Vertebral scale system to measure heart size in growing puppies JAVMA2001

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Avertebral scale system for measuring heart size onradiographic views has been described in adult
dogs and cats.1,2 The method is based on the fairly con-
stant relationship between vertebral length and heart
size in clinically normal dogs weighing 6.6 to 143 lb (3
to 65 kg). A midthoracic 5-vertebrae segment of verte-
bral length is used as an index of body size, and heart
size is represented by the sum of the long and short
axes measurements of the heart scaled against verte-
brae (v) on lateral radiographic views. In 100 clinical-
ly normal adult dogs, mean (± SD) vertebral heart size
(VHS) was 9.7 ± 0.5 v. In 100 clinically normal adult
cats, mean (± SD) VHS was 7.5 ± 0.3 v.2
In newborn human infants, the heart weight/body
weight ratio (6.3 g/kg) is greater than that of adults and
decreases to adult proportions (4.6 g/kg) by 3 years of
age.3 Radiographic cardiothoracic ratios in infants also
suggest there is a relative reduction in heart size with
growth; however, some of the reduction in cardiotho-
racic ratio may be attributable to lowering of the
diaphragm and consequent change in the cardiac axis.3
This is similar to what is seen in cats; mean heart
weight/body weight ratio in neonatal kittens was 9.3
g/kg, whereas the mean for adults was 4.0 g/kg.4 In
contrast, the heart weight/body weight ratio in neona-
tal puppies is 4.7 g/kg and increases to 7 to 8 g/kg in
adult dogs.5 To our knowledge, the age at which this
change in ratio is radiographically evident has not been
determined. One source states that young animals up
to approximately 3 months of age have relatively
rounder hearts than adults.6 The objectives of the study
reported here were to determine relative heart size
radiographically in clinically normal puppies and to
determine the influence of age on relative heart size. 
Materials and Methods
Dogs—Eleven 3-month-old puppies (6 mixed-breeds, 2
Golden Retrievers, 1 Labrador Retriever, 1 Beagle, and 1
German Shepherd Dog) were selected for the study. Seven
were females, and 4 were males. Examination by a cardiolo-
gist revealed no evidence of cardiac or pulmonary disease.
Radiographic heart size was considered subjectively normal
in all animals. The puppies were raised in household envi-
ronments and returned to the hospital for thoracic radi-
ographic assessment at 6 and 12 months of age. Radiographs
also were obtained in 6 of the puppies at 3 years of age.
Clinical abnormalities were not detected in any of the dogs,
and heart sizes remained subjectively normal throughout
the study.
Radiographic measurements—Radiography was per-
formed without sedation, using standard exposure tech-
niques; left lateral and dorsoventral (DV) radiographic views
were obtained. In left lateral radiographic views, the long and
short axes of the heart were measured, using the vertebral
scale system.1 The long axis was measured from the ventral
border of the left main stem bronchus to the most distant
ventral contour of the cardiac apex, using an adjustable
caliper. The caliper was then repositioned over the vertebral
column beginning with the cranial edge of T4. The distance
spanned by the caliper was estimated to the nearest 0.1 v. The
caliper was then placed on a metric ruler and the interval
recorded to the nearest millimeter to obtain more precise
measurements for statistical analysis. 
The maximal short axis of the heart in the central third
region, perpendicular to the long axis, was measured in the
same manner, beginning at the cranial edge of T4. The long
and short axes dimensions were then added to obtain a ver-
tebrae/heart sum that indicated heart size relative to body
length. Thus, overall VHS was expressed as total units of ver-
tebral length to the nearest 0.1 v. Heart size and vertebral
length also were determined in millimeters.
On DV radiographic views, the long and short axes of
the heart were determined with calipers and were recorded as
the number of vertebrae spanned on the lateral view begin-
ning at T4. This measurement also was determined in mil-
limeters.
