Radiographic assessment of cardiac dimensions may reveal an altered anatomic structure secondary to eccentric cardiac enlargement.1 Radiography is fairly reliable for evaluation of generalized cardiomegaly or pericardial effusion and some types of chamber enlargement such as left atrial enlargement and, to a lesser extent, right atrial and ventricular enlargements. Radiographic assessment of the cardiac dimensions may be important for initial evaluation of heart disease and could be a reliable index of pathological changes associated with the heart.1,2 However, echocardiography remains the gold standard for anatomic evaluation of the internal cardiac structures when a cardiac abnormality is suspected on the basis of clinical or historical information or an altered radiographic appearance of the cardiac silhouette.3
Cardiac size has been previously evaluated mathematically on the basis of the dimensions of other structures on thoracic radiographic views. A simple quantitative technique of cardiac measurement—the VHS—has been widely used to evaluate the size of the cardiac silhouette with respect to the length of the corresponding midthoracic vertebrae starting at T4 in both dogs and cats.1,4 However, potential sources of VHS variation included interobserver differences in the selection of reference points and transformation of cSAL and cLAL into VHS units.5 Additionally, thoracic vertebral anomalies such as butterfly vertebrae and hemivertebrae in brachycephalic-breed dogs and thoracic intervertebral disk disease increase the incidence of erroneously high assessments of VHS.6 Short thoracic vertebrae in some breeds, such as Labrador Retriever, Boxer, Cocker Spaniel, Bulldog, and Boston Terrier, may also result in a higher VHS and subsequent false-positive radiographic diagnosis of cardiomegaly in these dog breeds.6–8
Other radiographic techniques have relied on determination of the cardiothoracic ratios derived from lateral thoracic radiographs obtained after peak inspiration and expiration.9 Additionally, other studies have used these same techniques on both lateral and ventrodorsal radiographs after peak inspiration and expiration.10,11 These techniques were reported to be complicated and not suitable for clinical practice1,12 because they require a specific software program and were not effective in dogs with certain cardiovascular or pulmonary abnormalities.1,11 In addition, the marked variation in thoracic cavity conformation among dog breeds makes cardiothoracic ratios of little value.1 Even in the same individual, standard ratios are unreliable for assessment of sequential changes in cardiac size.1 All previously reported techniques (determination of VHS or cardiothoracic ratios) relied on evaluation of the overall size of the cardiac silhouette without separate assessment of each cardiac axis (cSAL and cLAL) on lateral and ventrodorsal thoracic radiographs. Alternatively, the use of an MHS eliminates some of the problems associated with the VHS and cardiothoracic ratios in some dogs. The manubrium of the sternum was selected because it is a relatively prominent, regularly elongated, bullet-shaped or rectangular bone segment that is easily identified and can be readily measured on lateral thoracic radiographic views.
Therefore, the objective of the study reported here was to determine MHSs from measurements of cSAL and cLAL normalized by the ML on right lateral and ventrodorsal thoracic radiographic views of clinically normal dogs. The cSAL:cLAL ratio was also calculated from measurements obtained on both radiographic views. After 3 MHSs were calculated on the basis of the cSAL:ML ratio, cLAL:ML ratio, and cSAL-and-cLAL:ML ratio from both radiographic views, the correlation of each of those scores with the VHS (derived from the right lateral radiographic view) was assessed. Our first hypothesis was that ML would be an appropriate reference measurement with which to assess cardiac size in a study population of 120 healthy small- and large-breed dogs. Our second hypothesis was that the VHS would be correlated with each of the 3 MHSs determined for the same population of dogs.
CXDI-50G digital plate, Canon USA Inc, Lake Success, NY.
Merge PACs, Merge Healthcare Inc, Chicago, Ill.
Prism 6, GraphPad Software Inc, La Jolla, Calif.
Cardiac long-axis length
Cardiac short-axis length
Manubrium heart score
Vertebral heart score
1. Buchanan JW, Bücheler J. Vertebral scale system to measure canine heart size in radiographs. J Am Vet Med Assoc 1995; 206: 194–199.
2. Root CR, Bahr RJ. The heart and great vessels. In: Thrall DE, ed. Textbook of diagnostic veterinary radiology. 4th ed. Philadelphia: WB Saunders Co, 2002;402–419.
3. Lamb CR, Boswood A. Role of survey radiography in diagnosing canine cardiac disease. Compend Contin Educ Pract Vet 2002; 24: 316–326.
4. Litster AL, Buchanan JW. Vertebral scale system to measure heart size in radiographs of cats. J Am Vet Med Assoc 2000; 216: 210–214.
