Sodium-Channel Blocker Toxicity
Objective: Recognize sodium-channel blocker toxicity from a wide QRS, a tall R wave in aVR, and the story. Bicarbonate is a protocol or poison-center decision. This page does not give a dose.
Why this matters
Open the airway first. Tricyclic antidepressants and several other drugs block cardiac sodium channels. The QRS widens. A tall R wave at the end of the QRS in lead aVR is the teaching sign. The patient may seize, and the blood pressure may fall. This can look like ventricular tachycardia, high potassium, or some other rhythm problem.
The story separates them: an overdose, a new prescription, or empty bottles. Many systems use sodium bicarbonate for this poisoning. Use it only if your protocol or the poison center says so. The dose is not on this page.
- A wide QRS after a sodium-channel blocker is a poisoning until you prove another cause.
- Airway, ventilation, and blood pressure come first. Acidosis makes the sodium-channel block worse.
- Do not treat this wide rhythm like stable supraventricular tachycardia (SVT). Do not copy a bicarbonate dose from memory or from a website.
- The QRS is wide. This may be a sodium-channel blocker. I am protecting the airway and the blood pressure.
- I am asking medical control or the poison center about bicarbonate. I am not inventing a dose.
- I am not giving a drug that blocks the atrioventricular node for this wide rhythm.
Clinical sequence
- Open the airway and support breathing. Hypoventilation and acidosis worsen the block. Put the monitor on and get a 12-lead if it does not delay care of a crashing patient.
- Look at aVR and the QRS width. A widening QRS and a prominent terminal R in aVR are the teaching pattern. Compare with hyperkalemia, which is a different membrane problem and a different drug path.
- Ask what was taken and when. Tricyclics are the classic example. Other sodium-channel blockers exist. Read the bottle. Do not guess the drug from a nickname.
- If the patient is in shock or the QRS is wide and your protocol includes sodium bicarbonate for this poisoning, follow that card and online medical control. Read sodium bicarbonate framing so you do not give it for every arrest.
- Treat seizures with the benzodiazepine your protocol names. Some protocols tell you to avoid particular antiarrhythmics that also block sodium channels. Follow that list.
Teaching points
- AHA care for arrest from a poisoning treats sodium-channel blocker toxicity as a special situation. It is not routine bicarbonate for every asystole.
- A regular wide rhythm with poor perfusion is still a ventricular tachycardia pathway until proven otherwise. The poisoning explains the QRS. It does not make an unstable patient stable.
- Serum levels will not come back in the ambulance. Do not wait for them to support the airway.
Common errors
- Giving a drug that blocks the atrioventricular node for a wide complex because the rate is “not fast enough.”
- Saying a bicarbonate dose from memory.
- Missing the empty pill bottle because the ECG “looked like hyperkalemia.”
Practice
One-minute check
QRS is widening, aVR has a tall R, and the family found an old antidepressant bottle. Say the airway plan and who you call before any drug number is spoken.
Sources & Further Study
Named guidelines for further study. They are not clinical orders and do not replace your protocol or medical direction.
- AHA 2025 Special Circumstances — toxicologic arrest, including sodium-channel blocker toxicity, is not routine bicarbonate for every arrest
- LITFL — sodium-channel blocker toxicity — wide QRS and terminal R in aVR as teaching signs
- Sodium bicarbonate framing — protocol owns the dose
Education only. Apply learning within your protocols and medical direction. This is not clinical care guidance.
Check Your Understanding
Questions drawn only from this lesson. After you check, the key is highlighted. Education practice — not a certification exam.