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Hypertropic cardiomyopathy and hyperthyroidism in the cat
Insights
Hyperthyroidism in cats commonly leads to hypertrophic cardiomyopathy, a thickening of the heart muscle. Some affected cats also develop congestive heart failure, indicating a significant link between the two conditions.
Area of Science:
- Veterinary Cardiology
- Endocrinology
Background:
- Hyperthyroidism is a common endocrine disorder in cats.
- Hypertrophic cardiomyopathy (HCM) is a primary heart disease in cats.
- The association between hyperthyroidism and HCM requires further investigation.
Purpose of the Study:
- To determine the prevalence of hypertrophic cardiomyopathy in hyperthyroid cats.
- To investigate cardiac changes in cats with hyperthyroidism.
- To differentiate HCM associated with hyperthyroidism from primary cardiac diseases.
Main Methods:
- Necropsy examination of 23 cats with hyperthyroidism.
- Comparison of body weight and heart weight to body weight ratios with control groups.
- Histopathological evaluation of cardiac tissue.
Main Results:
- Hypertrophic cardiomyopathy was found in 23 hyperthyroid cats.
- 17% of these cats exhibited signs of cardiac failure.
- Hyperthyroid cats with HCM had significantly lower body weight and higher heart weight to body weight ratios compared to controls.
Conclusions:
- Hypertrophic cardiomyopathy is a common finding in hyperthyroid cats.
- Congestive heart failure can develop secondary to hyperthyroidism-induced HCM.
- Clinical signs of hyperthyroidism should prompt suspicion of associated cardiac disease.
Abstract:
In a 21/2-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 less than 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.