J Korean Med Sci.  2007 Feb;22(1):114-116. 10.3346/jkms.2007.22.1.114.

The Effects of L-thyroxine Treatment on QT Dispersion in Primary Hypothyroidism

• Kweon KH
• Park BH
• Cho CG

• KMID: 1713247
• DOI: http://doi.org/10.3346/jkms.2007.22.1.114

Abstract

Hypothyroidism has various cardiovascular manifestation and exhibits electrocardiographic change. The QT dispersion on surface ECG reflects regional variations in myocardial repolarization. The effect of L-thyroxine treatment on ECG parameters, such as QT dispersion, in patients with primary hypothyroidism were investigated. This study involved 18 patients (3 men, 15 women, ages: 48+/-18 yr) with primary hypothyroidism. All patients were checked with a standard 12-lead ECG before and after L-thyroxine treatment. Various ECG parameters were then measured twice. The mean L-thyroxine treatment duration was 22+/-2.7 months. The mean thyroid-stimulating hormone levels of patients before and after therapy were 40.2+/-29.8 microU/mL, 3.6+/-4.6 microU/mL (p<0.001) and free-T4 levels were 0.44+/-0.38 ng/dL, 1.51+/-0.39 ng/dL (p<0.001). After L-thyroxine treatment, QT interval (395+/-42 vs. 380+/-24 msec, p<0.05), QTc interval (434+/-32 vs. 417+/-23 msec, p<0.05), QT dispersion (45+/-23 vs. 30+/-13 msec, p=0.008), QTc dispersion (49+/-23 vs. 32+/-14 msec, p=0.005) significantly decreased. There were no significant changes in the PR and RR intervals, as well as the QRS duration. Our findings suggest that the thyroid hormone affects ventricular inhomogenicity, and that L-thyroxine replacement therapy may reduce malignant ventricular arrhythmia and sudden cardiac death in primary hypothyroidism.

Keyword

Hypothyroidism; Thyroxine; Electrocardiography

MeSH Terms

Thyroxine/*therapeutic use
Middle Aged
Male
Hypothyroidism/*drug therapy/physiopathology
Humans
Female
Electrocardiography/*drug effects
Adult

Figure

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  Fig. 1 Serial Electrocardiograms. (A) An ECG before L-thyroxine treatment shows QT prolongation (QTc=485 msec) and T-inversion in left precordial leads. (B) An ECG after L-thyroxine treatment shows normal QT interval (QTc=432 msec) and an upright T-wave.

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