Which vasopressor is more likely to cause tachycardia due to beta-adrenergic activity?

Which vasopressor is more likely to cause tachycardia due to beta-adrenergic activity?

• A. Epinephrine
• B. Norepinephrine
• C. Vasopressin
• D. Phenylephrine

Answer: (A)

Tachycardia from beta-adrenergic activity occurs when a vasopressor directly stimulates beta receptors on the heart, especially beta-1 receptors in the SA node, which increases firing rate and conduction. Epinephrine stands out because it has potent activity on both beta-1 and beta-2 receptors, so it directly boosts heart rate and contractility. This beta-1 stimulation makes tachycardia more likely with epinephrine than with other agents. Norepinephrine mainly drives alpha-1 effects with some beta-1 activity, but its beta stimulation is less prominent, so tachycardia is less pronounced. Vasopressin acts through V1 receptors and has no beta-adrenergic activity, so it doesn’t cause beta-mediated tachycardia. Phenylephrine is a pure alpha-1 agonist and lacks beta activity, so any change in heart rate would be reflexive rather than due to direct beta stimulation.

Tachycardia from beta-adrenergic activity occurs when a vasopressor directly stimulates beta receptors on the heart, especially beta-1 receptors in the SA node, which increases firing rate and conduction. Epinephrine stands out because it has potent activity on both beta-1 and beta-2 receptors, so it directly boosts heart rate and contractility. This beta-1 stimulation makes tachycardia more likely with epinephrine than with other agents.

Norepinephrine mainly drives alpha-1 effects with some beta-1 activity, but its beta stimulation is less prominent, so tachycardia is less pronounced. Vasopressin acts through V1 receptors and has no beta-adrenergic activity, so it doesn’t cause beta-mediated tachycardia. Phenylephrine is a pure alpha-1 agonist and lacks beta activity, so any change in heart rate would be reflexive rather than due to direct beta stimulation.