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.