Which statement best describes the primary effect of digoxin on myocardial contractility?

Which statement best describes the primary effect of digoxin on myocardial contractility?

• A. Positive Chronotropic
• B. Positive Inotropic
• C. Negative Inotropic
• D. Negative Dromotropic

Answer: (B)

Increasing the force of myocardial contraction is the primary effect of digoxin. It works by inhibiting the Na+/K+ ATPase pump in cardiac cells, which raises intracellular sodium. This reduces the activity of the Na+/Ca2+ exchanger, leading to more calcium staying inside the cell during systole. The extra calcium boosts the interaction of actin and myosin, strengthening each heartbeat (positive inotropy) and improving stroke volume and cardiac output in systolic heart failure. Digoxin can also slow conduction through the AV node via enhanced vagal tone (a separate effect), but the question focuses on contractility, where the main action is increased contractile force.

Increasing the force of myocardial contraction is the primary effect of digoxin. It works by inhibiting the Na+/K+ ATPase pump in cardiac cells, which raises intracellular sodium. This reduces the activity of the Na+/Ca2+ exchanger, leading to more calcium staying inside the cell during systole. The extra calcium boosts the interaction of actin and myosin, strengthening each heartbeat (positive inotropy) and improving stroke volume and cardiac output in systolic heart failure. Digoxin can also slow conduction through the AV node via enhanced vagal tone (a separate effect), but the question focuses on contractility, where the main action is increased contractile force.