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Clinical trials in human medicine show that the cardiovascular system undergoes structural and functional changes with increasing age. These changes influence myocardial deformation and myocardial contraction velocities. When it comes to horses the effect of „age“ on these parameters has not been investigated up to date. There is no study in tissue Doppler imaging and 2D-Speckle Tracking concerning the impact of aging in horses.
In this context 60 crossbred horses, aged from 3 to 30 years, were tested. Comparative pulsed wave tissue Doppler and colour tissue Doppler imaging were used to measure radial myocardial velocities of the left- and right ventricular wall and the interventricular septum. 2DSpeckle Tracking was used to determine the radial strain and strain rate in the left ventricular wall and the interventricular septum. The present study shows that age has an influence on the radial myocardial velocity of horses. This influence was detected by pulsed wave tissue Doppler as well as by colour tissue Doppler, though the pulsed wave tissue Doppler´s reproducibility was higher due to lower intraindividual variation coefficients. At the left ventricular wall, age-dependent changes were seen that resemble those seen in humans. Systolic contraction velocity (p ≤ 0.01) and early diastolic relaxation velocity (p ≤ 0.001) decreased while late diastolic contraction velocity increase (0.001 < p ≤ 0.01) to maintain ventricular filling. At the interventricular septum early- and late diastolic contraction velocities increased with ageing (p ≤ 0.001). At the right ventricular wall, systolic and late diastolic contraction velocities increased with aging (p ≤ 0.001). Further the study shows that heart rate and gender also have a measurable effects on myocardial velocity. An increasing heart rate leads to a growth of systolic (0.01 < p ≤ 0.05) and late diastolic (0.001 < p ≤ 0.01) contraction in the left ventricular wall as well as in the interventricular septum. In comparison to male horses, female horses have slower early diastolic relaxation velocities at the interventricular septum and right ventricular wall (0.001 < p ≤ 0.01) and lower velocities in the systolic and late diastolic waves of the right ventricular wall (0.01 < p ≤ 0.05). The strain rate in 2D-Speckle Tracking is influenced by age in systolic contraction (0.01 < p ≤ 0.05) and early diastolic relaxation (0.001< p ≤ 0.01) at the left ventricular wall. Additionally, systolic contraction (0.001 < p ≤ 0.01) and late diastolic contraction (0.01 < p ≤ 0.05) of the interventricular septum is affected by age dependent changes the velocities increases with age. The Strain is not influenced by age. Heart rate, gender, weight and height have no significant impact on deformation parameters.
The coefficients of variation are obviously higher in 2D-Speckle Tracking than in tissue Doppler imaging. This corresponds to the results of other studies with horses. In the present study 2D-Speckle Tracking was less sensitive for age dependent changes than tissue Doppler imaging. Despite the limitation of measuring only the radial parameters, important information on myocardial function was obtained. Especially at the left ventricular wall the measurements show a high reproducibility and a distinct effect of age on the radial myocardial velocities of horses. This effect is explained by aged-induced structural changes in the myocardium and corresponds to a reduced ventricular function with older horses. An assessment of radial myocardial velocities of a horse`s heart with tissue Doppler imaging should always take physiological age-related changes in contractility into account. Based on the present study, further research into the physiological function of a horses´s heart could include the comparison of the effect of standardized exercise tests on myocardial contractility with young and old horses.