A 68-year-old man presents with progressive exertional dyspnoea, orthopnoea, and ankle swelling. Examination reveals elevated jugular venous pressure, bilateral basal crackles, and pitting oedema to the knees. His creatinine has risen from 90 to 160 µmol/L over 2 days, and urine output has fallen to 200 mL in 24 hours. Ultrasound shows bilaterally enlarged kidneys with no obstruction. Which is the most likely explanation for his acute kidney injury?