title: Cardiac oxidative metabolism, function, and metabolic performance in mild hyperthyroidism: a noninvasive study using positron emission tomography and magnetic resonance imaging.
abstract: Using noninvasive imaging, we have previously demonstrated that myocardial efficiency is impaired in hypothyroidism and improves after establishing euthyroid conditions. Little is known about the effects of abnormally elevated thyroid hormone exposure on cardiac metabolic performance. We studied 10 patients without evidence of heart disease in mild hyperthyroidism, and after therapy under euthyroid conditions. Cardiac oxidative metabolism was quantified by positron emission tomography with [(11)C]acetate. Left ventricular geometry was determined by cine magnetic resonance imaging. Myocardial efficiency, defined by the relation between work and oxygen consumption, was estimated using the work metabolic index [WMI = stroke volume * systolic blood pressure * heart rate/(oxidative metabolism * ventricular mass)]. In hyperthyroidism, heart rate and cardiac output were expectedly higher. Peripheral vascular resistance was reduced. Differences of blood pressure, stroke volume, and ventricular mass were not observed. Oxidative metabolism was significantly higher, but WMI was not different from the euthyroid state. In summary, while improvement of efficiency through thyroid hormone substitution was observed previously in hypothyroidism, our data in mild hyperthyroidism suggest an increase of oxygen consumption, paralleled by an increase of work. Thus, moderately elevated thyroid hormone levels neither result in further increase nor in reduction of cardiac metabolic performance.
authors.affiliation: Nuklearmedizinische Klinik und Poliklinik der Technischen Universität München, Germany.
authors.forename: Frank M
authors.initials: FM
authors.lastname: Bengel
authors.forename: Juliane
authors.initials: J
authors.lastname: Lehnert
authors.forename: Tareq
authors.initials: T
authors.lastname: Ibrahim
authors.forename: Christoph
authors.initials: C
authors.lastname: Klein
authors.forename: Hubertus P
authors.initials: HP
authors.lastname: Bülow
authors.forename: Stephan G
authors.initials: SG
authors.lastname: Nekolla
authors.forename: Markus
authors.initials: M
authors.lastname: Schwaiger
mesh_terms: D000085:Acetates / Q000737:chemistry / Q000378:metabolism; D002250:Carbon Radioisotopes / Q000493:pharmacokinetics; D005260:Female; D006321:Heart / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006439:Hemodynamics; D006801:Humans; D006980:Hyperthyroidism / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D008137:Longitudinal Studies; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009206:Myocardium / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014055:Tomography, Emission-Computed; D014284:Triiodothyronine / Q000097:blood; D016277:Ventricular Function, Left
chemical_list: D000085:Acetates; D002250:Carbon Radioisotopes; D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine; D010100:Oxygen