Vertebral scale system to measure heart size in growing puppies.

OBJECTIVE: To determine relative heart size in clinically 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 millimeters 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 vertebral 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 enlargement are similar in puppies and adult dogs.     

Radiographic measurement of vertebral heart size in healthy stray cats

The aims of this study were to determine vertebral heart size (VHS) in stray cats and to compare different radiographic views. This study was performed on 50 adult stray cats. All cats were short-haired and non-obese and were considered to be healthy based on physical examination and electrocardiography. Left and right lateral, dorsoventral and ventrodorsal radiographs were taken. The long and short axes of the heart were measured in millimetres. The thoracic vertebral length spanned by each dimension was measured caudally from the fourth thoracic vertebra. Mean+/-SD and the correlation coefficient between the measurements were calculated with standard statistical software. The sum of the long and short axes of the heart expressed as VHS was 7.3+/-0.49 vertebrae in right lateral, 7.3+/-0.55 vertebrae in left lateral, 7.5+/-0.68 vertebrae in dorsoventral and 7.5+/-0.53 vertebrae in ventrodorsal. The differences between right and left lateral as well as dorsoventral and ventrodorsal views were not significant (P>0.05). Absolute measurements and vertebral heart scale values were slightly smaller than those reported in the literature for mixed population of cats. It is, therefore, important to take the breed in to account.     

VERTEBRAL HEART SIZE RANGES SPECIFIC FOR WHIPPETS

To assess the influence of breed, breeding lines, and training on heart size, the vertebral heart size (VHS) was evaluated on left-to-right lateral, right-to-left lateral, dorsoventral, and ventrodorsal thoracic radiographs from 44 whippets free from cardiac and pulmonary disease. In lateral views, the VHS was 11.0 +/- 0.5 vertebrae (mean +/- SD) on right-to-left lateral and 11.3 +/- 0.5 vertebrae on left-to-right lateral radiographs, being larger than the 9.7 +/- 0.5 vertebrae proposed by Buchanan (P<0.0001). The VHS on left-to-right lateral views was larger than on right-to-left lateral views (P<0.0001). The VHS was 10.5 +/- 0.6 vertebrae on dorsoventral radiographs and 11.1 +/- 0.6 vertebrae on ventrodorsal radiographs. Both values were larger than the 10.2 +/- 1.5 vertebrae (dorsoventral) (P<0.0082) or 10.2 +/- 0.8 vertebrae (ventrodorsal) (P<0.0001) proposed by Buchanan. In addition, the VHS on ventrodorsal views was larger than on dorsoventral views (P<0.0001). Dogs out of racing pedigree lines had a significantly larger VHS than those out of show pedigree lines, and trained dogs had a significantly larger VHS than nontrained dogs. Because most trained dogs came out of racing pedigree lines, and all nontrained dogs came out of show pedigree lines, however, it is difficult to determine whether the higher VHS for trained dogs is due to genetic influences or training, or both. In conclusion, it is important to take into account the breed and the radiographic view when evaluating heart size in thoracic radiographs of whippets to avoid overinterpretation of cardiac enlargement in these dogs.     

Radiographic and electrocardiographic evaluation of cardiac morphology and function in captive cheetahs (Acinonyx jubatus).

