Monoplane Simpson’s Method Is Reliable for Left Atrial Volume Assessment in Small Dogs with Myxomatous Mitral Valve Disease

Left atrial enlargement is a key marker of disease progression and prognosis in dogs with myxomatous mitral valve disease. Echocardiographic assessment of left atrial volume provides a more comprehensive measure than linear dimensions, yet different two-dimensional methods may yield variable results. This study aimed to compare the monoplane Simpson’s method of discs and the biplane area–length method for estimating left atrial volume indexed to body weight in dogs across different stages of disease. Dogs were prospectively evaluated with transthoracic echocardiography, and left atrial volumes were calculated using both techniques. Both indices clearly distinguished dogs with enlarged atria from controls and stage B1 patients. However, the two methods were not interchangeable, regardless of atrial size, as demonstrated by the Bland–Altman analysis. In conclusion, both techniques are clinically useful for assessing left atrial remodeling, but because they are not interchangeable, clinicians should consistently use one method. The monoplane Simpson’s method may be particularly practical for routine clinical application due to its convenience.