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Hyperthyroidism is associated with lengthening of ventricular repolarization.
R M Colzani1, M Emdin, F Conforti
1Cardiovascular Neuroendocrine Unit, CNR Institute of Clinical Physiology, Via P. Savi, I-56126 Pisa, Italy.
Clinical Endocrinology
|July 17, 2001
Summary
Hyperthyroidism prolongs the corrected QT interval (QTc), increasing cardiac arrhythmia risk. Treatment to a euthyroid state normalizes QTc, indicating thyroid hormone
Area of Science:
- Cardiology
- Endocrinology
- Clinical Electrophysiology
Background:
- Prolonged ventricular repolarization (QT interval) on electrocardiogram (ECG) is linked to cardiac dysrhythmias.
- No prior in vivo data existed for heart rate-corrected QT interval (QTc) in hyperthyroidism.
Purpose of the Study:
- To investigate QTc interval duration in patients with hyperthyroidism.
- To assess QTc interval changes following normalization of thyroid hormone levels.
Main Methods:
- Collected 24-hour ambulatory ECG Holter recordings from 16 hyperthyroid patients and 13 healthy controls.
- Measured QT and RR intervals, calculating QTc using Bazett's formula.
- Assessed serum thyroid hormones (T4, T3, free T4, free T3) and plasma norepinephrine, electrolytes.
Main Results:
- Hyperthyroid patients exhibited significantly prolonged QTc intervals compared to controls (458 +/- 7 ms vs. 431 +/- 6 ms).
- QTc normalized after treatment to a euthyroid state (432 +/- 6 ms).
- QTc showed a strong positive correlation with free T3 (r=0.63) and free T4 (r=0.481) levels.
Conclusions:
- Hyperthyroidism is associated with prolonged QTc intervals.
- Normalization of QTc occurs upon achieving a euthyroid state.
- Thyroid hormones, particularly free T3, play a significant role in modulating QTc interval length.