The ECG in the poisoned patient

Most patients presenting to the ED with either accidental or intentional drug ingestion will get an ECG. In most departments I’ve worked in, the senior doctor looks at all the ECGs, primarily for STEMI, but for other findings too. The juniors will come to me later discussing the case and when I ask about the ECG, they frequently say it’s normal. This always starts me on a bit of a rant as when I ask them, it turns out they have no idea what they’re actually meant to be looking for in the ECG of a poisoned patient. [The same goes for syncope patients…]

So, after considering what I look for on the ECG, here’s my list of things to check in the poisoned patient.

What to look for on the ECG

  • long QT

    • all kinds of drugs

    • results from prolonged K efflux

  • wide QRS

    • Na Channel blockade

      • TCA

      • propanolol

      • cocaine

      • lots of other unexpected drugs too

  • dominant R aVR

    • Na channel blockade

  • scooped ST segments

    • digoxin

  • bradycardia

    • digoxin

    • beta blockers

  • AV block

    • beta blockers

    • digoxin

Or can be expressed as 5 main cardiac toxicities if you’re into the pathophysiology of it

  1. Na channel blockade [depolarisation]

    • wide QRS (>100ms is the cut off here)

    • prolongation of the last 40ms of the QRS which produces a right axis on ECG

    • dominant R aVR [PMID 7618783]

  2. potassium efflux blockade [repolarisation]

  3. Na/K/ATPase pump blockade

    • all about digoxin here

    • can produce almost any rhythm

    • tachys with AV blocks are a big clue

  4. beta blockade

    • brady

    • AV blocks

  5. calcium channel blockade

    • brady

    • AV blocks


If you know of any other interesting ECG patterns in tox patients please let me know in the comments.

Perhaps the best comment came from Domhnall:

Succinctly summarised as the “horizontal” ECG as opposed to the “vertical” ECG of IHD….


Critical Decisions in Emergency and Acute Care Electrocardiography. Brady and Truwit 2009 Wiley


Liebelt, E L, P D Francis, and A D Woolf. “ECG Lead aVR Versus QRS Interval in Predicting Seizures and Arrhythmias in Acute Tricyclic Antidepressant Toxicity..” Annals of Emergency Medicine 26, no. 2 (August 1995): 195–201. PMID 7618783


ECG Case 003

This is fairly simple straightforward case but it reinforced something for me.

4am standby call for a STEMI. At 4am. Was he shovelling snow at 4am?


Chest pain for 9 hours.



ECG Case 002

An older, but sprightly female is brought to the ED after developing multiple episodes of vomiting. Her husband had been vomiting as well but his symptoms had settled after a few hours.

She has minimal clinical history apart from hypertension for which she takes two separate agents.

The prompt to attend the ED came after the lady passed out for about 30 seconds following an episode of vomiting.

Her vitals are normal and her ECG is shown below.

Sick-sinus syndrome

  • I’m no Amal Mattu but that looks like pretty standard A Fib to me…

While you are enquiring about any further past medical history she becomes nauseated again and begins to retch. The retching quickly stops but she is no longer able to answer your questions. While you’re becoming increasingly frustrated with your patients reluctance to engage in conversation, the nurse shoves you out of the way and commences CPR.

Following about 30 secs of CPR and the patient pushes the nurse away. You review the telemetry reading from the monitor and it is shown below.

Sick-sinus syndrome

Whats the diagnosis

ECG Case 001

Inspired by Vince D. 

70 year old man with recent diagnosis of hyperthyroidism walks into the ED with palpitations. Has had them since the hyperthyroidism started but states something changed a few hours ago and now he feels a bit light headed with them.

Vitals are all stable, and the patient looks well.

His ECG looks like this:

Atrial Flutter 01


Click for answer

What happened?

What happened next?

How often does adenosine convert Atrial Flutter?


Blackouts and syncope.

I gave a talk to our registrars recently on falls and blackouts. Such a colossal topic in 45 minutes was never gonna cover all the material so I ended up focusing on the ECG in syncope and falls assessment in the elderly.

In the spirit of FOAM (Free Open-Access Meducation) I figured all the work I’d already done was worth spreading around to more than the 8 people that were there.

So here it is in video form…

Credits to:

Apologies to the international listeners if I get a bit speedy with the old talking.

As usual, I’d love to hear any comments or corrections you might have.

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