Depth and width ratios of the thorax were determined to
assess thoracic conformational change with growth. The
depth of the thorax was measured on lateral radiographic
views from the cranial edge of the xiphoid process to the ven-
tral border of the vertebral column along a line perpendicu-
JAVMA, Vol 219, No. 1, July 1, 2001 Scientific Reports: Original Study 57
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Vertebral scale system to measure heart size 
in growing puppies
Margaret M. Sleeper, VMD, DACVIM, and James W. Buchanan, DVM, MMedSci, DACVIM
Objective—To determine relative heart size in clini-
cally normal puppies and assess whether relative
heart size changes with growth. 
Design—Prospective radiographic study.
Animals—11 puppies without evidence of disease.
Procedure—Standardized measurements of the long
and short axes of the heart, midthoracic vertebrae,
and other structures were made at 3, 6, 12, and 36
months of age. Measurements were recorded in mil-
limeters and number of thoracic vertebral lengths
spanned by each dimension, measured caudally from
T4 on lateral radiographic views. The long and short
axis measurements of the heart, expressed in verte-
bral lengths, were added to yield vertebral heart size.
Results—Mean ± SD vertebral heart sizes on lateral
radiographic views at 3, 6, 12, and 36 months of age
were 10.0 ± 0.5, 9.8 ± 0.4, 9.9 ± 0.6, and 10.3 ± 0.6
vertebrae, respectively. Significant differences were
not detected.
Conclusions and Clinical Relevance—Vertebral
heart size measurements in puppies are within the
reference range for adult dogs (9.7 ± 0.5 vertebrae)
and do not change significantly with growth to 3 years
of age. Standards for determining cardiac enlarge-
ment are similar in puppies and adult dogs. (J Am Vet
Med Assoc 2001;219:57–59)
From the Department of Clinical Studies, School of Veterinary
Medicine, University of Pennsylvania, Philadelphia, PA 19104. 
Address correspondence to Dr. Buchanan.
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lar to the vertebral column. Thoracic width was measured on
DV radiographic views as the distance between the medial
borders of the eighth ribs at their most lateral curvatures. 
Statistical analyses—Linear random effects were fitted
for the time periods for each of the dogs. Student t-tests were
performed to compare the means against zero for the slope
and intercept of these linear functions. Significance was set at
P < 0.05. All analyses were performed using SAS statistical
software.a
Results
Differences among vertebral scale measurements
at each time point were not significant. Mean VHS on
lateral radiographic views were 10.0, 9.8, 9.9, and 10.3
v at 3, 6, 12, and 36 months of age, respectively. In DV
radiographic views, mean VHS were 10.3, 9.7, 9.8, and
10 v at 3, 6, 12, and 36 months of age, respectively
(Table 1). 
All absolute measurements increased with age as
expected (Table 2). Mean weight of 3-month-old pup-
pies increased from 11.7 to 22.2 lb (5.3 kg to 10.1 kg)
at 6 months of age (91% increase) and 26.4 lb (12.0
kg) at 12 months of age (18% increase). Increases of 21
to 30% were observed in all measurements at 6 months
of age, and an additional increase of 4 to 14% was
observed at 12 months of age. Additional increases of 1
to 6% were observed in measurements of VHS in 6 of
the dogs at 3 years of age.
Discussion
Heart/skeletal ratios to quantify heart size have
been used in recent years to overcome the limitations
caused by variable chest conformation and animal
size.1,2,7 The vertebral scale system has gained popular-
ity, because it is simple to explain and use, and there is
little interobserver variation.1,2,8 In addition to provid-
ing a reference for normal heart size, it can be used to
document sequential changesin heart size in response
to treatment or with progression of heart disease.8-10,b In
adult dogs, variables such as a wide or deep thoracic
conformation, sex, respiratory phase, and positioning
in right or left lateral recumbency for radiography were
found to be insignificant.1 Thus, many factors that have
limited other systems for measuring heart size are no
longer troublesome with this technique.
Results of our study indicated that heart size in
proportion to vertebral length does not change in dogs
older than 3 months of age, and the vertebral scale sys-
tem can be applied in puppies as well as adult dogs.
