the composite of CV death/MI/ischaemia-driven revascularisation versus culprit-only — supported by COMPLETE (NEJM 2019) and DANAMI-3-PRIMULTI (Lancet 2015).[11][10]
• In cardiogenic shock: culprit-only PCI is preferred — CULPRIT-SHOCK (NEJM 2017) showed culprit-only PCI reduced 30-day death or severe renal failure versus immediate multivessel PCI.[4]

ACS complicated by cardiogenic shock — the mechanical circulatory support ladder

Cardiogenic shock complicates ~6-10% of STEMI and is the leading cause of in-hospital death. The defining principle (SHOCK trial) is that early revascularisation (PCI or CABG within 24 hours) reduces long-term mortality — do not delay the catheter for medical stabilisation.[1] When shock persists despite revascularisation, vasoactive drugs (noradrenaline first-line; dobutamine/milrinone as inotropes) are added, and if these fail, mechanical circulatory support (MCS) escalates from IABP → Impella → VA-ECMO.[1][5]

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Mechanical complications of MI — the day 2-7 catastrophe

The mechanical complications result from myocardial necrosis weakening the wall, which then ruptures or dysfunction. They classically occur at days 2 to 7 post-MI (peak around days 3-5), and present as a sudden haemodynamic collapse in a patient who was previously improving.[1] A sudden deterioration in this window is a mechanical complication until proven otherwise — the immediate action is an urgent echocardiogram.[1]

[1]

Right ventricular infarction — a special case

RV infarction complicates ~30-50% of inferior STEMI (the RCA supplies the RV). It presents with hypotension, clear lung fields and raised JVP (the triad) in the setting of an inferior MI. The management is counterintuitive and frequently tested:[1]

• Maintain RV preload — give fluid boluses (250 mL aliquots); AVOID nitrates, diuretics, and preload-reducing agents (they collapse the RV and worsen hypotension).
• Restore AV synchrony — atrial contribution to RV filling is critical; atrial fibrillation or heart block is poorly tolerated — cardiovert / pace.
• Inotropic support — dobutamine if hypotension persists after volume.
• Reperfuse the RCA — primary PCI restores RV function (often recovers better than the LV — the RV is more tolerant of ischaemia).
• ECG clues: ST elevation in right-sided leads V3R-V4R, and ST elevation in V1 with ST depression in V2 (posterior involvement). [1]

Post-MI secondary prevention — the four pillars plus device therapy

After reperfusion, the goals are to prevent recurrent ischaemia, limit adverse LV remodelling, and reduce mortality. The evidence-based regimen is the "four pillars" of post-MI therapy.[1][14]

[1] [1] [1]

The ECG in ACS — high-yield patterns

• Hyperacute T waves: the earliest sign of STEMI — broad, tall, asymmetric T waves in the territory of occlusion, often within minutes of onset (before ST elevation develops).
• De Winter T waves: upsloping ST depression at the J point in V1-V3 with tall, symmetrical T waves — an LAD occlusion equivalent; treat as a STEMI.[1]
• Wellens syndrome: deep biphasic (or deeply inverted) T waves in V2-V3 with minimal ST elevation, in a pain-free patient with a history of recent chest pain — critical stenosis of the proximal LAD; urgent (not emergent) angiography. Do NOT stress-test.
• True posterior MI: ST depression in V1-V3 with tall R waves (the mirror image of posterior ST elevation) — confirmed by ST elevation in V7-V9 (posterior leads). Treat as STEMI. Often with RV infarction.
• Left main / triple-vessel ischaemia: diffuse ST depression with ST elevation in aVR (≥1 mm) — critical left main or proximal LAD disease; high risk.
• Right ventricular infarction: ST elevation in V3R-V4R in the setting of an inferior STEMI; haemodynamically significant.
• New LBBB: in the right clinical context, treat as a STEMI (Sgarbossa criteria for diagnosing MI in LBBB/paced rhythm — concordant ST elevation ≥1 mm, discordant ST depression in V1-V3, or concordant ST elevation ≥5 mm).[1]

Arrhythmias complicating ACS — ICU priorities

Arrhythmias in ACS arise from ischaemia, autonomic imbalance, electrolyte disturbance, and reperfusion injury:[1]

• Ventricular fibrillation (VF) / polymorphic VT: defibrillate (200 J biphasic), amiodarone 300 mg IV, correct K+ (≥4.0 mmol/L) and Mg²⁺ (≥0.9 mmol/L). Beta-blockade reduces recurrence. Ischaemia-driven VF requires revascularisation.
• Sustained monomorphic VT: if pulseless → defibrillate; if stable → amiodarone 300 mg IV over 20-60 min. Search for ongoing ischaemia and electrolyte disturbance.
• Atrial fibrillation: common in LV dysfunction and heart failure. Rate-control (beta-blocker, diltiazem, digoxin if heart failure); amiodarone for rhythm control. Anticoagulate (assess CHA₂DS₂-VASc and HAS-BLED). Avoid IV non-dihydropyridine CCBs in heart failure with reduced EF.
• Bradycardia and AV block: inferior MI — usually the AV node (RCA supply); narrow-complex escape; often transient; atropine, and a temporary pacemaker if symptomatic. Anterior MI — infranodal (septal necrosis); wide-complex escape; high-grade block; permanent pacemaker often needed; poor prognosis.[1]
• Idiopathic ventricular arrhythmia (reperfusion): brief runs of VT/AIVR within minutes of restoring flow are common and usually self-terminating; do not over-treat.

