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The aim of this study was to evaluate myocardial function of the anaesthetized horse by conventional echocardiography and by advanced methods such as tissue Doppler imaging (TDI) and 2D speckle tracking (2D ST). Twenty-five horses were selected that had been admitted to the Equine Hospital of the Faculty of Veterinary Medicine, LMU, Munich for elective surgery. To enter the study unsedated, standing horses underwent a thorough clinical, echo- and electrocardiographic examination, which had to be within the limits of normalcy.
M-Mode and TDI measurements and deformation analyses with 2D ST were performed before sedation (T1), as well as during (T2, T3) and after (T4) anaesthesia. A standardized anaesthetic protocol was used, which included initial sedation with a α2–adrenoreceptor agonist combined with an opioid, induction of anaesthesia with guaifenesin and ketamine, and inhaled isoflurane for maintenance. During anaesthesia all horses were kept in left lateral recumbency. T2, T3 and T4 were predetermined time points at 3 and 20 minutes following isofluorane inhalation and 30 minutes following rightening. With both PW- and Color-TDI the velocity of the radial myocardial movement in the left and right ventricular walls and the interventricular septum was evaluated. The TDI parameters included the isovolumetric contraction (IVC) and the systolic (S) as well as the early (E) and late diastolic (A) maximal velocities.
Data collection was successful in all horses. The PW-TDI measurements on the right ventricular wall were only conducted on 22 horses. During anaesthesia (T3) M-Mode echocardiography fractional shortening decreased significantly at an average of 1.6 ± 12.5 % (***p ≤ 0.001), the ejection fraction decreased significantly at an average of 11.3 ± 1.9 % (***p ≤ 0.001) and the diastolic left ventricular diameter showed a significant reduction of 7.2 ± 13.0 % (**p ≤ 0.01) compared to T1.
During anaesthesia there was a significant reduction of the systolic and diastolic wall velocities observed by PW-TDI and Color-TDI in most cases.
Significant reductions of the right ventricular parameters detected with Color-TDI were determined during anaesthesia (T3) compared to T1: A decreased by 78.3 ± 12.8 % (***p ≤ 0.001), E by 64.3 ± 23.4 % (*p ≤ 0.05), S by 73.8 ± 13,3 % (***p ≤ 0.001) and IVC by 63.8 ± 34.6 % (*p ≤ 0.05). On the left ventricular wall there were significant reductions during anesthesia (T3) compared to T1. A decreased by 43.0 ± 22.2 % (***p ≤ 0.001), E by 18.1 ± 23.9 % (***p ≤ 0.001) and S by 15.0 ± 24.6 % (**p ≤ 0.01). While performing the TDI measurements during anaesthesia (T3), various horses (60 %) had an absent Awave in the area of the interventricular septum, and other horses had a significant reduction of A by 68.2 ± 24.6 % (**p ≤ 0,01). S reduced significantly by 43.7 ± 43.7 % (**p ≤ 0,01) or was absent in 20 % of the cases and IVC reduced during anaesthesia (T3) by 32.2 ±
49.2 % (***p ≤ 0.001) compared to T1. Parameters determined by PW-TDI of the right ventricular wall velocities showed significant reductions comparing T1 to T3: A decreased by 50,6 ± 23.1 % (***p ≤ 0.001), S by 39.8 ± 38.6 % (***p ≤ 0.001) and IVC by 25.0 ± 37.2 % (**p ≤ 0.001). On the left ventricular wall there were significant reductions during anaesthesia (T3) compared to T1. A decreased by 37.8 ± 24.8 % (***p ≤ 0.001), E by 8.6 ± 34.0 % (*p ≤ 0.05) and S by 18.1 ± 26.2 % (***p ≤ 0.001). On the interventricular septum there were significant reductions during anaesthesia (T3) compared to T1: IVC decreased by 50.7 ± 22.3 % (***p ≤ 0.001) and S by 29.7 ± 43.8 % (***p ≤ 0.001).
The strain of the left ventricular wall and the interventricular septum was reduced significantly during anaesthesia comparing T1 to T3. The strain of the interventricular septum was decreased significantly during T3 by 33.1 ± 42.2 % (***p ≤ 0.001) and the strain of the left ventricular wall was decreased significantly during T3 by 33.1 % ± 54.1 % (**p ≤ 0.001). There were significant reductions of S and A of the left ventricular wall and the interventricular septum while performing the strain rate measurements comparing T1 to T3. On the left ventricular wall S decreased by 26.6 ± 23.2 % (***p ≤ 0.001) and A by 34.7 ± 37.2 % (***p ≤ 0.001). On the interventricular septum S decreased by 28.4 ± 42.4 % (***p ≤ 0.001) and A by 44.2 ± 23.6 % (***p ≤ 0.001).
Comparing T2 to T3, significantly reduced parameters were measured, which indicates that the decrease became more pronounced with the increasing duration of anaesthesia. The results of the present study indicate that PW-TDI and Color-TDI as well as 2D ST are suitable imaging techniques during anaesthesia. The results provide information on global cardiac and regional systolic as well as diastolic function. A direct impact of general anaesthesia on the kinetics of the heart was illustrated and negative effects on the contractility and the relaxation of the left and right ventricular wall and the interventricular septum were registered.