A 72-year-old man with ischaemic cardiomyopathy (LVEF 30%) presents for follow-up. He is clinically euvolaemic. Current medications are sacubitril-valsartan at target dose, bisoprolol at target dose, and spironolactone 25 mg daily. eGFR is 65 mL/min/1.73 m² and potassium 4.8 mmol/L. According to recent heart failure guidelines, which additional medication class should be routinely offered to reduce mortality and heart failure hospitalisation?