Accidental pediatric ingestions and therapeutic drug toxicities represent critical medical emergencies requiring rapid recognition of toxidromes and toxic electrocardiographic patterns.
1. Common Cardiotoxic Agents & Electrocardiographic Hallmarks
| Drug Class | Mechanism of Cardiotoxicity | Classical 12-Lead Electrocardiographic Hallmarks | Specific Antidote / Treatment |
|---|---|---|---|
| Tricyclic Antidepressants (TCA) | Fast $Na^+$ channel blockade ($I_{Na}$) + Anticholinergic effect. | Terminal R wave in aVR $>3\text{ mm}$, $R/S$ in aVR $>0.7$, prolonged QRS ($>100\text{ ms}$), sinus tachycardia, prolonged $QTc$. | IV Sodium Bicarbonate ($8.4\%$): $1-2\text{ mEq/kg}$ IV push to alkalinize serum to pH $7.45-7.55$. |
| Digoxin (Cardiac Glycosides) | $Na^+/K^+$ ATPase inhibition $\to$ intracellular $Ca^{2+}$ overload. | Effect: "Scooped" sagging ST depression (reverse tick mark), short QTc. Toxicity: Ventricular bigeminy, bidirectional VT, high-grade AV block. | Digoxin Immune Fab (DigiFab); IV Magnesium Sulfate; avoid electrical cardioversion if possible. |
| Beta-Adrenergic Blockers | Competitive antagonism of $\beta_1$ and $\beta_2$ receptors. | Severe sinus bradycardia, first/second/third-degree AV block, junctional escape rhythm, prolonged QRS (propranolol). | High-Dose Insulin Euglycemia (HIE) + IV Glucagon ($50-100\ \mu\text{g/kg}$) + Calcium Gluconate. |
| Calcium Channel Blockers (CCB) | L-type $Ca^{2+}$ channel blockade. | Sinus arrest, complete AV block, PR prolongation, refractory cardiogenic shock with hyperglycemia. | High-Dose Insulin Euglycemia (HIE) + IV Calcium Chloride $10\%$ + Lipid Emulsion Therapy ($20\%$). |
2. Emergency Management Protocols
ACUTE TRICYCLIC ANTIDEPRESSANT (TCA) OVERDOSE │ ┌──────────────────────┴──────────────────────┐ QRS Duration > 100 ms QRS Duration > 160 ms (Risk of Generalized Seizures) (High Risk of Ventricular Arrhythmias) │ │ IV Sodium Bicarbonate IV Sodium Bicarbonate (1-2 mEq/kg bolus -> Continuous (Immediate bolus + Infusion; Infusion to target pH 7.45-7.55) Avoid Physostigmine / Class IA)
3. Clinical Pearls & Diagnostic Traps
Red Flag Warning: Never administer Class IA (Procainamide, Quinidine) or Class IC (Flecainide) antiarrhythmics to treat wide-complex tachycardias caused by TCA or sodium channel blocker poisoning. They will compound myocardial sodium channel blockade and precipitate fatal asystole.