M-mode echocardiographic reference values in Pantja goats

Aim: The aim of this study was to establish M-mode echocardiographic reference values in Pantja goats and to study the effect of gender and body weight (BW) on these parameters. Materials and Methods: A total of 18, clinically healthy, adult Pantja goats of either sex, aged 2-4 years and weighing 10-44 kg were included in the study. Echocardiographic examination was performed in the standing unsedated animal. All measurements were made from the right parasternal long-axis left ventricular outflow tract view of the heart. The following parameters were recorded: Left ventricular internal diameter at diastole and systole, interventricular septal thickness at diastole and systole, left ventricular posterior wall (LVPW) thickness at diastole and systole, end diastolic and systolic volumes, stroke volume, fractional shortening, ejection fraction, percent systolic thickening of interventricular septum, percent systolic thickening of LVPW, cardiac output, left atrial (LA) diameter at diastole and systole, aortic (AO) root diameter at diastole and systole, LA/AO, LA posterior wall thickness at diastole and systole, left ventricular ejection time, DE amplitude, EF slope, AC interval and e-point to septal separation. Results: This study demonstrated specific reference ranges of M-mode echocardiographic parameters and indices in healthy Pantja goats. Normal echocardiographic values obtained in Pantja goats were quite different from other goat breeds. Gender had no influence on echocardiographic parameters, while high correlations were found between most echocardiographic parameters and BW. Conclusion: The echocardiographic values obtained in the study may serve as a reference for future studies in this breed, for cardiovascular disease diagnosis and for utilizing the goat as a model for cardiac disorders in humans.


Introduction
Echocardiography is a non-invasive method for assessment of cardiac structure and function. In goats, structural cardiac abnormalities are rarely diagnosed clinically because this species is relatively resistant to cardiac disease and is rarely presented for detailed medical evaluation at veterinary hospitals. Despite this, echocardiography has proved to be an interesting tool for diagnosing cardiovascular diseases in goats [1,2].
Unlike other animals, goats are easily manageable and have a heart size comparable with that of human beings, which makes them an ideal candidate for the developing of animal models for human cardiovascular research [3]. However, for accurate measurement of cardiac dimensions and to evaluate possible changes in the cardiac function, reference values are required. With the exception of a few goat breeds [4][5][6][7][8], published information on the full set of reference ranges for cardiac dimensions and indices for Indian goats is lacking in literature.
Pantja is the local goat of Tarai region of Uttarakhand. Studies on body weight (BW), body measurements, scrotal morphology, production traits, growth pattern, and mortality rate of Pantja goats [9][10][11] have been reported in literature. There are no reports available on the two-dimensional and M-mode echocardiographic study in Pantja goats. This study was designed to establish reference values of two-dimensional guided M-mode echocardiographic parameters and indices in healthy Pantja goats and to evaluate the possible effect of gender and BW on these parameters.

Ethical approval
This study was conducted in accordance with the guidelines laid down by the Institutional Animal Ethics Committee.

Animals
A total of 18, clinically healthy, adult Pantja goats (9 males, 9 females), aged 2-4 years and weighing 10-44 kg (males=29.22±8.44 kg, females=22.88±5.32 kg, mean=26.61±2.52 kg) were included in the study. Animals were acclimatized to approaching, handling and housing conditions for a period of 21-28 days before start of the echocardiographic examination. Animals were considered to be free of cardiovascular disease based on history, clinical examination, complete hematobiochemical examination, cardiac auscultation, normal lead II electrocardiogram, and routine echocardiography.

Echocardiographic protocol
Echocardiographic examination was carried out with a Scintilla Color Doppler Ultrasound Scanner (Larsen and Toubro Limited) equipped with 2.5-3.5 MHz multi-frequency phased-array transducer. Region between 3 rd to 5 th right intercostal spaces starting just caudal to the triceps muscle mass, from 3 to 5 cm below right olecranon to 5-10 cm above it was prepared for echocardiographic examination. Echocardiography was performed in a standing position with the right front leg pulled slightly forward by an assistant. M-mode echocardiographic evaluation of heart was guided by simultaneous display of real time two-dimensional echocardiographic images.

Measurements
Echocardiographic examination was performed using leading edge method as per the recommendations of the American Society of Echocardiography from frozen images on the screen [12]. All measurements were made from right parasternal long-axis left ventricular outflow tract view of heart ( Figure- Teicholz formula [13] was used to calculate the end diastolic volume and end systolic volume (EDV and ESV, respectively). Other parameters, viz., fractional shortening (FS), ejection fraction (EF), stroke volume (SV), cardiac output (CO), percent systolic thickening of IVS%, and percent systolic thickening of LVPW% were calculated using established formulae suggested by Kienle [14]. The animals were grouped into six classes based on their BW: Group I (10-16 kg), Group II (16-22 kg), Group III (22-28 kg), Group IV (28-34 kg), Group V (34-40 kg), and Group VI (40-44 kg) to study the effect of BW on various echocardiographic parameters.

