Long-tailed gorals (Naemorhedus caudatus) have been designated class I endangered wildlife and natural monuments in Korea. Thus, the restoration and proliferation of the gorals are actively pursued; however, veterinary research and case investigations are still insufficient (1,2,4,8). The main causes of death in gorals are respiratory, digestive, and infectious diseases (21). In addition, various cardiac disorders are currently being diagnosed through imaging evaluation in wild animals (3), and dilated cardiomyopathy and infective endocarditis were experientially diagnosed in gorals. Therefore, because the health status of gorals is directly related to survival, accurate disease diagnosis is required through history taking, physical examination, heart murmur evaluation, and various imaging diagnoses, including thoracic radiography and echocardiography (10,13,15,18). Thoracic radiography contributes significantly to a cardiovascular evaluation in most animals and is often the first diagnostic imaging technique essential for suspected cardiac disease (6,7,11,13).

The size and shape of the heart, the caudal vena cava (CVC) and pulmonary blood vessels, and the presence of ascites, necessary for diagnosing cardiac diseases, are visualized through thoracic radiography (16,20). Clinically, cardiomegaly can be objectively evaluated by measuring the vertebral heart scale (VHS), as reported in various animal species (6,16-18). Additionally, a dilated CVC can often be identified as a valuable indicator of right congestive heart failure in cattle with a circulatory impairment through comparison with the aorta (Ao) and length of the thoracic vertebrae (VL) (9,12). Furthermore, the CVC ratio has been useful in diagnosing cardiac diseases, such as heartworm disease and dilated cardiomyopathy, in dogs and cats (15,23).

In this study, standard radiographic cardiac measurements of gorals were obtained by measuring the VHS, CVC, and related values in 10 gorals (seven males and three females) who became healthy after treatment and were rescued by Kangwon National University Wildlife Medical Rescue Center (WMRC). This study will provide useful basic data for establishing a systematic healthcare protocol for gorals, improving medical treatment for injured individuals, and restoring gorals.

This study was conducted on ten gorals (seven males and three females) older than three years rescued by the WMRC between 2019 and 2021, clinically healthy after treatment, and free of cardiac auscultation problems and cardiac diseases (average weight 28.66 kg). For rapid and safe examination, xylazine HCl (Rompun^®, Elanco Korea, Ansan, Korea) 0.4 mg/kg was injected intramuscularly for sedation. Additionally, based on the findings of a study that showed a tendency for increased VHS in cats with severe anemia, blood tests were performed using Vetscan^® HM5 (Abaxis Inc., California, USA) and Vetscan^® VS2 (Abaxis Inc., California, USA) after blood collection from the jugular veins of gorals to exclude anemia by checking the complete blood count (19,24).

All thoracic radiographs were obtained in right lateral (RL) recumbency during inhalation using the digital radiography system VXR-9M (DRGEM, Seoul, Korea). The image data were stored and read using a communication system (Viewrex, TechHeim, Seoul, Korea). One observer performed the VHS measurements with standard calipers using the methods described by Buchanan and Bücheler (7). In the RL view of the thoracic radiographs, the cardiac long axis (LA) was measured from the apex of the heart to the carina of the main stem bronchus. The short axis (SA) of the heart was measured perpendicular to the LA at the CVC level. Calipers of the same values as the length of the LA and SA were repositioned on the anterior edge of the fourth thoracic vertebra (T4). The VHS value was added to the number of caliper-covered vertebrae, equal to the lengths of the LA and SA (Fig. 1A). The levels of CVC, Ao, and VL, which are indicators of circulatory disorders and can be used to diagnose congestive heart failure as, were measured using Lehmkuhl’s method (14). The maximum diameter of the CVC was measured at the portion that did not overlap with the heart or diaphragm, and VL and Ao were measured in the same intercostal space as the CVC measurement location for comparison (Fig. 1B). The ratio between Ao and VL, compared to that of CVC, was then calculated. Additionally, the thoracic morphology of gorals was determined as the ratio of thoracic depth (TD) to thoracic width (TW) (7). TD was measured from the ventral border of the spine to the cranial edge of the xiphoid process along a line perpendicular to the vertebrae in RL view. The TW was measured as the distance between the medial border of the eighth rib in the VD view (Fig. 2).

Figure 1. Vertebral heart scale (VHS) and caudal vena cava (CVC) size measurement methods of gorals. (A) VHS = long axis (LA) + short axis (SA), (B) A, CVC; B, aorta (Ao); C, the length of the thoracic vertebra (VL) in the right lateral view.

Figure 2. Thoracic depth (TD) and width (TW) measurement methods of gorals. (A) TD measurement in right lateral view, (B) TW measurement in ventrodorsal view.

