Which stimulus increases ERP in AV nodal tissue?

Which stimulus increases ERP in AV nodal tissue?

• A. Vagal activation
• B. Sympathetic activation
• C. Ischemia
• D. Exercise

Answer: (A)

The AV node’s refractory behavior is strongly shaped by autonomic tone. Parasympathetic (vagal) activation increases AV nodal refractoriness, meaning the effective refractory period gets longer and conduction through the AV node slows. Mechanistically, acetylcholine acting on M2 receptors opens GIRK (I_KACh) channels and reduces L-type calcium current, hyperpolarizing the cells and slowing conduction. This lengthens the time before the node can be re-excited, which is exactly what the ERP reflects in AV nodal tissue. In contrast, sympathetic activation raises cAMP, enhances calcium entry, and speeds conduction, effectively shortening the ERP. Exercise, which boosts sympathetic drive, would do the opposite of increasing ERP. Ischemia can disrupt conduction and refractoriness in a variable way, but it does not specifically and reliably increase AV nodal ERP like vagal activation does. So, the stimulus that increases AV nodal ERP is vagal (parasympathetic) activation.

The AV node’s refractory behavior is strongly shaped by autonomic tone. Parasympathetic (vagal) activation increases AV nodal refractoriness, meaning the effective refractory period gets longer and conduction through the AV node slows. Mechanistically, acetylcholine acting on M2 receptors opens GIRK (I_KACh) channels and reduces L-type calcium current, hyperpolarizing the cells and slowing conduction. This lengthens the time before the node can be re-excited, which is exactly what the ERP reflects in AV nodal tissue.

In contrast, sympathetic activation raises cAMP, enhances calcium entry, and speeds conduction, effectively shortening the ERP. Exercise, which boosts sympathetic drive, would do the opposite of increasing ERP. Ischemia can disrupt conduction and refractoriness in a variable way, but it does not specifically and reliably increase AV nodal ERP like vagal activation does.

So, the stimulus that increases AV nodal ERP is vagal (parasympathetic) activation.