Acute Myocardial Infarction Management

Management of a patient with acute myocardial infarction (AMI) is a medical emergency. Local guidelines for the management of myocardial infarction should be followed where they exist.

Pre-hospital management :-

- Arrange an emergency ambulance if an AMI is suspected. Take an electrocardiogram (ECG) as soon as possible, but do not delay transfer to hospital, as an ECG is only of value in pre-hospital management if pre-hospital thrombolysis is being considered.
- Advise any patient known to have ischaemic heart disease to call for an emergency ambulance if the chest pain is unresponsive to glyceryl trinitrate (GTN) and has been present for longer than 15 minutes or on the basis of general clinical state - eg, severe dyspnoea or pain.
- Cardiopulmonary resuscitation and defibrillation in the event of a cardiac arrest.
- Oxygen: do not routinely administer oxygen, but monitor oxygen saturation using pulse oximetry as soon as possible, ideally before hospital admission. Only offer supplemental oxygen to:
a. People with oxygen saturation less than 94% who are not at risk of hypercapnic respiratory failure, aiming for saturation of 94-98%.
b. People with chronic obstructive pulmonary disease who are at risk of hypercapnic respiratory failure, to achieve a target saturation of 88-92% until blood gas analysis is available.
- Pain relief with GTN sublingual/spray and/or an intravenous opioid 2.5-5 mg diamorphine or 5-10 mg morphine intravenously with an anti-emetic.[2] Avoid intramuscular injections, as absorption is unreliable and the injection site may bleed if the patient later receives thrombolytic therapy.
- Aspirin 300 mg orally (dispersible or chewed).
- Insert a Venflon® for intravenous access and take blood tests for FBC, renal function and electrolytes, glucose, lipids, clotting screen, C-reactive protein (CRP) and cardiac enzymes (troponin I or T).
- Pre-hospital thrombolysis is indicated if the time from the initial call to arrival at hospital is likely to be over 30 minutes. The National Institute for Health and Clinical Excellence (NICE) recommends using intravenous bolus (reteplase or tenecteplase) rather than an infusion for pre-hospital thrombolysis.

Management initiated in hospital :-

- If not already done, insert a Venflon® for intravenous access and take blood tests for cardiac enzymes (troponin I or T), FBC, renal function and electrolytes, glucose, lipids, CRP, and clotting screen.
- Continue close clinical monitoring, oxygen therapy and pain relief.
- ECG monitoring: features that increase the likelihood of infarction are: new ST-segment elevation; new Q waves; any ST-segment elevation; new conduction defect. Other features of ischaemia are ST-segment depression and T-wave inversion.

Reperfusion

Patency of the occluded artery can be restored by percutaneous coronary intervention (PCI) or by giving a thrombolytic drug. PCI is the preferred method. Compared with fibrinolysis, PCI results in less reocclusion, improved left ventricular function and improved overall outcome (including reduced risk of stroke).

Primary percutaneous coronary intervention (PCI)

= PCI (or percutaneous transluminal coronary angioplasty - PTCA) is regarded as superior to fibrinolysis in the management of AMI and is becoming increasingly available for initial patient care.
= Primary angioplasty provides an early assessment of the extent of the underlying disease.
= Any delay in primary PCI after a patient arrives at hospital is associated with higher mortality in hospital. Time to treatment should therefore be as short as possible. Door (or diagnosis) to treatment time should be less than 90 minutes, or less than 60 minutes if the hospital is PCI ready and symptoms started within 120 minutes.
= There is general agreement that PCI should be considered if there is an ST elevation acute coronary syndrome, if symptoms started up to 12 hours previously.
= Patients should receive a glycoprotein IIb/IIIa inhibitor to reduce the risk of immediate vascular occlusion, and should also receive either unfractionated heparin, a low molecular weight heparin (eg, enoxaparin), or bivalirudin.
= Prasugrel in combination with aspirin is an option for the prevention of atherothrombotic events in patients with acute coronary syndromes and undergoing PCI if immediate primary PCI is necessary, stent thrombosis occurs during treatment with clopidogrel, or the patient has diabetes mellitus.
= Balloon angioplasty following myocardial infarction reduces death, nonfatal myocardial infarction and stroke compared with thrombolytic reperfusion. However, up to 50% of patients experience restenosis and 3% to 5% recurrent myocardial infarction.
= There is no evidence to suggest that primary stenting reduces mortality when compared with balloon angioplasty but stenting seems to be associated with a reduced risk of re-infarction and target vessel revascularisation.

Fibrinolytic drugs

For patients who cannot be offered PCI within 90 minutes of diagnosis, a thrombolytic drug should be administered along with either unfractionated heparin (for maximum two days), a low molecular weight heparin (eg, enoxaparin) or fondaparinux. Thrombolytic drugs break down the thrombus so that the blood flow to the heart muscle can be restored to prevent further damage and assist healing.

Antithrombotic therapy without reperfusion therapy

- In patients presenting within 12 hours after the onset of symptoms but reperfusion therapy is not given, or in patients presenting after 12 hours, aspirin, clopidogrel and an antithrombin agent (heparin, enoxaparin or fondaparinux) should be given as soon as possible.
- For patients who do not receive reperfusion therapy, angiography before hospital discharge is recommended (as for patients after successful fibrinolysis) if no contra-indications are present.

Coronary bypass surgery

Other initial management :
1. Antiplatelet agent
2. Beta-blockers
3. Angiotensin-converting enzyme (ACE) inhibitors
4. Cholesterol-lowering agents
5. Patients who have a left ventricular ejection fraction of 0.4 or less and either diabetes or clinical signs of heart failure should receive the aldosterone antagonist eplerenone (started within 3-14 days of the myocardial infarction and ideally after ACE inhibitor therapy) unless contra-indicated by renal impairment or hyperkalaemia (left ventricular function should be assessed in all patients with AMI during the initial hospital admission).
6. Cardiac assessment and revascularisation