What is the recommended dose for isoprenaline (isoproterenol) infusion in an adult patient with bradycardia or heart block?

Isoproterenol Infusion Dosing for Bradycardia

For adult patients with symptomatic bradycardia or heart block, isoproterenol should be administered as an intravenous infusion at 2-10 mcg/min (or up to 2-20 mcg/min), titrated based on heart rate and blood pressure response, but only after atropine has failed and when coronary ischemia is not a concern. 1, 2

Standard Dosing Protocol

• The European Society of Cardiology recommends preparing isoproterenol as 1 mg in 100 mL normal saline, infused to a maximum of 75 mL/h, which delivers 2-12 mcg/min. 1

• The American Heart Association supports standard ACLS dosing of 2-10 mcg/min with titration based on heart rate and blood pressure. 2

• For electrophysiology laboratory use, dosing ranges from 1-20 mcg/min intravenously for diagnostic purposes. 2

• The American College of Cardiology recommends careful monitoring of heart rate, blood pressure, and continuous ECG during administration, as higher doses (>20 mcg/min) may result in vasoconstriction or arrhythmias. 2

Critical Position in Treatment Algorithm

• Isoproterenol is strictly a second-line agent, used only after atropine (0.25-0.5 mg IV, up to total of 1-2 mg) has failed to improve bradycardia. 1, 2

• If bradycardia remains atropine-resistant, transcutaneous or transvenous pacing should be used as the definitive interim measure, with isoproterenol serving as a temporizing bridge. 1

• The American College of Cardiology emphasizes that atropine, pacing, or other pressors (dopamine, epinephrine) are preferred over isoproterenol for unstable bradycardia. 2

Absolute Contraindications

• Any concern for coronary ischemia is an absolute contraindication to isoproterenol. 2

• The drug increases myocardial oxygen demand through beta-1 effects while simultaneously decreasing coronary perfusion through beta-2 vasodilatory effects, worsening the oxygen supply-demand mismatch. 2

• Isoproterenol should be avoided in acute myocardial infarction, particularly with right coronary artery occlusion, where bradycardia commonly occurs. 1, 2

• The American Heart Association advises against using isoproterenol in acute coronary syndromes or suspected ischemia. 2

Special Clinical Situations

AV Dissociation with Low Ventricular Response

• Isoproterenol 2-20 mcg/min can be infused in cases of AV dissociation with low ventricular response, but must be avoided in ischemic conditions. 1

Post-Heart Transplant Patients

• The American College of Cardiology recommends isoproterenol as a more appropriate choice for post-heart transplant patients, as atropine may cause paradoxical heart block or sinus arrest in 20% of transplant patients. 2

Infranodal Heart Block

• Patients with atrioventricular blocks at the level of the His-Purkinje fibers (infranodal) are at increased risk of adverse events following atropine administration and may paradoxically worsen with either atropine or isoproterenol. 3

• Paradoxical bradycardia during isoproterenol infusion occurs in approximately 7% of patients, with second-degree AV block development indicating organic conduction disturbance. 4

Evidence Limitations and Clinical Reality

• The American College of Cardiology explicitly states that there is no clinical trial or observational series that supports the use of isoproterenol for bradycardia treatment, despite numerous case reports. 2

• Isoproterenol failed to improve survival in cardiac arrest in randomized controlled trials and is not recommended for cardiac arrest. 2

• Historical data from 1969 showed that only 42% of patients with chronic heart block were maintained satisfactorily on oral long-acting isoprenaline, with survival rates of 76% at one year. 5

Common Pitfalls to Avoid

• Never rely on isoproterenol as primary therapy for unstable bradycardia—it is a bridge to pacing, not a definitive treatment. 2

• Do not use isoproterenol in patients with heart failure with slow ventricular rates or those with angina of effort, as they do not respond to sympathomimetic drugs. 5

• Avoid administering isoproterenol before attempting atropine, as approximately 50% of patients with hemodynamically unstable bradycardia respond to atropine alone. 6

• Be prepared for paradoxical worsening of bradycardia, particularly in patients with infranodal heart block, where ventricular standstill may occur. 3, 4

Alternative Therapies When Isoproterenol Fails

• Theophylline may be used in AMI patients with atropine-resistant bradycardia with bolus of 0.25-0.5 mg/kg followed by infusion at 0.2-0.4 mg/kg/h. 1

• Epinephrine or dopamine infusions are alternative pressors that may be more appropriate than isoproterenol in many clinical scenarios. 2

• Definitive management requires transcutaneous or transvenous pacing for atropine-resistant bradycardia. 1, 2