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Evaluating heart function in hyperthyroid cats

Sangster JK, Panciera DL, Abbott JA, et al. Cardiac biomarkers in hyperthyroid cats. J Vet Intern Med 2014;28:465-472.
The abnormalities of the cardiovascular system in hyperthyroid cats can vary from small subtle effects to clinically severe changes associated with the development of heart failure. Because of this diversity, it can be a diagnostic challenge to determine if abnormalities are due to hyperthyroidism or a concurrent primary cardiac disease. The authors of this study proposed to test the hypothesis that cardiac biomarker concentrations are higher in cats with primary myocardial disease than in cats with hyperthyroidism, and higher in cats with hyperthyroidism than in healthy control cats. The two cardiac biomarkers evaluated were plasma NT-proBNP (N-terminal probrain natriuretic peptide) and cTNI (cardiac troponin I). The study evaluated 23 hyperthyroid cats, 17 cats with subclinical hypertrophic cardiomyopathy (HCM), and 19 normal healthy cats at least 8 years of age. Fourteen of the hyperthyroid cats were re-evaluated 3 months after treatment with radioiodine.
The results found that hyperthyroid cats and cats with HCM had significantly higher plasma concentrations of both cardiac biomarkers than healthy cats, but also noted the difference was not significant between hyperthyroid cats and cats with HCM for either biomarker. In cats that received radioiodine treatment for hyperthyroidism, the plasma concentrations for both cardiac biomarkers as well as ventricular wall thickness of the heart had decreased significantly after treatment.

Some key points were determined from the study. There was no correlation found between blood pressure and either biomarker. Also, overall, the findings supported previous work in that thyrotoxic myocardial hypertrophy is largely reversible. NT-proBNP might have a potential use in monitoring the response to treatment of hyperthyroidism. If the plasma concentration of this biomarker remains elevated three months after resolution of hyperthyroidism, this could indicate underlying cardiomyopathy is also present and an echocardiogram would be recommended. Evaluating these particular cardiac biomarkers, in summary, did not aid in differentiating between cats with primary HCM and those with thyrotoxic cardiomyopathy. [VLT]

See also:
Oyama MA. Using Cardiac Biomarkers in Veterinary Practice. Veterinary Clinics of North America: Small Animal Practice 2013;43:1261-1272.