Age-related histologic features of the sinoatrial node from normal human hearts during the first 10 decades of life: a study of 200 cases

Knowledge of the histologic constituency of the sinoatrial (SA) node is based on small studies with unevenly distributed ages and subjective assessments of nodal composition, leading to difficulties in interpreting what constitutes true pathology of the SA node. SA nodes from two-hundred normal hearts (10 male and 10 female from each of the first 10 decades of life) were digitally analyzed to assess their histologic composition. Both nodal area and nodal fat content (≥5%) showed a quadratic relationship with age, peaking in the fifth to eighth decades of life. Increased fat content was also more prevalent with increased BMI (≥25 kg/m²). No differences between sexes were observed. Mean nodal collagen ranged from 7.1% to 50.3%, without a statistically significant differences by age or body mass index (BMI). The data suggests that the designation of pathologic fibrosis should be reserved for SA nodes with >50% collagen content. These findings expand and refine our understanding of the anatomy of the SA node.