5. Hansson K, Haggstrom J, Kvart C, et al. Interobserver variability of vertebral heart size measurements in dogs with normal and enlarged hearts. Vet Radiol Ultrasound 2005; 46: 122–130.
6. Jepsen-Grant K, Pollard RE, Johnson LR. Vertebral heart scores in eight dog breeds. Vet Radiol Ultrasound 2013; 54: 3–8.
7. Lamb CR, Wikeley H, Boswood A, et al. Use of breed-specific ranges for vertebral heart scale in the radiographic diagnosis of cardiac disease in dogs. Vet Rec 2001; 148: 707–711.
8. Gugjoo MB, Hoque M, Saxena AC, et al. Vertebral scale system to measure heart size in dogs in thoracic radiographs. Adv Anim Vet Sci 2013; 1: 1–4.
10. Castro MG, Tôrres RCS, Araújo RB, et al. Radiographic evaluation of the cardiac silhouette in clinically normal Yorkshire Terrier dogs through the vertebral heart size method. Arq Bras Med Vet Zootec 2011; 63: 850–857.
11. Torad FA, Hassan EA. Two-dimensional cardiothoracic ratio for evaluation of cardiac size in German Shepherd Dogs. J Vet Cardiol 2014; 16: 237–244.
12. Spasojevic-Kosic L, Krstic N, Trailovic RD. Comparison of three methods of measuring vertebral heart size in German Shepherd Dogs. Acta Vet (Beogr) 2007; 57: 133–141.
13. Gulanber EG, Gonenci R, Kaya U, et al. Vertebral scale system to measure heart size in thoracic radiographs of Turkish Shepherd (Kangal) dogs. Turk J Vet Anim Sci 2005; 29: 723–726.
14. Srivastava M, Pandey RP, Srivastava A, et al. Vertebral heart scale score of mongrel dogs. Indian J Canine Pract 2014; 6: 5–8.
15. Saida Y, Tanaka R, Yamane Y, et al. Relationships between vertebral heart size (VHS) and echocardiographic parameters in dogs with mitral regurgitation. Adv Anim Cardiol 2006; 39: 55–63.
16. Olive J, Javard R, Specchi S, et al. Effect of cardiac and respiratory cycles on vertebral heart score measured on fluoroscopic images of healthy dogs. J Am Vet Med Assoc 2015; 246: 1091–1097.
17. Bavegems V, Van Caelenberg AV, Duchateau L, et al. Vertebral heart size ranges specific for Whippets. Vet Radiol Ultrasound 2005; 46: 400–403.
19. Greco A, Meomartino L, Raiano V, et al. Effect of left vs right recumbency on the vertebral heart score in normal dogs. Vet Radiol Ultrasound 2008; 49: 454–455.
20. Webster N, Adams V, Dennis R. The effect of manual lung inflation vs spontaneous inspiration on the cardiac silhouette in anesthetized dogs. Vet Radiol Ultrasound 2009; 50: 172–177.
21. Lamb CR, Tyler M, Boswood A, et al. Assessment of the value of the vertebral heart scale in the radiographic diagnosis of cardiac disease in dogs. Vet Rec 2000; 146: 687–690.
22. Woolley R, Smith P, Munro E, et al. Effects of treatment type on vertebral heart size in dogs with myxomatous mitral valve disease. Int J Appl Res Vet Med 2007; 5: 43–48.
23. Lord P, Hansson K, Kvart C, et al. Rate of change of heart size before congestive heart failure in dogs with mitral regurgitation. J Small Anim Pract 2010; 51: 210–218.
24. Gugjoo MB, Hoque M, Saxena AC, et al. Pericardial effusion in dogs: diagnostic features of radiography, electrocardiography and echocardiography. Int J Curr Res 2013; 5: 4233–4237.
25. Buchanan JW. Vertebral scale system to measure heart size in radiographs. Vet Clin North Am Small Anim Pract 2000; 30: 379–393.
26. Kayar A, Gonul R, Or ME, et al. M-mode echocardiographic parameters and indices in the normal German Shepherd Dog. Vet Radiol Ultrasound 2006; 47: 482–486.
27. Muzzi RA, Muzzi LA, de Arau'jo RB, et al. Echocardiographic indices in normal German Shepherd Dog. J Vet Sci 2006; 7: 193–198.
28. Marin LM, Brown J, McBrien C, et al. Vertebral heart size in retired racing Greyhounds. Vet Radiol Ultrasound 2007; 48: 332–334.