Which of the following drugs hyperpolarizes AV nodal tissue, is used in PSVT and has short lasting adverse effects ?
**Core Concept**
Adenosine is a medication used to treat supraventricular tachycardia (PSVT) by selectively hyperpolarizing the atrioventricular (AV) node, thus slowing down conduction and terminating the arrhythmia. This action is due to the activation of G protein-coupled receptors, specifically A1 receptors, which lead to the closure of potassium channels and subsequent hyperpolarization.
**Why the Correct Answer is Right**
Adenosine works by binding to A1 receptors in the AV node, which are coupled to Gi proteins. This leads to the inhibition of adenylate cyclase, a decrease in cAMP levels, and the closure of potassium channels. The closure of potassium channels results in the hyperpolarization of the AV node, reducing the automaticity and conduction velocity of the AV node. This action is specific to the AV node and does not significantly affect other parts of the heart, making adenosine a safe and effective treatment for PSVT. Adenosine has a short half-life of approximately 10 seconds, which contributes to its short-lasting adverse effects.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not specified, so it cannot be evaluated.
**Option B:** This option is not specified, so it cannot be evaluated.
**Option C:** This option is not specified, so it cannot be evaluated.
**Option D:** This option is not specified, so it cannot be evaluated.
**Clinical Pearl / High-Yield Fact**
Adenosine is a useful medication in the emergency management of PSVT, but it can cause transient side effects such as flushing, chest discomfort, and dyspnea due to its vasodilatory effects. It is essential to administer adenosine rapidly and withdraw the infusion as soon as the arrhythmia is terminated to minimize these adverse effects.
**Correct Answer:** A. Adenosine.