What is the effect of beta blockers on heart rate?

What is the effect of beta blockers on heart rate?

• A. They increase heart rate by enhancing nodal cell excitability
• B. They decrease heart rate by preventing norepinephrine and epinephrine from binding to nodal cells
• C. They have no effect on heart rate
• D. They cause irregular heart rhythms by interfering with conduction

Answer: (B)

Beta blockers lower heart rate by blocking the heart’s response to sympathetic signals. They mainly block beta-1 receptors on nodal tissue, so norepinephrine and epinephrine can’t push the SA node to fire as quickly. With less cAMP, the funny current and calcium currents slow, reducing automaticity and the rate at which the SA node generates impulses. Conduction through the AV node also slows a bit, which helps decrease the overall heart rate, especially during stress or exercise. That’s why this option is the best choice: the drugs decrease heart rate by preventing sympathetic neurotransmitters from binding to nodal cells. They don’t increase heart rate, they don’t have no effect, and while they can affect conduction, they don’t typically cause irregular rhythms as their primary action.

Beta blockers lower heart rate by blocking the heart’s response to sympathetic signals. They mainly block beta-1 receptors on nodal tissue, so norepinephrine and epinephrine can’t push the SA node to fire as quickly. With less cAMP, the funny current and calcium currents slow, reducing automaticity and the rate at which the SA node generates impulses. Conduction through the AV node also slows a bit, which helps decrease the overall heart rate, especially during stress or exercise.

That’s why this option is the best choice: the drugs decrease heart rate by preventing sympathetic neurotransmitters from binding to nodal cells. They don’t increase heart rate, they don’t have no effect, and while they can affect conduction, they don’t typically cause irregular rhythms as their primary action.