Amiodarone does have an iodine base and can cause both hypothyroidism and
hyperthyroidism.  I am a cardiac nurse and I've seen either occur in many
patients.  It frequently causes the most problem by decreasing T4 to T3
conversion.  T4 is a storage form of thyroid hormone and it has to be
converted to T3 by the liver and peripheral tissues external to the thyroid
gland itself.  With amiodarone, the conversion process causes more Reverse
T3(RT3) to be formed rather than the active form of T3.  RT3 can block the
receptor sites for T3 so it further decreases the amount of T3 action.  I
cannot find any documentation to support this, but I suspect that RT3 has
the same effect on TSH as T3- it lowers it.

So the bottom line is, amiodarone not only can make a person hypoth
yroid
but it can mask the evidence (TSH) so that the doctor sees no explanation
for all of those horrible hypothyroid symptoms.  A well respected
electrophysiologist (cardiologist who specilizes in heart rhythm problems)
in my hospital said that you have to rely on TSH in patients on amiodarone
because RT3 gives false readings for the other tests.  I think this is
wrong but the literature that I can find always says the TSH is the best
thing to monitor in patients on amiodarone.  I think it seems reasonable
that free T3 would give the most accurate result.  I think total T3 can
include both active T3 and RT3 but free T3 may not.  If either test is
skewed, it is skewed to appear higher (due to RT3) than it really is.  So
if either test is low, it would be appropriate to increase the thyroid
dose.  For obvious reasons, T3 meds would be better because conversion
(which is faulty anyway) is bypassed.

How
ever, most doctors fear T3 meds due to an increased risk of arrhythmias
and this would be true in your case also.  I believe you when you say that
your arrhythmias come from being hypo.  I think this has something to do
with the adrenal glands trying to compensate for the low thyroid.  Also, in
hypothyroidism, the heart muscle does not contract or relax as effectively
as it should.  This can cause some stretching of the heart muscle and
conduction fibers which can certainly lead to some abnormal heart rhythms.
These are supposedly reversible effects once the thyroid hormones are
optimized.  Hypothyroidism as a cause of rhythm problems does not seem to
be appreciated by most doctors including cardiologists. The texts say that
hyPERthyroidism causes arrhythmias and they don't seem to think beyond that.

There are many different types of heart rhythm abnormalities that can
occur.  If your type was not life threatening (and it d
oesn't sound like it
was) then I'd try to get off of amiodarone.  It can have other serious side
effects too such as lung toxicity.  Be aware that it takes several months
for amiodarone to completely leave your tissues after it is discontinued.

Nancy

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