A 70-year-old woman with chronic heart failure due to ischaemic cardiomyopathy (LVEF 30%) is reviewed in the heart failure clinic. She is euvolaemic on physical examination. Current medications include sacubitril/valsartan at target dose, bisoprolol at target dose and spironolactone 25 mg daily. Her estimated GFR is 55 mL/min/1.73 m² and potassium is 4.5 mmol/L. According to the 2021 CCS/CHFS heart failure guideline, which additional therapy has the strongest evidence to further reduce cardiovascular mortality and heart failure hospitalisations?