[Studies on systolic performance of the left atrium]

To analyze left atrial (LA) pump function, aortic root echocardiograms and LA pressure (P) by a Millar 's catheter tip manometer were recorded simultaneously in 26 patients (pts) in regular sinus rhythm [six normal subjects (C), three with angina pectoris (AP), eight with old myocardial infarction (MI), three with congestive cardiomyopathy (CCM), three with hypertension (HT), one with hypertrophic cardiomyopathy (HCM), one with mitral regurgitation and mild stenosis (MRs), and one with mitral regurgitation (MR)]. The pressure-dimension curve of the LA composed of two loops; an A-loop (pump function of the LA) and a V-loop. The following parameters were measured: Da = LA dimension at the beginning of the active atrial shortening, S-A-loop = the area of the A-loop, mean V = mean LA velocity of fractional fiber shortening, and peak T = maximum (LAP X LAD) during active atrial shortening phase. The S-A-loop was directly proportional to Da (r = 0.62, p less than 0.001) and the mean V was inversely correlated with the peak T (r = -0.76, p less than 0.001). This indicated that Starling's mechanism was operative and force-velocity relation exited in the LA. In HT, Da, the S-A-loop, the ratio of the S-A-loop to Da, and the ratio of mean V to peak T tended to be larger than those in other pts groups. Thus, the present results suggested that LA pump function was augmented in HT, probably due not only to Starling's effect but also to enhanced inotropic state of the LA.