â– LECTURE OVERVIEW: Tricyclic Antidepressant (TCA) overdose is a major toxicological emergency characterized by multi-system receptors blockade.
â– THE CARDIOVASCULAR AND CENTRAL TOXICITIES:
1. Rapid Cardiac Sodium Channel Inactivation: TCAs block fast sodium channels (IKr) in myocardial tissue, slowing Phase 0 of the action potential and prolonging the QRS interval. This drives severe intraventricular conduction delays and lethal ventricular arrhythmias.
2. Anticholinergic Overdrive: Blocks muscarinic (M1) receptors, producing central and peripheral anticholinergic syndrome (altered mental status, dry skin, dilated non-reactive pupils, urinary retention, and hyperthermia).
3. Vascular Collapse: Inhibits alpha-1 adrenergic receptors, preventing peripheral vasoconstriction and causing refractory hypotension.
4. Neuronal Excitability: Blocks GABA-A receptors in the brain, lowering the seizure threshold and precipitating status epilepticus.
â– CLINICAL DIAGNOSTIC METRICS:
Establishing a definitive diagnosis requires combining serum biomarkers with gold-standard diagnostic modalities. High-sensitivity ELISAs are used initially to minimize false negatives, followed by highly specific confirmatory testing.
â– COMPENSATORY HORMONAL & VASCULAR FEEDBACK:
Acute systemic shifts trigger immediate neural and hormonal reflexes to preserve blood flow to vital organs like the brain and kidneys.
[HY-BOARD-1382]
🌟 Dynamic Clinical Key:
First-line, life-saving treatment is intravenous Sodium Bicarbonate (NaHCO3). The sodium load increases extracellular sodium concentration to overcome the TCA-mediated blockade, while the systemic alkalorization (raising pH to 7.45-7.55) converts the TCA molecule into its neutral, non-ionized form, reducing its affinity for sodium channels. Always correlate elevated serum spikes with continuous vital readings to rule out false laboratory spikes. Carefully evaluate the underlying cause of high blood pressure before aggressively suppressing compensatory vasoconstriction.