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Objective—To compare cardiac output (CO) obtained by the lithium dilution method (LiDCO) with CO calculated from the Fick principle (FickCO), in horses maximally exercising on a high-speed treadmill.

Animals—13 Thoroughbreds.

Procedures—In part 1 of the study, 5 horses performed a warm-up (walk, trot, and canter) and exercise test (walk, trot, canter, and gallop [90% to 100% maximum oxygen consumption [{O2max}]) with measurements of LiDCO and FickCO obtained simultaneously after 60 seconds at each exercise level, for a total of 7 measurements. In part 2 of the study, 8 horses performed a warm-up (walk, trot, and canter) followed by an exercise test (walk and gallop [90% to 100% O2max], repeated twice). Measurements of LiDCO and FickCO were obtained 60 seconds into the first walk and each gallop of the exercise tests, for a total of 3 measurements.

Results—Cardiac output increased significantly with increasing speeds by use of both methods. In part 1, lithium dilution significantly overestimated CO, compared with the Fick principle, during the exercise test (as both injection number and exercise intensity increased). Mean ± SD bias was 246 ± 264 mL of blood/min/kg in part 1 and 67 ± 100mLof blood/kg/min in part 2. Three injections of lithium (part 2) did not result in the same degree of overestimation of LiDCO that was observed with 7 injections (part 1).

Conclusions and Clinical Relevance—Lithium dilution may be an acceptable substitute for the Fick principle as a means to measure CO in maximally exercising client-owned horses.

Full access
in American Journal of Veterinary Research


Objective—To determine prevalence of myocardial injury in horses with colic on the basis of high concentrations of cardiac troponin I (cTnI), frequency of cardiac arrhythmias within the first 24 to 48 hours after hospital admission or surgery because of colic, and associations between high cTnI concentrations and cardiac arrhythmias, clinical course, and outcome (survival to discharge from hospital vs nonsurvival [death or euthanasia]).

Design—Prospective observational study.

Animals—111 horses with colic.

Procedures—Blood was drawn at admission and 12 and 24 hours after admission if horses were treated medically or 12 and 24 hours after surgery if treated surgically. A 24-hour ambulatory ECG was recorded beginning the morning after admission in medically treated cases or after surgery and evaluated for arrhythmias. Clinical and clinicopathologic data and outcome were obtained. Associations between cTnI concentrations and other variables were determined.

Results—An abnormal cTnI concentration (≥ 0.10 ng/mL) at admission was significantly associated with the occurrence of ventricular arrhythmias, outcome, and surgical treatment.

Conclusions and Clinical Relevance—The data suggested that horses with colic and high cTnI concentrations at admission were more likely to have ventricular arrhythmias and have a less favorable prognosis for recovery. High cTnI concentrations in horses with colic were suggestive of myocardial damage.

Full access
in Journal of the American Veterinary Medical Association


Objective—To determine whether echocardiographic variables differed between successful (elite) and less successful (nonelite) Arabian endurance horses.

Animals—34 Arabian horses that competed in endurance racing.

Procedures—Horses were assigned to either an elite or nonelite group on the basis of results of a previous competition, and a standardized echocardiographic examination was performed on each horse within 1 to 4 weeks after that competition. Multivariable logistic regression with backward stepwise elimination was used to create a prediction model for the determination of horse status (elite or nonelite) as a function of the measured echocardiographic variables.

Results—The elite and nonelite groups consisted of 23 and 11 horses, respectively. One horse in the nonelite group had a frequent ventricular dysrhythmia that could have negatively affected its performance and rider's safety, whereas none of the horses in the elite group had remarkable cardiac abnormalities. The left ventricular internal diameter during systole and diastole and left ventricular mass and stroke volume were significantly greater for horses in the elite group, compared with those for horses in the nonelite group. The final logistic regression model correctly predicted the horse status for all of the horses in the elite group and 8 of 11 horses in the nonelite group.

Conclusions and Clinical Relevance—Results indicated that heart size was significantly associated with performance for Arabian endurance horses in a manner similar to findings for Thoroughbred and Standardbred racehorses in active competition.

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in American Journal of Veterinary Research


Objective—To determine pharmacokinetics and excretion of phenytoin in horses.

Animals—6 adult horses.

Procedure—Using a crossover design, phenytoin was administered (8.8 mg/kg of body weight, IV and PO) to 6 horses to determine bioavailability (F). Phenytoin also was administered orally twice daily for 5 days to those same 6 horses to determine steadystate concentrations and excretion patterns. Blood and urine samples were collected for analysis.

Results—Mean (± SD) elimination half-life following a single IV or PO administration was 12.6 ± 2.8 and 13.9 ± 6.3 hours, respectively, and was 11.2 ± 4.0 hours following twice-daily administration for 5 days. Values for F ranged from 14.5 to 84.7%. Mean peak plasma concentration (Cmax) following single oral administration was 1.8 ± 0.68 µg/ml. Steady-state plasma concentrations following twice-daily administration for 5 days was 4.0 ± 1.8 µg/ml. Of the 12.0 ± 5.4% of the drug excreted during the 36-hour collection period, 0.78 ± 0.39% was the parent drug phenytoin, and 11.2 ± 5.3% was 5-(p-hydroxyphenyl)-5-phenylhydantoin (p-HPPH). Following twice-daily administration for 5 days, phenytoin was quantified in plasma and urine for up to 72 and 96 hours, respectively, and p-HPPH was quantified in urine for up to 144 hours after administration. This excretion pattern was not consistent in all horses.

Conclusion and Clinical Relevance—Variability in F, terminal elimination-phase half-life, and Cmax following single or multiple oral administration of phenytoin was considerable. This variability makes it difficult to predict plasma concentrations in horses after phenytoin administration. (Am J Vet Res 2001;62:483–489)

Full access
in American Journal of Veterinary Research