Myocardial injury aggravated by hypothyroidism in patients with idiopathic dilated cardiomyopathy: the evidence based on ⁹⁹Tc^m-MIBI SPECT/¹⁸F-FDG PET imaging and cardiac MRI

Objective: To explore the relationship between hypothyroidism and myocardial injury in patients with idiopathic dilated cardiomyopathy (IDC) by ⁹⁹Tc^m-MIBI SPECT/¹⁸F-FDG PET and late-gadolinium enhancement cardiac magnetic resonance imaging (cMRI-LGE). Methods: Sixty-three consecutive patients (42 males and 21 females, (52 ± 11) years) with IDC were enrolled from October 2010 to December 2012. Serum TT₃, TT₄ , FT₃, FT₄ and TSH were determined using a fully automated chemiluminescence immunoassay. All patients underwent ⁹⁹Tc^m-MIBI myocardial perfusion SPECT/¹⁸F-FDG myocardial metabolism PET imaging and cMRI-LGE. Seventeen segments model was used for segmental analysis. Patterns of perfusion/metabolism were classified as normal, mismatch, mild-to-moderate match and complete match. cMRI-LGE was classified into 3 categories (non-LGE, mid-wall LGE and transmural LGE). χ² test was used for data analysis. Results: All patients were divided into euthyroid group (n = 53) and hypothyroidism group (n = 10) according to the levels of serum thyroid hormones. The percentage of normal perfusion/metabolism segments in the euthyroid group was apparently higher than that in the hypothyroidism group: 71.8% (647/901) vs 57.6% (98/170), χ² = 13.50, P < 0.001; whereas the percentage of perfusion/metabolism mismatch segments in the euthyroid group was significantly lower than that in the hypothyroidism group: 17.8% (160/901) vs 31.2% (53/170), χ² = 16.20, P < 0.001. The euthyroid group had a higher percentage of non-LGE segments (88.0% (793/901) vs 69.4% (118/170), χ² = 35.70, P < 0.001) and a lower percentage of mid-wall LGE segments (4.8%(43/901) vs 24.1%(41/170), χ² = 74.70, P < 0.001) compared to hypothyroidism group. Conclusions: Hypothyroidism has a detrimental effect on myocardium. ⁹⁹Tc^m-MIBI SPECT/¹⁸F-FDG PET imaging is sensitive in detecting viable/ischemia myocardium, and cMRI-LGE is good at detecting moderate fibrosis. Combining SPECT/PET imaging and cMRI-LGE for assessing myocardial injury would provide more comprehensive information. (authors)