Doppler Echocardiographic Reference Values in Healthy Donkeys (1-Sep-2004)

Transcription

1 In: Veterinary Care of Donkeys, N.S. Matthews and T.S. Taylor (Eds.) Publisher: International Veterinary Information Service ( Ithaca, New York, USA. Doppler Echocardiographic Reference Values in Healthy Donkeys (1-Sep-2004) H. Amory 1, P. Bertrand 2, V. Delvaux 3 and C. Sandersen 4 1 Department of Clinical Sciences and 2 Department of Functional Sciences, Faculty of Veterinary Medicine, University of Liège, Liège, Belgium. Introduction Doppler echocardiography provides a means to non-invasively evaluate the anatomy and function of the heart, and is playing an increasingly important role in the evaluation and management of patients or animals with all forms of cardiac disease [1-3]. It has now become a routine for the diagnosis and evaluation of heart disease in veterinary medicine [4]. This is especially true in large animals in which most of the non-invasive cardiac diagnostic tools are of limited value because of the size and the specific anatomy and physiology of the heart in those species [5]. The diagnostic value of echocardiography must first be based on a global evaluation of the heart and on comparison between the visible structures which, in conjunction with the cardiologist experience, gives a preliminary general impression of the heart function [4,6]. Moreover, Doppler echocardiography allows an accurate quantitative assessment of cardiac morphology and function based on morphological echocardiographic, blood flow velocities and systolic time intervals measurements [2,3,6-10]. However, in any species, for echocardiography to allow such an accurate measure of cardiac dimensions and indices of cardiac function, it is important to dispose of reference values determined by using standardized measurement guidelines in this species [7-10]. Moreover, in most species, echocardiographic data have been shown to be affected by several physiological factors such as breed [10], body size [4,7-10] and shape [4], growth [7,8], aging [4], training [2,6,12,13] and heart rate [2,3,8,14,15]. Contrary to published reference values in most species including horses, there are very limited reported echocardiographic data in donkeys [16], which obviously limits the diagnostic and prognostic value of Doppler echocardiography in these animals. The purpose of this study was to determine, using a standardised guided technique developed in horses, normal values of echocardiographic dimension and functional indices and quantitative reference values of Doppler flow profiles in the healthy donkey, and to relate cardiac dimensions and indices to body size in this species. List of Abbreviations Ao BS - Aortic diameter at the level of its base (annulus) Ao JT - Aortic diameter at the level of the sino-tubular junction Ao VA - Aortic diameter at the level of the sinus of Valsalva BW - Body weight CI-D - Cardiac index derived from Doppler measurements CO-D - Cardiac output derived from Doppler measurements d - Diastolic measurement EDV - End diastolic left ventricular volume EDVI - EDV indexed for BW EF - Left ventricular ejection fraction ESV - End systolic left ventricular volume ESVI - ESV indexed for BW ET - Ejection time of the aortic or pulmonary flow FAC - Fractional area change FS - Fractional shortening of the left ventricle FWT IVS - Fractional wall thickening of the interventricular septum FWT LVW - Fractional wall thickening of the left ventricular free wall

2 HR - Heart rate IVS - Interventricular septum thickness LA - Left atrial diameter LV mass - Left ventricular mass LV mass index - LV mass indexed for body weight LVEA - Left ventricular external area LVIA - Left ventricular internal area LVID - Left ventricular internal diameter LVID index - LVID indexed for body weight LVW - Left ventricular free wall thickness MYAd - Myocardial surface in diastole MYAs - Myocardial surface in systole MWT - Mean wall thickness MWT IndexI - MWT indexed for body weight Peak A - Peak velocity of mitral or tricuspid blood flow during the atrial contraction Peak E - Peak velocity of mitral or tricuspid blood flow during the rapid ventricular filling PEP - Pre-ejection period of the aortic or pulmonary flow Pu - Pulmonary artery diameter RVID - Right ventricular internal diameter RWT - Relative wall thickness s - Systolic measurement SI-D - Stroke index derived from Doppler measurements SI-T - Stroke index issued from the Teicholz formula SV-D - Stroke volume derived from Doppler measurements SV-T - Stroke volume issued from the Teicholz formula TTP - Time to peak of the aortic or pulmonary flow Vmax - Peak velocity of blood flow of the aortic or pulmonary flow during systole VTI - Area under the velocity wave-form of the aortic or pulmonary flow Material and Methods Animals - Twenty-two healthy common donkeys (12 males (3 castrated and 9 stallions) and 10 females), aged from 4 months to 18 years (Mean + SD: years) and weighing from 45 to 260 Kg (Mean + SD: kg), were used in this study. All donkeys were determined to be free from cardiac disease on the basis of clinical, electrocardiographic, 2D and color flow mapping Doppler echocardiographic examination. Donkeys with an early systolic grade 1 or 2/5 ejection murmur with the point of maximal intensity over the aortic valve (9 of the 22 studied donkeys) were considered as normal. Three donkeys had second-degree atrioventricular blocks during the examination. However, in these animals, all measurements were made from normal sinus rhythm intervals. All donkeys were free from significant valvular regurgitation on periventricular Doppler echocardiography. To establish the normal echocardiographic data in adult donkeys, 20 of the 22 studied donkeys were selected. Their mean age was years (range: 4-18 years) and their mean body weight was kg (range kg). This adult group included 11 males (3 castrated and 8 stallions) and 9 females. Before imaging, the coat was bilaterally shaved from the 3rd to the 5th intercostal space just caudal to the triceps muscle mass, from 3 to 5 cm below the olecranon to 5 to 10 cm above it. The shaved areas were then copiously rinsed with water and acoustic coupling was obtained using ultrasound gel. Equipment - An RT 6800 ultrasound system (GE Medical Systems, London, United Kingdom) with a 2.5 MHz phased-array sector scanner and 2D, and B-mode, M-mode, colour flow mapping and spectral Doppler programs was used. The maximum imaging depth of the equipment was 25 cm and the maximum sector angle was 90º. The ultrasound machine had an integrated ECG function where the ECG traces were displayed simultaneously with the images. A base-apex bipolar DII lead system was used, with electrodes applied over the left jugular furrow and the ventral portion of the left abdomen over the girth place. Imaging Technique - Donkeys were examined standing. The forelimb of the investigated hemithorax was slightly pulled forward during investigation. All images were recorded on videotape for subsequent analysis. Terminology and image orientation were those