In a prospective study, eight (four males and four females) healthy, adult captive cheetahs (Acinonyx jubatus) were immobilized with a combination of tiletamine-zolazepam (4 mg/kg, i.m.), administered with a remote drug delivery system, to define normal cardiac morphology and function. Standard lateral and ventrodorsal (VD) radiographs were then taken to measure heart and thorax using a metric and vertebral scale system. Standard six-lead electrocardiograms were obtained with the animals in right lateral recumbency under isoflurane anesthesia. Mean chest depth and width was 18.7 +/- 1.3 cm and 13.0 +/- 0.6 cm, respectively. The mean lateral cardiac short axis (X) was 9.1 +/- 0.6 cm. the mean cardiac long axis (Y) was 13.6 +/- 0.7 cm, and the mean lateral heart sum (X + Y) was 22.6 +/- 1.2 cm. In the VD projection, mean cardiac short axis (V) was 10.1 +/- 0.7 cm, mean cardiac long axis (W) was 14.9 +/- 1.2 cm, and the heart sum (V + W) was 24.9 +/- 1.8 cm. The vertebral heart size was 8.2 +/- 0.9. All cheetahs had sinus rhythm, and no arrhythmias were noted. Mean heart rate was 126 +/- 15 beats/min, and the mean electrical axis was 82 + 5 degrees. P waves were always positive on lead II and had a width of 0.04 +/- 0.01 sec and a height between 0.1 and 0.3 mV. PR intervals were 0.11 +/- 0.01 sec. The height of the QRS complex was 1.25 +/- 0.24 mV and the width 0.06 +/- 0.01 sec. The ST segment was 0.04 sec, and the T wave (height: 0.25 +/- 0.05 mV) was positive in all cheetahs examined. Although these cardiac and thoracic measurements were larger than those of domestic cats (Felis catus), ratios of cardiac parameters were similar in both species. Electrocardiographic findings were similar to those reported from domestic cats.     

THE EFFECT OF DEXMEDETOMIDINE ON RADIOGRAPHIC CARDIAC SILHOUETTE SIZE IN HEALTHY CATS

Dexmedetomidine, an alpha₂‐adrenergic agonist, may be used in companion animals for chemical restraint, including cardiac evaluation. Echocardiographic changes associated with alpha₂‐adrenergic agonists have been described; however reports of radiographic changes in cats were not found at the time of this study. Aims of this observational, prospective, experimental study were to describe the effects of dexmedetomidine on the radiographic appearance of the cardiac silhouette in healthy, adult cats. Fourteen healthy adult cats received dexmedetomidine 40 mcg/kg IM. Right lateral, left lateral, ventrodorsal, and dorsoventral thoracic radiographs were obtained for each cat at three time points: presedation, intrasedation, and postsedation (≥ two hours after reversal with atipamezole). Radiographs were evaluated in a blinded, randomized fashion by two independent observers using the vertebral heart score on all four views, the number of intercostal spaces on lateral projections, and the percent width of thorax on ventrodorsal and dorsoventral projections. Median vertebral heart score on right lateral view was significantly increased intrasedation (median = 7.8; range = 7.25–8.25) compared to presedation (median = 7.5; range = 7–8 [P = 0.001]). Median percentage width was significantly higher intrasedation (70% on VD; range 65–80 [P = 0.001], and 75% on DV; range 65–80 [P = 0.006]) compared to presedation (65%; range 65–75 on both projections). Dexmedetomidine was associated with a small but significant increase in cardiac silhouette size on right lateral (vertebral heart score), ventrodorsal (percentage width), and dorsoventral (percentage width) radiographs in healthy adult cats. This effect should be taken into consideration for future interpretation of thoracic radiographs in dexmedetomidine‐sedated cats.     

RADIOGRAPHIC AND ECHOCARDIOGRAPHIC MEASUREMENT OF THE HEART IN OBESE CATS

A prospective study was undertaken to reconcile radiographic cardiomegaly and normal echocardiography in obese cats and to test a radiographic technique for better distinguishing between pericardial fat and the heart. Ten obese, but otherwise normal cats and 10 non-obese normal cats were used. A body condition scoring system was used to objectively group obese and non-obese normal cats. Two-dimensional echocardiograms were made to verify that all cats had a normal heart. Thoracic radiographs then were made using standard and altered exposure techniques. The hearts were measured on these radiographs using the metric and a vertebral scale system. Obese cats consistently had excessive fat around the heart especially if they also had a large amount of falciform fat. Altering exposure technique by increasing mAs and decreasing kVp sometimes enhanced the radiographic contrast between fat and myocardium. Enhanced radiographic contrast accentuated the double silhouette identifying the true cardiac silhouette within the fat expanded silhouette. Pericardial fat usually was distinguished more readily in lateral than in VD radiographs. In two cats, pericardial fat had a characteristic prominent square corner to the right cranial margin of the cardiac silhouette in VD radiographs. Obesity caused increased width and depth of the thoracic cage. 2D echocardiograms revealed normal cardiac dimensions in both groups of cats and increased precordial distance in the obese group.     

