Acute Myocardial Infarction

Presentation

• Chest pain - Central or epigastric chest pain which radiates to the arms, shoulders, neck, jaw, teeth or back may be associated with sweating, nausea, vomiting, dyspnoea, fatigue, and/or palpitations.
• Shortness of breath
• Altered mental state can be seen in elderly patients.
• Atypical presentations are common and tend to be seen in women, older men, people with diabetes and people from ethnic minorities.
• Atypical symptoms including abdominal discomfort or jaw pain.
• Associated diaphoresis or sweating.
• Syncope or near syncope without other cause
• Impairment of cognitive function without other cause

(Bolooki H. M. & Askari A., 2009)

Figure 1 : Symptoms of AMI

Source - simple.wikipedia.org

Causes

• Hyperlipidemia
• Atherosclerosis
• Diabetes mellitus
• Hypertension
• Tobacco use

(Bolooki H. M. & Askari A., 2009)

Investigations

• Electrocardiography (ECG) - It is the first diagnostic test. It may demonstrate that a MI is in progress or has already occurred.
• FBC - To check for anaemia.
• Monitor potassium levels - Electrolyte disturbances may cause arrhythmias, especially potassium and magnesium
• Renal function - Estimated glomerular filtration rate (eGFR). This should be measured before starting an angiotensin-converting enzyme (ACE) inhibitor.
• Lipid profile - This needs to be obtained at presentation because levels can change after 12-24 hours of an acute illness.
• Measure C-reactive protein (CRP) and other markers of inflammation.
• Cardiac enzymes - Cardiac troponins T and I are highly sensitive and specific for cardiac damage. The risk of death from an acute coronary syndrome is directly related to troponin level.
• Myocardial muscle creatine kinase (CK-MB) - CK-MB levels increase within 3-12 hours of onset of chest pain. They reach peak values within 24 hours, and return to baseline after 48-72 hours.
• CXR - To assess the patient's heart size and the presence or absence of heart failure and pulmonary oedema.
• Pulse oximetry and blood gases - To monitor oxygen saturation.
• Cardiac catheterization and angiography - Cardiac angiography defines the patient's coronary anatomy and the extent of the disease.
• Echocardiography can define the extent of the infarction and assess overall ventricular function and can identify complications, such as acute mitral regurgitation, left ventricular rupture or pericardial effusion.

(Tidy C. 2012)

Figure 2 : An ECG showing ST-Elevation

Source - www.clinicaljunior.com

Figure 3 : Diagnosis of AMI

Stepwise Management

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.
• Monitor oxygen saturation using pulse oximetry as soon as possible
• Only offer supplemental oxygen to people with oxygen saturation less than 94% who are not at risk of hypercapnic respiratory failure or with chronic obstructive pulmonary disease who are at risk of hypercapnic respiratory failure.
• 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.
• Aspirin 300 mg orally.
• 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 it takes more than 30 minutes to go to a hospital.

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 (including symptoms, pulse, blood pressure, heart rhythm and oxygen saturation by pulse oximetry), oxygen therapy and pain relief.
• ECG monitoring.

Reperfusion

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

• Facilitated PCI - The use of pharmacological reperfusion treatment given before a planned PCI.
• Rescue PCI - Performed on a coronary artery which remains occluded despite fibrinolytic therapy.

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, a low molecular weight heparin or fondaparinux. Thrombolytic drugs break down the thrombus. It restores the blood flow to the heart muscle and prevents 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.

Coronary artery bypass graft (CABG)

Only a few patients need a CABG in the acute phase but CABG may be indicated:

-       After failed PCI or the presence of refractory symptoms after PCI.

-       Cardiogenic shock, or mechanical complications

      Eg: ventricular rupture, acute mitral regurgitation, or ventricular septal defect.

-       Multivessel disease.

Other initial management

• Antiplatelet agent
• Beta-blockers
• Angiotensin-converting enzyme (ACE) inhibitors
• Cholesterol-lowering agents
• 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
• Other treatments:

        -      Heparin infusion
        -       Prophylaxis against thromboembolism
        -       Insulin-glucose infusion

(Tidy C. 2012)

REFERENCES

Bolooki H. M. & Askari A. 2009. Cleveland Clinic. [ONLINE] Available at: http://www.clevelandclinicmeded.com/medicalpubs/diseasemanagement/cardiology/acute-myocardial-infarction/ [Accessed 27^th April 15].

Tidy C. 2012. Patient.co.uk. [ONLINE] Available at: http://www.patient.co.uk/doctor/acute-myocardial-infarction [Accessed 27^th April 15].