Echocardiographic parameters and indices in the normal Beagle dog

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190. Laboratory Animals (1992) 26, 190-195. Echocardiographic parameters and indices in the normal. Beagle dog. L. CRIPPAl, E. FERR02, E. MELLONIl,.
Laboratory Animals (1992) 26, 190-195

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Echocardiographic parameters and indices in the normal Beagle dog L. CRIPPAl,

E. FERR02,

E. MELLONIl,

P. BRAMBILLA2

& E. CAVALLETTI'

IBoehringer Mannheim Italia, Research Centre, Monza, and 2Institute of Special Pathology and Clinical Medicine, Faculty of Veterinary Medicine, University of Milan, Italy Summary M-mode and two-dimensional echocardiographic measurements were made from the right sternal border of 50 healthy Beagles (25 males and 25 females) approximately 7 months old. The dogs were conscious and standing during the investigation. The following parameters, in systole and diastole, were measured on the echocardiographic images: left ventricular posterior wall

thickness (LVWT); intraventricular septum thickness (1ST); left ventricular internal dimension (LVID); and circumference (LVC). Fractional shortening (FS) and ejection fraction (EF) were also calculated. Mean, standard deviation, range and coefficient of variation are reported for each echocardiographic parameter and for body weight. Males and females were considered separately and together. Each parameter was analysed statistically to check for differences between the sexes and for correlations with body weight. A statistically significant difference between the sexes was only observed for L VWT in systole and diastole. A linear regression with body weight was obtained only for LVID in systole and in diastole. The results show that morphofunctional cardiac homogeneity is independent of size in dogs of this breed and age.

Keywords: Echocardiography; Beagle; Normal values Correspondence to: Dr L. Crippa, Department of Toxicology, Boehringer Mannheim Italia, Research Centre, Viale della Libertil Km 0.750, 20052 Monza, Italy. Received 7 August /99/; accepted 29 November /99/

In the last decade ultrasonography has become an important diagnostic method in veterinary medicine of small animals. It distinguishes between body fluids and soft tissues, defines spatial relationships between structures and serves to investigate moving organs; it has been widely employed in humans (Feigenbaum, 1981) and small animals (Bonagura, 1983) in the cardiovascular field. Ultrasonography is now considered an important non-invasive technique for studying the heart of the dog; this harmless technique is particularly suitable when repeated and frequent measurements are required for clinical (Bonagura, 1983) or research purposes (Allen, 1982). Ultrasonography could also be a useful and simple tool for pharmacological or toxicological research in the cardiovascular field (Hirota et al. , 1978) and with the advent of clinical ultrasonography, it is now possible to image cardiac lesions, quantitate heart size and assess cardiac function using the non-invasive formats of Mmode and two-dimensional echocardiography (Bonagura, 1983). This study was carried out principally to evaluate the normal values of the main echocardiographic parameters in Beagles in order to establish standards for the application of ultrasonography in this breed of dog, used in pharmacological and toxicological experiments. For each echocardiographic parameter, sexrelated differences and their correlation with the body weight were investigated. This relationship has already been studied by other authors on groups of animals differing in weight, breed and age, and there was a strong correlation between body weight and some echocardiographic

Echocardiograph in the dog

parameters such as left ventricular posterior wall thickness (LVWT), interventricular septum thickness (1ST)and left ventricular internal dimension (LVID) (Bonagura, 1983; Boon et al., 1983; Lombard, 1984). Our purpose therefore, was to confirm those results in a group of dogs differing in weight but homogeneous for age and breed. Methods Animals Beagles of both sexes (25 males and 25 females) from Stefano Morini (S. Polo d'Enza (RE), Italy) were used. The dogs were around 28 weeks old and their mean body weight was 9·1 kg for males and 8, 7 kg for females. Dogs were acclimatized in our kennel unit for 3 weeks before the study started. The animals were immunized against distemper, hepatitis and leptospirosis, and treated prophylactically with antihelminthics, and regularly checked by veterinarians. They were housed individually in areas under controlled conditions (temperature 19-22°C; humidity 30-700/0) and received about 400 g/day of a standardized dry pellet food [Altromin H, produced by Rieper (BZ) V, Italy] and drinking tap water ad libitum. A dark-light cycle of 12 h (0700-1900 h) was employed during the study. Electrocardiographic tracings were recorded on all dogs the week before the echocardiographic investigation and all dogs were within the normal range. Echocardiography Echocardiographic investigations were carried out, after having recorded body weight, in a quiet and dimly lit room with the Beagles conscious and standing. M-mode and two-dimensional echocardiograms were obtained using a sectorial-mechanicalechocardiograph (OTE-BIOMEDICA model SIM 4000/C) equipped with an ECG cable and a 3 . 5 MHz 90 rotatory mechanical transducer. The transducer was placed at the right sternal border between the second to fourth intercostal space (Echo-window) and contact with the chest wall was made with ultrasonic gel. 0

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Echocardiograms were recorded on VHS videotape for playback analysis. Echocardiographic parameters M-mode echo cardiography (one-dimensional). Echocardiographic measurements were made according to the recent literature (Bonagura, 1983; Lombard, 1984; Bonagura et al., 1985; Boccanelli & Gambelli, 1988) and to the recommendations of the American Society of Echocardiography (Sahn et al., 1978), in the second standard echocardiographic position as described by Feigenbaum (Feigenbaum, 1981). The following parameters were measured in systole (s) (corresponding to the maximal excursion of the septum and of the left ventricular posterior wall) and at end-diastole (d) (corresponding to the onset of the QRS complex): 1. LVWT (s) and (d) = left ventricular posterior wall thickness (in millimetres) 2. 1ST (s) and (d) = interventricular septum thickness (in millimetres) 3. LVID (s) and (d) = left ventricular internal dimension (in millimetres) Two-dimensional echocardiography (2DE). Echocardiographic measurements were made on short-axis views at the level of the papillary muscle (Thomas, 1984). The following measurements were made in systole and at end-diastole excluding the papillary image: LVC(s) and (d) = left ventricular internal circumference (in millimetres) Indices These indices were calculated using the following calculations as reported by Bonagura (1983). LVID(d) - LVID(s) FS= LVID(d) (FS = fractional shortening). LVID(d)3 - LVID(s)3 LVID(d)3 (EF = ejection fraction). EF = ----"---'------

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These indices can be employed to evaluate the true efficacy of the contractile strength of the heart (FS) and its haemodynamic characteristics (EF). Statistics Mean value, standard deviation (SO), range and coefficient of variation (CV%) of all echocardiographic parameters were calculated for males and females separately and together. To detect possible differences between sexes, one-way ANOV A was carried out for body weight and an ANCOV A, with body weight as covariant, was carried out for all the echocardiographic parameters and indices. Analysis of linear regression was used to assess the relationships between all echocardiographic parameters and body weight. This analysis was carried out separately for the two sexes only for the parameters which showed a

significant difference ANCOVA analysis.

between sexes at the

Results Mean, SO, minimum and maximum values and CVltJo of the body weight and all the echocardiographic parameters, for males and females separately and together, are reported in Tables 1 and 2. Table 3 sets out the results of statistical analysis of sex-related differences and correlations with body weight. The body weight of male dogs was about 4, 2% higher than females but this difference was not significant. The LVWT was 14'3% and 21,0% higher in males than in females when measured in systole and in diastole, respectively. These differences were statistically significant (P