Vertebral Heart Size (VHS) is a number that normalizes (indexes) heart size to body size using mid-thoracic vertebrae as units of measure (Figure 1). Various authors also have called VHS an acronym for vertebral heart score, vertebral heart sum or the vertebral heart system. VHS was introduced at the ACVIM annual forum i

n 1991 (1) and a formal article was published in 1995 (2). Since then, it has become the standard indicator of radiographic heart size in dogs (3-20) cats (21-23) and several other species (24-28). VHS values have been reported in hundreds of articles and textbooks worldwide to indicate the presence or absence of cardiomegaly and to describe progressive change in heart size.

1. Method for lateral radiographs in dogs
2. Method for DV and VD radiographs
3. Lateral results
4. DV/VD results
5. VHS in Cats
6. Growth
7. Cardiac enlargement
8. VHS -vs -standard cardiothoracic ratios
9. References

1. Method For Lateral Radiographs

Figure 1

Diagram of lateral view of the thorax of a dog illustrating the vertebral heart size measurement method. The long axis (L) and short axis (S) heart dimensions are transposed onto the vertebral column and recorded as the number of vertebrae beginning with the cranial edge of T4. These values are estimated to one decimal place and added to obtain the vertebral heart size (T = trachea).

Angiocardiography shows that the maximal short axis dimension in the middle third of the heart includes the right atrium and left heart chambers (Figure 2A). The long axis measurement between the tracheal carina and the cardiac apex includes the left atrium and left ventricle (Figure 2B). The measurements can be made with calipers or a ruler and transposed to the vertebral column. Alternatively, a sheet of paper can be placed over the heart with one corner of the paper at the carina. Mark the paper at the apex to record the long axis and then reposition the paper perpendicularly. Place the same paper corner at the cranial border of the heart where the diameter is greatest and mark the caudal border to record the short axis. Place the paper corner at the cranial edge of T4 and record the long and short axes as the number of vertebrae between the corner and the marked axes. The sum of these values is the VHS.

Figure 2A Lateral angiocardiograms of a normal 6-year-old Collie. In the dextrophase notice that the short axis dimension (S) includes left and right heart chambers in the region of the coronary groove. Right auricle (RA). Right ventricle (RV).

Figure 2B Lateral angiocardiograms of a normal 6-year-old Collie. In the levophase notice that the long axis measurement (L) from the carina to the cardiac apex includes the left atrium (LA) and the left ventricle (LV).

In dogs with marked left atrial enlargement and elevation of the left bronchus, the long axis measurement is made from the cardiac apex to the ventral border of the elevated bronchus to incorporate left atrial enlargement (Figure 3). The perpendicular short axis measurement is made at the dorsal border of the caudal vena cava.

Figure 3

Lateral radiograph of a dog with severe mitral regurgitation and marked cardiomegaly (VHS 14.1). The long axis is measured from the cardiac apex to the elevated left bronchus in order to include left atrial enlargement which would not be accounted for using the tracheal carina end point.

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2. Method for DV or VD Radiographs

The long axis dimension in DV or VD radiographs includes the right atrium and left ventricle (Figure 4). The maximal short axis is measured perpendicular to the long axis and includes right and left heart structures. It is recorded as the number of vertebrae in an accompanying lateral radiograph.

Figure 4

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3. Lateral Results

The average VHS in lateral radiographs of 100 normal dogs was 9.7 vertebrae (v) +/- 0.5v SD. The values ranged from 8.2 to 10.6v and were normally distributed (Figure 5) Some people regard values outside 2 standard deviations as abnormal but it should be realized that +/-2 SD only includes 95% of a normal population. Since +/-2.5 SD includes about 98% of a normal population a "clinical range" of normal VHS would have values of 8.5-11v (Figure 6).

Figure 5 Distribution of vertebral heart sizes in 100 dogs with no evidence of heart disease.

Figure 6 Theoretical bell shaped curve of normally distributed data applied to vertebral heart size. Single standard deviation limits (9.2-10.2v) include only 68% of a population. Two SDs (8.7-10.7v) include 95% of a population. Three SDs (8.2-11.2v) include 99% of the animals. An easy to remember normal "clinical range" is 8.5-11v.

