What are the expected ECG findings and management for a 59-year-old male with suspected amitriptyline (Elavil) overdose?

Amitriptyline Overdose: ECG Findings and Management

Expected ECG Findings

In a 59-year-old male with suspected amitriptyline overdose, the most critical ECG findings to identify are QRS prolongation ≥100 ms and rightward terminal QRS axis deviation (particularly in lead aVR), as these are specific and sensitive indicators of severe tricyclic antidepressant toxicity and predict life-threatening complications. 1, 2

Specific ECG Abnormalities to Assess

• QRS duration ≥100 ms is the single best indicator of overdose severity and predicts major toxicity including seizures, arrhythmias, and cardiovascular collapse 1, 3
• Terminal 40 ms QRS axis (T40-ms axis) ≥135 degrees indicates severe toxicity with increased likelihood of major complications 2, 3
• R wave amplitude in lead aVR ≥3 mm is a specific finding; absence of this finding has 100% negative predictive value for seizures 4
• Sinus tachycardia (often heart rate ≥120 bpm) is the most common rhythm abnormality due to anticholinergic effects 2, 3
• QTc prolongation >480 ms significantly increases risk of ventricular arrhythmias 3
• Prolonged PR interval may occur as conduction delays progress 1, 2

Critical Warning Signs

• QRS duration ≥110 ms is associated with ventricular tachyarrhythmias in experimental models 5
• Rightward axis shift in the terminal QRS complex combined with prolonged QT interval and sinus tachycardia are the most specific indicators of first-generation tricyclic overdose 1
• Brugada pattern (downsloping ST elevation in V1-V3 with right bundle branch block) may appear 2

Immediate Management Algorithm

1. Initial Stabilization and Monitoring

Obtain a 12-lead ECG immediately and initiate continuous cardiac monitoring for a minimum of 6 hours, extending monitoring if any signs of toxicity appear, as fatal dysrhythmias can occur late after overdose. 1

• Protect airway and establish IV access immediately 1
• Monitor continuously for CNS depression, respiratory depression, hypotension, cardiac dysrhythmias, conduction blocks, and seizures 1
• Patients with clinical evidence of significant poisoning require extended monitoring beyond 6 hours 1

2. Gastrointestinal Decontamination

• Perform large-volume gastric lavage followed by activated charcoal in all suspected cases 1
• Emesis is contraindicated 1
• Secure airway prior to lavage if consciousness is impaired 1

3. Cardiovascular Management

Administer intravenous sodium bicarbonate to maintain serum pH between 7.45-7.55 if QRS duration is ≥100 ms or if ventricular arrhythmias occur, as this is the primary treatment for life-threatening cardiotoxicity. 6, 1, 5

Sodium Bicarbonate Protocol

• Sodium bicarbonate rapidly converts ventricular tachycardia to normal sinus rhythm and abbreviates QRS duration 5
• Administer 1-2 mEq/kg (typically 50-100 mEq in adults) IV bolus over 1-2 minutes 6, 1
• Repeat boluses as needed to maintain target pH 1
• If pH response is inadequate, hyperventilation may be added with extreme caution and frequent pH monitoring 1
• Avoid pH >7.60 or pCO2 <20 mmHg 1

Mechanism of Action

• Sodium bicarbonate works through both alkalinization and increased extracellular sodium concentration, which diminishes sodium channel blockade 5
• The combination of sodium loading and pH increase has additive beneficial effects 6

4. Arrhythmia Management

• Class IA and IC antiarrhythmics (quinidine, disopyramide, procainamide) are contraindicated as they potentiate tricyclic toxicity through similar sodium channel blockade 1, 5
• Lidocaine (Class IB) may be reasonable for dysrhythmias unresponsive to sodium bicarbonate 6, 1
• Bretylium or phenytoin are alternative options for refractory arrhythmias 1

5. Seizure Management

• Control seizures with benzodiazepines as first-line therapy 1
• If benzodiazepines are ineffective, use phenobarbital or phenytoin 1
• Physostigmine is not recommended except for life-threatening symptoms unresponsive to other therapies, and only in consultation with poison control 1

6. Advanced Interventions for Refractory Cases

Consider VA-ECMO for refractory cardiogenic shock unresponsive to sodium bicarbonate and standard resuscitation measures. 6

• Intravenous lipid emulsion (ILE) may be reasonable as rescue therapy for cardiac arrest refractory to other treatments 6, 7
• Hemoperfusion may benefit acute refractory cardiovascular instability in rare instances 1
• Hemodialysis, peritoneal dialysis, and forced diuresis are generally ineffective 1

Risk Stratification

High-Risk Features Predicting Major Toxicity

• Amitriptyline specifically (versus other tricyclics) carries higher toxicity risk 2, 3
• Age ≥30 years increases likelihood of major complications 3
• Serum tricyclic level ≥800 ng/mL, though plasma levels should not guide acute management 1, 3
• Level of consciousness at presentation is the most sensitive clinical predictor of serious complications 2

Timeline of Toxicity

• Maximal ECG changes (QRS duration and T40-ms axis) typically occur within 12 hours of ingestion but may take up to one week to resolve 2
• Life-threatening arrhythmias and death usually occur within 24 hours of ingestion 2
• Rapid deterioration is common 2

Critical Pitfalls to Avoid

• Do not rely on plasma drug concentrations to guide management; ECG findings are superior predictors of toxicity 1, 2
• Do not use standard Class I antiarrhythmics, which worsen sodium channel blockade 1, 5
• Do not discharge patients after only 6 hours if any ECG abnormalities or clinical signs of toxicity are present 1
• Early intubation is advised in patients with CNS depression due to potential for abrupt deterioration 1