ST ELEVATION MYOCARDIAL INFARCTION (STEMI)

DESCRIPTION

Ischaemic chest pain that is ongoing beyond 30 minutes and associated with persistent ST elevation or new left bundle branch block (LBBB). (Repeat ECG regularly as clinically indicated).

MEDICINE TREATMENT

If clinically hypoxic:

  • Aspirin, oral, 300 mg immediately as a single dose (chewed or dissolved).
    • Followed with 75–150 mg daily with food. PLUS

Thrombolytic therapy:

  • Streptokinase, IV 1.5 million units diluted in 100 mL sodium chloride 0.9%, infused over 30–60 minutes. Do not use heparin if streptokinase is given.
    Indications Contra-indications
    » For acute myocardial infarction with ST elevation:

    >     if history of onset is less than 6 hours. (Beyond 6 hours treat as NSTEMI (see below),

    >     if on-going ischaemic pain, or

    >     for new left bundle branch block.

    » Absolute:

    > streptokinase used within the last year,

    >    previous allergy,

    >       CVA within the last 3 months,

    >    history of recent major trauma,

    >    bleeding within the last month,

    >    aneurysms,

    > brain or spinal surgery or head injury within the preceding month, or

    >     active bleeding or known bleeding disorder.

    » Relative:

    >    refractory hypertension,

    >    warfarin therapy,

    >    recent retinal laser treatment,

    >     subclavian central venous catheter,

    >    pregnancy,

    > TIA in the preceding 6 months, > traumatic resuscitation.

    Adjunctive treatment For pain:

    • Morphine, IV, 1–2 mg/minute. o Dilute 10 mg up to 10 mL with sodium chloride 0.9%.
      • Total maximum dose: 10 mg. o      Repeat after 4 hours if necessary.

     

    Pain not responsive to this dose may suggest ongoing unresolved ischaemia.

    Nitrates, e.g.:

    • Isosorbide dinitrate, SL, 5 mg immediately as a single dose. o May be repeated at 5-minute intervals for 3 or 4 doses.

    For ongoing chest pain, control of hypertension or pulmonary oedema:

    • Glyceryl trinitrate, IV, 5–200 mcg/minute, titrated to response.
      • Start with 5 mcg/minute and increase by 5 mcg/minute every 5 minutes until response or until the rate is 20 mcg/minute. o If no response after 20 mcg/minute increase by 20 mcg/minute every 5 minutes until pain response or drug no longer tolerated.
      • Flush the PVC tube before administering to patient.
      • Monitor blood pressure carefully.
    Volume of diluent Glyceryl trinitrate

    5mg/mL

    Concentration of dilution
    250 mL 5 mL (25 mg) 100 mcg/mL
    10 mL (50 mg) 200 mcg/mL
    20 mL (100 mg) 400 mcg/mL
    500 mL 10 mL (50 mg) 100 mcg/mL
    20 mL (100 mg) 200 mcg/mL
    40 mL (200 mg) 400 mcg/mL
    Solution

    Concentration

    (mcg/mL)

    100 mcg/mL solution 200 mcg/mL solution 400 mcg/mL solution
    Dose (mcg/min) Flow rate (microdrops/min = mL/hour)
    5 3
    10 6 3
    15 9
    20 12 6 3
    30 18 9
    40 24 12 6
    60 36 18 9
    80 48 24 12
    100 60 30 15
    120 72 36 18
    160 96 48 24
    200 60 30

    When clinically stable without signs of heart failure, hypotension, bradydysrhythmias or asthma:

    -blocker, e.g.:

    • Atenolol, oral, 50 mg daily.
    • Simvastatin, oral, 10 mg daily.

     

     

     

    For anterior  myocardial infarction, pulmonary congestion or ejection fraction < 40%:

    ACE inhibitor, e.g.:

    • Enalapril, oral 10 mg 12 hourly.

     

    REFERRAL

    »      Refractory cardiogenic shock.

    »     Refractory pulmonary oedema.

    »    Haemodynamically compromising ventricular dysrhythmia.

    » Myocardial infarction-related mitral regurgitation or ventricular septal defect (VSD).

    » Contraindication to thrombolytic therapy (only if within the period for stenting).

    »      Ongoing ischaemic chest pain.

    » Failed reperfusion (<50% reduction in ST elevation at 90 minutes in leads showing greatest ST elevation, especially in anterior infarct or inferior infarct with right ventricular involvement).

    HMGCoA reductase inhibitors (statins) that lower LDL by at least 25%, e.g.:

    Reference and further reading

    Standard Treatment Guidelines and Essential Medicines List for South Africa 2012 Edition

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