Thyroid dysfunction and electrocardiographic changes in subjects without arrhythmias: a cross-sectional study of primary healthcare subjects from Copenhagen

ObjectiveThe objective of the present study was to investigate associations of both overt and subclinical thyroid dysfunction with common ECG parameters in a large primary healthcare population.DesignCross-sectional study.Setting and participantsThe study population comprised of primary healthcare patients in Copenhagen, Denmark, who had a thyroid function test and an ECG recorded within 7 days of each other between 2001 and 2011.Data sourcesThe Danish National Patient Registry was used to collect information regarding baseline characteristics and important comorbidities.Outcome measure and study groupsCommon ECG parameters were determined using Marquette 12SL software and were compared between the study groups. The study population was divided into five groups based on their thyroid status. Euthyroid subjects served as the reference group in all analyses.ResultsA total of 132 707 patients (age 52±17 years; 50% female) were included. Hyperthyroidism was significantly associated with higher heart rate and prolonged QTc interval with significant interaction with age (p