Studies on the Right and Left Atrial Dynamics in Normal Subjects

To study the instantaneous dimensional changes in the right (RA) and left (LA) atria in man, esophageal echocardiography (Eso Echo) was performed in 11 normal healthy subjects. In all of the subjects studied, we could easily and simultaneously record the instantaneous echograms of the interatrial septum (IAS) and the right atrial wall (RAW) by Eso Echo. Throughout a cardiac cycle, IAS and RAW moved in the same direction, and RA dimension was always greater than that of LA. RA and LA dimensions increased during ventricular systole and the atria became maximum at around the biginning of the ventricular filling. The maximum RA dimension (RADmax : 42.4±0.5mm) was greater than that of the LA (LADmax : 26.2±0.8mm) (P＜0.001), and the mean ratio of maximum RA dimension to maximum LA dimension was 1.61±0.05 in normal subjects. During ventricular diastole, in which three different phases of dimensional changes could be identified : passive shortening (corresponding to ventricular rapid filling), diastasis (slow filling), active shortening (atrial contraction), both atrial dimensions decreased and became minimum at the end of the active atrial shortening. The minimum RA dimension (RADmin : 34.1±0.7mm) was greater than that of the LA (LADmin : 15.0±0.8mm) (P＜0.001). Total excursion (Tex) of RA (RADmax-RADmin) was 8.1±0.4mm, and that of the LA was 11.2±0.5mm(P＜0.01). Percent excursion (Tex/Dmax) of RA and LA were 19.4±0.9% and 43.2±2.0%, respectively, and the difference was significant (P＜0.001). During the passive atrial shortening, RAD decreased by 20.1±2.8% of the Tex while LAD by 63.8±3.3% (P＜0.001). During the active atrial shortening, RAD decreased by 79.9±2.8% of the Tex while LAD only by 36.2±3.3% (P＜0.001). Thus, RA and LA performance seems to be different in the passive as well as in the active atrial shortening periods in normal subjects.