Occlusion of a large and proximal vessel may lead to myocardial ischaemia of such an extent that the patient dies rapidly of pump failure.

A. Immediate management

Routine use of a sedative (e.g., Diazepam) is not recommended unless the patient is extremely anxious.

• Morphine: 2.5-10 mg intravenously (IV) with repeat doses as necessary

And

• Glyceryl trinitrate: 600 µg sublingually with a repeat dose in 5 minutes if no response

It should not be administered in patients with hypotension and suspected right ventricular infarction.

B. Limiting infarct size

Antiplatelet and anticoagulant co-therapies in patients undergoing primary percutaneous coronary intervention (PCI)1 –

• Aspirin: Loading dose of 150-300 mg orally or 75-250 mg IV (in patients who are not on an Aspirin maintenance dose), followed by a maintenance dose of Aspirin, i.e., 75-100 mg/day. It should be given before primary PCI. After PCI, Aspirin should be continued indefinitely.

A loading dose of a P2Y12 receptor inhibitor should be given immediately or at the time of primary PCI to patients with ST-segment elevation myocardial infarction (STEMI). Dual antiplatelet therapy, combining Aspirin and a P2Y12 inhibitor (i.e., Prasugrel, Ticagrelor, or Clopidogrel), is recommended in patients with STEMI undergoing primary PCI for up to 12 months. 

• Clopidogrel: Loading dose of 600 mg orally, followed by a maintenance dose of 75 mg/day
• Prasugrel: Loading dose of 60 mg orally, followed by a maintenance dose of 10 mg/day. In patients with a bodyweight ≤60 kg, a maintenance dose of 5 mg/day is recommended. In patients ≥ 75 years, it is not recommended, but a dose of 5 mg/day can be used.
• Ticagrelor: Loading dose of 180 mg orally, followed by a maintenance dose of 90 mg twice daily.

Intravenous glycoprotein (GP) IIb/IIIa receptor antagonists, such as 

• Abciximab: Bolus of 0.25 mg/kg IV and 0.125 µg/kg/minute infusion (maximum 10 µg/minute) for 12 hours.
• Tirofiban: 25 µg/kg over 3 minutes IV, followed by a maintenance dose of 0.15 µg/kg/minute up to 18 hours.
• Eptifibatide: Double bolus of 180 µg/kg IV (given at a 10-minutes interval), followed by an infusion of 2 µg/kg/minute for up to 18 hours.

Parenteral anticoagulant therapies in primary PCI:

• Unfractionated Heparin (UFH): 70-100 IU/kg IV bolus when no GP IIb/IIIa inhibitor is planned; 50-70 IU/kg IV bolus with GP IIb/IIIa inhibitors.
• Enoxaparin: 0.5 mg/kg IV bolus
• Bivalirudin: 0.75 mg/kg IV bolus, followed by IV infusion of 1.75 mg/kg/hour for up to 4 hours after the procedure.

Antiplatelet therapies in patients not receiving reperfusion therapy:

• Aspirin: Loading dose of 150-300 mg orally, followed by a maintenance dose of 75-100 mg/day
• Clopidogrel: Loading dose of 300 mg orally, followed by a maintenance dose of 75 mg/day orally

Parenteral anticoagulant therapies in patients not receiving reperfusion therapy:

• UFH: 60 IU/Kg IV bolus with a maximum of 4000 IU, followed by an infusion of 12 IU/kg with a maximum of 1000 IU/Hour for 24-48 hours.
• Enoxaparin: In patients below 75 years, 30 mg IV bolus followed 15 minutes later by 1 mg/kg subcutaneously (SC) every 12 hours until revascularisation or hospital discharge for a maximum of 8 days. The first two SC injection dosage should not exceed 100 mg/injection. In patients ≥75 years, no IV bolus should be given. Subcutaneous dose of 0.75 mg/kg with a maximum of 75 mg/injection for the first 2 SC doses.
• Fondaparinux (only with Streptokinase): 2.5 mg IV bolus, followed by an SC administration of 2.5 mg once daily for up to 8 days or hospital discharge.^[1]

Other measures:

• Oxygen: 4-6 L/minute by mask
• Fibrinolytic therapy [Used in chest pain that has developed within the previous 12 or preferably 6 hours with either development of new left bundle branch block (LBBB) or STEMI]:

• Streptokinase: 1.5 million International Units (IU) by IV infusion over 30-60 minutes. If blood pressure falls due to infusion, the rate should be reduced or stopped temporarily and restarted at a dose of half the previous rate.
• Alteplase: 15 mg IV bolus; 

0.75 mg/kg IV over 30 minutes (maximum 50 mg), followed by 0.5 mg/kg IV over 60 minutes (maximum 35 mg).

• Reteplase: 10 units+10 units IV bolus given 30 minutes apart
• Tenecteplase: Single IV bolus: 

30 mg (6000 IU) if < 60 kg; 

35 mg (7000 IU) if 60 to < 70 kg; 

40 mg (8000 IU) if 70 to <80 kg; 

45 mg (9000 IU) if 80 to < 90 kg; 

50 mg (10000 IU) if ≥ 90 kg; 

it is recommended to reduce to the half dose in patients ≥ 75 years.^[1]

• For mild or moderate allergic reactions to Streptokinase:

•          Promethazine: 25 mg IV

Or

•          Hydrocortisone: 100 mg IV

• For severe allergy:

•          Adrenaline: 1 in 1,000 solution, 0.5-1 ml (0.5-1 mg) IV over 5 minutes

If response is poor:

•          Adrenaline: 1 in 1,000 solution 2-5 ml (2-5 mg) IV over 5 minutes

And should be added:

•          Promethazine: 25 mg IV

Or

•          Hydrocortisone: 100 mg IV

C. Management in the post-infarct period

i. Beta-blockers (continued indefinitely)

•          Atenolol: 25-100 mg orally daily

Or

•          Propranolol: 40-80 mg orally 2-3 times daily

ii. Angiotensin-converting enzyme inhibitors (ACEIs)

•          Enalapril: 5-40 mg orally daily 

iii. Statins

Clinical trials have supported a combination of lifestyle modification and continuous treatment with Aspirin, beta-blocker, a statin, and, in many cases, ACEIs in the treatment of myocardial infarction.

Citation

1. ^a, b Ibanez B, James S, Agewall S et al. 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;39(2):119-177. doi: https://doi.org/10.1093/eurheartj/ehx393
   https://academic.oup.com/eurheartj/article/39/2/119/4095042