Atrioventricular block tricyclic antidepressants

Widening of the QRS complex duration to greater than 100 milliseconds is typical of tricyclic antidepressant and quinidine overdoses (Figure 59-1). The QTC interval may be prolonged to more than 440 milliseconds in many poisonings, including quinidine, tricyclic antidepressants, several newer antidepressants and antipsychotics, lithium, and arsenic (see also http //www.torsades.org/). Variable atrioventricular (AV) block and a variety of atrial and ventricular arrhythmias are common... 

A small dose of physostigmine (see p 489), 0.5-1 mg IV in an adult, can be given to patients with severe toxicity (eg, hyperthermia, severe delirium, or tachycardia). Caution physostigmine can cause atrioventricular block, asystole, and seizures, especially in patients with tricyclic antidepressant overdose. 

A. Ataxia, nystagmus, ophthalmoplegia, movement disorders (dyskinesia, dystonia), mydriasis, and sinus tachycardia are common with mild to moderate overdose. With more serious intoxication, myoclonus, seizures (including status epilepticus), hyperthermia, coma, and respiratory arrest may occur. Atrioventricular (AV) block and bradycardia have been reported, particularly in the elderly. Based on Its structure similarity to tricyclic antidepressants, carbamazepine may cause QRS and QT interval prolongation and myocardial depression however, in case reports of overdose, QRS widening rarely exceeds 100-120 msec and Is usually transient. 

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