3 recommended by the echocardiographic committee of the specialty of cardiology, ACVIM [17]. Imaging planes were selected according to identification of intracardiac landmarks as previously reported in horses [1,3,18-20]. For Doppler-mode views, alignment with blood flow was initially assessed from a 2D ultrasound image in order to minimize beam angulation. Accurate alignment with blood flow was assumed when the audible signal was clear and the spectral envelope of the Doppler wave-form was complete. The donkeys were first examined from the right hemithorax. The ultrasound beam was placed in the 4th or 5th intercostal space, perpendicular to the thoracic wall, just dorsal to the olecranon. The position of the beam was adjusted to obtain a 2Dmode right parasternal long-axis four-chamber reference view, with the interventricular septum orientated as horizontal as possible (Video 1). Video Mo - Bidimensional mode right parasternal long-axis four-chamber reference view obtained in a healthy donkey. - To view this video click on the QuickTime icon - General impressions of cardiac size and function were first obtained from this view. An M-mode long-axis view of the right and left ventricle was obtained by placing the M-mode cursor perpendicular to the interventricular septum and the left ventricular free wall at the chordae tendinae level, between the tips of the mitral valves leaflets and the left ventricular papillary muscles (Video 2). Video Mo - M-mode right parasternal long-axis view of the right and left ventricle obtained in a healthy donkey. - To view this video click on the QuickTime icon - From the 2D-mode long-axis four-chamber reference view, the beam was then rotated through in clockwise direction with slightly cranial and dorsal direction to produce a 2D-mode right parasternal long-axis five-chamber (outflow) view showing the left ventricle and left ventricular outflow tract (Video 3). In this view, the aorta was positioned perpendicular to the axial beam. Video Mo - Bidimensional mode right parasternal long-axis five-chamber (outflow) view obtained in a healthy donkey. - To view this video click on the QuickTime icon - Starting from the 2D-mode long-axis four-chamber reference view, the beam was then rotated clockwise toward the olecranon. In the produced transverse view, the beam was pivotated dorsally or ventrally until a 2D-mode right parasternal short-axis view of the left ventricle at the level of the chordae tendinae was obtained, in which the interventricular septum, the left ventricular free wall and the left ventricle were bisected at right angle and the left ventricle was circular (Video 4). The papillary muscles and mitral valve leaflets were not visible and chordae tendinae were clearly visible. In this view, an M- mode right parasternal short-axis view of the left ventricle at the chordal level was obtained by placing the cursor at right angle through the left ventricle, dividing the left ventricle in symmetric halves (Video 5). Video Mo - Bidimensional mode right parasternal short-axis view of the left ventricle at the level of the chordae tendinae obtained in a healthy donkey. - To view this video click on the QuickTime icon - Video Mo - M-mode right parasternal short-axis view of the left ventricle at the chordal level obtained in a healthy donkey. - To view this video click on the QuickTime icon -

