The relation of thyroid function and ventricular repolarization: decreased serum thyrotropin levels are associated with short rate-adjusted QT intervals.

CONTEXT: The linkage of thyroid dysfunction with ventricular repolarization properties has not been investigated extensively, although alterations might be associated with an increased ventricular vulnerability.
OBJECTIVE: The objective of the study was to investigate whether there is an association between functional thyroid status and rate-adjusted QT intervals (QTc). DESIGN, SETTING, AND PARTICIPANTS: The population-based Study of Health in Pomerania included 4310 subjects aged 20-79 yr. Data of 3610 subjects (1862 women and 1748 men) without branch bundle blocks or pacemaker were available for the present analyzes. MAIN OUTCOME MEASURES: QTc with respect to thyroid status. Short QTc was defined below the 25th percentile, and long QTc above the 75th percentile of the gender-specific distribution.
RESULTS: TSH levels were positively associated with QTc independent from potential confounders in multivariable analyses (P for trend = 0.001). Subjects with decreased TSH levels had shorter QTc than those with normal TSH levels (426.4 +/- 8.2 vs. 430.2 +/- 8.2; P < 0.001). Adjusted odds ratios for short QTc in subjects with elevated, normal, and decreased TSH were 0.87 (95% confidence interval 0.58-1.31), 1.00 (reference), and 1.53 (95% confidence interval 1.16-2.03), respectively (P for trend = 0.008).
CONCLUSION: TSH levels were positively related to QTc in a population-based sample. Subjects with decreased serum TSH levels had an increased risk for short QTc. Whether these findings are of clinical significance has to be investigated by further studies.