# A Novel Echocardiographic Index (Modified-Left-Atrium-to-Aorta Ratio) for Quantifying Left Atrial Size and Differentiating Stages in Dogs with Myxomatous Mitral Valve Disease

## TL;DR

This study introduces a new echocardiographic index to better measure left atrium size in dogs with heart disease, potentially improving early detection.

## Contribution

A novel echocardiographic index combining two views to more accurately assess left atrial size in dogs with myxomatous mitral valve disease.

## Key findings

- The modified-LA/Ao ratio showed strong correlation with traditional methods and improved discrimination between early disease stages.
- The new index had acceptable intra- and interobserver variability, making it practical for clinical use.
- It may help detect subtle cardiac changes in early-stage myxomatous mitral valve disease in dogs.

## Abstract

Myxomatous mitral valve disease is the most common heart disease in small dogs. In this disease, the left atrium becomes enlarged as the disease gets worse. Veterinarians commonly use two-dimensional echocardiography to measure this enlargement, but the traditional method relies on a single angle and might miss some changes in size due to the left atrium’s asymmetrical anatomical shape. In this study, a new index (modified-LA/Ao ratio) is developed to measure the left atrium size that combines two different views of the heart. (Modified-LA/Ao ratio = (LA diameter from right parasternal long-axis four-chamber view + LA diameter from right parasternal short-axis view)/Ao diameter)). This study reviewed a total of 136 dogs including both control dogs and myxomatous mitral valve disease dogs and found that our new index showed comparable performance to the traditional method and may be particularly helpful in detecting mild left atrium enlargement in early disease stages. This may help veterinarians detect changes earlier and make better treatment decisions. Our new index is simple to use and may be a helpful tool for monitoring heart disease in dogs.

Myxomatous mitral valve disease (MMVD) is the most common heart disease in small-breed dogs, and accurate assessment of the left atrial (LA) size is essential for diagnosis and management. The traditional echocardiographic method, LA-to-Aorta (LA/Ao) ratio, is widely used, but evaluates LA size in only one view. This study introduces a novel index—the modified-LA/Ao (M-LA/Ao) ratio—which combines two echocardiographic views to better reflect the true LA size. This study retrospectively analyzed thoracic radiographs and echocardiograms from 136 dogs, including healthy controls and dogs with MMVD classified into stages B1, B2, and C according to ACVIM guidelines. The ability of the M-LA/Ao ratio is compared to conventional indices using correlation analysis and receiver operating characteristic (ROC) curves. The M-LA/Ao ratio showed a strong correlation with existing indices and slightly improved discrimination between ACVIM stages B1 and B2, although performance between stages B2 and C was similar to the LA/Ao ratio. Intra- and interobserver variability were also acceptable. Our findings suggest that the M-LA/Ao ratio may provide a practical and sensitive method to evaluate LA enlargement in early-stage MMVD, helping clinicians detect subtle cardiac remodeling before progression to advanced disease.