Diagnosis of Tricyclic Antidepressant (TCA) Poisoning
Immediate ECG Assessment
Obtain an ECG or rhythm strip immediately upon presentation, as QRS duration >100 msec indicates severe toxicity requiring urgent intervention. 1
Key ECG Findings Indicating Severe Toxicity:
- QRS prolongation >100 ms is the single most important predictor of serious complications and is superior to serum TCA levels for risk stratification 1, 2, 3
- Terminal rightward axis deviation >120 degrees in lead aVR indicates need for immediate sodium bicarbonate administration 4, 3
- Wide-complex arrhythmias with QRS >100 msec warrant immediate stabilization and emergency department transport 2
The QRS duration serves as both a diagnostic marker and prognostic indicator, as it directly reflects the degree of sodium channel blockade causing cardiac toxicity 3, 5.
Clinical Presentation Assessment
Cardiovascular Manifestations:
- Ventricular dysrhythmias, hypotension, heart block, bradyarrhythmias, or asystole 3
- Sinus tachycardia (due to anticholinergic effects and catecholamine reuptake blockade) 5
- Hypotension unresponsive to fluid resuscitation 1
Neurological Manifestations:
- Altered mental status, drowsiness, weakness, dizziness 2
- Seizures or severe agitation 6
- Coma with loss of protective airway reflexes 6
Anticholinergic Symptoms:
- Tremulousness, palpitations, mydriasis, urinary retention 2
Any symptomatic patient (weak, drowsy, dizzy, tremulous, palpitations) after TCA ingestion requires immediate emergency department referral. 2
Dose-Based Risk Stratification
Threshold Doses Warranting Emergency Department Evaluation:
- Most TCAs (amitriptyline, imipramine, doxepin, clomipramine): >5 mg/kg 2
- Desipramine: >2.5 mg/kg 2
- Nortriptyline: >2.5 mg/kg 2
- Trimipramine: >2.5 mg/kg 2
- Protriptyline: >1 mg/kg 2
For patients already taking TCAs chronically, add the extra ingested dose to the daily therapeutic dose when calculating total exposure 2.
Temporal Considerations
Asymptomatic patients who remain symptom-free 6 hours after ingestion are unlikely to develop toxicity and do not require emergency department referral. 2
This 6-hour observation window applies only to unintentional poisonings in patients without evidence of self-harm 2. However, continuous monitoring with follow-up calls within 4 hours of initial assessment is recommended 2.
Special Populations Requiring Lower Threshold for Referral
- Patients with underlying cardiovascular disease should be referred at lower doses than otherwise healthy individuals 2
- Patients with neurological conditions (seizure disorders, arrhythmias) warrant earlier intervention 2
- All suspected self-harm cases require immediate emergency department referral regardless of dose or symptoms 2
Co-Ingestion Assessment
Evaluate for co-ingestions, particularly other psychopharmaceutical agents, benzodiazepines, or opioids, as mixed overdoses are common and may alter management. 1, 6
The presence of co-ingestants may warrant emergency department referral even at lower TCA doses 2.
Monitoring Parameters During Initial Assessment
- Continuous ECG monitoring for QRS duration and dysrhythmias 4
- Vital signs including respiratory rate and depth 6
- Mental status and neurological examination 2
- Core body temperature, as hyperthermia worsens toxicity 1, 5
Common Diagnostic Pitfalls
Distinguishing sinus tachycardia with QRS prolongation from ventricular tachycardia can be challenging. Esophageal or atrial electrodes may help determine the relationship between atrial and ventricular activity 5. When in doubt, treat as ventricular tachycardia with sodium bicarbonate 4.
Serum TCA levels are less useful than ECG findings for predicting complications and should not delay treatment decisions 3. The QRS duration remains the most reliable predictor of severe toxicity 1, 2.