Acute Coronary Syndrome – STEMI

Definition: clinical sx consistent w ACS w ECG features including any of:

1. Persistent ST-segment elevation of ≥1mm in 2 contiguous limb leads – limb leads (I, II, and III,AVR, AVL, and AVF)
2. ST segment elevation of ≥2mm in 2 contiguous chest leads OR
3. New LBBB (presumed new unless evidence otherwise; echo useful to detect regional wall contraction abnormalities)

Reperfusion Critera: 

• Chest pain >30 min and <12 hours
• ECG changes
  • Persistent ST-elevation ≥1 mm in 2 contiguous limb leads
  • persistent ST-elevation ≥2 mm in 2 contiguous chest leads
  •  or new or presumed new LBBB
• Myocardial infarct likely from history

Qwaves

• Small ‘septal’ Q waves are typically seen in the left-sided leads (I, aVL, V5 and V6) 
• Q waves are considered pathological if:
  • > 40 ms (1 mm) wide 
  • > 2 mm deep
  • > 25% of depth of QRS complex
  • Seen in leads V1-3
• Q wave AMIs are transmural
• Q waves take several days to manifest. 
• Caused by total thrombotic occlusion. 
• Diagnosis is made retrospectively. Do not thrombolyse.

Area of Infarction

• Anterior V2 to V5 : LAD
• Inferior II, III, aVF : Circumflex, RCA
• Lateral I, aVL, V5-6 : Circumflex
• Posterior tall R waves in V1 with ST depression : RCA – note RV infarct

• Arterial Supply:
  • RCA (Right Coronary Artery):
    • Supplies the inferior and posterior areas of the heart.
    • Provides blood to the
      • right atrium (RA)
      • right ventricle (RV)
      • SA node (60% of people, 40% by left circumflex)
      • AV node.
    • Gives off the Posterior Descending Artery (PDA) in 85% of people (right dominant)
      • supplies the inferior wall, ventricular septum, and posteromedial papillary muscle.
    • In 15% of people, PDA comes off the left circumflex (left dominant).
  • LAD (Left Anterior Descending Artery):
    • Supplies the anteroseptal and anteroapical regions.
  • LCx (Left Circumflex Artery):
    • Supplies the anterolateral region.

Posterior Infarcts:

https://lifeinthefastlane.com/ecg-library/basics/inferior-stemi

Posterior Circulation:

• Predominantly consists of branches from the RCA.

Posterior Infarction:

• Accompanies 40% of STEMIs, often in the context of an inferior infarction.
• Right ventricular (RV) infarction complicates up to 40% of inferior STEMIs.
• Patients with RV infarction are very preload sensitive due to poor RV contractility and can develop severe hypotension in response to nitrates or other preload-reducing agents.
• Hypotension in RV infarction is treated with fluid loading, and nitrates are contraindicated.
• 20% of patients with inferior STEMI will develop significant bradycardia due to second- or third-degree AV block.

Lateral Infarction:

• Posterior extension of an inferior or lateral infarct implies a larger area of myocardial damage, increasing the risk of left ventricular dysfunction and death.
• Isolated posterior infarction is an indication for emergent coronary reperfusion, but the lack of obvious ST elevation means the diagnosis is often missed.

ECG Diagnosis:

• V4R:
  • ST elevation in V4R has a sensitivity of 88%, specificity of 78% diagnostic accuracy of 83% in diagnosing RV MI.
• V7-V9:
  • ST elevation in leads V7-V9 requires 0.5 mm of ST elevation to diagnose posterior MI

Acute Management

1. Seek help promptly – chest discomfort at rest OR for prolonged period (>10mins, not relieved by sublingual nitrates) OR recurrent chest discomfort OR ax w syncope or acute heart failure
2. Apply defibrillator to avoid cardiac death from reversible arrhythmias
3. ECG – 12 lead, V4R
4. Nb: pt’s w normal ECG + cardiac markers after an appropriate period of observation should, where practicable, undergo provocative testing (ie: stress testing) before discharge. If not immediately available, provocative testing should be arranged at the earliest opportunity, optimally within 72hrs. 
5. Establish IV access and take blood tests.\
6. CXR
7. Blood tests
   1. serum troponin (Lipid + glucose within 24hrs)
   2. Troponins are not useful for dx re-infarction, remain elevated 5-14d
8. Continuous Cardiac Monitoring

Initial Management of ACS Patients

Oxygen Therapy

• Avoid routine use of oxygen therapy in patients with SaO2 > 93%.
• Use oxygen therapy when SaO2 is below 93% or if the patient is shocked (unless COPD or other reasons for a modified SaO2 target).

Analgesia

• Nitrates:
  • Sublingual glyceryl trinitrate:
    • 400 micrograms spray or 300 to 600 micrograms tablet.
    • Repeat every 5 minutes as needed, maximum of 3 doses (monitor for hypotension).
  • I.V.: INFUSION:
    • Commence at 5 microg/min, Increment dose by 5 microg/min 5 minutely until desired effect (i.e. no pain, target BP). SBP >100mmHg
    • Place 50mg ampoule into 490mL G 5% NaCl 0.9% glass bottle 100mcg=1mL
  • GTN contraindicated if RV infarct
• Opiates:
  • IV morphine: 2.5 to 5mg initial dose, titrate to effect every 5 to 10 minutes with further doses of 2.5 to 5mg.
  • In elderly or those with cardiorespiratory compromise: initial morphine dose less than 2.5mg, incremental doses of 0.5 to 1mg.
  • If contraindicated, consider IV fentanyl: 25 to 50 micrograms initial dose.

