Vertebral heart size and vertebral left atrial size reference ranges in healthy Miniature Schnauzers

Lisa Murphy DVM, DACVECC , Nicole Piscitelli DVM, DACVIM, Jessica Solomon MS, DVM, DACVIM, Donald Szlosek MPH, and Reid K Nakamura DVM, DACVECC, DACVIM

Background

The study aimed to establish reference ranges for vertebral heart size (VHS) and vertebral left atrial size (VLAS) in healthy Miniature Schnauzers, hypothesizing that Miniature Schnauzers would exhibit a higher VHS reference range compared to general canine references. This arises from the clinical use of VHS and VLAS in radiographic evaluations to screen for occult cardiac diseases in dogs, noting that interbreed variations in VHS reference ranges have been documented.

Methods

The study analyzed electronic medical records from IDEXX Telemedicine Consultants for Miniature Schnauzers that underwent thoracic radiographs between March 1, 2022, and February 28, 2023. Dogs with three-view thoracic radiographs showing no evidence of cardiopulmonary disease were included. Two board-certified cardiologists independently measured the VHS and VLAS from these radiographs.

Results

Out of 1000 radiographs, 272 met the inclusion criteria. The VHS ranged from 9.68 to 12.07 with a median of 10.9, while VLAS ranged from 1.71 to 2.4 with a median of 2.0. These findings confirmed that Miniature Schnauzers without cardiac disease have a VHS above the general canine reference range.

Limitations

The study acknowledged limitations such as reliance on telemedicine data, potentially incomplete demographic data, and variable radiograph quality. It also did not account for body condition or heartworm status, which could influence VHS measurements. The retrospective nature limited control over radiographic techniques and quality.

Conclusions

Miniature Schnauzers exhibit a higher VHS reference range compared to the standard canine reference, underscoring the importance of breed-specific reference ranges for accurate diagnosis of cardiomegaly. This study supports the notion that applying a universal VHS reference range across all dog breeds could lead to misdiagnosis, advocating for further research on breed-specific cardiac measurements.

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