VHS values in lateral radiographs of deep or broad chested dogs are not substantially different (Figure 7). This is in contrast to previously reported intercostal space guidelines of 2.5 or 3.5 ICS for normal sized hearts in deep or broad chested dogs respectively (8). Chest (thoracic cavity) depth is measured in lateral radiographs from the dorsocranial edge of the xyphoid process to the ventral border of the vertebral column along a line perpendicular to the vertebral column (Figure 8A). Chest width is measured in DV or VD radiographs as the distance between the medial borders of the eighth ribs at their most lateral curvatures (Figure 8B). Deep chested dogs have chest depth:width ratios ­equal to or greater than 1.25. Broad chested dogs have chest depth < 0.75 x width (Figure 9).

Figure 7

Correlation between the sum of long- and short-axis heart dimensions and a 10 vertebrae reference length in 100 normal dogs of various body types. Broad chested, small dogs are indicated by open squares. Deep-chested, large dogs are indicated by diamond-shaped symbols. The straight line is the line of identity between the metric sum of long and short axes and a 10 vertebrae reference length (obtained by doubling the 5 vertebrae measurement of T4-T8.)

Figure 8A Lateral radiographs showing measurement points to determine chest depth and width. Depth is the distance from the xyphoid process to the vertebral column. Width is the maximum interpleural distance between the 8th ribs.	Figure 8B Dorsoventral radiographs showing measurement points to determine chest depth and width. Depth is the distance from the xyphoid process to the vertebral column. Width is the maximum interpleural distance between the 8th ribs.
Figure 9A Lateral photographs of deep and broad chested dogs which had essentially the same chest width (discounting hair)	Figure 9B Dorsoventral photographs of deep and broad chested dogs which had essentially the same chest width (discounting hair)

Subsequent studies have shown breed differences (Table). Labrador retrievers, spaniels, and Boxers have average values of 10.8v to 11.6v because they have slightly shorter vertebrae (7). Whippets from racing pedigree lines have larger VHS than Whippets from show pedigree lines presumably due to selective breeding for performance (14). Several authors found significant differences between right and left lateral VHS and report 1-3% larger values in right lateral positioning (10,14,18,19).

Table. Breed specific VHS values in dogs (1995-2009)

* lateral recumbency
- not reported

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4. DV and VD Results

Comparison of dorsoventral (DV) and ventrodorsal (VD) views in 17 dogs revealed that VD heart sizes were 7% wider and 5% longer than in DV projection (2). There was poor correlation between DV/VD and lateral heart sizes. Deep chested dogs generally appear to have small hearts in DV/VD projection because the long axes of their hearts are relatively vertical (Figure 10). Thus, determination of VHS in DV or VD projection in dogs has little value.

Figure 10. Lateral radiograph (A) of a deep chested Irish Setter with a relatively vertical heart that minimizes heart size in dorsoventral (B) or ventrodorsal (C) projection.

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5. VHS In Cats

Feline hearts generally lie more parallel to the sternum than in dogs and the tracheal carina often does not indicate the dorsal border of the left atrium. Consequently, long axis measurements are made from the cardiac apex to the ventral border of the left apical vein just below the carina (Figures 11 and 12).

Figure 11 Diagram of lateral view of the thorax of a cat illustrating the vertebral heart size measurement method. The long axis (L) and short axis (S) heart dimensions are transposed onto the vertebral column and recorded as the number of vertebrae beginning with the cranial edge of T4. These values are estimated to one decimal place and added to obtain the vertebral heart size (T = trachea).

Figure 12 Distribution of vertebral heart sizes in lateral radiographs of 100 cats with no heart disease.

DV or VD radiographs in cats are more reliable than in dogs because of the more frontal plane orientation of the heart. VD positioning is preferred to avoid sternal compression. The VD short-axis dimension is scaled using vertebrae (v) in accompanying lateral radiographs beginning with the cranial border of T4. The short axis dimension in 93 cats was distributed in a normal fashion (Figure 13) and is the first dimension that is changed (increased) with most heart diseases in cats (Figure 14).

