Cardiovascular Drugs USMLE Step 1 Practice Question
A 73-year-old woman with systolic heart failure and chronic atrial fibrillation presents with dyspnea. Vitals: BP 98/62, HR 102, RR 20, SpO2 92%. She is prescribed digoxin for symptom improvement. Recent echocardiography shows ejection fraction of 28%. Serum potassium is 4.2 mEq/L. She denies chest pain. By inhibiting the sodium-potassium ATPase in cardiac myocytes, which intracellular change most directly increases contractility?
Answer choices
- ADecreased intracellular cyclic AMP in myocytes
- BIncreased potassium efflux during phase 3 repolarization
- CIncreased intracellular calcium due to reduced sodium calcium exchangeCorrect answer
- DBlockade of funny current in the sinoatrial node
- EActivation of guanylyl cyclase in vascular smooth muscle
- FDecreased intracellular sodium leading to reduced membrane potential depolarization
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