What is it about?

High and abnormal levels of thyroid hormones cause a common disease called hyperthyroidism. The patients suffer from weight loss, heat intolerance, sweating and tremulousness and in some bulging eyes. Heart palpitations with increased heart rate (more than 90-100 beats per minutes) called tachycardia is a common symptom and sign. Tachycardia was considered in the past as one of the classical most common signs of the disease, present in almost all patients (70-100 %). In this study we noticed that tachycardia is not so common in patients with hyperthyroidism today as was reported in the past. In fact, in our study of 248 hyperthyroid patients, tachycardia was present only in minority of the patients, 28.2%. In the lowest and highest thyroid hormone quartiles, tachycardia was present in 16.4% and 38.7% respectively.

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Why is it important?

How one can explain these big differences in prevalence of tachycardia as published in older medical literature and our findings? It appears that the explanation lies in the way medicine is practiced today in comparison to the past. In fact, the tests to diagnose hyperthyroidism in 1980s and before were very cumbersome and required admission of patients to special metabolic units and the blood tests were not very accurate. The doctors were doing these tests mainly in patients who had the symptoms suggesting the disease, including tachycardia. Today the diagnosis is easy with very accurate and quick blood tests. The doctors today are ordering the tests as routine tests, not necessarily because of presence of prominent symptoms of the disease. This surprising finding that many patients with the disease and even with very high thyroid hormone levels do not have tachycardia and some are almost without symptoms, is not easy to explain.


What we learned from this study is that high and abnormal levels of hormones and in this case thyroid hormones are not telling the entire story. The response of the body organs is different in different individuals to similar high levels of hormones and it may depend on different chemical composition of the receptors that are the targets of these hormones.

Leon Fogelfeld
Stroger Hospital of Cook County, Chicago

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This page is a summary of: Tachycardia in hyperthyroidism: Not so common, PLoS ONE, September 2022, PLOS, DOI: 10.1371/journal.pone.0273724.
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