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Hypothyroidism and
ischaemic heart disease are both common, so inevitably they will sometimes occur
together. Although angina may remain unchanged in severity or paradoxically
disappear with restoration of metabolic rate, exacerbation of myocardial
ischaemia, infarction and sudden death are well-recognised complications of
thyroxine replacement, even using doses as low as 25 μg per day. In patients
with known ischaemic heart disease, thyroxine should be introduced at low dose
and increased very slowly under specialist supervision. It has been suggested
that T3 has an advantage over T4, since T3 has
a shorter half-life and any adverse effect will reverse more quickly, but the
more distinct peak in hormone levels after each dose of T3 is a
disadvantage. Approximately 40% of patients with angina cannot tolerate full
replacement therapy despite the use of β-blockers and vasodilators; coronary
artery surgery or balloon angioplasty can be performed safely in such patients
and, if successful, allow full replacement dosage of thyroxine in the majority |
