- Defined as elevated/dynamic troponin, with evidence of acute ischaemia (history, imaging) plus ECG changes
- ECG changes
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- ST elevation in at least 2 contiguous leads
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- In lead V2 and V3: ≥ 2.5 mm in men under 40, ≥2mm in men over 40, ≥1.5mm in all women
- And/or, in all other leads: >1mm (in the absence of LVH or LBBB)
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- ST elevation in at least 2 contiguous leads
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- Only 10% of STEMI patients have a history of stable angina (widespread atheroma is more likely to lead to a STEMI than a single critical lesion)
Other occlusion-MIs (STEMI equivalents)
- New LBBB
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- In reality BBB is nearly always old (usually due to HTN), but often worth discussing with cardiology anyway if new chest pain
- In most cases STEMI resulting in LBBB is a massive event and patient will be unwell (ie. if it’s just a twinge, then BBB likely old)
- Can use the modified Sgarbossa’s criteria to help diagnose
- Check whether morphology of the LBBB the same or different to previous ECGs
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- Inferior STEMI
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- Might see ST elevation of less than 1mm in the inferior leads plus ST depression (any amount) in aVL
- Check right precordial leads V3R and V4R
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- Posterior MI
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- If ST depression in V1-V3 (esp if positive T wave) check posterior leads V7-V9 (usually left circumflex occlusion)
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- Left main coronary artery (LMCA) obstruction
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- Widespread horizontal ST depression (>1mm in 6 leads, often inferolateral, so prominent in leads I, II and V4-6) coupled with ST elevation in aVR of >1mm (and/or V1) – this is the key finding although not specific to LMCA occlusion.
- Patient may be haemodynamically compromised
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- New bifasicular block
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- New RBBB and left anterior fascicular block suggest proximal LAD occlusion
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- Hyperacute T waves
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- Often precede classic STEMI
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- De Winter T Waves
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- An anterior STEMI equivalent with upsloping ST depression (1-3mm) and peaked T waves in the precordial leads
- Occurs in 2% of acute LAD occlusions
- High risk of large STEMI
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- Wellen’s Syndrome / LAD syndrome
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- Deeply inverted T waves (‘arrow head’, type A Wellens) or biphasic T waves in V2-3 (type B Wellens) is highly specific for a critical stenosis of the proximal LAD.
- Can be deep Ts anteriorly or laterally. T waves can flip to upright during pain
- Patient can be pain free at the time of ECG, but they are at very high risk of anterior MI in days to weeks. 75% suffer anterior STEMI within one week
- Cardiac markers can be normal or slightly elevated.
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Management points
- Assess eligibility for PCI
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- Do not use GCS post cardiac arrest to decide
- Consider frailty, comorbidities, patient preferences, prognosis
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- If transferring to cardiac centre
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- Consider whether needs anaesthetic support required (eg if shocked)
- If haemodynamically stable may be able to go with a nurse escort
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- Antiplatelets / anticoagulation
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- Give 300mg aspirin and send to cath lab asap for PCI (‘PAMI call’) – within 1 hour if possible.
- Do not offer glycoprotein IIb/IIIa inhibitors or fibrinolytic drugs routinely before arrival at cath lab
- Give prasugrel too if not taking anticoagulation (esp if young and low risk of bleeding).
- If high risk of bleeding, consider ticagrelor or clopidogrel instead
- If anticoagulated – give clopidogrel
- Unfractionated heparin is given in the cath lab not before
- Consider bivalirudin if femoral access and undergoing PCI
- If not having PCI – give ticagrelor and aspirin (unless high bleeding risk, in which case give aspirin +/- clopidogrel)
- No indication for fondaparinux
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Percutaneous Coronary Intervention (PCI) in STEMI
- 70% of cath lab work is acute ACS (30% is stable CAD).