Figure 13 Distribution of cardiac short-axis dimensions in VD radiographs of 93 cats with no heart disease. The VD short-axis dimension is scaled in vertebrae (v) in accompanying lateral radiographs, beginning with the cranial border of T4.
Figure 14. Ventrodorsal radiographs of a 13 month-old cat before (A) and 2 years later after developing hypertrophic cardiomyopathy (B). An increased short axis due to left atrial enlargement is the initial sign of cardiac enlargement in most cats with heart disease.

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6. Growth

Radiographs of puppies had norrnal VHS and no significant change from 3 months to 3 years of age (Figures 15 and 16) (4). However, radiographs in 3 month-old kittens had VHS values mildly above the normal feline range at 3 months and 6 months but decreased to the normal range by 9 months of age (22).

Click on the image to see a larger view

Figure 15. Puppies from age 3 months to 3 years old showed no significant change in relative heart size.

Figure 16 VHS measurements from puppies age 3 months to 3 years old showed no significant change in relative heart size.

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7. Cardiac Enlargement

Varying degrees of cardiac enlargement occur in clinical cases and written reports require narrative descriptions for clients and referring veterinarians in addition to the VHS. Mild, moderate, marked, and extreme cardiac enlargement are indicated by VHS ranges of 11 to 14+ in dogs and 8-10+ in cats (Figure 17). In most cats with heart disease, an increased short axis dimension in VD radiographs is the earliest form of cardiac enlargement and is primarily due to left atrial enlargement (Figures 14 and 18).

Figure 17 Table of VHS values in lateral radiographs of dogs and cats indicating mild, moderate, marked and extreme heart enlargement.

Figure 18 Table of short axis values in VD radiographs of cats indicating mild, moderate and marked enlargement, primarily of the left atrium.

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8. VHS- vs- Cardiothoracic Ratio

The VHS method identifies changes in heart size better than previous methods because it is based on unchanging skeletal structures. Cardiothoracic ratios used in the past were based on changeable chest dimensions. Dogs with progressive cardiomegaly expand their chests as their hearts enlarge; thus, the ratio of cardiac dimensions to chest depth and width may not change significantly (Figures 19 and 20). Conversely, reduction in heart size is associated with reduction in chest size thus there is little or no change in the cardiothoracic ratio (Figures 21 and 22).

Figure 19 Chart showing parallel increase in cardiac and thoracic dimensions in radiographs of a dog with mitral regurgitation and progressive cardiomegaly from 5.5 to 7.5 years of age. The cardiothoracic ratio did not change significantly even though the heart became very large.	Figure 20 Lateral radiographs of the dog charted in Figure 19 at 5.5 to 7 years of age. Note the straightening of the costal arches as the heart enlarged and the sternum moved ventrally.
Figure 21 Preoperative (A) and 4 months postoperative (B) lateral radiographs of a 6-year-old miniature Poodle with patent ductus arteriosus. The chest depth decreased and VHS decreased from 13.4v to 10.8v after PDA closure.	Figure 22 Preoperative (A) and 4 months postoperative (B) dorsoventral radiographs of the dog in Figure 20 have essentially the same heart width/chest width ratio even though the heart size is obviously smaller after surgery. The upper horizontal lines in each illustration indicate the 2nd ribs and the lower lines indicate the levels of the 13th intervertebral spaces (ivs).

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9. References

1.  Buchanan JW: Vertebral scale system to measure heart size. Proc. 9^th ACVIM Forum, p 689-690, 1991.

2.  Buchanan, JW, and Bucheler, J: Vertebral scale system to measure canine heart size in radiographs. JAVMA 206:194-199, 1995.

3.  Buchanan JW. Vertebral Scale System to measure heart size in radiographs. In Veterinary Clinics of North America: Small Animal Practice Radiology. BJ Watrous (ed) 30:379-393, 2000.

4.  Sleeper MM, Buchanan JW: Vertebral scale system to measure heart size in growing puppies. JAVMA 219:57-59,2001.

5.  Melian C, et al: Radiographic findings in dogs with naturally-occurring primary hypoadrenocorticism. J Am Anim Hosp Assoc 35:208-212, 1999.

