Seric Concentration of Troponin I and Electrocardiographic Tracing in Dogs Submitted to Long-Term Sedation during 24 Hours

Background: General anesthetics and sedatives are commonly used for long-term sedation in veterinary medicine; however, they can lead to cardiac suppression. Cardiac troponin I is a biomarker used to detect myocardial pathology, monitor treatment, and assess outcomes in veterinary patients. The aim of this study was to evaluate the serum concentration of troponin I (cTnI), the electrocardiographic (ECG) tracing, and the ventricular stroke work index in dogs undergoing two long-term sedation protocols over 24 h.Materials, Methods & Results: Twelve healthy mongrel dogs with an average weight of 13.2 ± 2.3 Kg were admitted for this study. Twenty-four h before the experiment began (M-24), venous blood samples were collected for chemiluminescent cTnI evaluation and ECG data were obtained, specifically heart rate (HR); P, PR, QRS and T wave duration; P, R, T wave amplitude; and ST segment depression. On the day of the experiment, the animals were anaesthetized with propofol and isoflurane, and instrumented. After instrumentation, right and left ventricular stroke work index (RVSWI and LVSWI respectively) and intrapulmonary shunt (Qs/Qt) were performed as baseline parameters. The isoflurane was then discontinued and the animals randomly allocated to two groups (n = 6 each): Midazolam and fentanyl group (GMF), in which the animals received a bolus and continuous rate infusion (CRI) of midazolam (0.5 mg/kg and 0.5 mg/kg/h) and fentanyl (5 µg/kg and 10 µg/kg/h) or ketamine and morphine group (GKM), in which the animals received a bolus and CRI of ketamine (1 mg/kg and 0.6 mg/kg/h) and morphine (0.5 mg/kg and 0.26 mg/kg/h). Both groups also received propofol as a bolus and CRI (3 mg/kg and 0.3 mg/ kg/min) over 24 h. The ECG and cTnI parameters were evaluated at 6, 12, and 24 h during CRI (M6, M12, and M24) and 12 and 24 h after the end of infusion (T12 and T24). The hemodynamic parameters RVSWI, LVSWI, and Qs/Qt were evaluated every 2 h until the end of CRI. There was a non-significant increase in cTnI from M6 in both groups; however, a significant increase was only observed in GMF between M-24 and T12. During sedation, HR decreased an average of 46% in GKM and 51% in GMF compared to M-24. The QT interval (milliseconds) increased in both groups after CRI started, returning to baseline values at T24. There were no differences in P, QRS, and T wave amplitude or ST segment depression in either group.Discussion: The serum concentration of cTnI increased in GMF at T12, more probably due to hemodynamic changes during sedation rather than myocardial lesions, since the increase was relatively mild. A greater hemodynamic change was observed in GMF, with a greater increase in RVSWI compared to baseline than GKM, which may reflect an increase in cardiac effort and possibly cTnI release; however, in both groups, the cTnI values remained within the acceptable values for the species. Bradycardia was reported during long-term sedation, which may be due to the synergism between opioids as a result of vagal stimulation, central sympathetic inhibition, and a possible action on cardiac receptors, and propofol due to the inhibitory effect on the sympathetic nervous system. Increases in QT interval did not lead to marked changes in this study. T wave amplitude and ST segment depression remained unchanged and within acceptable values for the species, and thus agreed with cTnI data, implying that no myocardial lesions were produced by these protocols. It has been established that for both protocols, cTnI remained within physiological ranges for healthy dogs, and therefore, these methods could be used safely for long-term sedation without producing hypoxia/ischemia of the myocardium or ST-segment depression.