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Myocardial Oxidative Metabolism in Hyperthyroid Patients Assessed by PET with Carbon-11-Acetate

Departments of Nuclear Medicine and Laboratory Medicine, Kyoto University Faculty of Medicine, Kyoto, Japan

Correspondence: For correspondence or reprints contact: Tatsuo Torizuka, MD, Department of Nuclear Medicine, Kyoto University Faculty of Medicine, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto 606, Japan.

ABSTRACT

Hyperthyroid patients often complain of cardiovascular symptoms because of increased metabolism. This study was designed to quantitatively evaluate myocardial oxidative metabolism in these patients. Methods: Dynamic PET with ¹¹C-acetate was performed in 19 patients who had not undergone treatment for hyperthyroidism. Eight were restudied 2 wk after oral administration of propranolol. The clearance rate constant of ¹¹C-acetate (Kmono) was calculated with monoexponential fitting of tracer washout from the myocardium as a marker of myocardial oxidative metabolism. The results were compared with those in nine normal subjects both at rest and during dobutamine infusion. Results: Kmono in our patients (0.109 ± 0.028 min^–1) was significantly increased compared to normal subjects (0.066 ± 0.016 min^–1) (p < 0.05). After propranolol treatment, Kmono decreased (0.082 ± 0.014 min^–1) but remained significantly higher in eight patients than normal subject levels (p < 0.05), while the rate pressure product decreased significantly (7500 ± 1700) toward the normal range (7900 ± 1500). Conclusion: These results suggest the possibility of excessive myocardial oxygen consumption in hyperthyroid patients. The clearance rate ¹¹C-acetate is a new and valuable index to assess myocardial oxidative metabolism not closely related to the pressure rate product or thyroid hormones in these patients.

Key Words: hyperthyroidism • propranolol treatment • myocardial oxidative metabolism • carbon-11-acetate • positron emission tomography