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Objective—To determine the usefulness of magnetic motor-evoked potentials (MMEPs) for assessing the integrity of the cervical, thoracic, and thoracolumbar spinal cord in horses with bilateral hind limb ataxia.

Animals—9 horses and 1 donkey with bilateral hind limb ataxia of various degrees.

Procedure—The motor cortex was stimulated magnetically, and MMEPs were recorded bilaterally from the extensor carpi radialis and cranial tibial muscles.

Results—In 5 horses and 1 donkey, MMEPs with normal onset latencies and peak-to-peak amplitude were recorded from the extensor carpi radialis muscles, whereas abnormal onset latencies and peak-topeak amplitudes were recorded from the cranial tibial muscles. In these animals, a spinal cord lesion in the thoracic or thoracolumbar segments was suspected. In 4 horses, onset latencies and peak-topeak amplitude of MMEPs recorded from the extensor carpi radialis and cranial tibial muscles were abnormal. In these horses, a cervical spinal cord lesion was suspected.

Conclusions and Clinical Relevance—Transcranial magnetic stimulation can be considered a valuable diagnostic tool for assessing the integrity of the spinal cord, and MMEPs may be used for differentiating thoracic or thoracolumbar spinal cord lesions from mild cervical spinal cord lesions that cause ataxia in the hind limbs only. (Am J Vet Res 2003;64:1382–1386)

Full access
in American Journal of Veterinary Research


Objective—To investigate effects of IV administration of propafenone for naturally occurring and experimentally induced chronic atrial fibrillation in horses.

Animals—2 horses with naturally occurring atrial fibrillation and 4 horses with pacing-induced atrial fibrillation.

Procedures—Horses received a bolus of propafenone (2 mg/kg, IV over 15 minutes). If atrial fibrillation persisted after 20 minutes, a continuous infusion of propafenone (7 μg/kg/min) was given for 120 minutes. Before, during, and after treatment, plasma propafenone concentrations, hematologic and serum biochemical values, and electolyte concentrations analyses were determined and clinical signs were monitored. Surface ECGs were recorded. If propafenone treatment failed, quinidine sulfate was administered.

Results—Bolus and continuous infusion induced minimal adverse effects. During the 15-minute bolus administration, a slight increase in heart rate was observed and horses appeared more sensitive to external stimuli. Throughout treatment, no significant changes were observed in respiratory rate, QRS or corrected QT duration, or results of hematologic analyses. Although a significant increase in F-wave interval and atrial fibrillation cycle length was observed and plasma propafenone concentrations (569 to 1,268 ng/mL) reached the human therapeutic range (64 to 1,044 ng/mL), none of the horses cardioverted to sinus rhythm. Sinus rhythm could be restored in all horses via standard oral administration of quinidine.

Conclusions and Clinical Relevance—A slow IV bolus of 2 mg of propafenone/kg followed by a continuous infusion of 7 μg/kg/min over 2 hours was not an effective treatment for chronic atrial fibrillation in horses.

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in American Journal of Veterinary Research



To establish reference values for right ventricular maximal rate of increase in pressure (dP/dtmax) in horses and determine the usefulness of this variable to evaluate cardiac contractility.


15 crossbred horses, 3 to 20 years old.


Cardiac catheterization was performed, using a high-fidelity catheter tip micromanometer, to determine right ventricular dP/dtmax. The following mathematic corrections were made: for preload, (dP/dtmax)/instantaneous total pressure, (dP/dtmax)/instantaneous developed pressure, and (dP/dtmax)/end diastolic pressure; for afterload, (dP/dtCPIP)/common peak isovolumic pressure. Wedge pressure was measured simultaneously, using a Swan-Ganz catheter. A negative inotropic drug, detomidine hydrochloride, was administered to 6 horses to examine the effect of the negative inotropic drug on right ventricular dP/dtmax and derived variables.


The mean right ventricular dP/dtmax was 477 (± 84.1) mm Hg/s in 15 horses. A 40% decrease in dP/dtmax was found for 30 minutes after detomidine administration. Variables that correct for preload and afterload were influenced similarly. Detomidine administration also caused a 24% increase in mean wedge pressure, probably indicating reduced left-sided cardiac contractility.

Conclusions and Clinical Relevance

Right ventricular dP/dtmax may be a useful clinical variable for determining acute changes in cardiac contractility in horses. (Am J Vet Res 1999;60:1508–1512)

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in American Journal of Veterinary Research


Objective—To determine the clinical effects and pharmacokinetics of amiodarone after single doses of 5 mg/kg administered orally or intravenously.

Animals—6 healthy adult horses.

Procedure—In a cross over study, clinical signs and electrocardiographic variables were monitored and plasma and urine samples were collected. A liquid chromatography–mass spectrometry method was used to determine the percentage of protein binding and to measure plasma and urine concentrations of amiodarone and the active metabolite desethylamiodarone.

Results—No adverse clinical signs were observed. After IV administration, median terminal elimination half-lives of amiodarone and desethylamiodarone were 51.1 and 75.3 hours, respectively. Clearance was 0.35 L/kg•h, and the apparent volume of distribution for amiodarone was 31.1 L/kg. The peak plasma desethylamiodarone concentration of 0.08 μg/mL was attained 2.7 hours after IV administration. Neither parent drug nor metabolite was detected in urine, and protein binding of amiodarone was 96%. After oral administration of amiodarone, absorption of amiodarone was slow and variable; bioavailability ranged from 6.0% to 33.7%. The peak plasma amiodarone concentration of 0.14 μg/mL was attained 7.0 hours after oral administration and the peak plasma desethylamiodarone concentration of 0.03 μg/mL was attained 8.0 hours after administration. Median elimination half-lives of amiodarone and desethylamiodarone were 24.1 and 58.6 hours, respectively.

Conclusion and Clinical Relevance—Results indicate that the pharmacokinetic distribution of amiodarone is multicompartmental. This information is useful for determining treatment regimens for horses with arrythmias. Amiodarone has low bioavailability after oral administration, does not undergo renal excretion, and is highly protein-bound in horses.

Full access
in American Journal of Veterinary Research


Case Description—An 8-year-old warmblood mare was evaluated following an acute onset of neurologic abnormalities.

Clinical Findings—Computed tomography of the head revealed large masses in both lateral ventricles, and a presumptive diagnosis of cholesterinic granuloma was made.

Treatment and Outcome—Freehand biopsy of the intracranial masses was performed under computed tomographic guidance, and histologic examination of biopsy specimens confirmed the diagnosis. No adverse effects associated with the brain biopsy procedure were encountered. Clinical signs resolved, and long-term follow-up did not reveal any recurrence of neurologic deficits. The horse was able to return to its previous level of training.

Clinical Relevance—Findings suggested that computed tomographic–guided brain biopsy is feasible in horses and can be used to establish a diagnosis in horses with intracranial masses.

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in Journal of the American Veterinary Medical Association