Cardiac arrhythmia

1. Cardiac arrhythmia • Primary • quinidine–like drugs, sympathomimetic drugs, calcium channel blockers, β–blockers, digitalis, chloroquine • Secondary to metabolic/electrolyte abnormalities • salicylates, methanol, ethylene glycol

2. Cardiotoxic drugs • All patients should have • oxygenation and protection of airway • decontamination of the GIT • atropine pre–medication • correction of electrolyte abnormalities • acid base balance • cardioversion when appropriate • consultation

3. Cardiac arrest • Successful resuscitation has been well documented after 8 hours of CPR • Overdose patients usually have • a reversible cause for their arrest • good general health • novel treatments for arrhythmias • cerebral protection

4. Antidotes: asystole & bradycardia • Atropine everything • Bicarbonate tricyclic antidepressants • Calcium calcium channel blockers • Diazepam chloroquine, organochlorines • Epinephrine everything, β–blockers • Fab fragments digoxin • Glucagon β–blockers, CCBs

5. Cardiac case 1 • 18 yo female admitted 3 hours after self–poisoning with • 3.5 g of slow release verapamil (Isoptin SR) • 6 g of paracetamol • 4.5 g of tetracycline • 1 g of pseudoephedrine • On arrival in casualty • pr 120, BP 110/80, RR 20, afebrile • drowsy but oriented and cooperative

6. Cardiac case 1 • GI decontamination • emesis before arrival • lavaged with return of green tablets • 50 g of charcoal with sorbitol repeated 4 h later • Investigations • ECG • sinus tachycardia with normal QRS width • serum paracetamol at 4 h was 38 µmol/l • hepatotoxicity > 1300 µmol/l at 4 hours

7. Cardiac case 1 • In intensive care unit • 16 hours post overdose • BP fell to 70/40 and then 50/30 • PR 50 • oxygen saturation dropped to 75 % • ECG • absent p waves • prominent u waves • normal QRS duration and QT interval

8. Cardiac case 1 • Treatment • IV atropine 0.6 mgs – no response • IV calcium gluconate • 6 g over 20 minutes • further 6 g over the next hour • pr 60, sinus rhythm, BP 100/80 • oxygen saturation > 95 % • infusion of 10% calcium gluconate at 2 G/h for 10 hours • she was also given 2.5 L IV fluids

9. Cardiac case 1 • Outcome • non–cardiogenic pulmonary oedema • twenty four hours post admission • largely recovered , sinus rhythm PR 60, BP 115/70 • peak serum Ca was 4.8 (2.18–2.47 mmol/l) • serial verapamil levels at 6, 18, 22 and 46 hours were 616, 2374, 2518 and 1006 ng/ml • range during usual therapy • 100–300 ng/ml

10. Cardiac case 2 • 38 yo female admitted after self–poisoning with • amitriptyline 2525 mg • dothiepin 1650 mg • Found unconscious with suicide note carefully documenting tablets • last seen 9 a.m., brought in by ambulance at 6 p.m. • later said she had read that 2.5 g was a lethal dose

11. Cardiac case 2 • No past medical history • Depressed for several months, treated by a psychiatrist • On examination • absent gag • unconscious, flexes to pain • PR 40, BP 130/100, afebrile • hypoventilating, 02 saturation 94 % • flushed, dilated pupils, reduced bowel sounds

12. Cardiac case 2 • Investigations • FBC • EUC • paracetamol level • ECG • CXR ? aspiration • GI decontamination • gastric lavage and activated charcoal

13. Cardiac case 2 • Treatment and outcome • given NaHC03 IV • intubated and hyperventilated • IV normal saline • ABGs monitored to keep pH 7.5 • serial ECGs • prolonged unconsciousness • extubated 40 hours later • no long term sequelae

14. Cardiac case 3 • 26 yo female • found unconscious by police in caravan • empty bottle of tablets with label removed • no relatives/other history available • On examination • PR 140, BP 120/80, afebrile • unconscious • GCS 6

15. Cardiac case 3 • Investigations • ECG • QRS width 120 ms • PR interval 200 ms • CXR • aspiration pneumonia • Management • intubated, lavage, charcoal, antibiotics

16. Cardiac case 3 • Outcome • sudden deterioration 2 hours later • bradycardia • asystole • unable to be resuscitated

17. Tricyclic antidepressants • Ingestion of 15–20 mg/kg is potentially fatal • Mechanism of action • block re–uptake of noradrenaline and serotonin • competitive antagonists at H1 and H2 receptors • anticholinergic effects • membrane effects on sodium channel, quinidine–like effect

18. Toxico–kinetics • Absorption and distribution • highly lipid soluble • rapidly absorbed • high volume of distribution • delayed absorption due to anticholinergic effect in GIT • pH dependent protein binding > 95% • large variation in amount of free TCA • a change in the pH from 7.38 to 7.50 produces a 21% reduction in free TCA

19. TCA management • General • supportive care, ABG, ECG, electrolytes • lavage, charcoal with sorbitol/mannitol • CNS toxicity • seizures • IV diazepam • IV phenytoin (15–18 mg/kg) • anticholinergic delirium • benzodiazepines, haloperidol • seizure and fever consider physostigmine

20. TCA management • Arrhythmias • plasma alkalinisation to pH ~ 7.5 • sodium bicarbonate, hyperventilation • drug treatment • acute • magnesium • sotalol • lignocaine • prophylactic • phenytoin • overdrive pacing

21. TCA management • hypotension • volume expansion • pH correction • alpha agonists e.g. noradrenaline • inotropics e.g. dopamine, dobutamine