Updated July 2026 · 7 min read
Part of the ICU Emergencies Hub — browse every related guide in one place.
Tricyclic antidepressant overdose is a poisoning where the ECG is a crystal ball. TCAs block the fast sodium channels that drive the heart's electrical conduction, and the width of the QRS complex tells you, in real time, how much trouble the patient is in and whether a seizure or a lethal arrhythmia is coming. These patients can look deceptively awake and then collapse within minutes, which makes vigilant monitoring and a fast reach for sodium bicarbonate the difference between a save and a code.
TCAs have several toxic effects, but the one that kills is cardiac. By blocking the fast sodium channels responsible for the rapid upstroke of the cardiac action potential, they slow electrical conduction through the heart. On the monitor this shows up as a widening QRS complex and a rightward shift of the terminal QRS axis, producing the classic tall R wave in lead aVR. As conduction slows further, the patient is at risk for ventricular tachycardia, ventricular fibrillation, and a wide-complex bradycardic arrest. Layered on top are anticholinergic toxicity (hot, dry, dilated pupils, urinary retention, delirium, tachycardia), lowered seizure threshold, and vasodilatory hypotension.
The width of the QRS is one of the most useful numbers in toxicology because it correlates with what's about to happen.
| QRS duration | What it predicts | Bedside meaning |
|---|---|---|
| < 100 ms | Lower risk | Still monitor closely — can change fast |
| > ~100 ms | Increased seizure risk | Escalate vigilance; anticipate bicarbonate |
| > ~160 ms | Increased ventricular arrhythmia risk | High danger — aggressive sodium bicarbonate |
| Terminal R in aVR | Sodium-channel blockade present | Supports the diagnosis and the treatment |
Because the QRS can widen quickly, continuous ECG monitoring and serial 12-leads are core nursing work, not a formality. A QRS that is creeping wider is a patient heading toward seizures and arrhythmias, and it's your early warning to have bicarbonate and the crash cart ready.
Sodium bicarbonate is the cornerstone of treatment and works two ways: the sodium load helps overcome the blocked channels, and alkalinizing the blood reduces the drug's binding to the sodium channels. Given as boluses (and sometimes an infusion) for a widening QRS, ventricular arrhythmia, or significant hypotension, it can visibly narrow the QRS in front of you — the QRS is both the indication and the real-time response marker. Targets are typically a specific serum pH range; potassium is watched because alkalinization drives it down. For refractory hypotension, vasopressors are added, and IV lipid emulsion is a consideration in cardiovascular collapse unresponsive to standard measures.
Airway protection comes early if mental status declines, and here the ventilator strategy matters: mild hyperventilation supports the alkalinization goal, so avoid letting CO2 climb. Seizures are treated with benzodiazepines (and they worsen acidosis, which worsens cardiac toxicity, so stopping them fast is protective). Activated charcoal may be given early with a protected airway. Hypotension is treated with fluids and then vasopressors. Because TCAs are highly protein-bound and have a large volume of distribution, dialysis does not remove them — the game is supportive care and bicarbonate until the drug redistributes and is metabolized over hours to a day or more.
Tricyclic overdose is fundamentally a sodium-channel poisoning of the heart, and the QRS complex is the crystal ball: a widening QRS and a terminal R wave in aVR reveal the blockade, with roughly 100 ms marking rising seizure risk and 160 ms marking ventricular arrhythmia risk. Sodium bicarbonate is the treatment that overcomes the blockade and narrows the QRS in real time, guided by the ECG and serum pH, while benzodiazepines stop the seizures that would otherwise deepen the acidosis. These patients can crash from awake to arrest within minutes and cannot be dialyzed, so continuous monitoring and early, aggressive bicarbonate — not a reassuring blood pressure — are what keep them alive.
Related: Salicylate toxicity · Beta-blocker & CCB overdose · Serotonin syndrome vs NMS · Vasopressor guide
Educational content for licensed clinicians. Always follow your facility's protocol and provider orders. Not medical advice.
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