4 From the 2D-mode short-axis view of the left ventricle at the chordal level, the beam was pivoted dorsally in the direction of the heart base, pointed slightly dorsally, and rotated slightly clockwise or anticlockwise until a clear 2D-mode right parasternal image of the heart base at the level of the pulmonary valves was obtained (Video 6). It was often necessary to move the transducer one intercostal space cranially as compared to the reference view and to push the right foreleg of the donkey slightly more forward to obtain this view. In this view, the pulmonary artery was imaged in a long-axis view. The Doppler pulsed-wave mode was selected and the gate was placed just distal to the pulmonary valves, allowing recording the pulmonary Doppler outflow velocity spectrum. Video Mo - Bidimensional mode right parasternal view of the heart base at the level of the right ventricular outflow tract obtained in a healthy donkey. - To view this video click on the QuickTime icon - Coming back to a 2D-mode right parasternal long-axis four-chamber reference view, the transducer was directed as ventrally as possible to produce an angled view of the right ventricular inflow tract (Video 7). In this view, the Doppler pulsed-wave mode was selected and the gate was placed so that it was at the valves tips in systole and between the valve leaflets in diastole. This allowed obtaining the recording of the tricuspid inflow velocity spectrum. Video Mo - Bidimensional mode right parasternal long-axis angled view of the right ventricular inflow tract obtained in a healthy donkey. - To view this video click on the QuickTime icon - The donkeys were then examined from the left hemithorax. The beam was placed in the 4th or 5th intercostal space, perpendicular to the thoracic wall, just dorsal to the olecranon. As in the right hemithorax, the position of the beam was adjusted to obtain a 2D-mode long-axis four-chamber reference view, with the interventricular septum orientated as horizontal as possible. In this view, a M-mode left parasternal long-axis view of the left ventricle was obtained by placing the cursor perpendicular to the interventricular septum at the chordae tendinae level, between the tips of the mitral valves leaflets and the left ventricular papillary muscles. From the 2D-mode long-axis four-chamber view, the transducer was moved more ventrally and caudally to produce a 2Dmode left parasternal long-axis angled view of the left ventricle and left atrium optimized to produce the largest diameter of the LA (Video 8). In this view, the Doppler pulsed-wave mode was selected and the gate was placed as for tricuspid flow, which allowed to obtain a mitral inflow velocity spectrum recording (Video 9). From the left parasternal long-axis angled view, the transducer was rotated anticlockwise until the aorta was seen, producing the 2D-mode left parasternal apical five-chamber view. In this view, the Doppler pulsed-wave mode was selected and the gate was placed just distal to the aortic valves, allowing recording the aortic outflow velocity spectrum (Video 10). Video Mo - Bidimensional mode left parasternal long-axis angled view of the left ventricle and left atrium obtained in a healthy donkey. - To view this video click on the QuickTime icon - Video Mo - Pulsed-wave Doppler left parasternal mitral inflow velocity spectrum obtained in a healthy donkey. - To view this video click on the QuickTime icon - Video Mo - Pulsed-wave Doppler left parasternal aortic outflow velocity spectrum obtained in a healthy donkey. - To view this video click on the QuickTime icon - Echocardiographic Measurements - Measurements were made from examinations previously recorded on videotapes using

5 manual planimetry and electronic callipers provided within the analysis software system in-built in the RT 6800 General Electric Medical. All measurements were in-built as previously recommended in horses [1,3,18-20], and were made at resting heart rates and from 3 to 5 consecutive cardiac cycles, the median value from each individual donkey being used for analysis. Diastolic measurements were made at the onset of the QRS complex or at largest left ventricular dimension. Systolic measurements were made at smallest left ventricular dimension (2D-mode) or peak downward point of septal motion (Mmode). All measurements were made using the leading edge to leading edge method as recommended by the American Society of Echocardiography [21]. The right ventricular internal diameter (RVID) was measured at end-diastole in the M-mode right parasternal long-axis and short-axis view of the left ventricle. The interventricular septal and left ventricular free wall thicknesses (IVS and LVW, respectively) and the left ventricular internal diameter (LVID) were measured at end-diastole and at end-systole in the M- mode right parasternal long-axis and short-axis view of the left ventricle, in the 2D-mode right parasternal short-axis view of the left ventricle, and in the M-mode left parasternal long-axis view of the left ventricle. In each of those views, the following parameters were calculated [2,22]: Indexed LVIDd (LVIDI): LVIDI = LVIDd/ BW Where BW = body weight Fractional shortening of the left ventricle (FS): FS = [(LVIDd - LVIDs)/LVIDd] Where d and s refers to the diastolic and systolic measurement, respectively. Fractional wall thickening of the interventricular septum (FWT IVS) and of the left ventricular free wall (FWT LVW): FWT IVS = [(IVSs - IVSd)/IVSd] FWT LVW = [(LVWs - LVWd)/LVWd] Relative wall thickness (RWT): RWT = (LVWd + IVSd)/ LVIDd Mean wall thickness (MWT): MWT = (LVWd + IVSd)/ 2 Indexed mean wall thickness (MWTI): MWTI = MWT/ BW Moreover, the following parameters were calculated using the measurements obtained from the M-mode right parasternal short-axis view of the left ventricle: End-diastolic left ventricular volume (EDV) and end-systolic left ventricular volume (ESV), using the Teichholz formula [2]: EDV = (7 X LVIDd 3 )/(2.4 + LVIDd) ESV = (7 X LVIDs 3 )/(2.4 + LVIDs) Indexed EDV and ESV (EDVI and ESVI, respectively): EDVI = EDV/BW ESVI = ESV/BW Left ventricular ejection fraction (EF): EF = [(EDV-ESV)/EDV] Stroke volume issued from the Teicholz formula (SV-T): SV-T = EDV - ESV Stroke index issued from the Teicholz formula (SI-T): SI-T = SV-T/BW Left ventricular mass (LV mass), using the formula of Devereux and Reichek (1977) [23]: LVmass = (1.04 X ((LVIDd + LVFWd + IVSd) 3 LVIDd 3 )) 13.6 Indexed LV mass (LV mass index) LV mass index = LV mass/bw

