Cardiac Size Assessment in Veterinary Radiology

Radiographic evaluation of cardiac size in veterinary practice has become a standard tool for diagnosis and management of a range of cardiac pathologies across diverse companion animal species. The size and shape of the cardiac silhouette on thoracic radiographs provide crucial insights into structural changes such as chamber enlargement, cardiomegaly and left atrial dilation, often serving as the primary assessment when echocardiography is unavailable. Conventional approaches translate linear dimensions of the heart’s long and short axes into vertebral units, compensating for variations in patient size. Breed-specific reference ranges and standardised indices have been established to improve diagnostic accuracy, while evolving digital imaging and machine learning techniques are expanding the potential for automated and more precise measurements. The interplay of anatomical conformation, recumbency, and observer variability remains a key consideration, and the field continues to refine methods that balance reproducibility, sensitivity and practicability in everyday clinical settings.

Research from Nature Portfolio

Recent advances have harnessed deep learning to augment traditional radiographic metrics. A regressive vision transformer model was trained on large-scale canine heart X-ray datasets to bridge the clinically used vertebral heart score with automated cardiac size predictions, achieving state-of-the-art accuracy in cardiomegaly classification and offering improved generalisation to limited labelled data. Complementing this, another study introduced an adjusted heart volume index derived from segmented heart and vertebral regions, combining the heart silhouette area and height normalised to the fourth thoracic vertebra length. This automated index outperformed conventional standards in detecting cardiac enlargement, demonstrating the value of integrating semantic segmentation and novel computational indices into routine radiographic workflows.

Cardiac Size Assessment in Veterinary Radiology publication trend

The graph below shows the total number of articles in cardiac size assessment in veterinary radiology across all publications each year (not limited to Nature Index journals).

Technical terms

Vertebral Heart Score (VHS): Sum of the long and short cardiac axes measured against vertebral body lengths on lateral thoracic radiographs to assess heart size relative to patient size.

Vertebral Left Atrial Size (VLAS): Linear measurement of the left atrial dimension on lateral radiographs referenced to vertebral bodies for quantifying atrial enlargement.

Radiographic Left Atrial Dimension (RLAD): Distance from the intersection of the cardiac axes to the dorsal border of the left atrium, expressed in vertebral units, to detect left atrial enlargement.

Adjusted Heart Volume Index (aHVI): Automated index combining segmented heart area and height normalised to the fourth thoracic vertebra length to quantify cardiac enlargement.

Thoracic Inlet Heart Size (TIHS): Index calculated by summing cardiac long and short axes and dividing by the thoracic inlet length, providing a size-normalised assessment of heart silhouette.

References

1. Regressive vision transformer for dog cardiomegaly assessment. Scientific Reports (2024).
2. A radiographic measurement of left atrial size in dogs. Irish Veterinary Journal (2018).
3. Heart to spine measurements to detect left atrial enlargement in dogs with mitral insufficiency. Irish Veterinary Journal (2019).
4. Breed-specific values for vertebral heart score (VHS), vertebral left atrial size (VLAS), and radiographic left atrial dimension (RLAD) in pugs without cardiac disease, and their relationship to Brachycephalic Obstructive Airway Syndrome (BOAS). PLOS ONE (2022).
5. Methods of Radiographic Measurements of Heart and Left Atrial Size in Dogs with and without Myxomatous Mitral Valve Disease: Intra- and Interobserver Agreement and Practicability of Different Methods. Animals (2022).
6. An automated deep learning method and novel cardiac index to detect canine cardiomegaly from simple radiography. Scientific Reports (2022).
7. The Thoracic Inlet Heart Size, a New Approach to Radiographic Cardiac Measurement. Animals (2023).