TCA toxicity is a life-threatening poisoning driven by sodium channel blockade, anticholinergic effects, and alpha-adrenergic blockade. The primary cause of death is cardiovascular collapse from wide-complex arrhythmias and myocardial depression. [1-2] Toxicity develops rapidly, and the ECG — particularly QRS duration and R wave in aVR — is the most important prognostic tool. [1][3]
1. History
- Which TCA was ingested (amitriptyline, nortriptyline, desipramine, imipramine, doxepin, etc.)? Desipramine has a higher death rate in overdose compared to other TCAs [4]
- Dose ingested: Toxic range ~5–20 mg/kg; however, reported dose is neither reliable nor a good predictor of outcome [1]
- Time of ingestion: Critical for decontamination decisions and anticipating clinical trajectory
- Intentional vs. accidental: Multiple drug ingestion (including alcohol) is common in deliberate TCA overdose [2][5]
- Co-ingestants: Ask specifically about alcohol, benzodiazepines, other sedatives, opioids, other anticholinergics
- Formulation: Immediate-release vs. sustained-release; pill count if available
- Symptoms since ingestion: Drowsiness, confusion, palpitations, seizures, dry mouth, blurred vision
- Vomiting: Spontaneous emesis may have occurred but induced emesis is contraindicated [2]
2. Alarm Features
- QRS ≥100 ms — best single indicator of overdose severity; predicts seizures and ventricular arrhythmias [1][6]
- R wave in aVR >3 mm — good predictive value for seizures or arrhythmias [1]
- Seizures — may herald cardiovascular collapse
- Ventricular dysrhythmias (VT/VF) or Brugada-like pattern on ECG [1]
- Refractory hypotension (SBP <90 mmHg, MAP <65 mmHg) [7]
- Coma or rapidly declining GCS — early intubation advised due to potential for abrupt deterioration [8]
- Cardiac arrest — most deaths occur prehospital or within the first few hours [1]
- Late fatal dysrhythmias have been reported in patients with clinical evidence of significant poisoning who received inadequate GI decontamination [2-3]
3. Medications
Cornerstone treatment:
- Sodium bicarbonate (NaHCO₃): 1–2 mmol/kg IV bolus; repeat as needed up to max 6 mmol/kg. Target pH 7.45–7.55; do not exceed pH 7.55–7.60 or Na >155 mEq/L [7][9-11]
- Benzodiazepines: First-line for seizures [1-2]
Second-line agents:
- Lidocaine: For wide-complex tachycardia refractory to sodium bicarbonate (class Ib antiarrhythmic competes for sodium channel binding) [10-11]
- Phenytoin/phenobarbital: Alternative anticonvulsants if benzodiazepines fail [2]
- Norepinephrine/vasopressors: For refractory hypotension after fluid resuscitation
Rescue therapies:
- Intravenous lipid emulsion (ILE): Recommended after failure of standard therapies for life-threatening toxicity, particularly if VA-ECMO is unavailable; not first-line. Dose: 1.5 mL/kg bolus of 20% lipid emulsion, followed by 0.25 mL/kg/min infusion [10-12]
- VA-ECMO: For refractory cardiogenic shock/cardiac arrest [10-11]
Contraindicated medications:
- Type 1A antiarrhythmics (quinidine, procainamide, disopyramide) — absolutely contraindicated [2][6]
- Type 1C antiarrhythmics (flecainide, propafenone) — contraindicated [6]
- Physostigmine — not recommended except for life-threatening anticholinergic symptoms unresponsive to all other therapies, and only in consultation with poison control [2]
- Flumazenil — avoid if co-ingestion with benzodiazepines suspected (may precipitate seizures)
- Induced emesis — contraindicated [2]
4. Diet
- NPO in acute setting; aspiration risk is high given altered mental status and anticholinergic ileus
- No specific dietary triggers or long-term dietary management relevant to acute toxicity
5. Review of Systems
- Neuro: Altered mental status, agitation, delirium, drowsiness, coma, seizures, myoclonus, hyperreflexia, muscle rigidity [1-2]
- Cardiac: Palpitations, chest pain, syncope
- GI: Nausea, vomiting, abdominal distension (ileus from anticholinergic effects)
- GU: Urinary retention [1]
- Skin: Dry, flushed skin; hyperthermia [1]
- Eyes: Blurred vision, mydriasis [2]
- Psych: Hallucinations, confusion, agitation [2]
6. Collateral History and Family History
- Collateral is critical: Determine pill bottles, pill counts, suicide note, access to medications
- Confirm prescription holder (patient vs. family member — especially important in pediatric ingestions)
- Psychiatric history: Prior suicide attempts, current stressors, recent medication changes
- Family history is less relevant in acute toxicity but may inform psychiatric risk assessment
