CLINICAL PEARLS TCA toxicity primarily involves neurologic (altered mental status, myoclonus, seizures) and cardiovascular (tachycardia, QRS widening, ventricular arrhythmias, hypotension) derangements in addition to features of the anticholinergic toxidrome EKG evidence of fast sodium channel blockade (QRS widening, R wave >3 mm in aVR) is the most important prognostic indicator of clinically significant toxicity TCA-poisoned patients are at risk for rapid clinical decompensation Current Evidence Though now used less commonly as first-line therapy for depression and anxiety, tricyclic antidepressants are still used in treatment of chronic pain syndromes and for enuresis and thus remain a source of potentially serious exploratory and intentional ingestions in pediatric patients The ingestion of 10 to 20 mg/kg of most tricyclic antidepressants represents a moderate to serious exposure, with coma and cardiovascular symptoms expected The ingestion of 35 to 50 mg/kg may result in death Children have been reported to be more sensitive than adults to tricyclic antidepressants and often have symptoms at lower dosages Clinical Considerations Cyclic antidepressants have many pharmacologic effects Anticholinergic activity causes altered sensorium and sinus tachycardia α-Adrenergic blockade may lead to hypotension However, the more severe cardiovascular effects are primarily caused by the membrane-depressant or quinidine-like effects that depress myocardial conduction and may lead to multiple focal premature ventricular contractions and ventricular tachycardia A QRS interval over 0.1 second is associated with a significant morbidity and mortality; this conduction delay may progress to complete heart block and cardiac standstill and/or the previously mentioned ventricular arrhythmias Another typical electrocardiographic finding suggestive of cyclic antidepressant poisoning is the finding of an R wave of greater than 3-mm amplitude in the QRS complex in lead aVR Neurologic findings include lethargy, disorientation, ataxia, hallucinations, and, with severe overdoses, coma, and seizures Fever is commonly present initially, but hypothermia may occur later Additional anticholinergic symptomatology includes decreased GI motility, which delays gastric emptying time, and urinary retention Myoclonic jerking has been observed and may be associated with