LEFT ATRIAL FUNCTION STUDIED BY CINEANGIOCARDIOGRAPHIC VOLUME DETERMINATIONS

II. CLINICAL APPLICATION

Left atrial volume determinations were carried out on 13 cineangiocardiograms from 12 patients ranging in age from 1 month to 7 years. Seven of the patients had pulmonary valvular stenosis and were considered as a "normal" control group. Four patients had left ventricular outflow obstruction, in 1 this was combined with mitral stenosis and regurgitation. One child had severe mitral stenosis with severe myocardiopathy.

Left atrial and left ventricular volume curves were obtained by calculating the volumes frame by frame (50 frames/sec.). Arvidsson's method¹ (direct measurement of axes) was used to calculate left atrial volumes. Left ventricular volumes were calculated using the "area-length-method" of Dodge et al.^5,6

Average maximal atrial volume was 27.7 cc./m² BSA. Average minimal atrial volume was 9.4 cc./m² BSA and the average atrial volume difference was 18.8 cc./m² BSA. Per cent volume change was 63 per cent. Atrial volume difference on the average amounted to 40 per cent of the end-diastolic volume of the left ventricle; left atrial maximal volume was 51 per cent of the left ventricular end-diastolic volume.

Atrial volume difference was therefore markedly smaller than left ventricular stroke volume. This implies that the filling of the left ventricle is not solely accomplished by left atrial contraction. During ventricular systole, the left atrium is distended by the continuing blood flow from the pulmonary veins. After opening of the mitral valve, blood flows from the left atrium into the left ventricle; however, left atrial volume decrease is less than left ventricular volume increase. Therefore, some portion of blood is conveyed into the left ventricle without affecting left atrial volume difference. For this portion the left atrium serves only as a conductive pipe.

Three distinct phases of atrial emptying can be distinguished at heart rates below 100 beats/min. During the first phase approximately 50-65 per cent of the total atrial volume decrease takes place. Then a phase follows in which atrial volume decreases at a slower rate. It is during this phase that blood is conducted from the atrium into the left ventricle with little or no active contribution of the left atrium. Only at the end of ventricular diastole does atrial volume decrease again markedly as a result of active atrial contraction (at the end of the P-wave). These results are in close agreement with the investigations of Gribbe and associates⁹ in dogs and with the investigations of Grant et al.⁸ and Murray and co-workers¹¹ (who used serial angiocardiography) in adults.

In 5 patients with left atrial, left ventricular, and aortic lesions, marked alterations of their filling and emptying patterns were noted. In the cases with increased resistance to left ventricular ejection, atrial "stroke-volume" proved to be of greater significance for left ventricular filling than in the normal. In the 2 cases with cardiomyopathy, left atrial volume difference was decreased.

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