Two-dimensional echocardiographic assessment of the feline left atrium

Atrial size determined by echocardiography provides a surrogate measure of the hemodynamic burden of cardiac disease. Linear atrial dimensions often are indexed to aortic diameter. Whereas quantitative variables obtained from healthy cats, using 2-dimensional echocardiography (2DE), have been reported, indices from 2DE, have not. Using 2DE and M-mode echocardiography, we calculated indices of left atrial size and a single index of atrial function, left atrial fractional shortening, in 17 healthy cats. Specifically, left atrial dimensions from short- and long-axis 2DE planes were indexed to aortic diameter and also to end-diastolic left ventricular dimension. Additionally, left atrial circumference and area were indexed to aortic circumference and area, respectively. The same variables were obtained from 20 cats with hypertrophic cardiomyopathy (HCM), so that agreement between 2DE indices and indices from M-mode echocardiography could be evaluated over a clinically relevant range of atrial sizes. Atrial dimensions and indices of atrial size from cats with HCM exceeded those of healthy cats. Left atrial dimension from 2D short-axis images indexed to aortic diameter generally was less than the analogous index obtained from M-mode (mean bias, [95% limits of agreement] -0.13, [-0.42, 0.17]). Left atrial dimension from 2D long-axis images indexed to aortic diameter generally was greater than the index obtained from M-mode (0.15, [-0.28, 0.58]). We conclude that ratios of left atrial size and aortic diameter, from 2DE and M-mode echocardiography, are not interchangeable. Normative data that may serve as reference intervals for 2DE assessment of atrial size are presented.