Bedside echocardiography in the ACS patient

Bedside echo answers the critical ICU questions in ACS:[1]

1. Is there regional wall motion abnormality, and in which territory? (regional hypokinesis/akinesis = ischaemia)
2. What is the LVEF? (<40% → start GDMT, plan ICD if persistent)
3. Is there a mechanical complication? (VSD with left-to-right shunt on colour Doppler; flail leaflet with MR jet; pericardial effusion with tamponade)
4. Is there RV involvement? (RV dysfunction in inferior MI — affects management)
5. Is there LV thrombus? (in large anterior MI / aneurysm — needs anticoagulation)
6. Volume status (IVC for fluid responsiveness — the failing LV is on a flat Frank-Starling curve) [1]

Landmark trials — the ACS evidence base

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Clinical pearls

Additional red flags

Exam practice

[1]

Sample Viva 1 — Risk stratification in NSTEMI

Examiner: "A 72-year-old woman presents with rest chest pain. ECG shows T-wave inversion in the lateral leads. High-sensitivity troponin is elevated. How do you risk-stratify her, and what determines her management?" [1]

Expected response: "This is an NSTEMI — symptoms, troponin elevation, and ischaemic ECG changes. I would risk-stratify her using the GRACE score (Global Registry of Acute Coronary Events), which incorporates age, heart rate, blood pressure, creatinine, Killip class, cardiac arrest at admission, ST-segment deviation, and elevated biomarkers to estimate in-hospital and 6-month mortality. A GRACE score above 140 indicates high risk and mandates an early invasive strategy — coronary angiography within 24 hours. Very-high-risk features (refractory ischaemia, haemodynamic instability, mechanical complication, dynamic ST changes, life-threatening arrhythmia, or cardiac arrest) warrant immediate (≤2 hour) invasive angiography. She should receive aspirin plus ticagrelor (PLATO — ticagrelor preferred over clopidogrel) and parenteral anticoagulation (UFH or bivalirudin). At angiography, revascularisation by PCI or CABG is guided by the anatomy." [1]

Follow-up: "If her angiogram shows multivessel disease and she is in cardiogenic shock, what is your PCI strategy?" [1]

Response: "Culprit-only PCI — the CULPRIT-SHOCK trial (NEJM 2017) showed that treating only the culprit lesion reduced 30-day death and severe renal failure compared with immediate multivessel PCI, primarily because the larger contrast load and longer procedure of multivessel PCI worsened acute kidney injury. The non-culprit lesions are staged after the patient stabilises. This is the opposite of the strategy in stable STEMI, where COMPLETE showed complete revascularisation is superior." [1]

Sample Viva 2 — The troponin in the septic patient

Examiner: "A 65-year-old man is in the ICU with septic shock from a urinary source. His troponin is 800 ng/L (99th percentile 40). He has no chest pain and the ECG shows sinus tachycardia. The cardiology registrar wants to load him with ticagrelor and take him to the catheter lab. What is your response?" [1]

Expected response: "This is almost certainly a Type 2 MI — supply-demand mismatch from the sepsis, tachycardia, hypotension and hypoxia, with no evidence of a spontaneous plaque rupture. The Fourth Universal Definition (2018) requires, for a Type 1 MI, evidence of acute myocardial ischaemia — symptoms, dynamic ST/T changes, a new regional wall motion abnormality, or a coronary thrombus — none of which are present here. Treating him with ticagrelor and anticoagulation exposes him to bleeding without addressing the underlying problem, and a catheter trip is risky in septic shock. My response would be to treat the trigger — optimise oxygenation and ventilation, restore the blood pressure and perfusion, control the heart rate, transfuse if anaemic, and treat the sepsis with antibiotics and source control. I would order a bedside echocardiogram to look for a regional wall motion abnormality, and serial troponins — if they fall as the shock resolves, this confirms Type 2. I would only escalate to a coronary angiogram if there were objective evidence of ongoing ischaemia — new chest pain, dynamic ST changes, or a wall motion abnormality on echo." [1]