RADIOGRAPHIC AND ECHOCARDIOGRAPHIC ASSESSMENT OF LEFT ATRIAL SIZE IN 100 CATS WITH ACUTE LEFT‐SIDED CONGESTIVE HEART FAILURE

The aims of this study were to evaluate left atrial size in cats with acute left‐sided congestive heart failure. We hypothesized that left atrial size as determined by thoracic radiography can be normal in cats with acute left‐sided congestive heart failure. One hundred cats with acute left‐sided congestive heart failure in which thoracic radiography and echocardiography were performed within 12 h were identified. Left atrial size was evaluated using right lateral and ventrodorsal radiographs. Measurements were compared to two‐dimensional echocardiographic variables of left atrial size and left ventricular size. On echocardiography, left atrial enlargement was observed in 96% cats (subjective assessment) whereas maximum left atrial dimension was increased (>15.7 mm) in 93% cats. On radiographs left atrial enlargement (subjective assessment) was found in 48% (lateral view), 53% (ventrodorsal view), and 64% (any view) of cats whereas left atrial enlargement was absent in 36% of cats in both views. Agreement between both methods of left atrial size estimation was poor (Cohen's kappa 0.17). Receiver operating characteristic curve analysis identified a maximum echocardiographic left atrial dimension of approximately 20 mm as the best compromise (Youden index) between sensitivity and specificity in the prediction of radiographic left atrial enlargement. Left atrial enlargement as assessed by thoracic radiography may be absent in a clinically relevant number of cats with congestive heart failure. Therefore, normal left atrial size on thoracic radiographs does not rule out presence of left‐sided congestive heart failure in cats with clinical signs of respiratory distress.     

Accuracy of the modified vertebral heart score and the cardio-vertebral ratio for radiographic evaluation of cardiomegaly in ferrets

Thoracic radiography is commonly used to assess the size of the heart and diagnose cardiac disease in ferrets. Several standardized radiographic heart size indicators have been introduced in this species and values in healthy ferrets have been reported. To date, none of these indicators has been tested in ferrets with cardiac disease. The aim of this prospective and retrospective, analytical observational design study was to assess the accuracy of the modified vertebral heart score (mVHS) and the cardio-vertebral ratio (CVR) in the radiographic detection of cardiomegaly in ferrets. Thoracic radiographs of 24 ferrets with confirmed heart diseases, 22 ferrets with non-cardiac diseases and normal-sized hearts on echocardiogram, and 24 healthy ferrets were mixed and examined by three independent and blinded radiologists who measured mVHS and CVR in right lateral (RL) and ventrodorsal (VD) radiographs. For all readers, ferrets with cardiac disease had significantly higher mVHS and CVR than ferrets without cardiac disease on echocardiography. Optimal cut-points for predicting cardiac enlargement were 6.25 vertebrae and 7.25 vertebrae for RL-mVHS and VD-mVHS, and 1.58 and 1.80 for RL-CVR and VD-CVR, respectively. Using these cut-points, the accuracy was good for indicators measured in RL radiographs (92.9% for RL-mVHS; 91.4% for RL-CVR) and moderate for indicators measured in VD radiographs (88.6% for VD-mVHS; 85.7% for VD-CVR). Findings supported the use of mVHS and CVR for evaluating the size of the heart in diseased ferrets, with caution in values interpretation when pericardial fat prevents precise delineation of the cardiac silhouette contour especially on VD radiographs.     

