Tricyclic Overdose Flashcards
What are the clinical features of tricyclic overdose?
Rapid onset (within 1-2 hours):
- Sedation and coma
- Seizures
- Hypotension
- Tachycardia
- Broad complex dysrhythmias
- Anticholinergic syndrome
Why are tricyclics toxic?
Cardiotoxic effects:
- Via blockade of myocardial fast sodium channels (QRS prolongation, tall R wave in aVR), inhibition of potassium channels (QTc prolongation) and direct myocardial depression
Other toxic effects are produced by blockade at muscarinic (M1), histamine (H1) and α1-adenergic receptors
Overdose >10mg/kg with signs of cardiotoxicity (ECG changes) = a significant overdose
What are the ECG features of TCA overdose?
Features consistent with sodium channel blockade:
- QRS > 100ms in lead II (interventricular conduction delay)
- Right axis deviation of terminal QRS: terminal R wave >3mm in aVR, R/S ratio >0/7 in aVR
Also usually a sinus tachycardia due to M1/muscarinic blockade
What is the relationship between the QRS complex changes and the clinical picture?
QRS > 100 ms is predictive of seizures
QRS > 160 ms is predictive of ventricular arrhythmias (e.g. VT)
How do you manage TCA overdose?
Relocate to area that can secure an airway
IV access:
- Bolus and continuous fluids
High flow O2:
- Hyperventialte to maintain a pH of 7.50-7.55
Monitoring equipment:
- ECG, BP, sats etc
IV sodium bicarbonate 102mEq/kg
- Repeat every few minutes until BP improves and QRS complexes begin to narrow
- Give more if other arrhythmias occur
Once airway secure, place NG tube and give 1g/kg activated charcoal (if presenting <1hr)
Treat any seizures with IV benzodiazepines
Avoid antiarrhythmics (procainamide, flecainide), Bblockers and amiodarone as may worsen HoTN and conduction abnormalities
