ECG of the Week – 3rd April 2019 – Interpretation

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The ECG below is taken from a collapsed 70kg 56 yo man with a known mental health history, thought to have taken a multi-drug overdose.

On further collateral history it is apparent he has taken the following medications approx. 5 hours prior: Chlorpromazine 975mg, Aspirin 1.4g, Dothiepin 7g and Diazepam 250mg.

On presentation his observations are as follows:

GCS 3

HR 96

BP 100/58

Key Features:

Rate: 90

Rhythm: Sinus

Axis: Normal

Intervals:

  • PR 100
  • QRS 160 – prolonged – risk of Ventricular Dysrthymia
  • QTc 480 – prolonged

Additional:

  • Terminal R wave in aVR (R/S ratio >0.7)

Management:

Use an RRSIDEAD toxicology approach:

Resus:

  • A: Intubate if GCS <12
  • Importance of pre-optimising prior intubation: risk of acidosis during intubation will worsen TCA toxicity.
  • B: Hyperventilate (aiming for a pH of >7.5)
  • C: Correct hypotension – fluids, NaHCO3, Ad/NAd
  • C: Treat Dysrthymias – NaHCO3 2mmol/Kg IV every 1-2mins (aiming for a QRS <100), Lignocaine as 2nd line 1.5mg/Kg when pH>.5, DCCV unlikely to work
  • D: Seizures – benzos, bentos, benzos (other antieplieptics ineffective), don’t forget also likely to need NaHCO3 if seizing, consider GA if no cessation (most experienced operator, risk of cardiac dysthymia/arrest on intubation.

Risk:

  • 100ml/Kg of TCA Dothiepin = serious life threat
  • Those with dosing >30mg/Kg are significant of severe toxicity, symptoms expected within 2 hrs but may last for >24 hrs.
  • Severe toxicity overdoses demonstrate pH dependent cardiotoxicity.
  • QRS intervals: >100 risk of seizure >160 risk of ventricular dysrthymia
  • Aspirin = 20mg/Kg = no to low risk

Supportive Care

Investigations:

  • BSL
  • ECG
  • Paracetamol and Salicylate levels
  • VBG

Decontamination

  • Activated charcoal indicated in toxicity once airway secure

Enhanced Elimination

  • Not indicated in this case

Antidote

  • Consider NaHCO3 as an antidote. Give as boluses 1-2mmol/Kg to see effect in QRS
  • Together with hyperventilation aim for pH >7.5

Disposition:

  • Intubation, ICU

Key Points and Take Homes:

TCA Overdose

  • Mechanism of toxicity via Na channel blockade, alpha adrenergic blockade and anticholinergic effect.
  • All TCA overdose patients should be cardiac monitored for 6 hrs regardless of symptoms
  • >10mg/Kg = potential life threat
  • 5-10mg/kg = Mild anticholinergic features and drowsiness
  • >10mg/kg = Anticholinergic features may be masked by reduced GCS, Cardiac dysrhythmias, hypotension,  risk of seizures,
  • >30mg/kg = Severe toxicity. Cardiotoxicity is pH dependent
  • ECG intervals: Risk of dysrhythmia with QRS of >160 , Risk of seizure QRS >100

Aspirin Overdose

  • >150mg/Kg = acutely toxic dose
  • <300mg/kg =  moderate toxicity
  • 300-500mg/Kg = severe toxicity
  • >500mg/Kg = potentially lethal dose

References / Further Reading

Textbook

  • Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.