What does negative chronotropy refer to?

What does negative chronotropy refer to?

• A. Parasympathetic (vagal) activation decreases rate
• B. Sympathetic activation decreases rate
• C. Increase in rate due to catecholamines
• D. No change in rate

Answer: (A)

Negative chronotropy means slowing of the heart rate due to parasympathetic (vagal) influence. When the vagus nerve is activated, acetylcholine acts on M2 receptors in the SA node, opening GIRK channels, hyperpolarizing pacemaker cells, and slowing the slope of phase 4 depolarization. This reduces the firing rate of the SA node, lowering heart rate. The parasympathetic system also slows AV nodal conduction, but chronotropy specifically refers to rate. In contrast, sympathetic activation or catecholamines increase heart rate (positive chronotropy), and there is no change in rate would reflect neutral chronotropy.

Negative chronotropy means slowing of the heart rate due to parasympathetic (vagal) influence. When the vagus nerve is activated, acetylcholine acts on M2 receptors in the SA node, opening GIRK channels, hyperpolarizing pacemaker cells, and slowing the slope of phase 4 depolarization. This reduces the firing rate of the SA node, lowering heart rate. The parasympathetic system also slows AV nodal conduction, but chronotropy specifically refers to rate. In contrast, sympathetic activation or catecholamines increase heart rate (positive chronotropy), and there is no change in rate would reflect neutral chronotropy.