A 65-year-old woman with chronic stable angina controlled on amlodipine 5 mg daily and isosorbide mononitrate 40 mg once daily presents with increasing frequency of anginal episodes (now 4–5 times per week despite medication). She denies dyspnea, orthopnea, or lower limb edema. BP is 130/80 mmHg, HR 72/min, and echocardiography shows normal left ventricular function. What is the most appropriate next step in management?