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Echocardiography is the current method of choice in equine cardiology to assess valvular function, cardiac dimensions and myocardial thickness. M-Mode allows an assessment of myocardial function. However, despite new techniques in equine diagnostic cardiology such as tissue doppler imaging, prognosticating equine patients with cardiologic findings remains challenging.
The current study evaluated rotational deformation of the equine left ventricle (LV) by two-dimensional speckle tracking on three different scan planes. The rotational deformation was derived from three left parasternal short-axis images recorded at the level of the mitral valve (base), the medial level and the apical level. In these gray scale loops, natural acoustic markers (speckles) were tracked and traced by a dedicated software package (EchoPac PC, GE Healthcare) to determine myocardial deformation in the circumferential plane. Thirty-eight horses were included in the study. To establish reference values and to evaluate the reproducibility of our method, 16 healthy warmblood horses were examined (control group). Data was acquired on three consecutive days by two observers. Then, 22 horses of different breeds with cardiac problems were examined. In 8 horses diagnosed with valvular dysfunction, a deviation in cardiac dimensions could be identified. No alteration of cardiac dimensions was found in 9 additional patients with the same diagnosis. All horses underwent a standard echocardiographic examination with B-Mode, M-Mode and colour doppler echocardiography. All B-Mode recordings of the healthy horses were of adequate quality. We
identified a similar systolic rotational motion with different amplitudes at the three myocardial levels. As seen from the base, the motion starts with an initial (or early systolic) clockwise rotation (positive rotation angle) followed by a counterclockwise rotation (negative rotation angle). There was a significant difference between the rotational amplitudes at each level. We found an increase in left ventricular rotation from the basal to the apical level. The results of the group with cardiac findings also showed a significant difference in rotational amplitude between the scan levels. There was no significant difference between the group of horses with cardiac findings and the healthy group on each scan level. Horses with cardiac findings and a deviation of the left atrium and / or the left ventricle had a significant decrease in rotational amplitude compared to the healthy group (p < 0,0001).
Also the timespan to the systolic rotational peak increased from the basal to the apical level without significant differences between the groups. The coefficient of variation on the medial level was low to moderate (5,99 % bis 19,28 %) whereas the apical and basal level showed low to high variability (4,66% - bis 31,64%). In conclusion, we were able to show that left ventricular rotational motion can be evaluated noninvasively using two-dimensional speckle-tracking-based wall motion analysis applied to standard two-dimensional echocardiographic recordings of the LV in a right-parasternal short-axis view, especially at the level of the papillary muscles. We found a difference in left ventricular rotation between horses, humans and dogs. Additionally we showed that left ventricular rotational deformation is affected by changes in left ventricular and atrial size.
Further studies are necessary to prove the validity of this method in horses with cardiac dysfunction. Additionally this method should be evaluated at rest and in exercise.