Fig 1.
(A–C) Echocardiographic procedure in the elephants included in the study.
(A) A 4C-RS convex transducer was used, which provided a wide ultrasound field suitable for cardiac imaging in this large species. (B) Prior to imaging, the acoustic window located slightly dorsal and caudal to the left elbow was rinsed with lukewarm water to soften the thick skin and improve acoustic coupling with the large amount of ultrasound gel applied, a step that was well tolerated and appeared to be positively perceived by the elephants. (C) The elephant stood calmly and without restraint against the protective barrier while the trainer gently interacted with its head. The left forelimb was extended cranially, facilitated by resting it over a training ball placed on the ground, in order to optimize access to the cranial portion of the left cranial thoracic wall and echocardiographic window. Photos by Valérie Chetboul.
Fig 2.
(A-C) Transducer positioning for echocardiographic imaging of the elephants included in the study.
(A) and (B) Elephant positioning for transthoracic echocardiographic examination and probe placement to obtain the left parasternal long-axis view (1) and the left parasternal short-axis view at the level of the left ventricle (2). (C) Position of the transducer to obtain the left parasternal long-axis view. The probe is placed in an intercostal space located caudal and slightly dorsal to the left elbow, aligned parallel to the ribs. In both Fig 2A and 2C, the left forelimb is gently extended cranially, facilitated by resting over a training ball placed on the ground, in order to improve access to the cranial portion of the left cranial thoracic wall. For optimal imaging, this acoustic window was first moistened with lukewarm water to soften the skin, before application of a large amount of ultrasound gel, thereby enhancing ultrasound transmission. Illustration and photo by Valérie Chetboul.
Fig 3.
Representative transventricular M-mode echocardiogram obtained from the left parasternal long-axis view in one Asian elephant (Elephas maximus) from the study.
This view shows two complete cardiac cycles (heart rate = 32 bpm), with the left ventricular free wall (LVFW) proximally and the interventricular septum (IVS) distally, delineating the left ventricular (LV) cavity. The M-mode cursor is positioned perpendicular to the LV myocardial walls, immediately below the insertion of the papillary muscles to exclude them from the measurements. Note the presence of chordae tendineae (c), which were not included in the diameter measurements. A spontaneous echo contrast is typically observed (arrowhead). In addition, vertical anechoic artifacts (curved arrows), corresponding to integumentary shadowing artifacts, are also seen (see text for explanation). LVIDd and LVIDs: left ventricular internal diameter in end-diastole and end-systole, respectively. mv: mitral valve. RV: right ventricle. Image by Valérie Chetboul.
Fig 4.
(A and B) Representative two-dimensional left parasternal short-axis view of the left ventricle in one Asian elephant (Elephas maximus) from the study at end-systole, showing the left ventricular (LV) cavity in cross-section and the two papillary muscles (p).
An example of LV cavity tracing, excluding the papillary muscles, is illustrated in panel B. A similar tracing was performed on the frame obtained at end-diastole, and the LV fractional area change (FAC%) was calculated as [(LV area in diastole – LV area in systole)/ LV area in diastole] × 100. IVS: interventricular septum. LVFW: left ventricular free wall. Image by Valérie Chetboul.
Table 1.
Mean ± standard deviation (SD), minimum (Min), and maximum (Max) values of eight echocardiographic variables obtained from 72 transthoracic examinations performed in three Asian elephants (Elephas maximus, EL1–EL3). Results are presented for all elephants combined and individually. The echocardiographic variables included seven repeated M-mode parameters, i.e., interventricular septal thicknesses at end-diastole and end-systole (IVSd, IVSs), left ventricular internal diameters at end-diastole and end-systole (LVIDd, LVIDs) with calculation of the fractional shortening (FS%), and left ventricular free wall thicknesses at end-diastole and end-systole (LVFWd, LVFWs), as well as one two-dimensional parameter, the left ventricular fractional area change (LV FAC%). Heart rate (HR) was also calculated.
Table 2.
Within-day, between-day, and interindividual variability, expressed as standard deviations (SD) and coefficients of variation (CV), for eight echocardiographic variables obtained from 72 transthoracic examinations in three Asian elephants (Elephas maximus).
These variables included seven repeated M-mode parameters, i.e., interventricular septal thicknesses at end-diastole and end-systole (IVSd, IVSs), left ventricular free wall thicknesses at end-diastole and end-systole (LVFWd, LVFWs), and left ventricular internal diameters at end-diastole and end-systole (LVIDd, LVIDs) with calculation of the fractional shortening (FS%), as well as one two-dimensional parameter, the left ventricular fractional area change (LV FAC%).
Table 3.
Associations of heart rate (HR), body weight, and age with echocardiographic variables in Asian elephants (Elephas maximus) included in the study. HR are expressed in beats per minute, body weight in kilograms, and age in years.
Echocardiographic dimensions are in millimeters (mm), and indices in percent (%). Regression estimates are expressed per unit increase in the corresponding predictor. Multivariable linear mixed-effects models were fitted for each echocardiographic parameter with HR, body weight, and age as fixed effects and individual animal as a random effect. The table reports the estimated effect size (Estimate), the 95% confidence interval (CI), and the corresponding P-value for each predictor. Significant associations (P < 0.05) are shown in bold. IVSd and IVSs: interventricular septal thickness at end-diastole and end-systole, respectively. LVFWd and LVFWs: left ventricular free wall thickness at end-diastole and end-systole, respectively. LVIDd and LVIDs: left ventricular internal diameter at end-diastole and end-systole, respectively. FS%: fractional shortening. LV FAC%: left ventricular fractional area change.