A 32-year-old woman from rural Maharashtra presents with progressive dyspnea on exertion and orthopnea for 6 months. She has a history of recurrent severe anemia (Hb 6–7 g/dL) managed with transfusions and iron supplementation. On examination, she has a hyperdynamic precordium and a systolic flow murmur. Chest X-ray shows cardiomegaly with pulmonary congestion. Echocardiography reveals a dilated left ventricle with increased wall thickness and normal ejection fraction initially, but progressive decline. Which cellular adaptation in the myocardium is the primary pathologic mechanism underlying her cardiac dysfunction?