Adenosine exerts its action through A1, A2a, A2b and A3 receptors.
A1 receptor activation slows the heart rate and conduction through the AV node. Activation of these receptors is thought to explain most of the side effects.
A2a receptor activation produces almost maximal coronary vasodilatation within 55-120 seconds.
A2b receptor activation is responsible for systemic hypotension via the peripheral vasodilator effect.
A3 receptors are found in lungs and liver and responsible for the production of bronchospasm.
The half life is 2-10 seconds therefore a constant infusion is needed.
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Contraindications for adenosine stress test
Contraindications for adenosine stress test (as with exercise PLUS):
- Bronchospasm
- Second and third degree heart block/sick sinus without a pacemaker
- Hypotension, BP systolic <90mmHg
- Cerebral ischaemia
- Use of Dipyridamole within last 24 hours
Patient preparation
Patient preparation (as with exercise PLUS):
- No caffeine or Xanthines (e.g. Aminophylline) for 24-48 hours
- Nil by mouth for 4-6 hours to reduce nausea and vomiting
Procedure
- 140mg/kg/min for 6 minutes
- Inject tracer at 3 minutes
- Record pulse, BP, ECG at baseline and every 3 minutes
- Closely observe ECG for conduction/rhythm abnormalities
Some centres use low-level exercise concurrently as this reduces abdominal blood flow (better pictures) and reduces side effects.
Some centres use shortened protocols from 5 minutes down to 3 minutes.
Side effects
-
Flushing 40%
- Dyspnoea 20-35%
- Chest pain 25-30%
- GI discomfort 15%
- Headache 14%
- Dizzy 9%
- AV/SA problems 7%
- ECG changes 15-20%
MI (fatal or non-fatal) has been recorded in 1 in 1,000.
When to stop the test
When to stop the test (same criteria as exercise PLUS):
- Hypotension <80mmHg
- Persistent second degree heart block
- Wheezing
- Severe chest pain
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