Vertebral Heart Size (VHS)
A Method for Measuring the Size of the Canine Heart in Lateral RadiographsDifferences in the thoracic confirmation of various dog breeds have made previous methods used for estimating cardiac enlargement of limited value. A study by Buchanan and Bücheler (JAVMA, volume 206,#2, January15,1995, pp.194-199) provides a radiographic method to:
- quantify overall heart size for a given patient
- determine if this patient's heart size is within the normal population distribution
- permit ongoing radiographic monitoring of changes in heart size.
The VHS method measures heart size in two dimensions on the lateral view of thoracic radiographs:
- The long axis is measured from the ventral border of the left mainstem bronchus (cranioventral border of the carina) to the cardiac apex (the most distal point on the ventral contour of the cardiac radiographic image).
- The short axis is measured at the widest point of the cardiac image on a line perpendicular to the long axis.
The two measurements are then compared to the vertebrae starting at the cranial edge of T4, and a result, expressed in units of vertebral lengths, is obtained for each axis. The sum of the measurements on both axes constitute the VHS.
The criterion established by the study is that the upper limit for most dogs is 10.5 vertebral lengths. ( Possible exceptions: 11 lengths being the high normal for a breed with a short thorax, such as the miniature schnauzer, and 9.5 for a breed with a long thorax, such as the dachshund. The lower normal limit is 8.5 vertebral lengths.
In addition to a initial measurement of heart size, the VHS method is useful for periodic monitoring of heart size with the progression of heart disease, as well as in the response of a patient to therapy.