By Matt Luther FRCNA, Nurse Practitioner, Emergency Department, Calvary Health Care ACT and Shane Lenson FRCNA, Senior Nurse Advisor, Royal College of Nursing, Australia.
Acute coronary syndrome (ACS) is a broad term used to cover any group of clinical symptoms that may result in myocardial ischemia. ACS covers the spectrum of clinical conditions from unstable angina to non-ST elevation myocardial infarction (NSTEMI) and ST elevation myocardial infarction (STEMI). Chest pain associated with an ACS is caused by an insufficient oxygenated blood supply to the coronary tissue. This altered blood flow commonly results from coronary artery disease including arosclerotic plaque rupture, smooth muscle constriction or spasm and thrombus occulsion.
ACS typically follows the following disease process:
1) Non specific chest pain,decreased exercise tolerance
2) Unstable angina
3) Non-ST elevation myocardial infarction or ST elevation myocardial infarction
Unstable angina can be characterised as typical angina symptoms (shortness of breath, decreased exercise tolerance and chest pain) with increasing frequency, occurring recurrently and unpredictably and often not specific to exercise. A patient with unstable angina may have a normal ECG, however in some cases ST segment depression may be present. Cardiac enzymes are usually normal with unstable angina.
Non-ST elevation myocardial infarction
Non-ST elevation myocardial infarction patients have a history consistent with unstable angina, but do not show ST elevation on their ECG. These patients have symptoms at rest and/or prolonged pain, and show non-ST elevation ECG changes with a serum cardiac marker, troponin, rise.
ST elevation myocardial infarction
STEMI is defined as a presentation with clinical symptoms consistent with an ACS, with ECG changes including any of the following:
• persistent ST segment elevation of >1 mm in two contiguous limb leads
• ST segment elevation of >2 mm in two or more contiguous chest leads
• left bundle branch block not known to be old.
Patients with STEMI who present within 12 hours should have a reperfusion strategy, percutaneous coronary intervention (PCI) or thrombolysis, implemented urgently.
The choice of reperfusion therapy depends on several factors:
• time delay to percutaneous coronary intervention (PCI) or thrombolysis
• time from symptom onset
• contraindications to thrombolysis
• presence of cardiogenic shock.
For patients who present within one hour of the onset of their ACS symptoms, thrombolysis should be considered ahead of PCI. In those presenting between 1–3 hours of symptom onset, PCI is preferred if this can be achieved in a timely manner. For those presenting after three hours, PCI is regarded as superior to thrombolysis. PCI is the preferred option in the setting of cardiogenic shock.
Percutaneous coronary intervention
PCI is probably the better reperfusion strategy if performed promptly by an experienced interventional cardiologist in an appropriate institution with sufficient exposure to the procedure. Where PCI is not available or delayed, thrombolytic therapy should be given. A time delay of 90 minutes from first medical contact to balloon inflation is the maximum desirable timeframe; otherwise thrombolysis should be given.
Thrombolysis is still the most common method available for coronary reperfusion outside tertiary and major referral hospitals in Australia. The following are common thrombolytic agents used to manage STEMI presentations:
• streptokinase (SK) 1.5 million units over 30–60 minutes
• retaplase (rPA) two 10-unit boluses, 30 minutes apart
• alteplase (rt-PA) three weight dependent doses over 90 minutes
• tenecteplase (TNK) single bolus dose based on body weight.
Significant contraindications to thrombolysis include:
• active bleeding or bleeding disorder
• significant closed head injury or facial trauma
• any prior intracranial haemorrhage
• ischaemic stroke within three months
• known structural cerebral vascular lesion
• known malignant intracranial neoplasm.
Bleeding is the most common adverse event associated with the administration of thrombolytic agents. This may be obvious or concealed bleeding. Concealed intracranial bleeding may present as a cerebrovascular accident. Concealed gastrointestinal bleeding may initially only present as a patient in hypovolaemic shock.