Assessment of the value of the vertebral heart scale in the radiographic diagnosis of cardiac disease in dogs

In order to assess the influence of the vertebral heart scale (VHS) on the accuracy of the radiographic diagnosis of cardiac disease, thoracic radiographs of 50 dogs with proven cardiac disease, 26 with other thoracic diseases, and 50 with no clinical signs of cardiovascular or respiratory disease were mixed and examined by three independent, blinded observers chosen to represent a range of radiographic abilities. They first examined all the radiographs without making measurements of VHS and made a diagnosis. They then re-examined the radiographs, and measured VHS on both lateral and dorsoventral or ventrodorsal radiographs before again recording a diagnosis without reference to their original diagnoses. For all the observers, the dogs with cardiac disease had a higher mean VHS than the normal dogs. A VHS over 10.7 on the lateral radiograph was a moderately accurate sign of cardiac disease. The observers' accuracy of diagnosis did not change significantly as a result of using VHS as an adjunct to a subjective assessment of the radiographs.     

Cardiac measurements on thoracic radiographs of cats

Measurements of the heart and thorax were made on lateral and ventrodorsal thoracic radiographs of normal cats. The degree of correlation between selected cardiac and thoracic measurements was determined. Absolute measurements and ratios of measurements in normal cats and in cats with certain cardiac diseases were compared and their diagnostic value was evaluated. It was concluded that on the lateral thoracic radiograph the ratio of the cranio-caudal width of the heart to the distance between the cranial border of the fifth rib and the caudal border of the seventh rib was a highly reliable indicator of cardiac enlargement. On the ventro-dorsal radiograph the ratio of the maxium width of heart to the width of the thorax at the same level was the best indicator of increases in cardiac size.     

Comparisons of morphometric measurements and serum insulin-like growth factor concentration in healthy cats and cats with hypertrophic cardiomyopathy

OBJECTIVE: To compare morphometric measurements and serum insulin-like growth factor (IGF-1) concentration in cats with and without hypertrophic cardiomyopathy (HCM), and assess the hypothesis that cats with HCM have larger body size and skeletal features and higher serum IGF-1 concentrations than healthy cats. ANIMALS: 25 cats with HCM and 22 healthy control cats. PROCEDURES: Physical examination and echocardiography were performed to classify cats into the HCM and control groups. Data collected from each cat included diet history, body weight, body condition score, lengths of the humerus and 4th and 12th thoracic vertebrae, heart size, head length and width, and abdominal circumferences. Comparisons of these variables were made between groups. RESULTS: Body condition score in HCM-affected and control cats did not differ significantly. However, median head width; lengths of the head, 4th and 12th thoracic vertebrae, and humerus; and body weight in the HCM-affected group were significantly greater than values in the control group. Median serum concentration of IGF-1 was not significantly different between groups. CONCLUSIONS AND CLINICAL RELEVANCE: These data suggested that among the study cats, those with HCM were skeletally larger, but not more obese, than healthy cats. Whether this was attributable to differences in early growth or other causes requires additional investigation.     

CARDIAC AND PULMONARY ARTERY MENSURATION IN FELINE HEARTWORM DISEASE

A retrospective study was undertaken to quantify thoracic radiographic changes in cats with heartworm diseases, ( Dirofilaria immitis ). Using a blinded study format, the cardiac silhouette, thoracic cavity and pulmonary arteries were measured from thoracic radiographs of 21 cats with feline heartworm disease and 30 cats without known cardiac or pulmonary vessel pathology. Measured data were normalized to the thoracic cavity or bony structures within the radiographic field of view. The measurements were compared between the two groups of cats using an unpaired, two-tailed Student's t -test, with a p value of < 0.05 being considered significant. Cats with feline heartworm disease had enlargement of the craniocaudal aspect of the cardiac silhouette and normalized cardiac:thoracic ratio (p < 0.05) on the lateral view. Also, there was significant enlargement of the central and peripheral caudal lobar pulmonary arteries and their normalized ratios (p < 0.05) in the heartworm infected cats as visualized on the ventrodorsal projection. Tortuosity of the pulmonary arteries was seen in three of the 21 infected cats. Eleven of the 21 cats with feline heartworm disease had pulmonary parenchymal changes. Based on the present study, central and peripheral pulmonary artery enlargement as viewed on the ventrodorsal radiograph was the single best radiographic indicator of feline heartworm disease.     

