Isoprenaline Infusion for Patients with Heart Block or Symptomatic Bradycardia

Indication

Symptomatic advanced Atrioventricular (AV) block or bradycardia

Contraindications

• Allergy to isoprenaline or any other ingredients
• Patients with heart block due to digoxin toxicity (increased risk of tachyarrhythmias)
• Patients with cardiogenic shock following myocardial infarction and in patients with concurrent hypertension
• Recurrent ventricular arrhythmias requiring inotropic therapy
• Severe caution in significant aortic stenosis and uncontrolled hyperthyroidism
• Pregnancy/Breast-feeding

Warnings

• Always start at the lowest recommended dose (unless under cardiology advice).
• Doses which produce heart rates of >130bpm can increase the risk of arrhythmias.
• Use cautiously in patients with epilepsy/convulsions, diabetes, hypertension, and coronary heart disease.
• May exacerbate urinary retention.
• May potentiate hypokalaemia, hyperglycaemia, tachycardia and hypertension.

Interactions

• Cardiac effects may be antagonised by β-blockers.
• Avoid administration with tricyclic antidepressants or MAOIs (arrhythmia risk) or entacapone (tachycardia/arrhythmia risk).
• Significant arrhythmias may occur with epinephrine, digoxin, cyclopropane and halogenated hydrocarbon anaesthetics.

Adverse Effects

• Reported side effects include various CNS effects: headache, dizziness, restlessness, tension, palpitations, sweats and mild tremors.
• Tachycardia and ventricular ectopics/ventricular arrhythmias may be observed.
• Can rarely produce paradoxical transient heart block.

Monitoring

• All patients must be monitored on telemetry.
• Due to low pH, isoprenaline may cause venous irritation and tissue damage in cases of extravasation.
• If central venous access is unavailable, administration should be via a large peripheral vein and insertion site should be monitored closely.

Preparation and Administration

1. Administer via a central or large peripheral vein to reduce the risk of phlebitis.
2. Add isoprenaline 2mg to a 500ml bag of 5% Glucose (final concentration 4 micrograms/ml).
3. Commence at a rate of 1 microgram/min (pump rate = 15ml/hour).
4. Increase dose if required (max dose increase of 15ml/hour every 5 minutes.
5. Maximum dose is 5 micrograms/min (pump rate = 75ml/hour).
6. Adjust dose to achieve adequate heart rate (usually HR >50bpm) and blood pressure.
7. Discontinue by weaning dose slowly.