- Children are more sensitive than adults to acute TCA overdose; any amount in infants/young children must be considered serious and potentially fatal [13]
7. Risk Factors
- Psychiatric illness (depression, anxiety) — TCAs prescribed for these conditions; deliberate self-harm is common
- Access to large quantities of TCAs (e.g., new prescription, multiple refills)
- Pediatric patients — accidental ingestion; higher sensitivity to toxicity [13]
- Elderly patients — lower therapeutic doses, higher susceptibility to cardiac and anticholinergic effects
- Co-ingestion with alcohol, sedatives, or other cardiotoxic drugs
- Pre-existing cardiac conduction disease — increased risk of fatal arrhythmia
- Hepatic impairment — impaired TCA metabolism
8. Differential Diagnosis
- Other sodium channel blocker overdose: Cocaine, local anesthetics, class Ia/Ic antiarrhythmics, carbamazepine, propranolol [10-11]
- Anticholinergic toxidrome from other agents: Antihistamines (diphenhydramine), antipsychotics, atropine, jimsonweed
- Serotonin syndrome: If co-ingested with serotonergic agents (clonus, hyperreflexia, diaphoresis — note: diaphoresis distinguishes from pure anticholinergic toxidrome)
- Neuroleptic malignant syndrome: Rigidity, hyperthermia, altered mental status
- Sympathomimetic toxidrome: Cocaine, amphetamines (diaphoresis present, unlike anticholinergic)
- Hyperkalemia: Can cause QRS widening — check potassium
- Brugada syndrome: TCA can unmask Brugada pattern on ECG [1]
Key distinguishing feature: The combination of anticholinergic signs + QRS widening + sinus tachycardia + rightward terminal axis is highly specific for TCA toxicity [3]
9. Past Medical History
- Psychiatric diagnoses and prior overdose attempts
- Cardiac history (baseline conduction abnormalities, heart failure)
- Seizure disorder
- Hepatic or renal disease
- Current medications (especially other QT/QRS-prolonging drugs, MAOIs, serotonergic agents)
- Prior TCA use and dosing
10. Physical Exam
Vital signs:
- Tachycardia (sinus, often >120 bpm) — from anticholinergic and alpha-adrenergic effects
- Hypotension — from alpha blockade and myocardial depression
- Hyperthermia — anticholinergic impairment of sweating
- Tachypnea or respiratory depression depending on severity
Focused exam (anticholinergic toxidrome — "hot as a hare, blind as a bat, dry as a bone, red as a beet, mad as a hatter"):
- Pupils: Mydriasis (dilated, poorly reactive) [2]
- Skin: Dry, flushed, warm [1]
- Mucous membranes: Dry
- Abdomen: Decreased bowel sounds, distension (ileus) [1]
- Bladder: Distended (urinary retention) [1]
- Neuro: Altered mental status (agitation → obtundation → coma), hyperreflexia, myoclonus, muscle rigidity, seizures [1-2]
11. Lab Studies
- ABG/VBG: Assess pH (acidosis worsens toxicity by increasing free drug); guide bicarbonate therapy [10]
- BMP: Sodium (monitor during NaHCO₃ therapy, do not exceed 155 mEq/L), potassium (hypokalemia from alkalinization), glucose, renal function [11]
- Serum lactate: Marker of tissue hypoperfusion
- Urine drug screen: Qualitative TCA screen (note: false positives with carbamazepine, cyclobenzaprine, quetiapine, diphenhydramine)
- Serum TCA levels: Not useful for guiding management — ECG findings are more predictive than serum concentrations [1][6]
- Acetaminophen and salicylate levels: Rule out common co-ingestants in deliberate overdose
- Ethanol level
- CBC, LFTs, coagulation studies: Baseline
- Serial potassium and calcium: Monitor during bicarbonate therapy (hypokalemia, hypocalcemia are adverse effects) [1][11]
12. Imaging
- Chest X-ray: If intubated, or to evaluate for aspiration pneumonia or pulmonary edema [2]
- KUB: Rarely helpful; TCAs are not radiopaque
- CT head: Consider if altered mental status is disproportionate to expected toxicity or if trauma suspected
- Imaging is generally not the priority — ECG and clinical monitoring take precedence
13. Special Tests
- Poison Control Center consultation — recommended for all TCA overdoses [2][5]
- Urine TCA immunoassay: Qualitative confirmation (high false-positive rate; does not change management)
- Activated charcoal: 1 g/kg if presenting within 1–2 hours of ingestion and airway is protected [2][6]
- Gastric lavage: Considered if early presentation with large ingestion and airway secured; emesis is contraindicated [2]
14. ECG
The ECG is the single most important prognostic and monitoring tool in TCA toxicity. [1][6]
Key findings:
