A 6-month-old infant with uncorrected Tetralogy of Fallot is scheduled for surgery in 2 weeks. The child has had two cyanotic spells in the past month. Which drug is the preferred agent for prophylaxis of cyanotic spells in the preoperative period?

Explanation

## Prophylaxis of Cyanotic Spells in TOF — Preoperative Management **Key Point:** Oral propranolol is the preferred prophylactic agent for reducing the frequency and severity of cyanotic spells in infants with uncorrected TOF awaiting surgical repair. ### Rationale for Propranolol Prophylaxis **High-Yield:** Propranolol reduces infundibular contractility and dynamic obstruction, thereby decreasing the propensity for spells. It is given **chronically** (starting dose 0.5–1 mg/kg/day in 3 divided doses) to prevent spells, not just treat acute episodes. ### Prophylactic Drug Comparison in TOF | Drug | Mechanism | Efficacy in TOF | Indication | Drawback | |------|-----------|-----------------|-----------|----------| | **Propranolol (oral)** | β-blockade, ↓ RVOT obstruction | **Gold standard** | **First-line prophylaxis** | Contraindicated in asthma/reactive airway disease | | Atenolol (oral) | Selective β₁-blockade | Moderate | Alternative if propranolol intolerant | Less effective than propranolol in TOF; cardioselective may be insufficient | | Captopril (oral) | ACE inhibition, ↓ afterload | Weak | Not primary agent; adjunct only | Does not reduce RVOT obstruction; minimal benefit in spells | | Digoxin (oral) | Positive inotrope, ↑ contractility | **Harmful** | Contraindicated | Increases contractility → worsens right-to-left shunt | **Clinical Pearl:** The goal of preoperative prophylaxis is to **reduce spell frequency** and allow the infant to grow and gain weight before definitive surgical repair. Propranolol achieves this by stabilizing the dynamic obstruction. ### Preoperative Management Algorithm ```mermaid flowchart TD A[Uncorrected TOF + recurrent spells]:::outcome --> B[Surgery planned?]:::decision B -->|Yes, in weeks| C[Start prophylactic propranolol]:::action B -->|No, delayed| D[Optimize medical management]:::action C --> E[Dose: 0.5-1 mg/kg/day TDS]:::action E --> F[Monitor for spell reduction]:::action F --> G{Spells controlled?}:::decision G -->|Yes| H[Proceed to surgery]:::action G -->|No| I[Increase dose or add morphine]:::action I --> H ``` **Mnemonic:** **PROP** = **PRO**phylactic propranolol for **P**reoperative **P**revention of spells. **Warning:** ~~Digoxin~~ is **contraindicated** in TOF because positive inotropic effect increases right ventricular contractility and worsens the right-to-left shunt, precipitating or worsening spells.