Norwich terriers possess a greater vertebral heart scale than the canine reference value

Previous studies have demonstrated evidence that normal reference ranges for radiographic vertebral heart scale values can vary among dog breeds. The purpose of this retrospective, observational study was to determine whether the normal vertebral heart scale values published by Buchanan and Bücheler for lateral radiographs are applicable to the Norwich terrier. Secondary objectives were to determine if clinical signs of respiratory disease, age, sex, weight, body condition score, recumbency, or thoracic depth‐to‐width ratio had any influence on vertebral heart scale measurements in this breed. The electronic medical record systems of two universities were reviewed and Norwich terriers were included in the study if they had orthogonal thoracic radiographs performed and no historical or radiographic evidence of cardiopulmonary disease. A vertebral heart scale was calculated for each patient. Sixty‐one client‐owned, Norwich terrier dogs with no clinical signs of cardiovascular disease were evaluated. The vertebral heart scale for Norwich terriers without evidence of cardiac disease (10.6 ± 0.6) was found to be significantly greater than the canine reference value of 9.7 ± 0.5 initially established by Buchanan and Bücheler. No significant correlation was found between clinical signs of respiratory disease, sex, age, thoracic depth‐to‐width ratio or lateral recumbency, and vertebral heart scale. Norwich terriers with a body condition score ≥6 had a significantly higher vertebral heart scale than those with a body condition score ≤5. Breed‐specific ranges and body condition scores need to be considered when interpreting vertebral heart scale values for Norwich terriers.     

Comparison of different radiographic scores with associated echocardiographic measurements and prediction of heart enlargement in dogs with and without myxomatous mitral valve disease

IntroductionStaging of myxomatous mitral valve disease (MMVD) requires an echocardiographic examination along with thoracic radiographs. The aims of this study were to calculate mean values for radiographic scores vertebral heart size (VHS), left atrial width (LA_Width), radiographic left atrial dimension (RLAD), and vertebral left atrial size (VLAS) in conventional and grayscale inverted images in healthy dogs and dogs with different stages of MMVD, and to find cutoff values for a stage assignment.AnimalsOne hundred fifty dogs in different stages of MMVD and 50 unaffected dogs were evaluated.MethodsRadiographic scores, echocardiographic left atrium-to-aorta ratio and normalized left ventricular internal dimension at end-diastole, and results of a clinical examination were obtained. Analyses were performed to evaluate the correlation between radiographic scores and echocardiographic values, to determine cutoff values for a radiographic stage assignment, and to compare measurements in conventional and inverted radiographs.ResultsAfter excluding breed-specific higher VHS, the means of VHS, LA_Width, RLAD, and VLAS were similar in the control group and stage B1. All radiographic scores increased in stages B2 and C. The cutoff values identifying heart enlargement, and therefore differentiating stages B1 and B2, were 11.0 for VHS, 1.8 for LA_Width, 2.0 for RLAD, and 2.3 for VLAS. Besides RLAD, scores were similar in conventional and inverted radiographs.ConclusionCutoff values for the different radiographic scores for stage assignment were calculated. Radiographic cardiac scores using either conventional or inverted grayscale could be a tool to differentiate between different stages of MMVD when echocardiography is unavailable.     

