ukmla MCQ (SBA): Chronic Heart Failure (HFrEF)

A 67-year-old man with known heart failure (NYHA Class II, LVEF 35%) is managed with ramipril, bisoprolol, and furosemide. Despite optimal doses, he remains symptomatic with mild ankle oedema and shortness of breath on moderate exertion. His eGFR is >60 mL/min/1.73m$^2$ and K+ is 4.2 mmol/L. According to NICE NG106, what medication should be added next?