This is in contrast to results of a study performed in
kittens, in which heart size also was measured, using
the vertebral scale system described in this report.11
Clinically normal kittens had relatively larger hearts
(or smaller vertebrae) at 3 (VHS > 8.5 v) and 6 (VHS 
> 8.0 v) months of age than at 9 or 12 months of age,
at which time their VHS values decreased to reference
ranges in adult cats (VHS, 7.5 ± 0.3 v).2,11
It has been suggested that 3-month-old puppies
have more rounded hearts than adult dogs6; this was
not supported by the results of our study. Long and
short axes measurements of the heart, using both the
vertebral scale method and measurement of heart size
and vertebral length in millimeters, had essentially the
same proportions at 3, 6, 12, and 36 months of age.
This indicates that diameters of the heart were rela-
tively unchanged, and hearts were not more rounded at
3 months than at 6, 12, or 36 months of age. 
The vertebral scale system is helpful for inexperi-
enced observers to ascertain cardiac enlargement and
quantify it radiographically. However, it is not possible
to evaluate subtle changes, and therefore one must
keep in mind that considerable changes in contour of
the heart can exist without cardiac enlargement.1,10,12
For example, cardiac concentric hypertrophy, which
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Table 2—Thoracic and cardiovascular measurements (mm) for determination of relative heart size
(mean � SD)
Age 
Variable 3 mo (n = 11) 6 mo (n = 11) 12 mo (n = 11) 36 mo (n = 6) 
Lateral long axis of heart 74.0 � 12.9 91.0 � 17.7 99.0 � 18.2 108.0 � 19.7 
Lateral short axis of heart 63.0 � 10.1 81.0 � 12.5 86.0 � 15.7 95.0 � 17.4 
Lateral axis sum 137.0 � 22.8 172.0 � 30.6 185.0 � 34.2 203.0 � 36.1 
Length of 5 vertebrae 67.0 � 8.6 87.0 � 13.2 92.0 � 13.2 97.0 � 13.1 
Thoracic depth 105.0 � 21.5 130.0 � 29.7 146.0 � 33.7 165.0 � 39.7 
Thoracic width 120.0 � 15.8 145.0 � 28.3 159.0 � 29.4 168.0 � 24.1 
Depth/width ratio 0.86 � 0.07 0.90 � 0.08 0.92 � 0.07 0.97 � 0.11 
Dorsoventral long axis 78.0 � 13.9 97.0 � 17.7 104.0 � 21.2 109.0 � 19.2 
Dorsoventral short axis 61.0 � 11.4 76.0 � 14.2 79.0 � 14.9 86.0 � 14.8 
Dorsoventral axis sum 139.0 � 25.1 173.0 � 32.5 183.0 � 35.5 195.0 � 33.7 
Table 1—Measurement of relative heart size in growing puppies, using the vertebral scale system
(data are reported as mean � SD No. of vertebrae)
Age 
Variable 3 mo (n = 11) 6 mo (n = 11) 12 mo (n = 11) 36 mo (n = 6) 
Lateral long axis of heart 5.4 � 0.32 5.2 � 0.28 5.3 � 0.31 5.5 � 0.34 
Lateral short axis of heart 4.6 � 0.26 4.6 � 0.02 4.6 � 0.32 4.8 � 0.36 
Lateral axis sum 10.0 � 0.52 9.8 � 0.42 9.9 � 0.60 10.3 � 0.58 
Dorsoventral long axis 5.8 � 0.33 5.4 � 0.32 5.5 � 0.35 5.6 � 0.43 
Dorsoventral short axis 4.5 � 0.35 4.3 � 0.28 4.3 � 0.28 4.4 � 0.34 
Dorsoventral axis sum 10.3 � 0.64 9.7 � 0.54 9.8 � 0.66 10.0 � 0.75 
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typically develops secondary to pressure overload, may
develop at the expense of cardiac chamber volume, and
the size of the heart may appear normal radiographi-
cally.13
aSAS, version 6.12, SAS Institute, Cary, NC.
bNayakama H, Nakayama T, Nishijima Y, et al. Correlation of cardiac
enlargement between the vertebral scale system (Buchanan index)
and routine radiographic, echocardiographic, and electrocardio-
graphic findings in dogs with evolving cardiomegaly (abstr). J Vet
Intern Med 2000;14:375.
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