6 The left ventricular internal and external area (LVIA and LVEA, respectively) were measured by planimetry in diastole and in systole from the 2D-mode right parasternal short-axis view of the left ventricle at the chordal level. From those measurements, the following parameters were calculated: Fractional area change (FAC): FAC = (LVIAd-LVIAs/ LVIAd ) Myocardial surface in diastole (MYAd) and in systole (MYAs): MYAd = LVEAd-LVIAd MYAs = LVEAs-LVIAs The left atrium diameter (LA) was measured at end-diastole from the 2D-mode left parasternal angled four-chamber view. Aortic diameter measurements were made at end-diastole from the 2D-mode right parasternal long-axis left ventricular outflow view. A line connecting the annulus was made and measured (AoBS), and the sinus of Valsalva was measured at its largest dimension (Ao VA). The ascending aorta was measured during systole at its narrowest dimension distal to the sinus, at the sino-tubular junction (Ao JT). The pulmonary artery diameter (Pu) was measured at end-diastole and at its largest diameter from the 2D-mode right parasternal image of the heart base at the level of the right ventricular outflow tract. Doppler Measurements - The heart rate was measured from the ECG tracings recorded together with the Doppler spectral images. From the mitral and tricuspid velocity spectral recordings, the peak velocity of blood flow during the rapid ventricular filling (Peak E) and during the atrial contraction (Peak A) were measured by placing the cursor at the apex of the maximal upwards motion of blood flow. From those parameters, the ratio Peak E/Peak A (E/A) was calculated. From the aortic and pulmonary velocity spectral recordings, the peak velocity of blood flow (Vmax) was measured by placing the cursor at the apex of the maximal downwards motion of blood flow. The area under the velocity waveform (VTI) was measured by tracing the modal velocity (represented by the brightest line in the spectral Doppler waveform) envelope of the Doppler signal. The ejection time (ET) was measured from the onset to the end of the spectral waveform. The time to peak (TTP) was measured from the onset of the Doppler waveform to the start of the maximum velocity plateau. The pre-ejection period (PEP) was measured from the onset of the QRS complex to the onset of the spectral waveform. The stroke volume and cardiac output derived from the Doppler measurements (SV-D and CO-D, respectively) were calculated as follows: SV-D = VTI. [(Ao JT/2) 2.π] CO-D = SV-D. HR Where HR = heart rate The stroke and cardiac index derived from the Doppler measurements (SI-D and CI-D, respectively) were calculated by dividing SV-D and CO-D, respectively, by the donkey s body weight. Statistical Analysis - The mean + SD value was calculated for each echocardiographic and Doppler parameter within the group of adult donkeys. The mean value of systolic and diastolic IVS, LVID, and LVW, and of RWT, FS, FWT IVS, FWT LVW and MWT obtained from the M-mode right parasternal long-axis view, from the 2D-mode right parasternal short-axis view, from the M-mode right parasternal short-axis view, and from the M-mode left parasternal long-axis view were compared to each other using a paired Student s test. The mean values of RVIDd obtained from the M-mode right parasternal long-axis view and from the M-mode right parasternal short-axis view of the left ventricle were compared using a paired Student s test. The mean values of SI-T and of SI-D were compared using a paired Student s test. The relationship between each echocardiographic and Doppler parameter with body weight was evaluated by a linear regression analysis. For all tests, a P value < 0.05 was considered to be significant. Results In all examined donkeys, imaging of the heart was easy, except in the largest animals that were also the fattest. General impressions of cardiac size and function obtained from all views were comparable to those obtained in healthy horses, i.e., no

