A 72-year-old woman with heart failure with reduced ejection fraction (HFrEF) is reviewed. She remains symptomatic (NYHA Class II) despite taking Ramipril 10mg OD, Bisoprolol 10mg OD, and Eplerenone 50mg OD. Her LVEF is 30%. Her heart rate is 65 bpm in sinus rhythm and blood pressure is 110/75 mmHg. What is the most appropriate next step in management according to NICE guidelines?