TCA overdose — ECG thresholds and bicarbonate dosing

Recognition. Tricyclic antidepressants have anticholinergic properties: dry, flushed skin with tachycardia fits that toxidrome.^[12] A maximal limb-lead QRS of 0.10 second or more predicted seizures, ventricular arrhythmias were seen only from 0.16 second, and a terminal R wave in aVR of 3 mm or more was the only ECG variable that independently predicted seizures and arrhythmias.^[4][5]

Immediate management. A QRS longer than 100 msec indicates the patient should be stabilised and given sodium bicarbonate.^[8] Hypertonic sodium bicarbonate appears to act by raising extracellular sodium and pH, and is beneficial even when blood pH is normal.^[6] Bicarbonate combined with mechanical ventilation reached the target pH of 7.45–7.55 more often and narrowed the QRS twice as quickly; the authors advise a maximal bicarbonate dose below 400 mmol (6 mmol/kg).^[2] Hypotension is managed first with colloid or crystalloid, then bicarbonate, then inotropic support if it persists; norepinephrine appeared more effective than dopamine in an uncontrolled study.^[7] Benzodiazepines are recommended for tricyclic-associated convulsions.^[8] Activated charcoal is appropriate after tricyclic ingestion, weighing the complications of any intubation needed to give it.^[1]

Avoid. Flumazenil is not recommended in tricyclic poisoning.^[8] Class 1a and 1c antiarrhythmics worsen sodium-channel blockade.^[7] Physostigmine should be avoided with QRS prolongation.^[9]

Escalation. Lidocaine has been reported as effective adjunctive therapy in severe cardiotoxicity.^[10] For life-threatening amitriptyline toxicity, intravenous lipid emulsion is suggested if other therapies fail, but not as first-line therapy.^[11]