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  • Author or Editor: Henk J. Breukink x
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Objective—To determine whether electromyographic abnormalities are evident in skeletal muscles in horses with induced hypocalcemia and hypomagnesemia.

Animals—7 healthy adult Dutch Warmblood horses.

Procedure—Electromyographic examination was performed in the lateral vastus, triceps, and subclavian muscles before and after IV infusion of EDTA. An initial dose (mean ± SD, 564 ± 48 ml) of a 10% solution of sodium EDTA was administered IV during a period of 21 ± 7.3 minutes to establish a blood concentration of ionized calcium of approximately 0.5 mMol/L. Average rate of EDTA infusion to maintain ionized calcium at this concentration was 6.6 ml/min.

Results—Mean blood concentrations of ionized calcium and magnesium were 1.39 ± 0.06 and 0.84 ± 0.09 mM, respectively before EDTA infusion; after EDTA infusion, concentrations were 0.48 ± 0.05 and 0.44 ± 0.20 mM, respectively. This state induced positive waves; fibrillation potentials; doublets, triplets, and multiplets; complex repetitive discharges; and neuromyotonia. Analysis of motor unit action potentials (MUAP) after EDTA infusion revealed an increase in prevalence of polyphasic and complex MUAP in all muscles.

Conclusion and Clinical Relevance—None of the horses had classical signs of hypocalcemia and hypomagnesemia. In contrast, all horses had spontaneous activity in the measured muscles indicative of nerve hyperirritability. Calcium and magnesium deficits appear to have consequences, which may be subclinical, affecting functions of the neuromuscular system. This is of interest for equestrian sports in which hypocalcemia and hypomagnesemia are expected, such as during endurance rides. (Am J Vet Res 2002;63:849–856)

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in American Journal of Veterinary Research


Objective—To evaluate the application of analysis of motor unit action potentials (MUAP) in horses and to obtain values of MUAP for the subclavian muscle of horses.

Animals—10 healthy adult Dutch Warmblood horses.

Procedure—Electromyographic examination of the subclavian muscle in conscious nonsedated horses was performed to evaluate insertional activity, spontaneous activity, MUAP variables, and recruitment patterns. Muscle and body temperatures were measured at the beginning and end of the procedure. Amplitude, duration, number of phases, and number of changes in direction (ie, turns) for all representative MUAP were analyzed to determine values for this muscle in this group of horses.

Results—Mean ± SD duration of insertional activity was 471.7 ± 33.45 milliseconds. Mean MUAP amplitude in the examined horses was 379 µV (95% confidence interval [CI], 349 to 410 µV). Mean MUAP duration of the subclavian muscle was 7.27 milliseconds (95% CI, 6.84 to 7.71 milliseconds). Mean number of phases was 2.9, and mean number of turns was 3.0. Prevalence of polyphasic MUAP, defined as MUAP with > 4 phases, was 7.7%. Number of MUAP that had > 5 turns was 2.4%. Satellite potentials were found in 1.0% of the MUAP.

Conclusions and Clinical Relevance—This study revealed that electromyography including MUAP analysis can be performed in horses, and values for the subclavian muscle in healthy adult horses can be obtained. Analysis of MUAP could be a valuable diagnostic tool for use in discriminating between myogenic and neurogenic problems in horses. (Am J Vet Res 2002;63:198–203)

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in American Journal of Veterinary Research