Anti-Emetic

• IV metoclopramide: 10 mg.
• IV prochlorperazine: 12.5 mg.

Antiplatelet Therapy

• Aspirin:
  • 300 mg orally initially, then 100-150 mg daily thereafter.
  • Continue indefinitely unless not tolerated or anticoagulation is indicated.
• P2Y12 Inhibitors:
  • Ticagrelor: 180 mg loading dose, followed by 90 mg twice daily.
  • Clopidogrel: 300-600 mg loading dose, then 75 mg daily if contraindications to ticagrelor or prasugrel exist. (Clopidogrel 300mg – lysis, Clopidogrel 600mg – PCI)

Anticoagulation

• Enoxaparin: 1 mg/kg SC (0.75 mg/kg SC in elderly or those with renal impairment).
• Heparin: Loading dose followed by infusion if urgent PCI is required.

Glycoprotein IIb/IIIa Inhibitors

• Consider IV glycoprotein IIb/IIIa inhibitors in combination with heparin at the time of PCI for high-risk patients.
• Agents: Abciximab, Eptifibatide, Tirofiban (specific agent determined by treating cardiologist).

Bivalirudin (Direct Thrombin Inhibitor)

• Consider 0.75 mg/kg IV bolus followed by 1.75 mg/kg/h infusion as an alternative to glycoprotein IIb/IIIa inhibitors and heparin in ACS patients undergoing PCI with increased bleeding risk.

Reperfusion Therapy

• Very High Risk NSTEACS: Angiography and revascularization within 2 hours.
• High Risk NSTEACS: Within 24 hours.
• Intermediate Risk NSTEACS: Within 72 hours.
• Low Risk NSTEACS: Selective invasive strategy guided by testing for inducible ischemia.

Further Secondary Prevention Medications

• Statins: Highest tolerated dose of an HMG-CoA reductase inhibitor indefinitely; target LDL < 1.8 mmol/L.
• Beta Blockers: Initiate in patients with left ventricular ejection fraction < 40% unless contraindicated.
• ACE Inhibitors/Angiotensin Receptor Blockers: Initiate in patients with heart failure, left ventricular systolic dysfunction, diabetes, anterior MI, or co-existent hypertension.

Fibrinolysis

Dose

1. Dose Tenecteplase: IV Bolus 0.5mg/kg (max 50mg) 
2. Also, if giving Heparin due to high bleeding risk or eGFR <30: 
3. Heparin is administered post thrombolytic, (max 4000 Units), slow I.V. push followed by infusion 12 units/kg/hour (max 1000 units/hr) Check APTT every 4‐6 hours.

Complication risks:

• Risk : ICH 1-2%, risk increase with age, HTN, previous stroke
• Rx: urgent CT, IV Tranexamic acid 1g, FFP 2 units, neurosurg, ICU consult
• Major bleeding: 5% 2 units FFP
• Reperfusion dysarrthymias – accelerated idioventricular rhythm

Failed reperfusion:

• Persistant ischemic symptoms, HD instability
• < %50 ST reduction at 90 ins post reperfusion🡪 need rescue PCI

Conduct ECG at 90min, 6hrs and 12hrs post lysis

Continue medications

1. Aspirin 75-300mg PO OD
2. Nitrates
3. UH 5000-7500IU S/C 12hourly in mobile patients
4. High risk DVT/PE TEDS + Increased UH
5. Beta blocker especially in LV dysfunction and ongoing ischaemia. Doses atenolol 25-100mg PO OD or metoprolol 25-100mg PO BD with SBP >95 and HR>55
6. ACEI improves the outcome.
   • Give within 24-48 hours in patients with
     • Previous AMI
     • DM
     • HT
     • Anterior infarct
     • HR >80
     • CXR showing LVF
     • LVEF <45% (especially good in patients with poor LV f(x))
   • Low risk patients can be stopped in 6/52
   • C/I include Hypotension (SBP<100) and haemodynamic instability
   • Must monitor BP and EUC on alternate days

7. Calcium Channel Blocker
   • Only used if C/I to Betablockers.
8. Statins

COMPLICATIONS OF ACUTE CORONARY SYNDROMES

• cardiac failure
• post-infarction ischaemia
• ventricular free wall rupture
  • therapy: pericardiocentesis and repair
• ventricular septal rupture
  • therapy: IABP, inotropes, surgery
• acute mitral regurgitation
  • therapy: afterload reduction, IABP, inotropes, surgery ASAP
• right ventricular infarction
  • therapy: IV fluids, inotropes, AV synchrony, IABP, reperfusion
• arrhythmias
  • therapy: correct hypoxia, acidosis, hypovolaemia, K+, Mg2+ (controversial)
• cardiogenic shock
  • therapy: must get revascularisation (PCI or CABG) within 24 hours
• thromboembolism
  • therapy: mural thrombus -> anticoagulate
• pericarditis and Dressler’s syndrome
• complications of therapy, e.g. haemorrhage, coronary artery dissection, stent thrombosis, surgical complications