- Sinus tachycardia — often the earliest finding (anticholinergic)
- QRS prolongation ≥100 ms — best indicator of severity; associated with seizures [1][6]
- QRS ≥160 ms — associated with ventricular arrhythmias
- Terminal R wave in aVR >3 mm — highly predictive of seizures and arrhythmias; reflects rightward terminal axis deviation [1][4]
- Rightward axis shift of terminal 40 ms of QRS — recognized by terminal S wave in leads I and aVL, R wave in aVR [4]
- Brugada-like pattern (right bundle branch block with ST elevation in V1–V3) [1]
- Prolonged QT interval [3]
- Ventricular tachycardia / ventricular fibrillation — the lethal arrhythmias
- AV conduction blocks [1]
Monitoring: Continuous cardiac monitoring; serial 12-lead ECGs to track QRS duration response to therapy [3][9]
15. Assessment
TCA toxicity produces a triad of toxicity: (1) anticholinergic effects, (2) cardiovascular sodium channel blockade, and (3) CNS depression/seizures. [1] Severity stratification is primarily ECG-based:
- Mild: Sinus tachycardia, anticholinergic symptoms, QRS <100 ms
- Moderate: QRS 100–160 ms, altered mental status, hypotension responsive to fluids
- Severe: QRS ≥160 ms, seizures, ventricular arrhythmias, refractory hypotension, coma, cardiac arrest
Toxicity develops rapidly — patients can deteriorate from alert to cardiac arrest within minutes. [2] Most deaths occur prehospital or in the first few hours. [1] Dual therapy with sodium bicarbonate and mechanical hyperventilation achieves alkalinization targets more effectively and narrows QRS twice as fast as either alone. [9]
16. Treatment Plan
Initial stabilization (ABCs):
- Airway protection — early intubation for CNS depression (abrupt deterioration is possible) [8]
- IV access, continuous cardiac monitoring, 12-lead ECG
GI decontamination:
- Activated charcoal (1 g/kg) if within 1–2 hours and airway protected [2][6]
- Emesis is contraindicated [2]
Sodium bicarbonate protocol (for QRS ≥100 ms, hypotension, arrhythmias, or seizures):
- Bolus: 1–2 mEq/kg (mmol/kg) IV push; may repeat every 3–5 minutes [7]
- Target pH: 7.45–7.55 [6][10]
- Max dose: 6 mmol/kg total [7][9]
- Max sodium: Do not exceed 155 mEq/L [10]
- Adjunct: Mechanical hyperventilation (PCO₂ ~30–35 mmHg) synergistically improves alkalinization and QRS narrowing [7][9]
- Monitor and correct hypokalemia and hypocalcemia during therapy [1][11]
Seizure management:
- Benzodiazepines first-line (lorazepam 0.1 mg/kg IV or diazepam) [1-2]
- Phenobarbital or phenytoin if refractory [2]
Refractory arrhythmias:
- Lidocaine for wide-complex tachycardia unresponsive to NaHCO₃ [10-11]
- Avoid class Ia/Ic antiarrhythmics [6]
Refractory hypotension:
- IV fluid boluses → norepinephrine
- Consider ILE (20% Intralipid: 1.5 mL/kg bolus, then 0.25 mL/kg/min) if standard therapies fail [10-11]
- VA-ECMO for refractory cardiogenic shock or cardiac arrest [10-11]
17. Disposition
- All suspected TCA overdoses require hospital monitoring [2][5]
- Minimum 6 hours of cardiac monitoring with observation for CNS depression, respiratory depression, hypotension, arrhythmias, conduction blocks, and seizures [2-3]
- If any signs of toxicity during observation → extended monitoring required (typically ICU) [2]
- ICU admission criteria: QRS ≥100 ms, seizures, arrhythmias, hypotension, altered mental status, need for NaHCO₃ therapy or intubation
- Asymptomatic with normal ECG at 6 hours → may be medically cleared for psychiatric evaluation if intentional ingestion
- Poison Control Center consultation recommended for all cases [2]
- Psychiatric consultation — since overdose is often deliberate, patients may attempt suicide by other means during recovery [2]
18. Follow Up / Return Precautions
- Psychiatric follow-up is essential — patients may reattempt suicide during recovery phase [2]
- Restrict access to TCAs and other lethal medications upon discharge
- Return precautions: Seek immediate care for palpitations, chest pain, syncope, seizures, confusion, or recurrent suicidal ideation
- Expected recovery: With appropriate treatment, most patients who survive the first 24 hours recover fully; cardiac toxicity typically resolves within 24–48 hours
- Late dysrhythmias: Rare but reported — patients with significant initial toxicity should have extended monitoring [2-3]
- Medication reconciliation: Consider switching to a safer antidepressant (e.g., SSRI) in consultation with psychiatry
References
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