Effect of levothyroxine treatment on QT dispersion in patients with subclinical hypothyroidism.
OBJECTIVE
To examine the effect of levothyroxine treatment in patients with subclinical hypothyroidism on electrocardiographic variables, especially on ventricular repolarization-related factors.


METHODS
Sixteen women (mean age, 48.2 years) with subclinical hypothyroidism were treated with levothyroxine for 16 weeks. All standard 12-lead electrocardiographic recordings were scanned and transferred to a computer, and the QT intervals were measured on 300 times magnified recordings. QT dispersion, which reflects the heterogeneity of the ventricular repolarization, was calculated by the difference between the QT maximum and the QT minimum.


RESULTS
We found that, after 16 weeks of levothyroxine treatment, the QT interval decreased from 387.2 +/- 10.8 ms to 345.6 +/- 13.0 ms (P<0.0001). The study patients exhibited a significant reduction of QT dispersion from 46.5 +/- 5.3 ms to 30.7 +/- 5.8 ms (P<0.0001). On linear regression analysis, a positive relationship was found between QT dispersion and logarithmic serum TSH levels (r = 0.492; P<0.0001).


CONCLUSIONS
We conclude that serum TSH concentration has a role in ventricular inhomogeneity and, therefore, that subclinical hypothyroidism may predispose to ventricular arrhythmias. A large-scale, multicenter, randomized trial should be undertaken to address the benefit-to-risk ratio of levothyroxine treatment on cardiac inhomogeneity in patients with subclinical hypothyroidism.
Unal
Oguzkaan
O
Department of Endocrinology, Uludag University School of Medicine, Bursa, Turkey.
Erturk
Erdinc
E
Ozkan
Hakan
H
Kiyici
Sinem
S
Guclu
Metin
M
Ersoy
Canan
C
Yener
Feyza
F
Imamoglu
Sazi
S
D000328:Adult; D001145:Arrhythmias, Cardiac / Q000209:etiology; D004562:Electrocardiography; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000150:complications / Q000188:drug therapy* / Q000503:physiopathology*; D016014:Linear Models; D008875:Middle Aged; D011446:Prospective Studies; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000009:adverse effects* / Q000097:blood / Q000627:therapeutic use; D014284:Triiodothyronine / Q000097:blood
D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine