Acute Myocardial Infarction Management

For a fuller discussion of all aspects of myocardial infarction, please see the separate articles on:

• Acute Myocardial Infarction
• Acute Coronary Insufficiency
• Complications of Acute Myocardial Infarction
• Posterior Infarction
• Coronary Revascularisation
• Cardiac Rehabilitation

There are also articles discussing primary and secondary prevention of cardiovascular disease.

• Arrange an emergency ambulance if suspect an acute myocardial infarction. It is essential that the patient gets to hospital as soon as possible and nothing should cause any delay. An ECG is only of value in pre-hospital management if pre-hospital thrombolysis is being considered.
• If the patient is known to have ischaemic heart disease then advise an emergency ambulance if the chest pain is unresponsive to GTN and has been present for longer than 15 minutes or on the basis of general clinical state, e.g. severe dyspnoea.
• Cardiopulmonary resuscitation and defibrillation in the event of a cardiac arrest
• High concentration oxygen
• Pain relief with 2.5-5 mg diamorphine or 5-10 mg morphine intravenously with an anti-emetic. Avoid intra-muscular injections as absorption is unreliable and the injection site may bleed if the patient later receives thrombolytic therapy (see below).
• Aspirin 300 mg orally (dispersible or chewed)
• Insert a venflon for intravenous access and take blood tests for full blood count, renal function and electrolytes, glucose, lipids, clotting screen, CRP and cardiac enzymes (Troponin I or T)
• Pre-hospital thrombolysis (see below) is indicated if the time from the initial call to arrival at hospital is likely to be over 30 minutes. NICE recommends using intravenous bolus (reteplase or tenecteplase) rather than an infusion for pre-hospital thrombolysis.

• If not already done, insert a venflon for intravenous access and take blood tests for cardiac enzymes (Troponin I or T), full blood count, renal function and electrolytes, glucose, lipids, CRP, and clotting screen.
• ECG: 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.
• Chest x-ray: to assess heart size and presence or absence of heart failure and pulmonary oedema. May also assist in differential diagnosis.
• Insulin-glucose infusion followed by intensive glucose control with subcutaneous insulin for all people with Type 1 and Type 2 diabetes.
• Antiplatelet agent: aspirin reduces mortality, non-fatal reinfarction, non-fatal stroke and vascular death and the survival benefit is maintained for at least four years.
  • Clopidogrel, in combination with low-dose aspirin, should be given for at least 4 weeks after MI with ST segment elevation (STEMI), and 1 year after the most recent non-ST segment elevation MI (NSTEMI).¹
  • Long-term use of clopidogrel with aspirin increases the risk of bleeding and there is little evidence for the benefit of the combination in the long term, so unless there are other reasons to continue patients can revert to standard antiplatelet therapy thereafter (aspirin alone).
  • Clopidogrel alone can be used for patients with aspirin hypersensitivity.
  • If patient is unable to take clopidogrel consider treatment with aspirin and warfarin (INR 2-3) combined.
  • Warfarin (INR 2-3) for up to ≥4 years can be considered in patients unable to take aspirin or clopidogrel.¹
• Beta blockers: When started within hours of infarction, beta blockers reduce mortality, non-fatal cardiac arrest and non-fatal reinfarction. Unless contraindicated, the usual regime is to give intravenously on admission and then continue orally, titrate upwards to the maximum tolerated dose.¹
• Angiotensin-converting enzyme inhibitors: reduce mortality whether or not patients have clinical heart failure or left ventricular dysfunction. They also reduce the risk of non-fatal heart failure. Titrate dose upwards to the maximum tolerated or target dose. Measure renal function, U+E and blood pressure before starting an ACE inhibitor (or ARB) and again within 1-2 weeks.¹
• Heparin infusion is used as an adjunctive agent in patients receiving alteplase but not with streptokinase. Heparin is also indicated in patients undergoing primary angioplasty
• Prophylaxis against thromboembolism: If not already receiving heparin by infusion, then patients should be given regular subcutaneous heparin until fully mobile
• 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 MI and ideally after ACE inhibitor therapy) unless contraindicated by renal impairment or hyperkalaemia (left ventricular function should be assessed in all patients with acute myocardial infarction during the initial hospital admission).²
• Cholesterol lowering agents: Ideally initiate therapy with a statin as soon as possible on all patients with evidence of CVD unless contraindicated - after discussing risks and benefits with the patient, taking into account comorbidities and life expectancy.

• Primary percutaneous transluminal coronary angioplasty (PTCA) is regarded as superior to fibrinolysis in the management of acute myocardial infarction and is becoming increasingly available for initial patient care.³
• Balloon angioplasty following myocardial infarction reduces death, non-fatal MI and stroke compared to thrombolytic reperfusion. However up to 50% of patients experience restenosis and 3% to 5% recurrent myocardial infarction.⁴
• Although thrombolysis remains the commonest method of revascularisation for acute myocardial infarction, there is a risk of early or late reocclusion and a 1-2% risk of intracranial haemorrhage.
• Primary angioplasty provides an early assessment of the extent of the underlying disease.
• There is no evidence to suggest that primary stenting reduces mortality when compared to balloon angioplasty but stenting seems to be associated with a reduced risk of reinfarction and target vessel revascularisation.⁴
• Cardiac angiography and angioplasty are particularly indicated in patients with large infarcts, anterior infarction, cardiogenic shock, those who do not fit the criteria for thrombolytic therapy, when thrombolysis is contraindicated or has failed and have persistent ischaemia.
• Coronary artery bypass surgery is indicated in patients in whom angioplasty fails and in patients who develop mechanical complications such as a ventricular septal defect, left ventricular rupture, or a papillary muscle rupture.

Thrombolysis⁵

• Reduces short-term mortality if given within six hours of symptoms.
• The greatest benefit is in patients with ST elevation or bundle branch block.
• Thrombolysis benefits patients with all types of infarction, but the benefit is several times greater in those with anterior infarction.
• The earlier the treatment is given, the greater the absolute benefit.
• Streptokinase and alteplase are given by intravenous infusion. Reteplase and tenecteplase can be given by rapid bolus injection.

Indications for thrombolytic therapy

• ST elevation of at least 1mm in two or more limb leads or at least 2mm in any two or more chest leads
• New onset left bundle branch block
• Presentation within 12 hours (but thrombolysis must be started as soon as possible, ideally within 1 hour)
• Presentation within 12-24 hours if continuing chest pain and/or ST elevation

Contraindications to thrombolytic therapy

• Normal ECG or ECG not available
• Unconsciousness without known cause
• Cerebrovascular accident within the last six months
• Possible aortic dissection
• Known intracranial pathology
• Active pulmonary disease with cavitation
• Severe hypertension with blood pressure above 180/110
• Coagulation defects, bleeding diatheses or anticoagulants
• Surgery (including dental extraction), major trauma, dental extraction or haemorrhage (including heavy vaginal bleeding) within the last two weeks
• Acute gastrointestinal bleeding, recent peptic ulcer, acute pancreatitis, oesophageal varices or severe liver disease
• Laser therapy for retinopathy within the last week
• Infective endocarditis, pericarditis
• Pregnancy or up to 18 weeks postnatal
• Prolonged or traumatic CPR
• In the case of streptokinase, previous allergic reactions to either streptokinase or anistreplase (no longer available)
• Prolonged persistence of antibodies to streptokinase may reduce the effectiveness of subsequent treatment, therefore streptokinase should not be used if recently used 5 days to 12 months previously.

Early risk assessment will help identify high risk patients, who may require early further management with angiography, and coronary revascularisation. Methods of cardiac assessment vary according to local availability and expertise.

