Abstract
Objective
To evaluate vertebral heart score (VHS) and vertebral left atrial reference intervals in Miniature Australian Shepherds, American Eskimos, Tibetan Terriers, and Border Terriers.
Methods
The electronic medical records of IDEXX Telemedicine Consultants were searched for Miniature Australian Shepherds, American Eskimos, Tibetan Terriers, and Border Terriers undergoing radiography from January 1, 2022, through December 31, 2023. The same board-certified cardiologist performed the VHS and vertebral left atrial size (VLAS) measurements in all dogs.
Results
During the study period, a total of 1,052 Miniature Australian Shepherds, 685 American Eskimos, 583 Tibetan Terriers, and 504 Border Terriers were identified. Of these, 844 Miniature Australian Shepherds, 495 American Eskimos, 453 Tibetan Terriers, and 360 Border Terriers were excluded, leaving 208 Miniature Australian Shepherds, 190 American Eskimos, 130 Tibetan Terriers, and 144 Border Terriers available for analysis. The reference interval for Miniature Australian Shepherds was 9.4v to 11.5v for VHS and 1.7v to 2.5v for VLAS. The reference interval for American Eskimos was 9.5v to 11.5v for VHS and 1.7v to 2.4v for VLAS. The reference interval for Tibetan Terriers was 9.2v to 11.4v for VHS and 1.7v to 2.3v for VLAS. The reference interval for Border Terriers was 9.3v to 11.6v for VHS and 1.7v to 2.3v for VLAS.
Conclusions
Miniature Australian Shepherds, American Eskimo Dogs, Tibetan Terriers, and Border Terriers have breed-specific VHS and VLAS reference intervals.
Clinical Relevance
Clinicians should be aware of these results to accurately diagnose cardiac disease in these breeds.
Screening dogs for occult cardiac disease can be difficult as pet owners may lack access to veterinary specialty care due to geographical and financial constraints. Thoracic radiography is a more accessible diagnostic test compared to echocardiography and can serve as an alternative screening tool for cardiac disease compared to an echocardiogram. The vertebral heart size (VHS) was developed as a means to objectively evaluate cardiac size in a simple and reproducible fashion on thoracic radiography.1 The initial report1 suggested that 98% of dogs had a VHS < 10.5v. Soon after, studies2–12 reported different canine breeds without structural cardiac disease whose VHS exceeded this 10.5v threshold. Consequently, several breeds have been reported to have breed-specific VHS reference intervals.2–12 The investigators’ hypothesis is that Miniature Australian Shepherds, American Eskimos, Tibetan Terriers, and Border Terriers have breed-specific VHS reference intervals.
Methods
The electronic medical record system of IDEXX Telemedicine Consultants was searched for Miniature Australian Shepherds, American Eskimos, Tibetan Terriers, and Border Terriers undergoing thoracic radiography from January 1, 2022, through December 31, 2023. This range was later expanded to January 1, 2022, through June 30, 2024, to improve case numbers for Tibetan Terriers only. The radiographs had been previously submitted to IDEXX Telemedicine Consultants for telemedicine review. If a patient presented multiple times during the study period, only the first examination was considered for inclusion in the study. Dogs were included if they had 2-view or 3-view thoracic radiographs performed (at least a right lateral thoracic radiograph and 1 ventrodorsal or dorsoventral view) and no evidence of cardiopulmonary or systemic disease detected. All dogs with incomplete radiographic studies and/or known extracardiac disease were excluded. Radiographic studies with poor positioning that limited the accuracy of VHS and vertebral left atrial size (VLAS) measurements were also excluded. All dogs included in the study must have had a normal cardiac auscultation as noted by the original veterinarian performing the physical examination that was documented in the telemedicine consultation form. All dogs with a reported heart murmur were excluded. If a dog had no reported heart murmur but had subjective cardiomegaly reported by the initial IDEXX radiologist or cardiologist, was receiving a cardiac medication that could affect cardiac size (ie, pimobendan or diuretics), had a history of receiving a grain-free diet, or had a history of an elevated N-terminal probrain natriuretic peptide, they were termed “suspected cardiac disease” and also excluded.
