Severe Short-Term Hypothyroidism Is Not Associated with an Increased Incidence of Myocardial Ischemia as Assessed by Thallium-201 Stress/Rest Myocardial Scintigraphy

Reversible silent myocardial ischemia associated with treatment of long-standing hypothyroidism has recently been reported using thallium-201 (²⁰¹T1) myocardial single photon emission tomography (SPET). The aim of the present study was to evaluate whether patients with short-term hypothyroidism (serum thyrotropin [TSH] levels above 30 mU/L) have an increased risk of silent myocardial ischemia. We studied 20 patients with differentiated thyroid carcinoma that had undergone thyroidectomy and ablative ¹³¹I therapy. None of the patients had a known history of atherosclerotic cardiovascular disease. In the course of a planned follow-up examination, suppressive levothyroxine (LT₄) therapy was discontinued 7 weeks prior to scintigraphy and replaced by triiodothyronine (T₃) therapy for 4 weeks. No thyroid hormone medication was given during the 3 weeks preceding the diagnostic procedures. All patients were hypothyroid (TSH 87.2 ± 30.8 mU/L, mean ± SD) at the time of the examination. ²⁰¹T1-SPET was performed immediately after bicycle exercise stress test and again after a delay of 4 hours. In case of abnormal results, (n = 3) the examination was repeated after patients were euthyroid. Two patients showed effects of soft-tissue attenuation (breast attenuation in a female and diaphragmatic attenuation in a male subject). Myocardial ischemia was revealed in 1 patient but was seen in both hypothyroid and euthyroid examinations. The results of the present study show that short-term severe hypothyroidism as encountered in athyreotic patients after cessation of thyroxine medication for several weeks, is not associated with an impairment of myocardial perfusion.