Statistical analysis
Data were analyzed using statistical software SPSS 14.0. Independent sample t-test was used to study differences between male and female dogs. Mean values among different groups based on BW was compared using one-way ANOVA and Duncan's  Available at www.veterinaryworld.org/Vol.10/January-2017/5.pdf multiple range test as per methods described by Snedecor and Cochran [15]. Linear regression analysis was done to assess the relationship between echocardiographic parameters and BW. The correlation was considered positive and significant when correlation coefficient was >0.40 and significance was <0.01. Values of p<0.01 was considered significant for all statistical tests.

Results and Discussion
M-mode echocardiographic reference values in Pantja goats were determined and its subjective comparison with other goat breeds was done. In addition, the possible effect of gender and BW on echocardiographic parameters was determined. Mean±standard error of M-mode echocardiographic parameters and indices in Pantja goats is presented in Table-1. Data on the basis of gender and BW are presented in Tables-1  and 2, respectively. Regression equations, coefficient of determination, and correlation coefficients of various echocardiographic parameters, when compared with BW, are presented in Table-3. Subjective comparison of echocardiographic parameters in Pantja goats with published values in various breed of goats is presented in Table-4.
Nonsignificant influence of gender on various echocardiographic parameters (LVDd, LVDs, IVSd, IVSs, LVPWd, LVPWs, EDV, ESV, SV, FS, EF, IVS%, LVPW%, LAs, AOd, LAPWd, LAPWs, LA/AO, DE amplitude and EPSS) in Pantja goats (Table-1) was in accordance with findings reported in Spitz, Labrador retriever and non-descript dogs [16]. On contrary, significant differences in several echocardiographic parameters were observed between male and female Philippine native sheep [19]. EDV, ESV, SV and CO in male Pantja goats was slightly higher than females, although the differences were non-significant (Table-1). Insignificant variation in heart rate with respect to gender of animals could have led to   (Table-1) was unaffected by gender. Similar findings were reported in Spitz, Labrador retriever and non-descript dogs [16]. Significantly (p<0.01) higher DE amplitude in male Pantja goats (Table-1) was in accordance with findings in Spitz dogs [20]. The reason for this could be higher average BW of males compared to females used in above studies. Non-significant effect of gender on values of EF slope, AC interval, and EPSS was in accordance with findings in Spitz, Labrador retriever and non-descript dogs [16]. Males had slightly higher EPSS which might be due to greater left ventricular dimensions in male Pantja goats compared to females.
BW correlated significantly (p<0.01) with most M-mode echocardiographic parameters (LVDd, LVDs, IVSd, LVPWd, LVPWs, EDV, ESV, SV, CO, LAs, AOd, LAPWs, DE amplitude, and EPSS) in Pantja goats (Tables-2 and 3). Similar findings were observed in Philippine sheep and sedated healthy growing female sheep [19,21]. It is seen that as BW of animal increases, the heart size also increases, and this might have contributed to the above findings. Significant (p<0.01) positive correlation between BW and IVSd, LVPWd and LVPWs in Pantja goats (Tables-2 and 3) was in accordance with findings in sedated healthy growing female sheep [21]. Left ventricular volumes, viz., EDV, ESV, SV, and CO showed significant (p<0.01) correlation with BW (Tables-2 and 3). This might be explained by the fact that with increase in BW, cardiac size increases and with increase in cardiac size, cardiac volume and CO also increases. A weak negative correlation of FS and EF with BW in Pantja goats was in accordance with previous findings in sheep [21]. Variation in the observation of these parameters can be explained by the fact that FS and EF are influenced by many parameters which include preload, afterload and contractility, all of which may act independently or in combination to affect this parameter [16]. Non-significant decrease in FS and EF values with increase in BW (Table-2) could also be due to the reduction of the fractional contraction which occurs as a result of BW increase in animals [16]. LADs, LADd, AOd, AOs and LAPWs correlated significantly (p<0.01) with BW in Pantja goats (Tables-2 and 3). Similar findings were reported in sedated healthy growing female sheep [21]. Among MV parameters, only DE amplitude showed significant (p<0.01) correlation with BW in Pantja goats (Tables-2 and 3). The increase in DE amplitude with an increase in BW can be explained by the rapid increase of left ventricular diameter with animal's increasing BW and age.   Similar findings were reported in Spitz and Labrador retriever dogs [16]. EPSS shows a very weak correlation to BSA and weight in some studies and no correlation in others; therefore, body size is generally not considered when assessing normal EPSS values [22]. However, significant (p<0.01) positive correlation between EPSS and BW in our study (Tables-2 and 3) could either be due to BW differences or small sample size. Similar findings were reported in sedated healthy growing female sheep [21].

Conclusion
From the results of this study, it can be concluded that echocardiographic values in Pantja goats differ from other goat breeds. Gender had no influence while most echocardiographic parameters were influenced significantly by animal's BW. Values obtained in the study may serve as a reference for future studies in this breed as well as for cardiovascular disease diagnosis in humans.