American Board of Surgery Qualifying Exam (ABS QE) Practice Test

What mechanism does milirinone primarily use to exert its effects?

1. Beta-receptor stimulation

2. Phosphodiesterase inhibition

3. Calcium channel blockade

4. Alpha receptor activation

The correct answer is: Phosphodiesterase inhibition

Milrinone primarily exerts its effects through phosphodiesterase inhibition, specifically targeting phosphodiesterase type 3 (PDE3). This inhibition leads to an increase in intracellular levels of cyclic adenosine monophosphate (cAMP). Elevated cAMP enhances cardiac contractility, making milrinone an effective inotrope, particularly in the setting of acute decompensated heart failure. Additionally, the increase in cAMP levels causes vasodilation, which can help reduce systemic vascular resistance and lower the workload on the heart. The other mechanisms listed do not accurately describe the primary action of milrinone. While beta-receptor stimulation involves catecholamine action leading to increased contractility, milrinone works independently of direct receptor activation. Calcium channel blockade is associated with other agents that decrease intracellular calcium influx, leading to reduced contractility, which is contrary to the effect of milrinone. Alpha receptor activation typically causes vasoconstriction and increased vascular resistance, which is not the action promoted by milrinone’s mechanism of action.