If a beta blocker is given, which statement best describes the expected impact on heart rate?

If a beta blocker is given, which statement best describes the expected impact on heart rate?

• A. Heart rate would increase
• B. Heart rate would decrease
• C. Heart rate would remain the same
• D. Heart rate would become highly variable

Answer: (B)

Blocking beta-adrenergic receptors in the heart lowers sympathetic stimulation, which slows the heart. In the SA node, beta-1 activation normally raises cAMP, boosting the funny current and calcium currents that speed diastolic depolarization. A beta blocker blunts this pathway, so the SA node fires more slowly, decreasing heart rate. Conduction through the AV node is also modestly slowed, reinforcing the overall effect. So the expected impact is a decrease in heart rate. The other options don’t fit because they would require increased stimulation, no effect, or an unstable rhythm that beta blockade alone does not predict.

Blocking beta-adrenergic receptors in the heart lowers sympathetic stimulation, which slows the heart. In the SA node, beta-1 activation normally raises cAMP, boosting the funny current and calcium currents that speed diastolic depolarization. A beta blocker blunts this pathway, so the SA node fires more slowly, decreasing heart rate. Conduction through the AV node is also modestly slowed, reinforcing the overall effect. So the expected impact is a decrease in heart rate. The other options don’t fit because they would require increased stimulation, no effect, or an unstable rhythm that beta blockade alone does not predict.