RADIOGRAPHIC MEASUREMENT OF CARDIAC SIZE IN NORMAL FERRETS

Right lateral, left lateral and ventrodorsal radiographs were obtained in 20 normal ferrets (11 male). Three independent observers recorded measurements of the cardiac silhouette and results for each parameter were averaged. Long axis (length), short axis (width) and total of length plus width (L+W) were recorded in each view. Comparative measurements were calculated, including the ratio of L+W/length of thoracic vertebrae 5-8, and a modified vertebral heart score (VHS) method, measuring the heart in vertebral units. Measurements made in ventrodorsal views were usually larger than corresponding measurements in lateral views. Weight and most absolute measurements differed significantly between male and female ferret (P<0.05), but the differences in absolute measurements were not apparent when related to measures of body size (Ratio and modified VHS methods). Given the variability in body weight and size in ferrets, measurements of the cardiac silhouette normalized for body size may be more universally applicable than absolute measurements.     

Evaluation of the radiographic liver length/11th thoracic vertebral length ratio as a method for quantifying liver size in cats

Abdominal radiography is a standard diagnostic test for cats with suspected liver disease, however, absolute measurements of radiographic liver size can be affected by other factors such as positioning, radiographic technique, and obesity. This prospective and retrospective, analytical, cross‐sectional study evaluated the liver length/11th thoracic vertebral length (LL/T11) ratio as a method for minimizing these outside effects. In a prospectively recruited sample of 25 clinically healthy cats, measurements of radiographic LL/T11 ratio were compared with CT measurements of liver volume. Effects of radiographic technical factors (body posture, recumbency state, and beam center to LL/T11 ratio) and observer were also tested. In a retrospectively recruited sample of 324 cats with no evidence of liver disease, radiographic measurements of the LL/T11 ratio were performed using right lateral radiographs and compared among signalment groups (age, sex, body weight, and body condition score). There was a strong significant correlation between the LL/T11 ratio and CT liver volume (P < .001), and this ratio was not affected by radiographic technical factors. The reference value of the LL/T11 ratio was 4.22 ± 0.54 and the LL/T11 ratio did not differ among signalment groups. Findings supported the use of the LL/T11 ratio as a novel quantitative index of radiographic liver size in cats. Future studies in clinically affected cats are needed to further validate this method.     

Distribution of new methylene blue injected into the lumbosacral epidural space in cats

OBJECTIVE: To determine the effects of injection volume and vertebral anatomy on the spread of new methylene blue (NMB) injected into the lumbosacral epidural space in cats. STUDY DESIGN: Prospective experimental study. SAMPLE POPULATION: Sixteen cats. METHODS: Cats were randomly assigned to four groups and received from 0.1 to 0.4 mL kg(-1) of 0.12% NMB in 0.9% saline. Injection was made into the lumbosacral epidural space using a dorsal approach with the cats in sternal recumbency. The extent of cranial migration of the dye as indicated by the staining of epidural fat and dura mater was measured. RESULTS: The mean +/- SD (range) number of stained vertebrae in the 0.3 and 0.4 mL kg(-1) groups, were 11.5 +/- 1.5 (T7-T11) and 12.4 +/- 1.8 (T6-T10), respectively. This was significantly greater than the number in the 0.1 and 0.2 mL kg(-1) groups, 4.3 +/- 0.6 (L3-L4) and 6.0 +/- 0.7 (L1-L2) vertebrae, respectively (p < 0.001). Linear regression analysis showed that the volume injected correlated significantly with the number of stained vertebrae (R2 = 0.83, p < 0.001). In the dorsal and lateral aspect of the spinal cord, NMB solution distributed between epidural fat and dura mater. Migration under the spinal cord occurred along the two longitudinal epidural veins. CONCLUSIONS AND CLINICAL RELEVANCE: The larger the volume of solution injected into the lumbosacral epidural space in cats, the greater the spread.     