Data collected from the patient record and radiographs included age, weight, sex, VHS, and VLAS. The VHS and VLAS measurements were performed by the same board-certified cardiologist in all breeds. As the radiographs were all in a digital format, measurements were performed using a digital caliper, and measurements were performed on the right lateral radiograph. The measurement of VHS was performed using the technique initially described by Buchanan and Bücheler,1 where the long axis of the heart was measured from the center of the carina to the most distal contour of the ventral apex of the heart. The carina was defined as the radiolucent circular structure within the trachea, which represents the bifurcation of the left and right mainstem bronchi. The short axis of the heart was measured in the central third region of the heart, perpendicular to the long axis. Both axis measurements were then positioned over the thoracic vertebral bodies beginning at the cranial edge of the fourth thoracic vertebra. The sum of both axes was used to determine the number of vertebral units to the nearest 0.1 vertebra. All measurements were performed on the right lateral thoracic radiograph in all cases to maintain consistency (Supplementary Figure S1).
For the VLAS measurement, a line was drawn from the center of the ventral aspect of the carina to the caudal aspect of the left atrium where it intersected with the dorsal border of the caudal vena cava. The measurement was then positioned over the fourth thoracic vertebra as before, and the total vertebral units were used to calculate the VLAS (Supplementary Figure S2).13
Statistical analysis
Continuous variables were described using median values and the IQR, whereas categorical variables were presented in terms of proportions. Methodologic adherence to the Clinical and Laboratory Standards Institute’s EP28-A3 guidelines was maintained by employing a 95% nonparametric bootstrap method with a 90% CI for calculations. All statistical analyses were conducted using R software, version 4.3.4 (R Foundation for Statistical Computing; https://www.R-project.org/).
Results
During the study period, a total of 2,824 dogs across the 4 breeds were screened, with 2,152 included in the final analysis population (see the case log files in Supplementary Tables S1–S4). Reasons for exclusion by breed are detailed in Supplementary Table S5. A complete breakdown of the number of dogs per breed and their demographic characteristics is provided in Table 1. Median VHS, VLAS, and reference intervals for all breeds are shown in Figures 1 and 2, Table 2, and Supplementary Table S6.
Demographic characteristics in Miniature Australian Shepherds, American Eskimos, Tibetan Terriers, and Border Terriers.
| Miniature Australian Shepherds | American Eskimos | Border Terriers | Tibetan Terriers | |
|---|---|---|---|---|
| Characteristic | N = 208 | N = 190 | N = 144 | N = 130 |
| Sex | ||||
| Female | 30 (15%) | 24 (13%) | 19 (13%) | 10 (8.1%) |
| Female spayed | 67 (34%) | 66 (36%) | 56 (39%) | 43 (35%) |
| Male | 33 (17%) | 17 (9.2%) | 19 (13%) | 17 (14%) |
| Male castrated | 70 (35%) | 78 (42%) | 48 (34%) | 54 (44%) |
| Unknown | 8 | 5 | 2 | 6 |
| Age (y) | 5.1 (2.0–10.0). Min, 0.1; max, 16.0 | 10.3 (5.9–13.0). Min, 0.2; max, 16.0 | 10.2 (6.8–13.0). Min, 0.2; max, 18.2 | 10.9 (7.8–13.2). Min, 0.1; max, 18.7 |
| Unknown | 6 | 0 | 2 | 0 |
| Weight (kg) | 11.0 (7.3–14.1). Min, 0.9; max, 18.1 | 10.0 (7.7–14.0). Min, 0.5; max, 23.0 | 9.0 (7.3–10.9). Min, 2.0; max, 18.1 | 12.0 (10.0–14.5). Min, 2.7; max, 20.4 |
| Unknown | 0 | 28 | 9 | 9 |
| VHS (vertebrae) | 10.6 (10.1–11.0). Min, 9.0; max, 12.3 | 10.3 (10.0–10.8). Min, 9.3; max, 11.7 | 10.9 (10.5–11.1). Min, 8.9; max, 12.0 | 10.4 (10.0–10.8). Min, 9.0; max, 11.8 |
| VLAS (vertebrae) | 2.0 (1.9–2.1). Min, 1.6; max, 2.6 | 2.1 (1.9–2.2). Min, 1.6; max, 2.6 | 2.0 (1.9–2.1). Min, 1.5; max, 2.6 | 2.1 (2.0–2.2). Min, 1.6; max, 2.6 |
Categorical variables are reported as frequency and percentage, and continuous variables are reported as median and IQR.
