| PURPOSE: The aim of this study was to evaluate cardiac change caused by hyperthyroidism through 99Tcm-MIBI myocardial perfusion tomography (MPT) and the relationship among N-terminal B-type natriuretic peptide (NT-proBNP), thyroid hormone (TH) and left ventricular (LV) volume. MATERIALS AND METHODS: Twenty five hyperthyroid patients (group A), eight hyperthyroid in remission stage (group B) and seventeen healthy volunteers as control (group C) were involved in the study. Gated myocardial perfusion SPECT was performed on all patients with a lower than 10% likelihood of coronary artery disease and serum levels of NT-proBNP were measured (including 9 heart failure patients). Qualitative and semi-quantitative methods were used to evaluate the characteristics of myocardial perfusion in all patients. Uptake in each segment was graded on a 4-point scale (0, normal perfusion; 1, mildly decreased; 2, moderately decreased; 3, severely decreased or absent perfusion). Myocardial perfusion defects were defined as followed: reversible defects, part reversible defects, fixed defects and reverse redistribution. The LV functional parameters were calculated using an automatic gated myocardial perfusion SPECT processing software. LV functional parameters with correction for body surface area were expressed as followed: end-diastolic volume index (EDVi), end-systolic volume index (ESVi), stroke volume index (SVi). RESULT: The abnormalities of MPT in group A amounted to 58 segments. The distribution of these segments were as followed: anterior segment (27%), apical segment (21%), basal septal segment (17%), basal inferior segment (14%), basal inferolateral segment (7%), others (14%). Most focuses on MPT were reversible defects (48 segments). A few of them accompanied by fixed defects (8 segments) and reverse redistribution (2 segments). All of them scored 1. The abnormalities of MPT in group B amounted to 2 segments, which were 3 segments in group C, all of them scored 1. According to the course of hyperthyroidism, group A were grouped into three subgroups: A1 (the course less than 2years), A2 (the course between 2 and 5 years), A3 (the course more than 5years). Among 160 segments in subgroup A1, 4 segments (2.5%) showed abnormal perfusion defects distribution, which was 10.6% in subgroup A2 and 20.6% in subgroup A3.There was significant difference among them (P<0.05). Serum levels of NT-proBNP were more than three times higher in group A than group B and C, with mean values of 97.69 pg/ml (21.05～969.3),35.29 pg/ml(16.95～72.7),34.88pg/m(16.39～77.47). Serum levels of NT-proBNP in heart failure patients were 859.4pg/ml(80.7～22609.0). A multiple linear regression analysis demonstrated that FT4 estimates were independently associated with a high serum NT-proBNP (P<0.01), whereas LV volumes were not. EDVi, ESVi, SVi in group A were higher than group C, respectively (P<0.05). CONCLUSION: 1. Serum levels of NT-proBNP are affected by TH. A multiple linearregression analysis demonstrated that FT4 estimates were independently associated with a high serum NT-proBNP (P<0.01). 2. It seems that TH exerts a direct, positive stimulatory of expression and secretion of BNP and NT-proBNP. 3. Hyperthyroidism makes NT-proBNP levels increase slightly. It seems that there is no relationship between NT-proBNP and LV volumes. 4. The characteristic of MPT abnormalities in hyperthyroidism is irregular, scattered, mild perfusion defects distribution. Most of them are reversible defects. The longer course of hyperthyroidism is, the higher ratio myocardial perfusion SPECT abnormality exists. Hyperthyroidism probably causes the coronary microvascular and myocardium damage. 5. BNP can antagonise some influence on cardiovascular system causing by TH. This relationship is a compensatory reaction which is produced by organism in order to maintain homeostasis. |
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