Compare conditions

Put any two — or three — conditions side by side, adult or pediatric, to spot the look-alike differences fast, row by row.

Tricyclic Antidepressant (TCA) Overdose

—

In one line

·Tricyclic antidepressants block sodium channels in the heart, shut off acetylcholine (the body's 'rest and digest' messenger), block alpha receptors on blood vessels, and turn down GABA (the brain's main calming signal).

—

Normal physiology

·The heart beats because sodium channels in heart muscle cells open and close in a precise rhythm, letting electrical signals zip from cell to cell so the whole heart squeezes in the right order. Acetylcholine (the body's main 'rest and digest' messenger) keeps pupils small, the mouth and skin moist, the bladder emptying, the gut moving, and the heart rate calm. Alpha-1 receptors on blood vessel walls respond to norepinephrine (the body's 'squeeze' signal) and keep vessels tight enough to hold blood pressure steady. GABA (gamma-aminobutyric acid, the brain's main calming neurotransmitter) acts like a brake pedal on nerve cells, keeping them from firing too fast and preventing seizures. All four systems run at the same time, each doing its own job to keep the body steady.

—

What goes wrong

·Too much tricyclic antidepressant blocks all four systems at once: it jams the sodium channels in the heart (so the electrical signal slows and the rhythm gets wide and chaotic), shuts off acetylcholine receptors everywhere (so the body swings into a hot-dry-mad anticholinergic pattern), blocks alpha-1 receptors on blood vessels (so vessels relax and blood pressure drops), and turns down GABA in the brain (so the brake pedal lifts and seizures can start). One drug, four breaks, and every weird finding flows from these upstream blockades.

—

Hallmark signs

·You find a patient who is drowsy
·QRS is wide
·Blood pressure is low
·Anticholinergic poisoning signs are there
·The electrocardiogram shows QRS over 100 or tall R in aVR
·This means arrhythmia risk

—

Red flags · escalate now

·QRS complex wider than 100 milliseconds on the EKG — the single most important danger sign in TCA overdose. It predicts seizures and deadly heart rhythms, and it is the trigger to give IV sodium bicarbonate right away.
·A tall R wave in lead aVR (taller than 3 mm) — an EKG fingerprint of the sodium-channel poisoning TCAs cause in the heart's wiring.
·Rapid crash in the first 1 to 2 hours — a TCA patient can go from awake and talking to seizing, with low blood pressure (hypotensive), and unconscious (comatose) in minutes. Never trust an early 'looks fine.'
·Seizures — each seizure makes the blood more acidic, and too much acid in the blood (acidosis) makes the TCA grip the heart's sodium channels even harder (a vicious cycle: treat aggressively and re-check the EKG).
·Blood pressure that stays low after IV fluids — both the heart pump and the blood vessels are poisoned; norepinephrine is the vasopressor of choice.
·Falling level of consciousness — plan for early airway protection; slow, shallow breathing raises CO2, worsens too much acid in the blood (acidosis), and feeds the cardiotoxicity loop.

—

Workup

·12-lead electrocardiogram (ECG)
·Arterial blood gas (ABG)
·Basic metabolic panel (sodium, potassium, bicarbonate, creatinine)
·Serum lactate
·Urine drug screen and specific tricyclic level (if available)
·Creatine kinase (CK)

—

Treatment

·Sodium bicarbonate 1–2 mEq/kg IV bolus, repeat to keep arterial pH between 7.45 and 7.55
·IV normal saline bolus (500–1,000 mL) and norepinephrine infusion (starting 0.05–0.1 mcg/kg/min) to raise blood pressure
·Benzodiazepine (lorazepam 2–4 mg IV or diazepam 5–10 mg IV) for seizures
·Activated charcoal 1 g/kg by mouth or nasogastric tube if the patient took the pills within 1–2 hours and can protect their airway
·Continuous cardiac monitor and repeat 12-lead ECG every 2–4 hours until QRS stays normal for 24 hours
·20% lipid emulsion IV (1.5 mL/kg bolus, then 0.25 mL/kg/min infusion) if the patient goes into cardiac arrest that does not respond to standard resuscitation

—

NCLEX trap

·Never use physostigmine in tricyclic overdose. It worsens seizures and can stop the heart. Use benzodiazepines (like lorazepam) to stop seizures and sodium bicarbonate to protect the heart. Physostigmine blocks acetylcholinesterase (the enzyme that breaks down acetylcholine), which can make the heart even more unstable when sodium channels are already clogged by the tricyclic drug.
·Start with IV fluids first. If pressure stays low, use norepinephrine (which squeezes vessels AND speeds the heart). Pure alpha drugs like phenylephrine squeeze vessels so hard they can trigger dangerous heart rhythms when sodium channels are already blocked. Norepinephrine's beta effect helps the heart pump stronger, which is safer here.
·Tricyclic overdose causes anticholinergic signs too, but tricyclics are far more deadly because they also block sodium channels in the heart. The wide QRS (over 100 milliseconds) and tall R wave in lead aVR on the electrocardiogram are the giveaways that tell you this is tricyclic, not simple atropine. Atropine rarely widens the QRS.
·The electrocardiogram is the most important clue. If the QRS is over 100 milliseconds or the R wave in lead aVR is tall, give sodium bicarbonate right away. Sodium bicarbonate opens the blocked sodium channels in the heart muscle. Fluids and pressors help blood pressure, but they don't fix the electrical danger that can stop the heart without warning.
·Seizures are a double danger in tricyclic overdose. They make the blood acidic (low pH), and acidic blood makes sodium channels block even harder, raising the risk of deadly rhythms. Stop seizures fast with benzodiazepines (like lorazepam or diazepam) and keep the blood alkaline (pH 7.45–7.55) with sodium bicarbonate.
·If the QRS is over 100 milliseconds, give sodium bicarbonate immediately. Do not wait. The wide QRS means the heart's electrical system is in danger. Cardiac arrest and deadly rhythms (like ventricular a fast heart rate (tachycardia) or torsades de pointes) can strike without warning, even if the patient looks stable.

—

Install Maldek by Hill as an app — studies work even offline