• Routine exercise ECG testing: submaximal testing is increasingly performed before hospital discharge at 4-7 days. A symptom-limited test can be performed at 3-6 weeks post-infarction in order to assess prognosis and to identify those patients with reversible ischaemia (who should then have an angiogram to assess the need for or coronary artery bypass graft).
• Myocardial perfusion imaging scintigraphy using SPECT can be performed before hospital discharge to assess the extent of residual ischemia if the patient has not already undergone cardiac catheterisation and angiography. NICE recommends that myocardial perfusion scintigraphy using SPECT should be the first test used for:⁶
  • People where stress ECG may not give accurate or clear results, e.g. women, people who have certain unusual patterns in the electrical activity of their heart, people with diabetes or people for whom exercise is difficult or impossible.
  • The diagnosis of people who are less likely to have coronary artery disease and who are at lower risk of having heart problems in the future. The likelihood of a person having coronary artery disease can be assessed by considering a number of factors, e.g. age, sex, ethnic background and family history as well as the results of physical examination and investigations.
  • As an investigation in people who still have symptoms following a myocardial infarction or despite having had treatment to improve coronary artery blood flow.
• Echocardiography is helpful if the diagnosis is in question, can define the extent of the infarction and can identify complications, such as acute mitral regurgitation, left ventricular rupture or pericardial effusion
• Coronary angiography: defines the patient's coronary anatomy and the extent of the disease. Whether all patients with acute myocardial infarction should ideally undergo cardiac catheterization is controversial and present consensus is for angiography only if indicated by recurrent chest pain or significant ischaemia shown by exercise ECG or perfusion imaging. Patients with cardiogenic shock, intractable angina despite medications or severe pulmonary congestion should undergo cardiac catheterization immediately.

• Physical activity:
  • Patients should be advised to be physically active for 20–30 minutes a day to the point of slight breathlessness.
  • Patients who are not achieving this should be advised to increase their activity in a gradual, step-by-step way, aiming to increase their exercise capacity.
• Smoking: all patients who smoke should be advised to quit and be offered assistance from a smoking cessation service.
• Diet: patients should be advised to eat a Mediterranean-style diet (more bread, fruit, vegetables and fish; less meat; and replace butter and cheese with products based on vegetable and plant oils).
• Cardiac rehabilitation should be available for all patients after an MI.
• Medication:
  • All patients who have had an acute MI should be offered treatment with a combination of: ACE inhibitor, beta-blocker, aspirin, statin.
  • For patients who have had an acute MI and who have symptoms and/or signs of heart failure and left ventricular systolic dysfunction, treatment with an aldosterone antagonist licensed for post-MI treatment should be initiated within 3–14 days of the MI, preferably after ACE inhibitor therapy.
  • Treatment with clopidogrel in combination with low-dose aspirin should be continued for 12 months after the most recent acute episode of non-ST-segment-elevation acute coronary syndrome. Then standard care, including treatment with low-dose aspirin alone, is recommended unless there are other indications to continue dual antiplatelet therapy.
  • After an ST-segment-elevation MI, patients treated with a combination of aspirin and clopidogrel during the first 24 hours after the MI should continue this treatment for at least 4 weeks. Then standard treatment including low-dose aspirin should be given, unless there are other indications to continue dual antiplatelet therapy.
  • Antiplatelet therapy, ACE inhibitors, beta blockers and statins all reduce the risk of ischaemic coronary events with long term treatment. NICE recommends that in the absence of a clear reason to stop treatment, it is reasonable to continue antiplatelet therapy, beta blockers, ACE inhibitors and statins indefinitely.
• Coronary revascularisation: all patients should be offered a cardiological assessment to consider whether coronary revascularisation is appropriate.

• Group 1 entitlement: ordinary driving licence for car or motorcycle:
  • After an MI, driving must cease for at least 4 weeks.
  • Driving may recommence thereafter provided there is no other disqualifying condition.
  • After a non-ST elevation MI, driving may recommence 1 week after successful angioplasty, provided there is no other disqualifying condition.
  • The DVLA need not be notified.
• Group 2 entitlement: vocational drivers of large goods vehicles or passenger carrying vehicles:
  • All acute coronary syndromes disqualify the licence holder from driving for at least 6 weeks.
  • Relicensing may be permitted thereafter provided:
    • The exercise/functional test requirements can be met.
    • There is no other disqualifying condition.
  • The DVLA must be notified.

• Advice will vary according to the type of employment, general health of the patient, severity of infarction and complications.
• As a general guide, assuming an uncomplicated myocardial infarction, sedentary workers can return after 4-6 weeks, light manual workers after 6-8 weeks and manual workers after 3 months.

See the separate article on Complications of Myocardial Infarction.

• Up to 50% of people die within 30 days of an infarction. Over half these deaths occur before the patient reaches hospital.
• Prognosis is worse in women, increasing age, increasing ventricular dysfunction and recurrent infarction.
• Other indicators of a poorer prognosis are anterior infarction, number of leads showing ST elevation, bundle branch block and systolic blood pressure less than 100 mm with tachycardia greater than 100 per minute.