- Remember an angiogram is an illuminogram – doesn’t tell you about plaque burden
- Time is muscle
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- Pain to balloon time is critical to outcomes
- Any delay is bad. Could be due to patients presenting late, delay in transfer to PCI centre or misdiagnosis of STEMI
- Aim to do within 120 minutes of ECG diagnosis. If not feasible – give thrombolysis (if presenting within 12 hours) and transfer to a PCI centre
- If presenting 12-48 hours after onset, PCI should still be considered (and is better than thrombolysis) but evidence is weaker. Strong evidence of benefit if ongoing pain, haemodynamic instability or life threatening arrythmias
- PCI probably not indicated urgently if presenting >48 hours and symptoms not persistent
- Aim to do complete revascularization during index PCI, or within 45 days (non-infarct related arteries are generally treated if more severely stenosed on angiography)
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- Complication rate often quoted as 0.1-1% for most patients (but could be much higher if complex PCI, advanced age, HF, CKD, shock, PVD or femoral access)
- Consent involves explaining risks of arterial damage, stroke, death and emergency CABG
- Oxygen not routine unless indicated – can even increase infarct size. Do not over oxygenate. Only give if sats <90%.
- If pulmonary oedema, consider whether patient needs to be tubed/offloaded prior to PCI (contrast and fluids can make them worse)
- Consider ABG and urgent echo pre-PCI
- Consider thrombus aspiration
- Consider GP IIb/IIIa inhibitor (eg tirofiban, eptifibatide) in lab once coronaries imaged and high thrombus burden confirmed. Consider in bailout (no reflow post PCI) and those with thrombotic complications. Never prior to cath lab
- Use drug-eluting stents – now on 3rd generation which are slimmer (70-80 micrometres) and have low thrombosis rates (0.3%)
- Now mostly radial access
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- Femoral has higher rate of complications incl false aneurysm, haemorrhage etc
- Radial access has lower all-cause mortality
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- Can be primary, or preventative, or both (‘bystander disease’ is > 50% stenosis but no infarct). Now generally do multivessel PCI whilst doing primary PCI (but no benefit in cardiogenic shock – get in and get out). The data generally supports treating bystander disease but no clear reduction in mortality. It reduces risk of reinfarction.
Thrombolysis (fibrinolysis)
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- Can use Tenecteplase or Alteplase
- Indicated if presenting within 12 hours of pain, and delay to getting PCI (ie can’t be done within two hours of time fibrinolysis can be done)
- Prevents 30 early deaths / 1000 patients treated within 6 hours (biggest benefit for those with highest risk)
- Can be given pre-hospital ideally within 10 minutes of STEMI diagnosis and without waiting for a troponin
- Still give 300mg aspirin, 300mg clopidogrel (or Ticagrelor) and LMWH
- Consider half dose Tenecteplase if aged >75
- Absolute contraindications – previous haemorrhagic CVA, ischaemic CVA in last 6/12, cerebral neoplasm, active bleeding, major surgery within 3 weeks, aortic dissection, bleeding disorder
- Relative contraindciations – BP > 180 systolic, TIA within 6/12, oral anticoagulation, pregnancy, traumatic CPR, PUD, CLD, IE
- Do ECG at 1-hour post thrombolysis – failure of ST elevation resolution by 50% = failure
- If failed – consider rescue PCI, do not re-thrombolyse
- Symptoms not a good guide to reperfusion
- 25% will need rescue angioplasty
- Accelerated idioventricular rhythm can occur indicating reperfusion (in PCI too)
- Thrombolysed patients require PCI even if thrombolysis has been successful, ideally within 2-24 hours from injection time. Therefore transfer all patients immediately to a PCI centre after thrombolysis given
Other considerations in STEMI
- Emergency CABG
- Sometimes undertaken if a large myocardial area in jeopardy, cardiogenic shock or mechanical complications of MI that require surgical repair
- Occasionally if failed PCI / occlusion not amenable to PCI (but benefits uncertain)
- Consider CABG if multivessel disease, post PCI, if not shocked. (during the same admission)
- Non-intervention
- May be appropriate if patient very frail and highly comorbid, for whom PCI is particularly risky, and life expectancy is limited
- Seek patient views and d/w cardiology
- Out of hospital cardiac arrest
- If ROSC, still need urgent PCI if ST elevation persists (providing reasonable benefit/risk ratio). Best evidence is for non-comatose patients but consider for all