7 bowing of the interventricular septum, a right ventricle wall approximately half thickness of the LVW, a right ventricular chamber size approximately half of the left ventricular size, a mitral valve excursion almost to the interventricular septum, and no valvular lesions [2]. Spontaneous contrast was occasionally seen in the right and left ventricular chamber as in healthy horses [2]. Mean values of right and left ventricular dimensions and wall thickness and of left ventricular functional indices obtained from the four T views of the left ventricle used in this study are compared in Table 1. Corresponding values previously reported in small ponies [10] and in horses [1,20,22,24,25] are also given in this table for comparison. Table 1. Right and left ventricular dimensions and functional indices obtained from various echocardiographic views and modes in 20 healthy adult donkeys as compared with reference values previously reported in healthy adult horses and ponies. Present study: Donkeys Ponies [10] Horses [1,20,22,24,25] BW Kg Kg Kg View L LAx M R LAx M R SAx 2D R SAx M R SAx M R SAx M RVIDd (cm) IVSd (cm) IVSs (cm) LVIDd (cm) LVID I (cm/kg.10 2 ) LVIDs (cm) LVWd (cm) LVWs (cm) MWT (cm) MWT I (cm/kg.10 2 ) FS (%) FWT IVS (%) FWT LVW (%) RWT NM ( ) ( ) ( ) (2.4 - ( ) a 3.8) (4.5 - ( ) 9.6) ( ) ( ) ( ) ( ) ( ) ( ) (28-62) ( ) ( ) ( ) ( ) ( ) ( ) (25-58) (11-91) a (32-124) (21-107) (39-157) (44-70) (43-78) NM ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) (41-55) (47-108) (21-154) (38-76) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) (38-54) (47-111) (35-103) (39-65) None of the measured parameters showed significant difference between echocardiographic modes and views, with the exception of systolic IVS and FWT IVS that were significantly lower when measured from left parasternal view than from each of the right parasternal views. The left ventricular dimensions obtained in donkeys in this study were closely comparable to previously reported data in small ponies of the same body weight, and were clearly lower than previously reported data in adult horses. The LVIDI and MWTI tended to be higher in donkeys of this study than previously values NR ( ) ( ) ( ) NR ( ) ( ) ( ) NR NR ( ) [20] ( ) [1] ( ) [1] ( ) [1] ( ) [22] ( ) [22] ( ) [1] ( ) [1] ( ) [1] ( ) [22] ( ) [22] NR (29-45) [1] NR NR NR T: ;U: [24] T: ; U: [24] T: ; U: [25] See list of abbreviations for legend. BW = body weight; L = left parasternal; LAx = long-axis view; SAx = short-axis view ; M = M-mode; 2D = bidimensional mode; NM = not measured; NR = not reported; a = significantly lower than corresponding value obtained from the R LAx M, from the R SAx 2D and from the R SAx M, paired T- test, P < T: mean value in trained horses; U: mean value in untrained horses

8 reported in adult horses. Mean values of left atrium, aortic and pulmonary diameters, and of left ventricular area, myocardial indices and functional indices obtained in adults donkeys in this study are given in Table 2 with corresponding values reported in adult horses [1,3,22]. All dimensional parameters obtained in donkeys were clearly lower than in adult horses, and FAC and EF tended to be slightly higher in donkeys than in adult horses. The indexed LV mass obtained in donkeys was lower than previously reported data in adult horses. Table 2. Echocardiograhic parameters obtained in 20 healthy adult donkeys as compared with reference values previously reported in healthy adult thoroughbred or standardbred horses. Parameter Present study ( kg) Horses [1,3,22] ( kg) LA (cm) ( ) ( ) [1] Ao BS (cm) ( ) ( ) [1] Ao VA (cm) ( ) ( ) [1] Ao JT (cm) ( ) ( ) [1] Pu (cm) ( ) ( ) [1] LVIAd (cm 2 ) ( ) ( ) [22] LVIAs (cm 2 ) ( ) LVEAd (cm 2 ) ( ) LVEAs (cm 2 ) ( ) FAC (%) ( ) MYAd (cm 2 ) ( ) MYAs (cm 2 ) ( ) EDV (ml) ( ) EDVI (ml/kg) ( ) NR ESV (ml) (26-164) ESVI (ml/kg) ( ) NR EF (%) (66-84) LV mass (g) ( ) ( ) [22] LV mass indexed (g/kg) ( ) ( ) [22] SV-T (ml/beat) (86-315) SI-T (ml/beat/kg) ( ) NR See list of abbreviations for legend. All dimensional echocardiographic parameters were poorly or moderately but significantly correlated with body weight, with the exception of IVSd and LVWd measured in the 2D-mode right parasternal short-axis view and LVWs measured in the M- mode right parasternal short-axis view. The linear regression equations of each parameter with body weight are given in Table 3.

9 Table 3. Linear regression equation and correlation coefficients of echocardiograhic parameters with body weight in 22 healthy donkeys. Parameters View Linear equation R P RVID IVSd IVSs LVIDd LVIDs LVWd LVWs R LAx M BW R SAx M BW R LAx M BW R SAx 2D BW 0.42 NS R SAx M BW L LAx M BW R LAx M BW 0.80 < R SAx 2D BW R SAx M BW 0.74 < L LAx M BW R LAx M BW 0.78 < R SAx 2D BW 0.75 < R SAx M BW 0.79 < L LAx M BW 0.87 < R LAx M BW R SAx 2D BW R SAx M BW L LAx M BW 0.76 < R LAx M BW R SAx 2D BW 0.32 NS R SAx M BW L LAx M BW 0.82 < R LAx M BW 0.72 < R SAx 2D BW R SAx M BW 0.43 NS L LAx M BW 0.77 < LVIAd (cm 2 ) R SAx 2D BW 0.79 < LVIAs (cm 2 ) R SAx 2D BW LVEAd (cm 2 ) R SAx 2D BW LVEAs (cm 2 ) R SAx 2D BW MYAd (cm 2 ) R SAx 2D BW MYAs (cm 2 ) R SAx 2D BW EDV (ml) R SAx M BW ESV (ml) R SAx M BW LV mass (g) R SAx M BW SV (ml/beat) R SAx M BW 0.78 < LA (cm) L LAx 2D BW 0.84 < Ao VA (cm) R LAx 2D BW 0.88 < Pu (cm) R SAx 2D BW See list of abbreviations for legend.

