Bradycardia physostigmine

In the heart, the effects on the parasympathetic limb predominate. Thus, cholinesterase inhibitors such as edrophonium, physostigmine, or neostigmine mimic the effects of vagal nerve activation on the heart. Negative chronotropic, dromotropic, and inotropic effects are produced, and cardiac output falls. The fall in cardiac output is attributable to bradycardia, decreased atrial contractility, and some reduction in ventricular contractility. The latter effect occurs as a result of prejunctional inhibition of norepinephrine release as well as inhibition of postjunctional cellular sympathetic effects. 

Physostigmine Suggested for antimuscarinic anticholinergic agents not for tricyclic antidepressants Adult dose is 0.5-1 mg IV slowly. The effects are transient (30-60 minutes), and the lowest effective dose may be repeated when symptoms return. May cause bradycardia, increased bronchial secretions, seizures. Have atropine ready to reverse excess effects. Do not use for tricyclic antidepressant overdose. 

Adverse effects The effects of physostigmine on the CNS may lead to convulsions when high doses are used. Bradycardia may also occur. Inhibition of acetylcholinesterase at the skeletal neuromuscular junction causes the accumulation of acetylcholine and ultimately results in paralysis of skeletal muscle. However, these effects are rarely seen with therapeutic doses. 

One herb, the calabar bea, actually causes cholinergic toxicity (as seen with pesticide overdoses) due to the physostigmine content in the ripe seeds. This toxicity includes bradycardia and hypotension, potentially leading to cardiac and respiratory arrest. ... 

Therapy for phenothiazines is generally supportive and similar to that for tricyclic antidepressant overdose. Physostigmine can reverse the central and peripheral anticholinergic manifestations of phenothiazines however, because these manifestations are rarely life-threatening and because physostigmine may cause severe bradycardia or asystole it is not recommended for treatment of pheno-thiazine overdose. Because of the large volume of distribution and extensive protein binding, hemodialysis or hemoperfusion is not beneficial for phenothiazine overdose. 

Physostigmine has the potential for induction of seizure activity. In addition, the increase in cholinergic activity does not significantly affect the bradycardia caused by the quinidine-like effects of tricyclics. 

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