[Two-dimensional echocardiographic evaluation of left atrial shape and size]

We investigated the influence of the miscellaneous structures surrounding the left atrium on left atrial shape and examined the feasibility and problems in evaluating its size using the anteroposterior dimension of the M-mode echocardiogram. Using two-dimensional echocardiography, left atrial anteroposterior short-axis dimension (S), long-axis dimension (L), transverse-axis dimension (T) which cross perpendicularly one another, and area in the long-axis section (AREA) were measured in 84 subjects. The left atrial size was defined as AREA X T. The population of this study consisted of 24 subjects without heart disease, 24 with mitral valve disease and 34 with miscellaneous heart diseases other than mitral valve disease. Some of them were associated with the thin chest, chest deformity by thoracoplasty or the markedly dilatated right atrium. In subjects with the thin chest the left atrium was compressed in the anterior and posterior directions, in patients who underwent thoracoplasty it was elongated in the cranial and caudal directions, and in those with the markedly dilatated right atrium it was compressed in the right and left directions. It can be speculated that surrounding structures have some direct effects on left atrial dynamics. As left atrial size increased, these three dimensions (S, L and T) increased disproportionally. Because the contribution of each dimension to the left atrial volume change is proportional to the ratio of dimensional change and S has the largest ratio, S contributed to left atrial volume change more than the others. That is the reason that left atrial volume was not proportional to S or S3. The relationship between S and AREA during one cardiac systole was almost linear in individual studies. The slope in the S-AREA relation, however, was greater in the cases with a larger value of S. Therefore, when the extent of the change in S is used as an index of atrial volume change, it should be normalized by S. Because the left atrium expanded in any directions, either S or other dimensions reflected its size. In cases with the distorted left atrium, however, evaluation of left atrial size by the use of a single dimension alone was inadequate.(ABSTRACT TRUNCATED AT 400 WORDS)