10 All functional indices and parameters indexed for body weight calculated from dimensional echocardiographic parameters were not significantly correlated with body weight, with the exception of FAC that presented a significant positive linear regression with body weight (R = 0.58). In Table 4, the mean values of pulsed-wave Doppler quantitative data obtained in adult donkeys in this study are given and compared to corresponding values reported in adult horses [11,26,27]. Most of those parameters were closely similar between donkeys and horses, with the exception of mitral and tricuspid Peak E and A that tended to be lower in the present study in donkeys than in previously reported data in horses. The previously reported Doppler-derived stroke volume and cardiac output in adult horses were clearly higher than those obtained in the present study in donkeys, but when those parameters were indexed for body weight, they were closely comparable in donkeys and horses. Mean heart rate during the Doppler examination obtained in this study was beats/min. Amongst the Doppler-derived parameters, the following presented a significant positive linear regression with body weight: tricuspid Peak A (R = 0.55), pulmonary Vmax (R = 0.53) and VTI (R = 0.51), and aortic Vmax (R = ), SV-D (R = ), and CO-D (R = 0.67). The aortic ET and TTP presented a negative significant linear regression with body weight (R = 0.51). The other Doppler-derived parameters were not significantly related to body weight. The heart rate significantly correlated to body weight according to a negative linear regression (R = 0.55). The stroke volume was not significantly different when calculated using the Teicholz formula as compared when calculated from the Doppler data. Table 4. Doppler echocardiograhic parameters obtained in 20 healthy adult donkeys as compared with reference values previously reported in healthy adult horses. Parameters Present study Horses [11,26,27] Tricuspid flow Peak E (cm/sec) ( ) ( ) [11] Peak A (cm/sec) ( ) ( ) [11] E/A ( ) ( ) [11] Mitral flow Peak E (cm/sec) ( ) ( ) [11] Peak A (cm/sec) ( ) ( ) [11] E/A ( ) ( ) [11] Pulmonary flow Vmax (cm/sec) ( ) ( ) [11] [26] T: ; DT: [27] VTI (cm) ( ) ( ) [11] [26] T: ; DT: [27] TTP (msec) ( ) ( ) [11] PEP (msec) (35-83) (20-100) [11] T: DT: [27] ET (msec) ( ) ( ) [11] T: ; DT: [27] PEP/ET ( ) T: ; DT: [27]

11 Table 4. Doppler echocardiograhic parameters obtained in 20 healthy adult donkeys as compared with reference values previously reported in healthy adult horses. (Continued) Aortic flow Vmax (cm/sec) ( ) ( ) [11] [26] T: ; DT: [27] VTI (cm) ( ) ( ) [11] [26] T: ; DT: [27] TTP (msec) (92-185) (90-170) [11] PEP (msec) (42-123) (40-110) [11] T: ; DT: [27] ET (msec) ( ) ( ) [11] [27] PEP/ET ( ) T: ; DT: [27] SV-D (ml/kg) ( ) [26] SI-D (ml/beat.kg-1) ( ) [26] CO-D (l/min) ( ) T: ; DT: [26] CI-D (l/min.kg-1) ( ) [26] See list of abbreviations for legend. T: values obtained after a training period; DT: values obtained after 12 weeks of detraining. Discussion In equines, Doppler echocardiography has been shown to be feasible, repeatable and accurate, and has been demonstrated to be a powerful tool to detect cardiac abnormalities or drug-or training-induced cardiac changes [3,6,20]. Initially, numerous M-mode [5-8,12,24], two-dimensional real time or 2D-mode [9,29-31] and Doppler [32,33] echocardiography reference values using non standardized imaging techniques have been established in this species. However, results of most of those studies were not in good agreement to each other because different echocardiographic measurement methods were used [14], and for Doppler measurements, because angles between the Doppler beam and blood flow were large and required angle correction for flow velocities determination, which is known to cause important errors in the estimation of blood flow velocities [11]. In 1992, a standardized imaging technique for accurate guided M-mode and Doppler echocardiographic measurements has been developed in horses [20]. This standardized technique has thereafter been adapted and easily comparable reference Doppler echocardiographic values have been published in adult thoroughbred or cross-thoroughbred [1,3,10,11,22], standard bred [14] or warm blood [13] horses. In the present study, the same standardized technique has been used to establish reference values of echocardiographic and pulsed-wave derived data in healthy donkeys. Most of the echocardiographic morphologic parameters obtained in the present study in adult donkeys were logically smaller than corresponding parameters reported in adult horses. On the contrary, they were closely comparable to values reported in small ponies of the same body weight (i.e., 125 to 306 kg; mean: 158 kg) [10] than the donkeys of the present study (i.e., 98 to 260 kg; mean: 159 kg). Therefore, body weight seems to be an important factor affecting cardiac dimensions in equids, as it has been demonstrated in other species [2]. Previously reported data on the relationship between echocardiographic morphologic parameters and body weight in the equine species are controversial: some authors did not find any relationship between those parameters [6,14,20], whilst others demonstrated that echocardiographic morphological parameters were significantly correlated with body weight [4,7-10]. However, the studies that demonstrated no relationship between the echocardiographic parameters and body weight included horses of homogeneous size [14]. When working on extremely large equids such as draft horses or extremely small equids such as ponies or donkeys, cardiac dimensions measured by echocardiography are more obviously affected by the body size [10]. It was thus useful to determine the normal reference values of morphologic echocardiographic parameters in healthy donkeys. Moreover, within the relatively small range of body weight investigated in the present study, echocardiographic

