Which one of the following drugs is most likely to block K+ channels in the heart responsible for the delayed rectifier current?
## **Core Concept**
The question targets the understanding of cardiac electrophysiology, specifically the ion channels responsible for the repolarization phase of the cardiac action potential. The delayed rectifier potassium current (IKr and IKs) plays a crucial role in repolarizing the cardiac myocyte. Drugs that block these channels can prolong the action potential duration and the QT interval on the electrocardiogram.
## **Why the Correct Answer is Right**
Sotalol is a non-selective beta-blocker that also has class III anti-arrhythmic properties. Its class III effects are primarily due to its ability to block potassium channels, specifically the rapid component of the delayed rectifier potassium current (IKr). This blockade results in a prolongation of the action potential duration and the QT interval. Sotalol's effect on potassium channels is well-documented and is a key reason it is used in the treatment of certain types of arrhythmias.
## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is blank and cannot be evaluated.
- **Option B:** This option is blank and cannot be evaluated.
- **Option D:** This option is blank and cannot be evaluated.
## **Clinical Pearl / High-Yield Fact**
A critical clinical pearl related to this question is that drugs which block the IKr potassium channel can increase the risk of Torsades de Pointes, a potentially life-threatening arrhythmia. Sotalol, by blocking IKr, carries this risk, and monitoring of the QT interval is recommended during its use.
## **Correct Answer: C. Sotalol**