Hyperthyroidism is a condition with increased production of thyroid hormone from the thyroid gland. Hyperthyroidism affects the heart's inotropy (contractile force) and chronotropy (rhythm). Therefore, patients often experience symptoms such as increased/irregular heart rate, pounding heartbeats, and shortness of breath. The cardiac symptoms often improve when hyperthyroidism is treated and biochemical euthyroidism is achieved. However, knowledge of the long-term effects on the heart is limited. Existing studies have generally shown that patients with hyperthyroidism have an increased morbidity and mortality.

The investigators conducted a questionnaire survey which showed that about 38% of patients with Graves' disease continue to experience cardiac symptoms even months after normalization of thyroid hormone concentrations in the blood. This observation supports the presence of a persistent cardiovascular dysfunction, which may be due to a modulation of genomic or non-genomic factors with an effect on the cardiovascular system. These reflections are the focus of this clinical study. The aim of the study is to investigate the possible pathophysiology for this new "syndrome" in biochemically euthyroid patients. It is not a repetition of previous similar experiments.

Cardiac symptoms are common i patients with Graves' disease. These symptoms often disappear when hyperthyroidism is treated. However, a subgroup of patients with Graves' disease experiences persisting cardiac symptoms after treatment. The aim of the study is to describe these symptoms and investigate their origin.

A total of 75 patients are included in the study. Patients were recruited from the Department of Nephrology and Endocrinology at Copenhagen University Hospital Rigshospitalet and the Department of Internal Medicine, Section of Endocrinology at Herlev Gentofte Hospital, Denmark. The patients were identified by extracting a list of patients with the International Classification of Diseases 10 codes (ICD 10 codes) E050 and E059. Also, a list of patients with positive thyrotropin receptor antibody (TRAbI measurements was extracted.

All patients had a thorough cardiac work up including blood samples, 12-lead resting electrocardiogram, 24-hour electrocardiogram monitoring (Holter), transthoracic echocardiography, and exercise stress test. The focus was to investigate whether the cardiac symptoms could be explained by structural or functional changes of the heart or by cardiac arrhythmias.

All patients were questioned about their symptoms including: type of cardiac symptoms, frequency and when they occured. The focus was to gain knowledge on the clinical presentation of cardiac symptoms in the subgroup.

Inclusion Criteria:

• Patient with Graves' disease
• Between the ages of 18 and 55 years
• Has been euthyroid for at least three months prior to inclusion
• Experiences cardiac symptoms

Exclusion Criteria:

• Cardiovascular disease
• Deemed unsuitable by project staff (e.g. due to language problems)
• Pregnancy
• Alcohol abuse or other abuses

Participants are recruited from the Endocrinology Outpatient Clinic at Rigshospitalet and Herlev/Gentofte Hospital.