Which vasopressor lowers systemic vascular resistance and mean arterial pressure, with marked tachycardia?

Which vasopressor lowers systemic vascular resistance and mean arterial pressure, with marked tachycardia?

• A. Dopamine
• B. Norepinephrine
• C. Epinephrine
• D. Isoproterenol

Answer: (D)

This question hinges on how different adrenergic receptor activations affect heart rate and vascular tone. Isoproterenol is a nonselective beta-adrenergic agonist, stimulating both beta-1 and beta-2 receptors. Activation of beta-1 receptors increases heart rate (and contractility), producing marked tachycardia. At the same time, beta-2 receptor stimulation causes vasodilation of vascular smooth muscle, especially in skeletal muscle beds, which lowers systemic vascular resistance. The net effect is a drop in mean arterial pressure due to the decreased SVR, accompanied by significant tachycardia from the beta-1 effect. Other agents tend to increase vascular tone and blood pressure through alpha effects or at least do not produce the same vasodilatory and chronotropic pattern. Dopamine’s effects depend on dose and can increase BP, norepinephrine raises systemic vascular resistance and MAP, and epinephrine elevates heart rate and blood pressure with vasoconstriction via alpha action. None match the combination of pronounced tachycardia with vasodilation and reduced MAP seen with isoproterenol.

This question hinges on how different adrenergic receptor activations affect heart rate and vascular tone. Isoproterenol is a nonselective beta-adrenergic agonist, stimulating both beta-1 and beta-2 receptors. Activation of beta-1 receptors increases heart rate (and contractility), producing marked tachycardia. At the same time, beta-2 receptor stimulation causes vasodilation of vascular smooth muscle, especially in skeletal muscle beds, which lowers systemic vascular resistance. The net effect is a drop in mean arterial pressure due to the decreased SVR, accompanied by significant tachycardia from the beta-1 effect.

Other agents tend to increase vascular tone and blood pressure through alpha effects or at least do not produce the same vasodilatory and chronotropic pattern. Dopamine’s effects depend on dose and can increase BP, norepinephrine raises systemic vascular resistance and MAP, and epinephrine elevates heart rate and blood pressure with vasoconstriction via alpha action. None match the combination of pronounced tachycardia with vasodilation and reduced MAP seen with isoproterenol.