Metformin-induced thyrotropin suppression is not associated with cardiac effects.
OBJECTIVE
Metformin treatment may induce a decrease/suppression in serum TSH levels, mimicking sub-clinical hyperthyroidism (SHT). The aim of the present study was to retrospectively evaluate changes in several electrocardiographic indices in euthyroid subjects with diabetes who, after starting metformin treatment, developed a low serum TSH as compared to patients with SHT resulting from an underlying thyroid disease or TSH suppressive treatment with L-thyroxine.


METHODS
Heart rate, P wave duration, P wave dispersion, QTmax, QTmin and QT-dispersion were assessed in 23 patients with diabetes treated with metformin before and after 6 months of TSH-suppression and in 31 control patients with SHT.


RESULTS
No significant changes in electrocardiographic parameters were observed from baseline to the TSH-suppression measurement. A significant difference in P wave duration (102.9 ± 7.4 vs. 92.1 ± 5.8 ms, p<0.001), P wave dispersion (13.1 ± 3.4 vs. 7.1 ± 3.5 ms, p<0.001), QTmax (399 ± 18 vs. 388 ± 16 ms, p=0.024), QTmin (341 ± 14 vs. 350 ± 17 ms, p=0.038) and QT dispersion (49.9 ± 9.6 vs. 30.9 ± 9.2 ms, p<0.001) were observed between the control group with SHT and the group of diabetic patients with low serum levels of TSH.


CONCLUSIONS
Our results show that the TSH-suppressive effect observed in patients taking metformin is not associated with peripheral markers of thyroid hormone excess, at least at the cardiac level.
Department of Medical and Surgical Sciences, Endocrine and Metabolic Unit, University of Brescia; Italy.
Carlo
C
Cappelli
Unit of Internal Medicine and Endocrinology, Fondazione Salvatore Maugeri Istituto di Ricovero e Cura a Carattere Scientifico, Istituto Superiore Prevenzione e Sicurezza Lavoro Laboratory for Endocrine Disruptors, University of Pavia; Italy.
Mario
M
Rotondi
Department of Medical and Surgical Sciences, Endocrine and Metabolic Unit, University of Brescia; Italy.
Ilenia
I
Pirola
Diabetic Unit, Spedali Civili di Brescia; Italy.
Barbara
B
Agosti
Department of Medical and Surgical Sciences, Endocrine and Metabolic Unit, University of Brescia; Italy.
Ana Maria
AM
Formenti
Unit of Internal Medicine and Endocrinology, Fondazione Salvatore Maugeri Istituto di Ricovero e Cura a Carattere Scientifico, Istituto Superiore Prevenzione e Sicurezza Lavoro Laboratory for Endocrine Disruptors, University of Pavia; Italy.
Pasquales
P
De Cata
Department of Medical and Surgical Sciences, Endocrine and Metabolic Unit, University of Brescia; Italy.
Massimo
M
Salvetti
Unit of Internal Medicine and Endocrinology, Fondazione Salvatore Maugeri Istituto di Ricovero e Cura a Carattere Scientifico, Istituto Superiore Prevenzione e Sicurezza Lavoro Laboratory for Endocrine Disruptors, University of Pavia; Italy.
Luca
L
Chiovato
Department of Medical and Surgical Sciences, Endocrine and Metabolic Unit, University of Brescia; Italy.
Maurizio
M
Castellano
D015415:Biomarkers / Q000097:blood; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000175:diagnosis / Q000188:drug therapy*; D015536:Down-Regulation; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate / Q000187:drug effects*; D006801:Humans; D007004:Hypoglycemic Agents / Q000009:adverse effects / Q000627:therapeutic use*; D008297:Male; D008687:Metformin / Q000009:adverse effects / Q000627:therapeutic use*; D008875:Middle Aged; D012189:Retrospective Studies; D018570:Risk Assessment; D013972:Thyrotropin / Q000097:blood*; D013997:Time Factors
D015415:Biomarkers; D007004:Hypoglycemic Agents; D013972:Thyrotropin; D008687:Metformin