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Case 2.5 – Acute Myocardial Infarction & Cardiopulmonary Arrest

Category: Cardiovascular | Discipline: Medicine | Setting: Emergency Department

Case

Maud Gyer, aged 79, presents by ambulance with severe chest pain. On arrival she is distressed and breathless. The ambulance driver tells you Maud has central crushing chest pain and is hypotensive and tachycardic. Her oxygen saturation is 80% on pulse oximetry and she is cold and clammy. Maud has a past history of hypertension and non-insulin dependent diabetes mellitus.

Questions

1. What further history and examination would you undertake?

Further history must try and ascertain whether this could be a presentation of a myocardial infarction. This includes:

  • Type and nature of the pain, radiation of the pain
  • Whether there was a change in the pain with the application of nitrate
  • Associated physical symptoms such as breathlessness, light-headedness, nausea, vomiting, sweating
  • A sense of fear or impending doom

Examination:

  • Signs of sympathetic activation: pallor, sweating and tachycardia
  • Signs of vagal activation: bradycardia and vomiting
  • Pallor and cool peripheries
  • Pulse (character and rate)
  • Blood pressure (hypotension)
  • JVP
  • Character of the apex beat
  • Auscultation findings in AMI: Muffled heart sound, decreased intensity of S1, audible S4, S3, paradoxical splitting of S2
  • Auscultation of base of both lungs may reveal late or pan-inspiratory crackles due to pulmonary congestion from left ventricular failure
2. What emergency management would you commence?

The most important concern is that this patient is at risk of death from acute myocardial ischaemia (and/or malignant arrhythmias) and therefore requires urgent admission to hospital.

Patients with suspected myocardial infarction require immediate access to medical care with defibrillation facilities.

On arrival:

  • O2 and aspirin are administered
  • Immediate IV access established
  • Blood should be taken immediately
  • IV analgesia (e.g. morphine) administered if there is ongoing pain

Immediate investigations:

  • 12-lead ECG is taken
  • Continuous ECG monitoring established

If there are ST-elevations consistent with acute myocardial infarction (STEMI) or newly onset left bundle branch block:

  • Acute reperfusion therapy is indicated either with PTCA (PCI) (if facility is available) or thrombolysis therapy

Patients are best managed in specialist units where they can be monitored and receive therapy for acute complications should they develop.

3. Maud has classic ECG changes of an inferior acute myocardial infarction. Describe what these changes would be?

Inferior myocardial infarct ECG changes:

  • ST elevation on leads II, III and aVF

Important to remember:

  • Up to 50% (10-50%) of inferior infarcts are associated with a right ventricular infarct
  • Look for ST segment elevation in leads V3R and V4R
  • Tall R waves & ST depressions in V1-V3
4. What cardiac enzymes would you order and why?

Myocardial infarction causes detectable rises in plasma concentrations of some enzymes and proteins that are usually only detectable in myocardial cells.

The markers that are most used are:

  • The cardio-specific proteins troponin T and I
  • The cardio-specific creatine kinase enzyme CKMB

Troponins:

  • Most sensitive markers of myocardial damage
  • Start to rise in the blood within 4-6 hours of the injury
  • May remain elevated for up to 2 weeks

CK and CKMB:

  • Start to rise 12 hours after the injury
  • Taper off within 48-72 hours
  • CK is not specific for cardiac muscle and may be elevated following defibrillation or intramuscular injections
  • CKMB and troponins are specific

When troponins are available, this is the better investigation.

5. Maud suddenly develops acute cardiopulmonary arrest in the emergency department. Describe your immediate series of responses?
  1. Call for assistance
  2. Precordial thump if witnessed arrest
    • May be considered for patients with monitored, pulseless ventricular tachycardia if a defibrillator is not immediately available
    • Relatively ineffective for ventricular fibrillation, and no longer recommended for this rhythm
    • Insufficient evidence to recommend for or against use for witnessed onset of asystole caused by AV-conduction disturbance
    • Should NOT be used for unwitnessed cardiac arrest
  3. Attach defibrillator and check the monitor is in place
  4. Check rhythm and pulse
  5. Prompt assessment and restoration of:
    • Airway
    • Administration of oxygen via mask
    • Circulation using CPR
6. What is the evidence base behind the use of thrombolytic and antiplatelet drugs in the emergency department in the setting of acute myocardial infarction?

Thrombolytic therapy:

Has been shown to improve survival rates in patients with acute myocardial ischaemia if administered in a timely fashion in the appropriate group of patients.

Indications for thrombolysis (if PCI not available or delayed >90 minutes):

  • Within 12 hours of onset of symptoms
  • ST-segment elevation >0.1 mV in 2 or more contiguous ECG leads
  • New left bundle-branch block (LBBB)
  • Anterior ST depression consistent with posterior infarction

Tissue plasminogen activator (t-PA):

  • Superior to streptokinase in achieving higher rate of coronary artery patency
  • Key to efficacy lies in the speed of delivery of therapy
  • IIb/IIIa receptor antagonist combined with half dose of thrombolytic may prove preferred method for medical reperfusion

Percutaneous coronary angiography (PCI):

Treatment of choice in most patients with STEMI, assuming the intervention can be initiated in less than 90 minutes of arrival in hospital.

Advantages of PCI:

  • Greater coronary patency
  • Lower risk of bleeding
  • Instant knowledge about the extent of underlying disease
  • May provide mortality benefit over thrombolytic therapy

PCI is treatment of choice for:

  • Patients with cardiogenic shock
  • Patients in whom thrombolysis failed
  • Those with high risk of bleeding or contraindications to thrombolytic therapy

Requirements for PCI:

  • Limited to experienced operators
  • Operators should have at least 75 cases per year
  • Centre should perform at least 200 cases per year (American College of Cardiology recommendations)