Negative chronotropic agents include which of the following?

Negative chronotropic agents include which of the following?

• A. Parasympathetic stimulation and beta blockers.
• B. Sympathetic stimulation.
• C. Norepinephrine.
• D. Epinephrine.

Answer: (A)

Chronotropic effects describe how the heart rate changes in response to autonomic input. Negative chronotropic influence lowers the rate. Parasympathetic stimulation slows the heart by releasing acetylcholine at the SA and AV nodes, which makes pacemaker cells less likely to fire rapidly and slows conduction. Beta blockers produce the same downward effect by blocking beta-1 receptors, dampening the heart’s response to sympathetic stimulation and thus reducing both heart rate and conduction velocity. Other options drive the opposite change: sympathetic stimulation, norepinephrine, and epinephrine all raise heart rate by activating beta-1 receptors, increasing the rate of pacemaker depolarization and speeding conduction.

Chronotropic effects describe how the heart rate changes in response to autonomic input. Negative chronotropic influence lowers the rate. Parasympathetic stimulation slows the heart by releasing acetylcholine at the SA and AV nodes, which makes pacemaker cells less likely to fire rapidly and slows conduction. Beta blockers produce the same downward effect by blocking beta-1 receptors, dampening the heart’s response to sympathetic stimulation and thus reducing both heart rate and conduction velocity.

Other options drive the opposite change: sympathetic stimulation, norepinephrine, and epinephrine all raise heart rate by activating beta-1 receptors, increasing the rate of pacemaker depolarization and speeding conduction.