Pharmacology  ·  Cardiovascular

Digoxin, Inotropes, and Vasopressors

Acute hemodynamic support — mechanisms, limitations, and the cardiogenic shock hierarchy

• Digoxin inhibits the sodium-potassium ATPase pump, weakening the sodium gradient that drives the sodium-calcium exchanger, raising intracellular calcium and increasing contractility — unlike catecholamine inotropes, it does this without significantly increasing myocardial oxygen demand, and also slows atrioventricular conduction by increasing vagal tone.
• Digoxin does not reduce mortality — its role is limited to reducing hospitalizations in patients who remain symptomatic despite optimized four-pillar therapy; its narrow therapeutic index and the critical risk of hypokalemia (which competes with digoxin at the ATPase binding site and amplifies toxicity) require careful monitoring.
• Classic digoxin toxicity produces yellow-green visual disturbance and halos around lights, caused by drug effects on retinal photoreceptors; toxicity can also cause dangerous arrhythmias.
• Dobutamine (beta-1 agonist) and milrinone (phosphodiesterase type 3 inhibitor) both increase contractility, but milrinone acts independently of the beta-1 receptor — an advantage in chronic heart failure where receptor downregulation reduces dobutamine's effectiveness; milrinone also produces vasodilation that dobutamine does not.
• Vasopressors are distinct from inotropes: they raise blood pressure by constricting blood vessels rather than by increasing contractility; norepinephrine, acting on alpha-1 receptors, is the preferred vasopressor in cardiogenic shock and is often combined with an inotrope when both problems coexist.