[Endocardial myocardial biopsy and ultrastructural characteristics in heart failure patients with reduced ejection fraction].

<b>Objective:</b> To investigate the endocardial myocardial biopsy and ultrastructural features of heart failure patients with reduced ejection fraction, to determine their histopathologic phenotype, and to explore the diagnostic utility of endomyocardial biopsy in such patients. <b>Methods:</b> A total of 35 patients with heart failure with reduced ejection fraction diagnosed at Beijing Anzhen Hospital and underwent endomyocardial biopsy were collected between January 2022 and December 2023. The clinical features, histopathological, and ultrastructural characteristics were analyzed and compared with 11 patients with heart failure with preserved ejection fraction. <b>Results:</b> The age ranged from 35-58 years, with median age of 51 years; there were 26 males and 9 females. Myocardial fibrosis and myocardial fiber disorders were the most common histopathologic changes [97.1% (34/35) and 74.3% (26/35), respectively]. Myocardial fibrosis was not statistically different between the heart failure with reduced ejection fraction group and the heart failure with preserved ejection fraction group [13.3% (5.7%-21.4%) vs. 13.2% (9.3%-34.2%), <i>P=</i>0.279]. Significant ultrastructural changes were dense mitochondrial proliferation, vacuolar degeneration, and disorganized arrangement of myocardial fibers with localized lysis and fracture. After endomyocardial biopsy, the etiology was identified in 11 patients (31.4%,11/35), with a prevalence of cardiac amyloidosis of 17.1% (6/35). <b>Conclusions:</b> Endomyocardial biopsy is useful for early diagnosis and precise treatment in patients presenting with heart failure with reduced ejection fraction. Histopathological and ultrastructural analyses can uncover potential treatments, and predict and improve prognosis by providing relevant information for understanding the pathogenesis and clinical evolution.