12 morphologic parameters were shown to be related with body weight in donkeys. The use of the linear regression equations given in the study could be helpful in increasing the accuracy of cardiac size determination in a donkey suffering from a cardiac disease, especially when examining a tall donkey, such as a donkey of the Catalan or of the Andalucian breed, or a small donkey, such as a donkey of the Miniature Mediterranean breed. Whatever the investigated species, including horses, functional echocardiographic parametera do not correlate with body weight [1,2,8,10,20]. In the present study, most of the functional echocardiographic parameters were also not related with body weight in donkeys. Doppler flow profiles are known to be difficult to obtain in equids primarily because of the large angles of incidence that are encountered and the lack of alternative imaging sites [2,11,32]. An angle correction is not recommended because it is known to overestimates the velocity [11,32]. An other limitation to use of Doppler in equids is depth limitations: the deeper the sample volume is placed within the heart, the higher the frequency of the transducer, the poorer the quality of the pulsedwave Doppler signal, until blood flow velocities can no longer be determined [32]. These problems were also encountered in the donkeys in the present study, although in the views used to image the flows, depth limitation was not a major problem because of the small size of the animals. Most of the Doppler parameters obtained in adult donkeys in the present study were very similar to data previously reported in adult horses [2,11,26,27]. Only the tricuspid and mitral peak flow velocities were lower in donkeys in the present study than in horses. This could be due to a poorer beam alignment with auriculo-ventricular flow or an inappropriate placement of the sampling site in this study as compared to previous studies in horses. Moreover, in some of the previous studies performed in horses, the sample volume was not always placed at the same place to measure the E and the A peak. A different and optimal positioning of blood flow being taken into account to measure those peaks in the reported values [11]. In the present study, the E and the A peaks were measured in the same auricle view and at the same cardiac cycle, and this could have induced an underestimation of the tricuspid and mitral inflows. Finally, a lower auriculo-ventricular pressure drop or a greater area of the tricuspid or mitral annulus in donkeys as compared with horses could also partly explain the lower peak E and peak A obtained in the present study [2,11,32]. Little or no correlation has been found between velocities spectra and age, sex or breed in dogs [34,35]. The results concerning the relationship between body weight or heart rate and blood flow velocity in this species were more controversial: some authors showed no correlation between blood flow measurements and body weight or heart rate, whereas other authors demonstrated a positive relationship between blood flow measurements and heart rate, and a negative relationship between blood flow measurements and body weight [32,34-36]. In the equine species, the relationship between pulsed-wave Doppler-derived parameters and body size has not been studied sufficiently. In a study performed in 30 adult thoroughbred horses, tricuspid peak E negatively correlated with body weight, and pulmonary Vmax and VTI were positively correlated with body weight [11], the latter being thus the opposite of what was found in dogs. In the present study in donkeys, pulmonary Vmax and VTI also positively correlated to body weight. Moreover, tricuspid Peak A and aortic Vmax positively correlated with body weight, and aortic ET and TTP negatively correlated to body weight. Echocardiographic parameters indexed for body weight have seldom been reported in horses. The LVmass indexed for body weight was lower in donkeys in the present study than values previously reported in elite racing thoroughbred horses [22]. This could be due to species or breed differences and/or to exercise-induced increase in left ventricular mass in thoroughbred horses [24,25,27]. However, the higher LVID index and RWT found in the sedentary donkeys in the present study as compared to values obtained in thoroughbred horses, could not be due to training, because LVID and RWT have been shown to increase with race training in horses [2,24,25]. It could thus be due to a specific cardiac morphology in donkeys. In dogs, left ventricular dimensions measured from a short-axis image tended to be higher than those measured from a longaxis view [37]. In horses, there were no significant differences between measurements obtained from those two planes [10], as was the case in the present study in donkeys. Therefore, the long-axis or short-axis can both be used to perform left ventricular and wall thickness measurements in donkeys, as it has been suggested in horses. However, short-axis view of the left ventricle at the chordal level is easier than the long-axis reference four-chamber view to standardize and to correctly orientate the M-mode cursor [2]. In previous studies performed in small animals and in horses and in the present study in donkeys, measurements taken from 2D- or M-mode long-axis or short-axis views have been shown to be similar, the most important point to produce reliable measurements being to first obtain a standardized 2D-mode view with correct orientation and of good quality, allowing a good alignment of the M-mode cursor [1,2,14]. However, to measure left ventricular dimensions in clinical cases, M-mode measurements have been recommended by some authors because it allows easier identification of systole and diastole and do not necessitate high quality videotape recorder with still frames if measurements are not done directly [1]. Some authors found higher LVID when measured from left parasternal views as compared with right parasternal views