Key takeaways

• ACS spans STEMI (immediate reperfusion), NSTEMI (risk-stratified by GRACE) and UA (no troponin rise), unified by the Fourth Universal Definition of MI's five types.[9]
• All ACS receives aspirin + a P2Y12 inhibitor (ticagrelor preferred per PLATO) + parenteral anticoagulation (heparin or bivalirudin).[2][7]
• In MI with cardiogenic shock, early revascularisation is the standard (SHOCK); culprit-only PCI beats multivessel (CULPRIT-SHOCK); routine IABP (IABP-SHOCK II) and routine VA-ECMO (ECLS-SHOCK) confer no mortality benefit.[1][3][4][5]
• The mechanical complications (VSD, papillary muscle rupture, free wall rupture) occur at days 2-7 and present with sudden haemodynamic collapse — a mechanical complication until proven otherwise → urgent echo.[1]
• Post-MI secondary prevention: DAPT 12 months + beta-blocker + ACEi/ARB + high-intensity statin + MRA if LVEF <40% with heart failure; consider ICD if LVEF ≤35% at ≥40 days on optimal GDMT.[13][14]

References

1. [1]Hochman JS, Sleeper LA, Webb JG, et al.; SHOCK Investigators. Early revascularization in acute myocardial infarction complicated by cardiogenic shock. SHOCK Investigators. Should We Emergently Revascularize Occluded Coronaries for Cardiogenic Shock N Engl J Med, 1999.PMID 10460813
2. [2]Wallentin L, Becker RC, Budaj A, et al.; PLATO Investigators. Ticagrelor versus clopidogrel in patients with acute coronary syndromes N Engl J Med, 2009.PMID 19717846
3. [3]Thiele H, Zeymer U, Neumann FJ, et al.; IABP-SHOCK II Trial Investigators. Intraaortic balloon support for myocardial infarction with cardiogenic shock N Engl J Med, 2012.PMID 22920912
4. [4]Thiele H, Akin I, Sandri M, et al.; CULPRIT-SHOCK Investigators. PCI Strategies in Patients with Acute Myocardial Infarction and Cardiogenic Shock N Engl J Med, 2017.PMID 29083953
5. [5]Thiele H, Zeymer U, Neumann FJ, et al.; ECLS-SHOCK Investigators. Extracorporeal Life Support in Infarct-Related Cardiogenic Shock N Engl J Med, 2023.PMID 37634145
6. [6]Wiviott SD, Braunwald E, McCabe CH, et al.; TRITON-TIMI 38 Investigators. Prasugrel versus clopidogrel in patients with acute coronary syndromes N Engl J Med, 2007.PMID 17982182
7. [7]Stone GW, Witzenbichler B, Guagliumi G, et al.; HORIZONS-AMI Trial Investigators. Bivalirudin during primary PCI in acute myocardial infarction N Engl J Med, 2008.PMID 18499566
8. [8]Schupke S, Neumann FJ, Menichelli M, et al.; ISAR-REACT 5 Trial Investigators. Ticagrelor or Prasugrel in Patients with Acute Coronary Syndromes N Engl J Med, 2019.PMID 31475799
9. [9]Thygesen K, Alpert JS, Jaffe AS, et al.; Executive Group on behalf of the Joint European Society of Cardiology / American College of Cardiology Foundation / American Heart Association / World Heart Federation Task Force for the Universal Definition of Myocardial Infarction. Fourth Universal Definition of Myocardial Infarction (2018) Circulation, 2018.PMID 30571511
10. [10]Engstrom T, Kelbaek H, Helqvist S, et al.; DANAMI-3-PRIMULTI Investigators. Complete revascularisation versus treatment of the culprit lesion only in patients with ST-segment elevation myocardial infarction and multivessel disease (DANAMI-3—PRIMULTI): an open-label, randomised controlled trial Lancet, 2015.PMID 26347918
11. [11]Mehta SR, Wood DA, Storey RF, et al.; COMPLETE Trial Steering Committee and Investigators. Complete Revascularization with Multivessel PCI for Myocardial Infarction N Engl J Med, 2019.PMID 31475795
12. [12]Mega JL, Braunwald E, Wiviott SD, et al.; ATLAS ACS 2-TIMI 51 Investigators. Rivaroxaban in patients with a recent acute coronary syndrome N Engl J Med, 2012.PMID 22077192
13. [13]Bonaca MP, Bhatt DL, Cohen M, et al.; PEGASUS-TIMI 54 Steering Committee and Investigators. Long-term use of ticagrelor in patients with prior myocardial infarction N Engl J Med, 2015.PMID 25773268
14. [14]Collet JP, Thiele H, Barbato E, et al.; ESC Scientific Document Group. 2020 ESC Guidelines for the management of acute coronary syndromes in patients presenting without persistent ST-segment elevation Eur Heart J, 2021.PMID 32860058
15. [15]Ibanez B, James S, Agewall S, et al.; ESC Scientific Document Group. 2017 ESC Guidelines for the management of acute myocardial infarction in patients presenting with ST-segment elevation: The Task Force for the management of acute myocardial infarction in patients presenting with ST-segment elevation of the European Society of Cardiology (ESC) Eur Heart J, 2018.PMID 28886621