A 64-year-old man with ischaemic cardiomyopathy (left ventricular ejection fraction 28%) remains NYHA class II despite maximally tolerated sacubitril-valsartan, bisoprolol, and spironolactone. His blood pressure is 118/72 mmHg, estimated glomerular filtration rate 65 mL/min/1.73 m², and potassium 4.6 mmol/L. According to contemporary Canadian heart failure guidelines, which additional therapy should be prioritised to reduce cardiovascular death and heart failure hospitalisation?