This study evaluated the effects of exercise on cardiac troponin I (cTnI) concentrations in healthy, adult horses. Fifteen fit, healthy horses determined to have a normal cardiovascular system completed a standardized exercise test on a high-speed treadmill. Heparinized blood was collected for plasma cTnI concentrations before maximal exercise, and 1, 3, 6, 9, 12 and 24 h post-exercise. The cTnI concentrations were measured with a commercial system (Stratus CS, Dade Behring, Inc.). Results were analysed by a multivariate ANOVA, where indicated post hoc analysis was done by Tukey-Kramer HSD and significance was placed at p , 0.05.All horses had elevations in cTnI concentrations after maximal exercise. Values for cTnI trended higher at 3 h (0.066^0.011 ng ml 21 ) and 6 h (0.062^0.011 ng ml 21 ) post-exercise compared with pre-exercise (0.039^0.007 ng ml 21 ), although this did not reach statistical significance. Mean cTnI concentrations were within our normal reference range at all time points, although four individuals were above our normal range after exercise.These data show that short-term, high-intensity exercise induces a small rise in plasma cTnI in normal horses. This should be kept in mind when evaluating cTnI concentrations in horses that have recently completed intense exercise. In addition, these data suggest that 3-6 h after intense exercise may be the optimal time for measurement of cTnI concentrations in horses with suspected exercise-induced myocardial damage.
SummaryReason for performing study: The repeatability of various echocardiographic measurements is unknown. Objectives: To determine the intraoperator, intraobserver and interoperator variability of echocardiographic measures in healthy foals. Methods: Echocardiographic examinations were carried out on 6 healthy foals by 3 experienced echocardiographers. Intraoperator variability was determined by having a single echocardiographer obtain and measure images from 6 foals scanned on 3 consecutive days. Interoperator and intraobserver variability were determined by having 3 echocardiographers each obtain images from an additional 6 sedated foals. Within-day interoperator variability was determined by having each echocardiographer measure their own images. Intraobserver variability was determined by having a single echocardiographer measure images obtained by all 3 echocardiographers. The coefficient of variation (CV) and standard error were calculated for each measure. Results: The variability for most measurements was either very low (CV<5%) or low (CV = 5-15%). Measurements of right ventricular internal diameter (RVID) in systole and E-point to septal separation (EPSS) showed moderate (CV 15-25%) to high variability (CV>25%) in all 3 categories. Measurements of the left ventricular ejection time (LVET) and velocity time integral from the right parasternal long axis view of right outflow tract in the fourth intercostal space showed moderate intraoperator variability. Measurements of the LVET, RVID in diastole and left atrial appendage (LAA) showed moderate interoperator variability and measurements of the RVID in diastole and acceleration time from the short axis view of the right outflow tract in the right third intercostal space showed moderate interobserver variability. Conclusion:The intraoperator, intraobserver and interoperator variabilities for most echocardiographic measurements in foals are low. Potential relevance: Most standard transthoracic echocardiographic measurements in foals have a low enough variability to warrant their use in serial clinical evaluations or experimental studies. Repeated measurements of RVID, EPSS, LVET and LAA should be interpreted with caution.
Background: Myocarditis is thought to occur secondary to equine influenza virus (EIV) infections in horses, but there is a lack of published evidence. Hypothesis/Objectives: We proposed that EIV challenge infection in ponies would cause myocardial damage, detectable by increases in plasma cardiac troponin I (cTnI) concentrations. Animals: Twenty‐nine influenza‐naïve yearling ponies: 23 were part of an influenza vaccine study (11 unvaccinated and 12 vaccinated), and were challenged with 108 EID50 EIV A/eq/Kentucky/91 6 months after vaccination. Six age‐matched healthy and unvaccinated ponies concurrently housed in a separate facility not exposed to influenza served as controls. Methods: Heparinized blood was collected before and over 28 days after infection and cTnI determined. Repeated measures analysis of variance, chi‐square, or clustered regression analyses were used to identify relationships between each group and cTnI. Results: All EIV‐infected ponies developed clinical signs and viral shedding, with the unvaccinated group displaying severe signs. One vaccinated pony and 2 unvaccinated ponies had cTnI greater than the reference range at 1 time point. At all other times, cTnI was <0.05 ng/mL. All control ponies had normal cTnI. There were no significant associations between cTnI and either clinical signs or experimental groups. When separated into abnormal versus normal cTnI, there were no significant differences among groups. Conclusions and Clinical Importance: This study demonstrated no evidence of severe myocardial necrosis secondary to EIV challenge with 108 EID50 EIV A/eq/Kentucky/91 in these sedentary ponies, but transient increases in cTnI suggest that mild myocardial damage may occur.
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