Right atrial volumes and strains in healthy adults: is the Frank-Starling mechanism working?—detailed analysis from the three-dimensional speckle-tracking echocardiographic MAGYAR-Healthy Study

BACKGROUND: With larger blood volume flowing into a cardiac chamber, by stretching muscle fibers, increased contraction force could be detected. This phenomenon is called Frank-Starling mechanism, allowing the output of a cardiac chamber to be synchronized without external regulation. The purpose of the present study was to investigate the Frank-Starling mechanism in the right atrium (RA) represented by its volumes, volume-based functional properties and strains respecting the cardiac cycle in healthy adults by three-dimensional (3D) speckle-tracking echocardiography (3DSTE). METHODS: The present single center retrospective cohort study comprised 179 healthy adult volunteers (mean age: 33.2±12.0 years, 92 males), in whom complete two-dimensional Doppler echocardiography with 3DSTE was performed. Subjects were divided into 3 groups according to the mean value of maximum RA volume (V(max)) ± standard deviation: V(max) <30 mL, 30 mL ≤ V(max) <60 mL and V(max) ≥60 mL. RESULTS: All RA volumes respecting the cardiac cycle of all subjects and calculated separately for females and males and their indexed equivalents increased with V(max). RA stroke volumes increased with V(max) regardless of the phase it was measured in. While total atrial emptying fraction representing the reservoir phase remained unchanged with the increase of V(max), a significant increase in passive atrial emptying fraction representing the conduit phase could be detected, in case of V(max) >60 mL (28.9%±15.1% vs. 32.5%±12.6%, P<0.05). Active atrial emptying fraction representing the booster pump function did not change with the increase of V(max). Most global and mean segmental peak RA strains did not show significant changes with increasing RA volumes except for the RA area strain, it was the largest when V(max) was larger than 60 mL (64.7%±44.9% vs. 83.3%±49.4%, P<0.05). RA circumferential, longitudinal and area strains at atrial contraction decreased with increasing V(max), RA radial and 3D strains did not change significantly with increasing V(max). CONCLUSIONS: Increasing RA volumes do not cause significant increase in RA contractility represented by strains, but reduction in strains in longitudinal and circumferential directions could be detected in end-diastolic booster pump function. In contrast to the left atrium, obvious signs of Frank-Starling mechanism could not be detected in case of the RA.