A 58-year-old man with a 20-year history of poorly controlled hypertension (BP 160–180/100–110 mmHg) presents with dyspnea and fatigue. Physical examination reveals a sustained apical impulse and an S4 gallop. Echocardiography shows a small left ventricular cavity with marked wall thickening (interventricular septum 18 mm), normal ejection fraction, and diastolic dysfunction. Histopathology of a myocardial biopsy specimen would most likely reveal which cellular adaptation?