| In a 2.5-year
period, hypertrophic cardiomyopathy was found at necropsy of 23 cats that
died (13 cats) or were euthanatized (10) because of problems associated
with hyperthyroidism. Of these, 4 (17%) also had evidence of cardiac failure
(pulmonary edema or pleural effusion). The mean body weight of the cats
with hyperthyroidism and hypertrophic cardiomyopathy was significantly
less (P less than 0.001) than that of clinically normal cats and cats
with primary cardiomyopathy (congestive or restrictive) or excessive moderator
band cardiomyopathy. In addition, the ratio of heart weight to body weight
was significantly greater (P < 0.001) in the 23 hyperthyroid cats than
in the normal cats and cats with primary cardiomyopathy. Twenty (87%)
of the cats had symmetric hypertrophy of the ventricular septum and left
ventricular free wall, whereas the remaining 3 cats had disproportionate
thickening of the ventricular septum, compared with the free wall, similar
to what is found in cats with asymmetric hypertrophic cardiomyopathy.
Histologic cardiac abnormalities included large, hyperchromatic nuclei,
interstitial fibrosis, endocardial fibroplasia, fibrosis of the atrioventricular
node, and marked disorganization of cardiac muscle cells. The study showed
that hypertrophic cardiomyopathy develops in most hyperthyroid cats, some
of which also develop congestive heart failure. Although the signs of
heart disease in primary myocardial disease and thyrotoxic disease are
similar, the characteristic signalment and clinical signs of hyperthyroidism
should lead one to suspect the association of hypertrophic cardiomyopathy
with the hyperthyroidism. |