**Question:** In a patient of congenital prolonged QT syndrome and intermittent Torsades de pointes, which of the following should be prescribed?

**Core Concept:** Congenital prolonged QT syndrome is a genetic disorder that affects the heart's electrical system, leading to prolonged QT interval on electrocardiogram (ECG) and an increased risk of life-threatening arrhythmias like Torsades de pointes. Torsades de pointes is a polymorphic ventricular tachycardia that develops due to an abnormal prolongation of the QT interval.

**Why the Correct Answer is Right:** The correct answer is to be chosen based on understanding the pathophysiology of the condition. In congenital prolonged QT syndrome, medications that can precipitate or worsen the condition should be avoided.

**Why Option A, B, and C are Incorrect:**

A. **Option A (Amiodarone):** It is a class III antiarrhythmic agent that prolongs the QT interval. Given its mechanism of action, its use can precipitate Torsades de pointes in patients with congenital prolonged QT syndrome.

B. **Option B (Sotalol):** It is another class III antiarrhythmic agent that prolongs the QT interval. Similar to amiodarone, its use in patients with congenital prolonged QT syndrome can lead to Torsades de pointes.

C. **Option C (Digoxin):** It is a cardiac glycoside that can also cause QT interval prolongation. Like amiodarone and sotalol, digoxin should be avoided in patients with congenital prolonged QT syndrome to prevent worsening of the condition and Torsades de pointes.

**Why Option D is Right:**

D. **Option D (Propafenone):** It is a class III antiarrhythmic agent that does not significantly prolong the QT interval. Unlike amiodarone and sotalol, propafenone does not pose a high risk of causing QT interval prolongation or Torsades de pointes in patients with congenital prolonged QT syndrome.

**Why Option D is Right:**

Propafenone is a class III antiarrhythmic agent that primarily affects the potassium channels in the cardiac myocytes, blocking the rapid delayed rectifier potassium current (IKr) and increasing the effect of the slow delayed rectifier potassium current (IK1). This results in a more effective antiarrhythmic effect without significantly prolonging the QT interval or increasing the risk of Torsades de pointes.

**Core Concept:** In congenital prolonged QT syndrome, it is crucial to avoid medications that significantly prolong the QT interval or increase the risk of Torsades de pointes. Class III antiarrhythmic agents (e.g., amiodarone, sotalol) should be avoided while class Ia and class III antiarrhythmic agents (e.g., propafenone) can be considered.

**Why Option D is Right:** Propafenone is a class III antiarrhythmic agent that does not significantly prolong the QT interval or increase the risk of Torsades