13 [1,31]. However, Long et al., (1992) did not found significant differences in left ventricular dimensions or wall thicknesses measured from the left or right hemithorax [20]. The same was observed in the donkeys of this study, with the exception of IVSs and IVS FWT that were lower when measured from the left parasternal long-axis view than when measured in any of the right parasternal views. This could be due to differences in plane or axis used or in positioning of the M-mode cursor throughout the ventricular septum and the left ventricle, because perpendicular positioning of the interventricular septum was more difficult to obtain from the left than from the right hemithorax, as it has also been reported in horses [1]. In conclusion, the standardized imaging technique for guided M-mode and pulsed-wave Doppler measurements previously developed in horses has been shown in this study to be applicable to donkeys, and echocardiographic morphological parameters obtained using this technique have been shown to be correlated with body weight in healthy donkeys. The specific reference values established in healthy donkeys in this study should be taken into account when evaluating a donkey suffering from a cardiac disease. References 1. Patteson MW, Gibbs PR, Wotton PR, et al. Echocardiographic measurements of cardiac dimensions and indices of cardiac function in normal adult thoroughbred horses. Equine Vet J Suppl 1995; 19: Boon J. Evaluation of size, function, and hemodynamics. In: Boon JA, ed. Manual of Veterinary Echocardiography. Philadelphia: WB Saunders Co, 1998; Kriz NG, Rose RJ. Repeatability of standard transthoracic echocardiographic measurements in horses. Aust Vet J 2002; 80: Brown DJ, Rush JE, MacGregor J, et al. M-mode echocardiographic ratio indices in normal dogs, cats, and horses: A novel quantitative method. J Vet Intern Med 2003; 17: Reef VB. Evaluation of the equine cardiovascular system. Vet Clin North Am: Equine Pract 1985; 1: Lescure F, Tamzali Y. Valeurs de référence en échocardiographie TM chez le cheval de sport. Revue Med Vet 1984; 7: Lombard CW, Evans M, Martin L, et al. Blood pressure, electrocardiogram and echocardiogram measurements in the growing pony foal. Equine Vet J 1984; 16: Stewart JH, Rose RJ, Barko AM. Echocardiography in foals from birth to three months old. Equine Vet J 1984; 16: Voros K, Holmes JR, Gibbs C. Measurement of cardiac dimensions with two-dimensional echocardiography in the living horse. Equine Vet J 1991, 23: Slater JD, Herrtage ME Echocardiographic measurements of cardiac dimensions in normal ponies and horses. Equine Vet J 1995; Suppl 19: Blissitt KJ, Bonagura JD. Pulsed wave Doppler echocardiography in normal horses. Equine Vet J Suppl 1995; 19: Stadler P, Rewel A, Deegen E. Die M-Mode Echokardiographie bei S-Dressur-, S-Springpferden und bei untrainierten Pferden. J Vet Med A 1993; 40: Stadler P, Robine F. Die kardiometrie beim gesunden Warmblutpferd mit Hilfe der Schnittbildechographie im B-Mode. Pferdeheilkunde 1996; 1: Bakos Z, Voros K, Jarvinen T, et al. Two-dimensional and M-mode echocardiographic measurements of cardiac dimensions in healthy standardbred trotters. Acta Vet Hung 2002, 50: O Callaghan MW. Comparison of echocardiographic and autopsy measurements of cardiac dimensions in the horse. Equine Vet J 1985; 17: Delvaux V, Kirschvink N, Amory H, et al. Spécificités de la fonction cardiorespiratoire de l âne (Equus asinus). Pratique Vet Equine 2001; 33: Thomas WP, Gaber CE, Jacobs GJ, et al. Recommendations for standards in transthoracic two-dimensional echocardiography in the dog and cat. J Vet Int Med 1993; 7: Reef VB. Echocardiographic examination in the horse: the basics. Comp Cont Edu Pract Vet 1990; 12: Long KL. Two-dimensional and M-mode echocardiography. Equine Vet Educ 1992; 4: Long KJ, Bonagura JD, Darke GG. Standardised imaging technique for guided M-mode and Doppler echocardiography in the horse. Equine Vet J 1992, 24: Sahn DJ, De Maria A, Kisslo J, et al. Recommandations regarding quantitation in M-mode echocardiography: results of a survey of echocardiographic measurements. Circulation 1978; 58: Young LE, Marlin DJ, Deaton C, et al. Heart size estimated by echocardiography correlates with maximal oxygen uptake. Equine Vet J Suppl 2002; 34: Devereux RB, Reichek N. Echocardiographic determination of left ventricular mass in man: Anatomic validation of the

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