What are the clinical features and management of Tricyclic Antidepressant (TCA) overdose?

Features of TCA Overdose

TCA overdose presents with characteristic cardiovascular, neurological, and anticholinergic manifestations that require prompt recognition and management with sodium bicarbonate as the cornerstone of treatment for life-threatening toxicity. 1

Clinical Manifestations

Cardiovascular Features

• ECG abnormalities:
  • QRS prolongation (>100 ms) - primary marker of sodium channel blockade 1, 2
  • Terminal 40 ms right axis deviation in lead aVR - sensitive marker for TCA toxicity 2
  • Tachycardia (often sinus) due to anticholinergic effects 3
  • Brugada-like ECG pattern 1
• Hemodynamic instability:
  • Hypotension due to myocardial depression and peripheral vasodilation 1
  • Ventricular dysrhythmias (including ventricular tachycardia) 1, 3
  • Cardiac arrest in severe cases 1

Neurological Features

• Seizures - more common with QRS >100 ms 4
• Altered mental status ranging from agitation to coma 4
• Myoclonus and hyperreflexia 1

Anticholinergic Features

• Hyperthermia
• Dry mucous membranes
• Urinary retention
• Mydriasis (dilated pupils)
• Decreased bowel sounds

Risk Assessment

The severity of TCA overdose can be assessed by:

1. ECG parameters:

   • QRS duration >100 ms predicts risk of seizures and arrhythmias 4, 5
   • Terminal 40 ms frontal plane QRS vector changes 5

2. Clinical parameters:

   • Time between ingestion and symptom onset 5
   • Age of patient 5
   • Plasma TCA levels >1,000 ng/ml indicate severe toxicity 4

Management Algorithm

1. Initial Stabilization

• Secure airway, breathing, circulation
• Early endotracheal intubation for severe toxicity 1
• IV access and cardiac monitoring

2. Cardiovascular Support

• Sodium bicarbonate therapy:

  • Administer 1-2 mEq/kg IV bolus for QRS >100 ms, ventricular arrhythmias, hypotension, or acidosis 1, 2
  • Repeat doses to maintain arterial pH 7.45-7.55 2
  • Avoid extreme hypernatremia (serum sodium not to exceed 150-155 mEq/L) 1
  • Monitor and treat hypokalemia during alkalemia therapy 1

• Fluid resuscitation:

  • 5-10 mL/kg boluses of normal saline for hypotension 2

• Vasopressors:

  • Epinephrine or norepinephrine preferred over dopamine for persistent hypotension 2

3. Management of Arrhythmias

• Sodium bicarbonate is first-line treatment for ventricular arrhythmias 1, 3
• Lidocaine may be used as second-line therapy for wide-complex tachycardia 1
• AVOID Class IA, IC, or III antiarrhythmics as they may worsen cardiac toxicity 2

4. Seizure Management

• Benzodiazepines are first-line treatment 1

5. Refractory Cases

• Consider extracorporeal life support (ECMO) for cardiac arrest or refractory shock 1
• Intravenous lipid emulsion may be considered if other therapies fail 1, 2

Monitoring and Disposition

• Continuous cardiac monitoring for at least 6 hours after ingestion
• Patients with normal vital signs and ECG (QRS <100 ms) after 6 hours of observation may be medically cleared 6
• Patients with abnormal ECG findings or symptoms require continued monitoring until clinical improvement 6

Common Pitfalls to Avoid

1. Misdiagnosis: Sinus tachycardia with QRS prolongation may be difficult to distinguish from ventricular tachycardia 3

2. Delayed recognition: Patients may initially appear stable then rapidly deteriorate 7

3. Inappropriate antiarrhythmic use: Class IA, IC, or III antiarrhythmics can worsen sodium channel blockade 2

4. Inadequate monitoring: Even asymptomatic patients require cardiac monitoring due to risk of delayed toxicity 6

5. Failure to monitor electrolytes: Hypokalemia can develop during sodium bicarbonate therapy 1