All statistical analyses were performed using SPSS software (SPSS^® 17.0, SPSS for Windows). The mean ± standard deviation (SD) was calculated for all measurements, and the correlation between CVC and Ao compared with the VHS of gorals was determined using the Pearson bivariate correlation test. In addition, the correlation between sex and weight compared with the VHS was determined using the Student’s t-tests and Pearson bivariate correlation tests. Values of p < 0.05 were considered significant.

Table 1 summarizes the cardiac measurements of gorals obtained using radiographic measurements. Additionally, a Pearson bivariate correlation analysis was conducted to determine whether there was a correlation between CVC and Ao compared to VHS variables (Table 2). The correlation between VHS and CVC was r = 0.678, p = 0.031, and that between VHS and Ao was r = 0.691, p = 0.027, confirming a significant but low positive correlation between VHS and CVC and between VHS and Ao (Fig. 3). However, no correlation was observed between CVC and Ao. In addition, sex and weight were not significantly correlated with VHS. The mean ± SD of the TD-to-TW ratio was 1.04 ± 0.09, within the range of 0.75-1.25, and it was confirmed that the gorals had an intermediate thorax.

Table 1 . Radiographic cardiac and thoracic measurements of the gorals (n = 10).

Measurements	Mean ± SD	Max	Min
VHS (v)	9.31 ± 0.55	9.8	8.2
LA (v)	5.59 ± 0.27	5.9	5.1
SA (v)	3.72 ± 0.33	4.0	3.1
CVC (mm)	15.88 ± 1.71	19.17	12.63
Ao (mm)	19.20 ± 3.07	23.94	15.70
VL (mm)	23.98 ± 1.21	25.93	22.45
CVC/Ao	0.84 ± 0.13	0.99	0.63
CVC/VL	0.67 ± 0.09	0.78	0.53
TD (mm)	194.72 ± 9.27	206.11	172.58
TW (mm)	188.47 ± 17.54	214.36	164.22
TD:TW	1.04 ± 0.09	1.22	0.93

n, number of gorals; SD, standard deviation; Max, maximum; Min, minimum; VHS, vertebral heart scale; LA, long axis; SA, short axis; v, vertebrae; CVC, caudal vena cava; Ao, aorta; VL, length of thoracic vertebrae (T7); TD, thoracic depth; TW, thoracic width..

Table 2 . Correlation between VHS and cardiovascular system (CVC and Ao).

	VHS	CVC	Ao
VHS	1
CVC	0.678*	1
Ao	0.691*	0.429	1

VHS, vertebral heart scale; CVC, caudal vena cava; Ao, aorta..

*p < 0.05..

Figure 3. Correlation between vertebral heart scale (VHS) and cardiovascular system (A, caudal vena cava [CVC] (r = 0.678, p = 0.031), and B, Aorta [Ao] (r = 0.691, p = 0.027)).

The core purpose of the VHS measurement method is to objectively determine the presence or absence of cardiomegaly to help diagnose cardiac diseases (15). In particular, SA measurement of the heart, as both left and right hearts are used, is useful for monitoring the progression of cardiomegaly over time (7). Since the number of gorals in this study was small (ten individuals), the effects of specific parameters, such as radiographic posture, and TD-to-TW ratio, that could affect VHS could not be verified. However, congestive heart failure is generally diagnosed based on the detection of jugular venous pressure, hepatomegaly, splenomegaly, and ascites (14). Additionally, there was a significant correlation between the VHS and CVC and VHS and Ao. Therefore, the measurement of CVC, Ao, and VL levels and comparison of each level could be useful for diagnosing cardiac diseases with VHS.

In this study, the TD-to-TW ratio was calculated to determine the thoracic morphology of gorals. In dogs, a TD-to-TW ratio greater than 1.25 corresponds to a deep thorax, less than 0.75 to a broad thorax, and between 0.75 and 1.25 to an intermediate thorax (7). However, the correlation between VHS and thoracic morphology could not be investigated because all gorals had an intermediate thorax.

The evaluation criteria for thoracic radiography of gorals in this study are clinically essential and will help diagnose cardiac diseases in gorals in the future. However, there are cardiac diseases in which there are no significant changes in heart size, such as arrhythmias or atrial and ventricular septal defects. Therefore, accurate differential diagnosis is required through additional imaging, including echocardiography, even if an average heart size is observed on thoracic radiography (5,22). Also, as this study was conducted with only ten individuals rescued by WMRC and who became healthy after treatment, the results do not apply to all gorals in Korea. A retrospective study with a larger number of gorals is needed.

In conclusion, this study presented the normal reference values of VHS and CVC/Ao ratio in clinically normal long-tailed gorals in Korea. The long-tailed gorals are undergoing restoration, and continuous research on various disease diagnosis methodologies is needed to improve treatment.

The authors express their deepest gratitude to the Yanggu Long-tailed goral and Muskdeer Center for their valuable support in the rescue of goral and medical assistance. This manuscript represents a portion of the Ph.D. thesis by Sangjin Ahn.

The authors have no conflicting interests.