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
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
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
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)