19. Drug Effects, Toxicities, and Poisonings in Children
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.