Can isoprenaline be given in patients with a recent myocardial infarction (MI)?

Isoprenaline Should Not Be Used in Recent Myocardial Infarction

Isoprenaline (isoproterenol) is contraindicated in patients with recent myocardial infarction due to its potential to increase myocardial oxygen demand, worsen ischemia, and increase mortality. 1

Rationale Against Isoprenaline Use in Recent MI

Physiological Effects

• Isoprenaline is a non-selective beta-adrenergic agonist that:
  • Increases heart rate (chronotropic effect)
  • Increases myocardial contractility (inotropic effect)
  • Increases myocardial oxygen demand
  • Can worsen existing myocardial ischemia

Evidence Against Use

• In patients with acute coronary ischemia or recent MI, increased heart rate from beta-agonists like isoprenaline can worsen ischemia 2
• Isoprenaline has been used experimentally to induce myocardial infarction in research models, highlighting its potential to cause cardiac damage 3, 4
• Research shows that isoprenaline administration can lead to:
  • Abnormal ECG patterns
  • Elevation of cardiac marker enzymes
  • Increased lipid peroxidation
  • Histopathological damage to cardiac tissue 3

Preferred Alternatives for Bradycardia in Recent MI

First-Line Treatment

• Atropine (0.5-1.0 mg IV) is the first-line agent for symptomatic bradycardia 2
  • Should be given in increments of 0.5 mg every 3-5 minutes
  • Maximum total dose of 3 mg
  • Note: Doses less than 0.5 mg may paradoxically worsen bradycardia

Second-Line Treatments

If bradycardia persists despite atropine:

1. Transcutaneous pacing should be considered
2. Epinephrine (2-10 μg/min) may be used in emergency situations, though it should be used cautiously as it can increase myocardial oxygen demand 1
   • Note: A 2018 study showed epinephrine was associated with higher incidence of refractory shock compared to norepinephrine in cardiogenic shock after MI 5
3. Dopamine (5-20 μg/kg/min) may be considered as an alternative

Management of Bradycardia in Recent MI

Assessment Algorithm

1. Determine if bradycardia is symptomatic (hypotension, altered mental status, chest pain, heart failure)
2. If symptomatic:
   • Start with atropine 0.5 mg IV
   • Repeat every 3-5 minutes if needed (max 3 mg)
3. If no response to atropine:
   • Initiate transcutaneous pacing
   • Consider dopamine infusion (5-20 μg/kg/min)
   • Consider epinephrine infusion (2-10 μg/min) with caution

Special Considerations

• In patients with AV block at the infranodal level (type II second-degree or third-degree AV block with wide QRS complexes), atropine may be ineffective 2
• In patients with heart transplantation, atropine may cause paradoxical high-degree AV block 2

Overall Management of Recent MI

The ACC/AHA guidelines recommend the following for patients with recent MI 1:

• Aspirin (160-325 mg daily)
• Beta-blockers (which would be antagonistic to isoprenaline's effects)
• ACE inhibitors for patients with LV dysfunction
• Nitroglycerin for ongoing ischemia
• Careful hemodynamic monitoring

Conclusion

Isoprenaline should be avoided in patients with recent myocardial infarction due to its potential to increase myocardial oxygen demand and worsen ischemia. For bradycardia management in these patients, atropine, transcutaneous pacing, and cautious use of dopamine are preferred alternatives.