Isoprenaline Dosing for Bradycardia
For symptomatic bradycardia refractory to atropine, administer isoprenaline as a continuous IV infusion at 1-20 mcg/min, titrated to heart rate response, or as an initial bolus of 20-60 mcg IV followed by 10-20 mcg boluses or infusion of 1-20 mcg/min. 1, 2
Treatment Algorithm
First-Line: Atropine
- Administer atropine 0.5-1 mg IV as initial therapy for symptomatic bradycardia 1, 2, 3
- Repeat every 3-5 minutes up to a maximum total dose of 3 mg 1, 2, 3
- Avoid doses <0.5 mg as they may paradoxically worsen bradycardia 3
- Onset of action occurs within 3 minutes after IV administration 1
Second-Line: When Atropine Fails
Isoprenaline is the preferred second-line agent when atropine is ineffective and there is low likelihood of coronary ischemia. 1, 2
Isoprenaline Dosing Options:
- Infusion: 1-20 mcg/min IV, titrated to heart rate response 1, 2
- Bolus: 20-60 mcg IV initially, followed by 10-20 mcg boluses as needed 1
- Alternative: Start infusion at lower end (1-2 mcg/min) and titrate upward based on response 2
Alternative Second-Line Agents:
- Epinephrine: 2-10 mcg/min IV or 0.1-0.5 mcg/kg/min IV 1, 3
- Dopamine: 5-10 mcg/kg/min IV, titrated to effect 3
Critical Precautions with Isoprenaline
Absolute Contraindications:
- Avoid isoprenaline when coronary ischemia is suspected or present 2
- Isoprenaline increases myocardial oxygen demand while potentially decreasing coronary perfusion 2
Monitoring Requirements:
- Continuously monitor heart rate, blood pressure, and ECG during administration 2
- Higher doses (>20 mcg/min) may cause vasoconstriction or arrhythmias 2
When Atropine May Be Ineffective:
- Type II second-degree AV block or third-degree AV block with wide QRS complex (block likely in non-nodal tissue) 3
- Post-cardiac transplant patients without autonomic reinnervation (atropine may paradoxically cause high-degree AV block) 3
- Infranodal blocks at the His-Purkinje level 4
Clinical Decision-Making
Choose Isoprenaline When:
- Patient has sinus node dysfunction with hemodynamic compromise 2
- Low likelihood of coronary ischemia 1, 2
- Need for chronotropic and inotropic effects without vasopressor effects 3
Choose Epinephrine or Dopamine When:
- Concern for coronary ischemia exists 2
- Need for additional vasopressor support 3
- Isoprenaline is unavailable or contraindicated 1
Common Pitfalls
- Do not delay transcutaneous pacing in unstable patients who fail atropine 3
- Paradoxical bradycardia can occur with isoprenaline infusion (7% incidence), particularly in young patients with hypervagotonia 5
- In acute myocardial infarction, increasing heart rate with any chronotropic agent may worsen ischemia or increase infarct size 3, 6
- Prepare for transvenous pacing if patient does not respond to medications or transcutaneous pacing 3