A 71-year-old man with HFrEF presents with nausea, yellow-gr…

A 71-year-old man with HFrEF presents with nausea, yellow-green visual halos, and new-onset ventricular ectopy. He has been compliant with his digoxin therapy and recently had his furosemide dose increased for volume overload. Labs: K⁺ = 2.8 mEq/L, Cr = 1.0 mg/dL. Which factor most likely precipitated his digoxin toxicity?