TCA Toxicity

TCA is a sodium-channel blocker. The two main adverse effects of sodium-channel blocker poisoning include:
·       Seizures
·       Ventricular dysrhythmias (due to blockade of sodium channels in the CNS and myocardium)
In overdose, the tricyclics produce rapid onset (within 1-2 hours) of:
·       Sedation and coma
·       Seizures
·       Hypotension
·       Tachycardia
·       Broad complex dysrhythmias
·       Anticholinergic syndrome
·       Remember the 3 C’s: Coma, Convulsion, and Cardiotoxicity. So, get an EKG ASAP! 
What does TCA do exactly?
1.                    Blockade of myocardial fast sodium channels = QRS prolongation, and tall R wave in aVR
2.                    Inhibition of potassium channels= QTc prolongation, and direct myocardial depression.
3.                    Muscarinic (M1) receptor blockade= sinus tachycardia 
4.                    QRS > 100 ms is predictive of seizures
5.                    QRS > 160 ms is predictive of ventricular arrhythmias (e.g. VT)
Worsening TCA toxicity:
Management of Significant Tricyclic Overdose (> 10mg/kg) with Signs of Cardiotoxicity (ECG changes):
·       Don’t panic!
·       Intubate as soon as possible.
·       Hyperventilate to maintain a pH of 7.50 – 7.55.
·       IV, 02, monitor
·       Administer IV sodium bicarbonate 100 mEq (1-2 mEq / kg); repeat every few minutes until BP improves and QRS complexes begin to narrow.
·       Once the airway is secure, place a nasogastric tube and give 50g (1g/kg) of activated charcoal.
·       Treat seizures with IV benzodiazepines (e.g. diazepam 5-10mg).
·       Treat hypotension with a crystalloid bolus (10-20 mL/kg). If this is unsuccessful in restoring BP then consider starting vasopressors (e.g. norepinephrine infusion).
·       If arrhythmias occur, the first step is to give more sodium bicarbonate. Lidocaine (1.5mg/kg) IV is a third-line agent (after bicarbonate and hyperventilation) once pH is > 7.5.
·       Avoid Ia (procainamide) and Ic (flecainide) antiarrhythmics, beta-blockers and amiodarone as they may worsen hypotension and conduction abnormalities.
Sources: Life in the Fastlane, UpToDate