N (%); Median (Q1, Q3), Min, min, Max, max. N = number of subjects (%). Q1 is 25th percent quartile and Q3 is 75th percent quartile.
Max = Maximum. Min = Minimum. VHS = Vertebral heart score. VLAS = Vertebral left atrial size.
Vertebral heart score (VHS) histogram for all 4 breeds. Solid lines represent the upper and lower reference limits, and the area between those lines represents the reference interval. The dashed lines represent the CI for those reference limits.
Citation: American Journal of Veterinary Research 2025; 10.2460/ajvr.25.02.0058
Vertebral left atrial size (VLAS) histogram for all 4 breeds. Solid lines represent the upper and lower reference limits, and the area between those lines represents the reference interval. The dashed lines represent the CI for those reference limits.
Citation: American Journal of Veterinary Research 2025; 10.2460/ajvr.25.02.0058
Reference intervals for VHS and VLAS in Miniature Australian Shepherds, American Eskimos, Tibetan Terriers, and Border Terriers.
| Lower reference limit | Upper reference limit | |||
|---|---|---|---|---|
| Estimate | 95% CI | Estimate | 95% CI | |
| VHS (vertebrae) | ||||
| Miniature Australian Shepherds | 9.4 | 9.3–9.5 | 11.5 | 11.4–11.8 |
| American Eskimos | 9.5 | 9.4–9.5 | 11.5 | 11.2–11.6 |
| Tibetan Terriers | 9.2 | 9.1–9.3 | 11.4 | 11.2–11.6 |
| Border Terriers | 9.3 | 9.0–9.7 | 11.6 | 11.3–12.0 |
| VLAS (vertebrae) | ||||
| Miniature Australian Shepherds | 1.7 | 1.7–1.8 | 2.5 | 2.3–2.5 |
| American Eskimos | 1.7 | 1.7–1.7 | 2.4 | 2.4–2.4 |
| Tibetan Terriers | 1.7 | 1.7–1.8 | 2.3 | 2.3–2.5 |
| Border Terriers | 1.7 | 1.5–1.8 | 2.3 | 2.3–2.4 |
For all 4 breeds, the lower 95% confidence bound of their upper reference limit was above the general canine VHS reference interval of 10.5v, suggesting that there is a large difference in the proportion of dogs that would be classified as having abnormal VHS scores. To dogs that would be misclassified as being abnormal, the frequency of dogs with VHS values between 10.5v and VHS values less than or equal to the 95% lower bound of their upper reference interval were calculated: Miniature Australian Shepherds (n = 111 [53.4%]), American Eskimos (n = 74 [38.9%]), Tibetan Terriers (n = 53 [40.7%]), and Border Terriers (n = 104 [72.2%])
Discussion
As hypothesized, Miniature Australian Shepherds, American Eskimos, Tibetan Terriers, and Border Terriers have breed-specific VHS and VLAS reference intervals that exceed the parameters initially published.1 The results of this study suggest that these breeds have higher upper reference values than the accepted normal VHS1 and VLAS14 range. The underlying cause of these findings is unclear. Studies15 have found that some breeds, such as English Springer Spaniels, have larger, rounder ventricles, whereas Whippets, Greyhounds, and Italian Greyhounds have thicker left ventricular walls compared to other breeds of comparable size.16 Alternatively, vertebral body size relative to body size is not standardized across dog breeds as a study17 found that Miniature Schnauzers have shorter lumbar vertebrae compared to other breeds. Further studies to determine if Miniature Australian Shepherds, American Eskimos, Tibetan Terriers, or Border Terriers possess variations in echocardiographic morphology or vertebral body size compared to other breeds appears warranted.
