Vertebral scale system to measure heart size in radiographs of cats.

OBJECTIVE

To determine absolute and relative heart size in clinically normal cats by correlating heart size and selected skeletal structures.

DESIGN

Prospective radiographic study.

ANIMALS

100 cats that did not have thoracic radiographic abnormalities.

PROCEDURE

Standardized measurements of the long and short axes of the heart, midthoracic vertebrae, and other structures were made. Measurements were recorded in millimeters and number of thoracic vertebral lengths spanned by each dimension, measured caudally from T4 in a lateral radiograph. The long- and short-axis measurements of the heart, expressed in vertebral lengths, were added to yield vertebral heart size.

RESULTS

Mean +/- SD vertebral heart size in lateral radiographs was 7.5 +/- 0.3 vertebrae. The long-axis dimension correlated with the length of 3 sternebrae, measured from S2 to S4. The cardiac short-axis dimension correlated moderately with the length of 3.2 vertebrae, measured from T4 to T6. The cardiac short-axis dimension in ventrodorsal radiographs was 3.4 +/- 0.25 vertebrae.

CONCLUSIONS AND CLINICAL RELEVANCE

The vertebral heart-size method is easy to use, allows objective assessment of heart size, and may be helpful in determining cardiomegaly and comparing heart size in sequential radiographs.