Irregular heartbeat

[Anna Wolfe <awolfe@bacavalley.com>]

Dear Ridecampers,

I'm wondering if any of you might shed any light on my mare's irregular
heartbeat at the Amarillo ride yesterday.  It hasn't happened before,
and she has a nice low resting pulse normally, and stays low in work,
and drops fast.  Yesterday, however, the monitor showed high rates, and
at the first vet check the very efficient PR guy noted an irregular
pulse.  The vet didn't say anything, but I pointed it out at the second
check, for my sister and I had both listened to it by then, and it would
go fast for a few beats, then slow.  The vet suspected something to do
with electrolytes, and more specifically potassium.  He thought she
might be getting too much potassium.  We had made doses with two scoops
of Enduromax, because it had been very hot - into the 100's there - but
yesterday it was only 87, with a bit of cloud over the sun, so she
wasn't sweating all that much.  He told me not to electolyte at the
second stop.  She felt strong, and was eating and drinking well, and
getting almost all A's on her scores.  We did the 50 in just under six
hours (the winner came in in 4 hours and 50 min).

At the end her heart was still irregular, and it hung at about 60 for an
hour.  An hour later it was more regular, and about 48.  This afternoon
when she finished her supper, it was 44 and regular.

Could it be too much potassium?  Something else?  Last December I had
blood drawn during the 60 mile Deming ride for the Pride project, and
the only result that was out of the normal range was a low potassium
reading.  Any ideas?

Thanks!

Anna