Certified Registered Nurse Anesthetist (CRNA) Practice Exam

What is the result of increased cAMP in the heart due to milrinone?

1. Decreased cardiac output

2. Bradycardia

3. Increased cytosolic calcium

4. Vasodilation of peripheral blood vessels

The correct answer is: Increased cytosolic calcium

Increased cAMP in the heart due to milrinone leads to an increase in cytosolic calcium. Milrinone is a phosphodiesterase inhibitor that prevents the breakdown of cAMP, which results in elevated levels of this signaling molecule in cardiac myocytes. The rise in cAMP ultimately stimulates protein kinase A (PKA) activation, which enhances calcium influx through L-type calcium channels during the action potential. As cAMP levels rise, PKA phosphorylation of key proteins increases the release of calcium from the sarcoplasmic reticulum, further contributing to the increased availability of calcium for cardiac contraction. This mechanism enhances myocardial contractility, which is particularly beneficial in heart failure scenarios where improved contractile function is critical. Although increased cAMP can have a multitude of effects, such as relaxation of vascular smooth muscle leading to vasodilation, the most direct and relevant consequence of milrinone’s action in the heart specifically relates to increased cytosolic calcium leading to enhanced cardiac contractility.