First line management of ACS
The initial management of patients with suspected ACS requires a coordinated response resulting in the simultaneous stabilisation of the patient, investigation of symptoms and treatment. A presumptive diagnosis of ACS can usually be made on history and examination alone. Once the diagnosis of ACS is likely, initial management should be provided following the ‘MONA’ acronym:
Morphine sulphate (morphine) is used to reduce cardiogenic chest pain. Morphine acts on the CNS to reduce pain and anxiety, decreases rate of AV node conduction, improving cardiac output, and assists with coronary vasodilatation.
Supplemental oxygen, 15L per minute by face mask, is administered for the purpose of relieving hypoxemia and preventing tissue/cell damage as a result of a hypoxia. Increasing the fraction of inspired oxygen will increase end point tissue oxygenation even in a patient with pulse oxymetry of 100%.
Glyceryl-trinitrate (GTN) (anginine) decreases preload by increasing venous capacity through the pooling of venous blood in the peripheral veins and reducing ventricular filling pressure. GTN also decreases arterial blood pressure (after load), causes coronary artery vasodilatation and may assist redistribution of blood flow along collateral vascular channels of the heart.
Acetylsalicylic acid (aspirin) initiates an antithrombotic action by reducing platelet aggregation at sites of vascular injury such as coronary plaques. Contraindications include known severe adverse reaction to aspirin or to non-steroidal anti-inflammatory drugs (NSAIDs), bleeding disorders, GI bleeding and suspected leaking aortic aneurysms.
An ECG should be performed early as it is the sole test used to identify whether patients are suitable for interventional reperfusion, or whether thrombolysis is most suitable. However, a normal ECG does not exclude ACS.
Current evidence-based practice is to continue the cardiac monitoring of potential ACS patients with normal initial ECGs, where there is concurrent chest pain. Other studies have identifed that patients who are pain free on assessment and have normal or non-specific ECG findings on initial ECG are at extremely low risk of arrhythmias. Therefore, these limited resources might be used more efficiently by moving such low-risk patients from cardiac monitoring while continuing to investigate their symptoms.
Australian guidelines recommend the measurement of troponin on arrival and repeated eight hours after the last episode of pain if initially normal. CKMB should be measured if troponin assays are not available. Post initial management, serial monitoring of cardiac enzymes should be undertaken with creatine kinase (CK).
Other pathology tests
Australian guidelines also recommend the following tests in the management of a patient presenting with ACS symptoms:
• full blood examination (FBE)
• electrolytes, particularly potassium (K) in the acute phase
• serum lipids within 24 hours
• blood glucose.
In the event of cardiac arrest, immediate commencement of basic life support followed by advanced life support intervention is essential. It is strongly recommend that nurses undertake regular basic and advanced life support training based from the Australian Resuscitation Council Guidelines. For more information about resuscitation guidelines and advanced life support courses go to the Australian Resuscitation Councils webpage: www.resus.org.au.
Australian Resuscitation Council. Guideline 8.2 – Heart attack. Retrieved from http://www.resus.org.au/.
Berger J., Buclin T., Haller E., Van Melle G. and Yersin B. (2009). Right arm involvement and pain extension can help to differentiate coronary diseases from chest pain of other origin: a prospective emergency ward study of 278 consecutive patients admitted for chest pain. Journal of Internal Medicine. Volume 227, Issue 3, Pages 165-172.
HealthInsite, Australian Government. Risk factors for heart disease. Retrieved from http://www.healthinsite.gov.au/topics/Risk_Factors_for_Heart_Disease.
Heart Foundation. Acute coronary syndromes. Retrieved from http://www.heartfoundation.org.au/Professional_Information/Clinical_Practice/ACS/Pages/default.aspx.
Heart Foundation. Risk factors for coronary heart disease. Retrieved from http://www.heartfoundation.org.au/Heart_Information/Risk_Factors/Pages/default.aspx.
Ornato, J. (1999). Chest pain emergency centers: Improving acute myocardial infarction care. Clinical Cardiology. Volume 22, Supplement IV, Pages IV-3-IV-9.
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