TCA Overdose (Tricyclics)

TCA Overdose:
Tricyclic antidepressants (TCAs) are a class of drugs used to treat depression, chronic pain, and other neuropsychiatric disorders.
TCA overdose can lead to severe toxicity and even death.
In this lecture, we will discuss the clinical and ECG features of TCA overdose, as well as its management.
Clinical Features of TCA Overdose:
Symptoms and signs of TCA overdose usually occur within 1-2 hours, which include:
Sedation and coma
Seizures
Hypotension
Tachycardia
Wide complex dysrhythmias
Anticholinergic syndrome (tachycardia, mydriasis, dry mouth)
TCAs are rapidly absorbed in the gastrointestinal tract.
Toxic effects are produced by blockade at muscarinic (M1), histamine (H1), and alpha1-adrenergic receptors.
ECG Features of TCA Overdose:
An ECG is a vital tool in the prompt diagnosis of poisoning with sodium-channel blocking medications such as TCA, which cause CNS and cardiovascular toxicity in overdose in the form of seizures and ventricular dysrhythmias. The most common ECG features of TCA overdose include:
Intraventricular conduction delay: QRS greater than 100 ms in lead II
Terminal R wave greater than 3 mm in aVR or R/S ratio greater than 0.7 in aVR
Sinus tachycardia secondary to muscarinic (M1) receptor blockade
Terminal right axis deviation of the QRS complex, which manifests as a dominant R’ wave in aVR due to the right-sided intraventricular conducting system being more susceptible to the effects of sodium channel blockade.
The degree of QRS widening on ECG is correlated with adverse events:
QRS greater than 100 ms is predictive of seizures.
QRS greater than 160 ms is predictive of ventricular arrhythmias (e.g. VT).
Management of Tricyclic Overdose:
Overdose greater than 10mg/kg with signs of cardiotoxicity (ECG changes) requires resuscitative management:
Patients need to be managed in a monitored area equipped for airway management.
Secure IV access, administer oxygen, and attach monitoring equipment.
Administer IV sodium bicarbonate.
Intubate as soon as possible and hyperventilate to maintain a pH of 7.50 to 7.55.
Once the airway is secure, place a nasogastric tube and give 50g (1g/kg) of activated charcoal.
Treat seizures with IV benzodiazepines (e.g. midazolam 1-2mg)
Treat hypotension with a crystalloid bolus (10-20 mL/kg). If this is unsuccessful in restoring BP then consider starting vasopressors (e.g. noradrenaline 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 greater than 7.5.
Avoid Ia (procainamide) and Ic (flecainide) antiarrhythmics, beta-blockers, and amiodarone as they may worsen hypotension and conduction abnormalities.
Admit the patient to the intensive care unit for ongoing management.
Take home message:
TCA overdose can lead to severe toxicity and even death. The best markers for suspected overdose are a history of depression, suicidality, and overdose with a sudden deterioration in mental status and vital signs. Clinical and ECG features of TCA overdose include sedation, seizures, hypotension, tachycardia, wide complex dysrhythmias, and anticholinergic syndrome. An ECG is a vital tool in the prompt diagnosis of TCA overdose. Management of significant TCA overdose requires resuscitative management, including IV sodium bicarbonate, intubation and hyperventilation, and treatment of seizures and hypotension.