Certified Registered Nurse Anesthetist (CRNA) Practice Exam

What is the main action of the drug milrinone in the context of heart failure treatment?

1. Increases preload

2. Reduces heart rate

3. Improves cardiac contractility

4. Increases systemic vascular resistance

The correct answer is: Improves cardiac contractility

Milrinone is a phosphodiesterase inhibitor that primarily acts to improve cardiac contractility. It does this by increasing the levels of cyclic AMP in myocardial cells, which enhances calcium influx during depolarization, ultimately leading to a stronger and more efficient contraction of the heart muscle. This action is particularly beneficial in the context of heart failure, where the heart's pumping ability is compromised. By improving contractility, milrinone helps to increase cardiac output and can provide symptomatic relief in patients with heart failure. The other options relate to different cardiovascular effects that milrinone does not predominantly produce. For instance, it does not significantly increase preload, as this could lead to volume overload, which is not desirable in heart failure management. It also does not primarily reduce heart rate; in fact, it can sometimes lead to a slight increase in heart rate due to enhanced contractility. Lastly, milrinone does not increase systemic vascular resistance; it tends to have a vasodilatory effect, which actually reduces afterload and can further assist in improving heart function. Therefore, the key action of milrinone in heart failure treatment is its ability to improve cardiac contractility.