A patient with acute decompensated heart failure on maximal chronic beta-blocker therapy requires inotropic support. Which agent remains effective despite beta-receptor blockade because its action does not depend on beta-adrenergic signaling?
- A Dobutamine
- B Isoproterenol
- C Milrinone ✓
- D Dopamine at intermediate doses
Correct answer: C. Milrinone
Explanation
Milrinone inhibits phosphodiesterase type 3 in cardiac myocytes, preventing cAMP degradation and thereby increasing calcium influx and contractility independently of beta receptors. This makes it valuable when patients are on chronic beta-blockade, where catecholamine agonists like dobutamine, dopamine, and isoproterenol lose much of their efficacy. Milrinone also causes vasodilation, producing the inodilator profile useful in low-output states with elevated filling pressures.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.
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