A 35-year-old woman presents to the outpatient clinic with a 6-month history of progressive dyspnea on exertion and palpitations. She has a 10-year history of uncontrolled hypertension (BP 160/100 mmHg on today's visit). Physical examination reveals a sustained apical impulse displaced 2 cm lateral to the midclavicular line, and a grade 2/6 systolic murmur at the apex. Echocardiography shows concentric left ventricular hypertrophy with preserved ejection fraction and normal wall motion. What is the most appropriate immediate next step in management?