USMLE Step 1 Practice Test 14
10 free USMLE Step 1 practice questions in the real exam format, covering the official content areas, with an explanation for every answer.
Question 1 of 10
Cardiovascular SystemA 79-year-old woman is brought to the emergency department by her daughter because of 3 days of nausea, loss of appetite, and confusion. She says that lights in the room look yellow and have halos around them. She has chronic kidney disease, heart failure with reduced ejection fraction, and atrial fibrillation. She takes several medications for these conditions, and the doses were not changed when her kidney function worsened last month. Pulse is 48/min, and blood pressure is 104/62 mm Hg. An ECG shows atrial fibrillation with frequent premature ventricular complexes and scooped ST segments. Laboratory studies are shown. Which of the following is the mechanism of action of the drug most likely responsible for these findings?
| Test | Result |
|---|---|
| Serum | |
| Na⁺ | 136 mEq/L |
| K⁺ | 5.9 mEq/L |
| Cl⁻ | 101 mEq/L |
| HCO₃⁻ | 22 mEq/L |
| Urea nitrogen | 42 mg/dL |
| Creatinine | 2.3 mg/dL |
| Glucose | 104 mg/dL |