A hospitalized 77-year-old man develops reduced urine output while being treated for acute myocardial infarction. His blood pressure is 85/55 mm Hg. The blood urea nitrogen (BUN) level is 35 mg/dL, and the serum creatinine level is 1.3 mg/dL. Urinalysis reveals few hyaline casts. His fractional excretion of sodium (FENa) is 0.5%.Which of the following is the most likely cause of this patient’s reduced urine output?