In this study, the right lateral radiograph was used to measure the VHS and VLAS values, and if there was no right lateral radiograph provided, the radiographic study was excluded from analysis. A study18 in Dachshunds reported significant differences in VHS values when measured from a right or left lateral radiograph. However, a study19 in Welsh Pembroke Corgis found no difference in VHS values when measured on the right or left lateral thoracic radiograph. Therefore, it is unclear if the VHS and VLAS reference intervals reported here are interchangeable between the right and left lateral thoracic radiograph. To be safe, the investigators advise only using the right lateral projection for the evaluation of VHS and VLAS values for the 4 breeds reported here. Comparing VHS and VLAS reference intervals between left and right projections in different breeds may require further evaluation.
The minimum study population size for each breed was based on the current consensus statement from the American Society of Veterinary Clinical Pathologists, which recommends more than 120 subjects be utilized to derive reference intervals.13 Initially, the investigators did not have enough Tibetan Terriers to meet these criteria, which is why the data collection period had to be expanded for this breed only. Interestingly, most of the previously reported breed-specific VHS reference intervals are derived from exceedingly small populations that do not meet the 120-subject recommendation. As such, further studies reevaluating larger populations of dogs for each previously reported breed-specific reference interval may be warranted.
As stated previously, dogs with a heart murmur were excluded to exclude dogs with structural cardiac disease. In addition, dogs with subjective cardiomegaly reported by the initial IDEXX radiologist or cardiologist were also excluded in an attempt to rule out dogs with potential occult cardiac disease. It would have been ideal for all dogs included to have an echocardiogram at the time of radiography for inclusion in the study, but this was unfortunately not performed. A previous study20 reported that less than 5% of stage B2 dogs with myxomatous mitral valve had soft murmurs (defined as grade 1 or 2 heart murmurs). As such, it is possible that a small population of dogs with stage B2 myxomatous mitral valve disease were inadvertently included in this study population, which may have affected the results reported here.
This study has several additional limitations. There was a large amount of data from telemedicine consultations, and in some cases the demographic data were incomplete (ie, age, weight, and/or sex). The study included cases throughout the country, and therefore radiographic technique and positioning were not standardized. Some studies9 have shown that higher body conditions were associated with higher VHS scores in some breeds, but body condition score was not reported and was therefore not evaluated here. The dogs included did not have a reported heart murmur or significant systemic disease, but the detection of underlying cardiac disease or systemic disease is dependent on the clinical proficiency of submitting veterinarians. The authors are unable to control for the phase of respiration, which may have a mild effect on the accuracy of VHS measurements.21 The heartworm status was not known for all dogs, and heartworm disease causes VHS to increase in affected patients.22 However, to minimize this effect, all dogs that were reported to be heartworm positive were also excluded from analysis. Other diseases that can affect VHS measurement, such as pericardial effusion,23 cannot be completely ruled out in the absence of an echocardiography for all cases. Dogs that were reported to receive grain-free diets were excluded given the association with dilated cardiomyopathy.24 However, diet was also not universally reported in all cases, and therefore it is possible that a small population of dogs receiving a grain-free diet was inadvertently included in the study population as well. Finally, it also would have been ideal to compare between cardiologists to look for evidence of inter observer variability, but that was not performed here.
In conclusion, the authors reported the reference intervals for VHS and VLAS in Miniature Australian Shepherds, American Eskimos, Tibetan Terriers, and Border Terriers. Clinicians should be aware of these results to avoid erroneously diagnosing cardiomegaly in these breeds. Continued investigation into breed-specific VHS measurements in other canine breeds appears warranted.
Supplementary Materials
Supplementary materials are posted online at the journal website: avmajournals.avma.org.
Acknowledgments
None reported.
Disclosures
The authors have nothing to disclose. No AI-assisted technologies were used in the composition of this manuscript.
Funding
The authors have nothing to disclose.
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