Vertebral heart size in healthy Australian cattle dog

The vertebral heart score or size (VHS) measurement is routinely used to provide a more objective measurement of cardiomegaly in dogs. However, breed or body conformation can influence the VHS. To assess the specific VHS for the Australian Cattle Dog, left‐to‐right lateral, right‐to‐left lateral, dorsoventral and ventrodorsal thoracic radiographs from 20 individuals free from cardiac and pulmonary disease were obtained. The mean VHS was significantly higher in Australian Cattle Dog (10.5 ± 0.4 vertebrae), when compared with the average VHS for 100 normal dogs of different breeds that had been initially published (9.7 ± 0.5 vertebrae). This emphasizes the importance of breed‐specific VHS ranges. In our study group of normal Australian Cattle Dogs, the mean VHS was 10.5 ± 0.5 vertebrae (mean ±SD) on right lateral and 10.3 ± 0.5 vertebrae on left lateral radiographs. The VHS on right lateral views was significantly larger than on left lateral views. The VHS was 10.5 ± 0.6 vertebrae on dorsoventral and 11.1 ± 0.6 vertebrae on ventrodorsal radiographs. The VHS on ventrodorsal views was significantly larger than on dorsoventral views.     

VERTEBRAL HEART SIZE IN RETIRED RACING GREYHOUNDS

The vertebral heart size (VHS) is used to objectively assess cardiac dimensions on thoracic radiographs. A high VHS suggest the presence of cardiac pathology, such as dilated cardiomyopathy, degenerative atrioventricular valvular disease, pericardial effusion, pericardioperitoneal diaphragmatic hernia, tricuspid dysplasia, ventricular septal defect, or patent ductus arteriosus, among others. However, breed or body conformation can influence the VHS. Because Greyhounds have a high prevalence of physiologic systolic murmurs associated with high aortic velocity, and large cardiac dimensions when compared with dogs of similar size, they are frequently suspected of having heart disease. The purpose of this study was to compare the VHS in normal Greyhounds with those in Rottweilers, and a group of dogs from various other breeds using both analog and digital radiology. The VHS was significantly higher in Greyhounds (P< 0.0001), when compared with Rottweilers and to other dog breeds. The mean VHS on lateral radiographs for Greyhounds was 10.5 +/- 0.1, for Rottweilers it was 9.8 +/- 0.1, and for mixed breed dogs it was 10.1 +/- 0.2. This study confirms that the relative cardiomegaly reported in necropsy and echocardiographic studies in Greyhounds is easily detected using plain radiography and the VHS.     

THE EFFECT OF MANUAL LUNG INFLATION VS. SPONTANEOUS INSPIRATION ON THE CARDIAC SILHOUETTE IN ANESTHETIZED DOGS

The purpose of this study was to assess radiographic heart size in anesthetized dogs, comparing radiographs made with the patient breathing spontaneously to radiographs obtained using positive pressure manual lung inflation. The hypothesis was that manual inflation would cause reduction in the cardiac size. With dogs in right recumbency a radiograph was made at peak spontaneous inspiration followed immediately a radiograph made with application of positive pressure manual inflation of the thorax. Cardiac size was assessed, both subjectively and objectively using the vertebral heart scale (VHS). Two hundred and six dogs were studied. Manual inflation resulted in a significantly greater degree of lung inflation assessed radiographically ( P <0.0001). The subjectively assessed heart size was significantly smaller in radiographs made with manual inflation, leading to different subjective categorization of heart size in 67 (32%) of dogs. The objectively measured VHS was also significantly smaller in the radiographs made using manual inflation by a mean of 0.24 of a vertebral length (95% CL of mean difference: −0.29, −0.19, P <0.0001). A statistically significant reduction in subjective heart size and in VHS occurred with manual inflation of the lungs, and these differences may be clinically significant. Thus, if serial radiographs are obtained to assess cardiac size, the radiographic technique used should be the same.