6.  Lamb CR, et al: Assessment of the value of the vertebral heart scale in the radiographic diagnosis of cardiac disease in dogs. Vet Rec. 146:687-90, 2000.

7.  Lamb CR, et al: Use of breed-specific ranges for the vertebral heart scale as an aid to the radiographic diagnosis of cardiac disease in dogs. Vet Rec 148:707-711, 2001.

8.  Buchanan JW: Radiology of the heart. Proc. 35^th Annual Meeting of the American Animal Hospital Association p 34-45,1968.

9.  Nakayama H, et al: Correlation of cardiac enlargement as assessed by vertebral heart size and echocardiographic and electrocardiographic findings in dogs with evolving cardiomegaly due to rapid ventricular pacing. J Vet Int Med 15:217-221, 2001.

10. Pinto AC, et al: [Radiographic methods in the cardiac evaluation in dogs] Veterinaria Noticias. Univ Fed Uberlandia Brazil 8: 67-75, 2002.

11. Ana Carolina BC, et al: [Radiographic evaluation of the cardiac silhouette in clinically normal Poodles through the vertebral heart size (VHS) method]. Braz J Vet Res Anim Sci 41:261-266, 2004.

12. Hansson, K, et al: Interobserver variability of vertebral heart size measurements in dogs with normal and enlarged hearts. Vet Radiol & Ultrasound 46:122-130, 2005.

13. Litster A, et al: Radiographic cardiac size in cats and dogs with heartworm disease compared with reference values using the vertebral heart scale method: 53 cases. J Vet Card 7:33-40, 2005.

14. Bavegems V, et al: Vertebral heart size ranges specific for Whippets. Vet Radiol & Ultrasound. 46:400-3, 2005.

15. Gulanber EG, et al: Vertebral Scale system to measure heart size in thoracic radiographs of Turkish Shepherd (Kangal) dogs. Turk J Vet Anim Sci 29:723-726, 2005.

16. Marin LM, et al: Vertebral heart size in retired racing Greyhounds. Vet Radiol & Ultrasound. 48:332-4, 2007.

17. Woolley R, et al: Effects of treatment type on vertebral heart size in dogs with myxomatous mitral valve disease. Intern J Appl Res Vet Med 5:43-48, 2007.

18. Kraetschmer S, et al: Vertebral heart scale in the Beagle dog. J Sm Anim Prac 49:240-243,2008.

19. Greco A, et al: Effect of left vs. right recumbency on the vertebral heart score in normal dogs. Vet Radiol & Ultrasound. 49:454-5, 2008.

20. Guglielmini C, et al: Use of the vertebral heart score in coughing dogs with chronic degenerative mitral valve disease. J Vet Med Sci. 71:9-13, 2009.

21. Litster AL, Buchanan JW: Vertebral scale system to measure feline heart size in radiographs. JAVMA 216:210-214, 2000.

22. Gaschen L, et al: Cardiomyopathy in dystrophin-deficient hypertrophic feline muscular dystrophy. J Vet Int Med 13;346-356, 1999.

23. Ghadiri A, et al: Radiographic measurement of vertebral heart size in healthy stray cats. J Feline Med & Surg. 10:61-5, 2008.

24. Stepien RL, et al: Radiographic measurement of cardiac size in normal ferrets. Vet Radiol & Ultrasound. 40:606-610, 1999.

25. Mattoon JS, et al: Thoracic radiographic appearance in the normal llama. Vet Radiol & Ultrasound. 42:28-37, 2001.

26. Schumacher J. et al: Radiographic and electrocardiographic evaluation of cardiac morphology and function in captive cheetahs (Acinonyx jubatus). J Zoo & Wildlife Med. 34:357-63, 2003.

27. Wagner WM. Kirberger RM: Radiographic anatomy of the thorax and abdomen of the common marmoset (Callithrix jacchus). Vet Radiol & Ultrasound. 46:217-24, 2005.

28. Lee MY, et al: Comparative analysis of heart functions in micropigs and conventional pigs using echocardiography and radiography. J Vet Sci. 8:7-14, 2007.

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