Atropine and Amiodarone

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Another question posed to me during clinical this week that took me a while to find ... anyone know the reason why you can't treat bradycardia with atropine in a patient on amiodarone?

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Specializes in Nurse Practitioner/CRNA Pain Mgmt.

Just thinking it out in my head here...

Amiodarone prolongs the action potential, therefore decreasing the time in between beats. It is considered a vagolytic and can therefore cause atropine resistant bradycardia in patients. This is the simplest explanation I can come up with. Am I in the right direction?

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Atropine produces its effects by blocking muscarinic receptors in the heart. Amiodarone, although considered a class III antidisrythmic has class I and class II actions, and like said above prolongs the refractory period. Because of amiodarones mechanism of action giving atropine might not be beneficial when trying to increase the heart rate. It is like a pt who is in complete HB from B-Blockers. Atropine does not always help. It might help prevent further bradycardia by preventing stimulation of muscarinic receptors in the heart by ACh, but does not correct the initial problem. I have had to give glucagon to a pt in complete heart block because it produces its inotropic actions by a way other than direct stimulation of adrenergic receptors.

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