Changes in linear dimensions of the heart, relative to body weight, as measured by M-mode echocardiography in growing dogs.

The growth of the heart, relative to body weight, was measured by M-mode echocardiography in dogs during the first year of life. Echocardiographic measurements were obtained from 16 English Pointers at 1, 2, 4, and 8 weeks of age and at 3, 6, 9, and 12 months of age. Left atrial (LA), aortic (AO), left and right ventricular internal dimensions, interventricular septal and left ventricular wall thickness measurements increased in curvilinear fashion relative to increasing body weight. Least-squares regression analysis, performed on logarithmically transformed data, was used to develop power-law equations describing the relationship of echocardiographic measurements to body weight. Linear dimensions of the LA, AO, left and right ventricular internal dimensions and interventricular septal and left ventricular wall thickness changed proportionally to slightly differing exponential powers of body weight (BW), varying from 0.31 to 0.45 (BW0.31 to BW0.45). Fractional shortening and the LA to AO ratio decreased slightly, but significantly, as body weight increased. Indexing echocardiographic measurements to BW1/3 was more appropriate than indexing such measures linearly to body weight, offering a practical method for developing accurate normative graphs or tables for M-mode echocardiographic dimensions in growing dogs.