NON-ST ELEVATION MYOCARDIAL INFARCTION

(NSTEMI) AND UNSTABLE ANGINA (UA)

DESCRIPTION

Non-ST elevation MI: Chest pain that is increasing in frequency and/or severity, or occurring at rest. The chest pain is associated with elevated cardiac enzymes and ST segment depression or T wave inversion on ECG.

 

Unstable angina pectoris: Chest pain that is increasing in frequency and or severity, or occurring at rest. It also encompasses post-infarct angina. The chest pain may be associated with ST segment depression or T wave inversion on ECG. There is no rise in cardiac enzymes.

 

MEDICINE TREATMENT

If clinically hypoxic:

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

Anticoagulation:

For acute myocardial infarction with no ST elevation:

  • Unfractionated heparin, IV bolus, 5 000 units.
    • Follow with 1 000–1 200 units hourly monitored by aPTT. o Continue infusion for 3–5 days.

 

OR

Low molecular weight heparin, e.g.:

  • Enoxaparin, SC, 1 mg/kg 12 hourly for two days.

Note:

Thrombolysis is not indicated except if new left bundle branch block (LBBB).  See section 3.2.1: ST elevation myocardial infarction (STEMI).

 

To relieve spasm and pain and to reduce preload:

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

 

For persistent pain and if oral therapy is insufficient:

  • 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.
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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
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To relieve pain:

  • Morphine, IV, 1–2 mg/minute. o Dilute 10 mg up to 10 mL with sodium chloride 0.9%. o Total maximum dose: 10 mg. o Repeat after 4 hours if necessary. o Pain not responsive to this dose may suggest ongoing unresolved ischaemia.

 

If there is cardiac failure or LV dysfunction:

ACE inhibitor, e.g.:

  • Enalapril, oral, 10 mg 12 hourly.

 

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