A 70-year-old man with stable angina, hypertension, and type 2 diabetes is reviewed. His current medications include aspirin 75mg od, atorvastatin 40mg od, ramipril 10mg od, bisoprolol 5mg od, and metformin 1g bd. His blood pressure is 135/82 mmHg and heart rate is 58 bpm. He still experiences angina symptoms twice a week when walking uphill. What is the most appropriate next step in his angina management according to NICE guidelines?