The cardiovascular effects of muscarinic receptor antagonists are of limited clinical application. Atropine may be considered in the initial treatment of patients with acute myocardial infarction in whom excessive vagal tone causes sinus or nodal bradycardia. Dosing must be judicious; doses that are too low can cause a paradoxical bradycardia; excessive doses will cause tachycardia that may extend the infarct by increasing O2 demand. Atropine occasionally is useful in reducing the severe bradycardia and syncope associated with a hyperactive carotid sinus reflex. Atropine will protect the SA and AV nodes from the effects of excessive ACh in instances of poisoning with anti-cholinesterase pesticides.
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