Cardiac Abnormalities in Feline Hyperthyroidism

Hyperthyroidism is a common endocrine disorder in elderly cats, often leading to concurrent cardiac abnormalities. Understanding the development of these cardiac abnormalities and the effect of treatment is crucial for optimizing monitoring strategies and long-term management. Hyperthyroid cats frequently develop cardiomegaly, with left ventricular concentric and/or eccentric hypertrophy, and left atrial dilation. Cardiac abnormalities described in humans with multinodular toxic goiter may differ from those in cats, but, as in humans, these abnormalities are often reversible once thyroid hormone levels are normalized. Definitive treatment options for hyperthyroidism, such as radioiodine therapy and thyroidectomy, are the most successful at restoring the normal thyroid hormone levels. Medical therapy and iodine-restricted diets can also help normalize thyroid hormone levels, thereby aiding the reversal of cardiac abnormalities. However, cats with pre-existing cardiac diseases, like hypertrophic cardiomyopathy, may not show reversible cardiac changes due to these concurrent primary cardiac diseases. Cats with hyperthyroidism should routinely undergo echocardiographic evaluations to monitor for concurrent cardiac abnormalities, both before and after treatment. More importantly, every cat older than 6 years of age with echocardiographic or clinical signs of heart disease should be screened for hyperthyroidism. With appropriate treatment of hyperthyroidism, heart failure can be prevented.