Which statement best describes norepinephrine's effect on afterload and myocardial oxygen demand?

Which statement best describes norepinephrine's effect on afterload and myocardial oxygen demand?

• A. Decreases afterload and decreases myocardial oxygen demand
• B. Decreases afterload but increases oxygen demand
• C. Increases afterload and may increase myocardial oxygen demand
• D. Has no effect on afterload or oxygen demand

Answer: (C)

Norepinephrine raises afterload through alpha-adrenergic vasoconstriction, which increases systemic vascular resistance. The left ventricle must generate higher pressure to eject blood, so afterload goes up. It also stimulates beta-1 receptors in the heart, increasing contractility and heart rate, which raises myocardial oxygen consumption. Because oxygen demand depends on the balance of increased work and heart rate, it may rise with norepinephrine. So the best description is: increases afterload and may increase myocardial oxygen demand.

Norepinephrine raises afterload through alpha-adrenergic vasoconstriction, which increases systemic vascular resistance. The left ventricle must generate higher pressure to eject blood, so afterload goes up. It also stimulates beta-1 receptors in the heart, increasing contractility and heart rate, which raises myocardial oxygen consumption. Because oxygen demand depends on the balance of increased work and heart rate, it may rise with norepinephrine. So the best description is: increases afterload and may increase myocardial oxygen demand.