Anatomical diversity and age-related histological changes in the human right atrial posterolateral wall

AIMS: Recent clinical observations suggest that the right atrial posterolateral wall structures originate ectopic beats and function as anatomical obstacles. Because atrial arrhythmias increase in incidence after middle age, we investigated histological diversity and age-related changes in right atrial posterolateral wall. METHODS AND RESULTS: Twenty-six autopsied hearts (mean 65.2 years, 16 men and 10 women) were studied. The entire posterolateral right atrium was cut serially. We determined the distribution of the sinoatrial node and localized it in relation to the crista terminalis and sinus venosus. We also compared histopathological changes in these tissues between three groups consisting of 31- to 50-year-old, 51- to 70-year-old and 71- to 90-year-old hearts. Total mean length of the crista terminalis, the sinoatrial node, and the sinus venosus was 46 mm, 21 mm and 29 mm, respectively, and showed no age-related changes, but the distribution of the sinoatrial node was varied. Mean muscular volume of the sinus venosus was significantly reduced in the two older groups, though that of the crista terminalis showed no age related-changes. CONCLUSION: Histological diversity of the sinoatrial node and age-related changes in the sinus venosus beneath the sinoatrial node may enhance histological heterogeneity and hence arrhythmogenicity.