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- Which of the following is the most likely effect of adenosine on nodal conduction?
Which of the following is the most likely effect of adenosine on nodal conduction?
Dr. Shoaib Ahmad Baig
January 13, 2025
🔍 Question
A researcher is conducting an experiment using a mouse model to evaluate how adenosine affects cardiac nodal conduction during episodes of paroxysmal supraventricular tachycardia (PSVT). Electrodes are positioned at the right atrium and the intraventricular septum to measure conduction velocity and current. After inducing PSVT through electrical stimulation of the heart, adenosine is administered to terminate the arrhythmia.
Which of the following is the most likely effect of adenosine on nodal conduction?
• A. Hyperpolarization of the AV node
• B. Prolonged repolarization at the AV node
• C. Prolonged slow depolarization at the AV node
• D. Prolonged slow depolarization at the SA node
Correct Answer 🎯: A. Hyperpolarization of the AV Node
Adenosine increases potassium efflux via specific K⁺ channels (IK-Ado).
This hyperpolarizes the AV node, making it less excitable and reducing the likelihood of reentrant arrhythmias.
🧠 Key Insight: Hyperpolarization is central to adenosine’s rapid termination of SVT.
⚙️
🧠 Adenosine Mechanism of Action in Cardiac Nodal Tissue
⬇
Activation of A1 Adenosine Receptors on Cardiac Cells
⬇
Coupling with Gi-Protein
⬇
Inhibition of Adenylyl Cyclase
⬇
↓ cAMP Levels
⬇
⬇ Activation of L-Type Calcium Channels
⬇
⬇ Inward Ca²⁺ Current (ICa)
⬇
⬇ Hyperpolarization of AV Node via Increased Potassium Efflux (IK-Ado)
⬇
⬇ Prolonged AV Nodal Conduction Delay⬇
⬇ Termination of Reentrant Circuitry
⬇
⬇ Conversion to Normal Sinus Rhythm
⚖️ Explanation of Other Differentials
Differential ⚖️ | Mechanism ⚙️ | Why Incorrect? 🔴 |
|---|---|---|
B. Prolonged Repolarization at AV Node | No direct effect on repolarization duration. | Hyperpolarization ≠ delayed repolarization; they’re mechanistically distinct. |
C. Prolonged Slow Depolarization at AV Node 🔍 | Adenosine ⬇ ICa, shortening depolarization phase. | Does not “prolong”; instead, reduces calcium influx for faster suppression |
D. Prolonged Slow Depolarization at SA Node ⚖ | Minor effect on SA node, primarily acts on AV node. | Focus is on AV node due to its role in SVT termination. |
/
📝 Flashcards
Stay Hungry, Stay Curious!
Your Brother In This Struggle
Dr. Shoaib Ahmad
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