Endocrinol Metab.  2021 Oct;36(5):1121-1130. 10.3803/EnM.2021.1216.

Association between Thyroid Function and Heart Rate Monitored by Wearable Devices in Patients with Hypothyroidism

• Kim KH
• Lee J
• Ahn CH
• Yu HW
• Choi JY
• Lee HY
• Lee WW
• Moon JH

• KMID: 2521959
• DOI: http://doi.org/10.3803/EnM.2021.1216

Abstract

Background
Heart rate (HR) monitored by a wearable device (WD) has demonstrated its clinical feasibility for thyrotoxicosis subjects. However, the association of HR monitored by wearables with hypothyroidism has not been examined. We assessed the association between serum thyroid hormone concentration and three WD-HR parameters in hypothyroid subjects.
Methods
Forty-four subjects scheduled for radioactive iodine therapy (RAI Tx) after thyroid cancer surgery were included. Thirty subjects were prepared for RAI Tx by thyroid hormone withdrawal (hypothyroidism group) and 14 subjects by recombinant human thyrotropin (control group). Three WD-HR parameters were calculated from the HR data collected during rest, during sleep, and from 2:00 AM to 6:00 AM, respectively. We analyzed the changes in conventionally measured resting HR (On-site rHR) and WDHR parameters relative to thyroid hormone levels.
Results
Serum free thyroxine (T4) levels, On-site rHR, and WD-HR parameters were lower in the hypothyroid group than in the control group at the time of RAI Tx. WD-HR parameters also reflected minute changes in free T4 levels. A decrease in On-site rHR and WD-HR parameters by one standard deviation (On-site rHR, approximately 12 bpm; WD-HR parameters, approximately 8 bpm) was associated with a 0.2 ng/dL decrease in free T4 levels (P<0.01) and a 2-fold increase of the odds ratio of hypothyroidism (P<0.01). WD-HR parameters displayed a better goodness-of-fit measure (lower quasi-information criterion value) than On-site rHR in predicting the hypothyroidism.
Conclusion
This study identified WD-HR parameters as informative and easy-to-measure biomarkers to predict hypothyroidism.

Keyword

Wearable electronic devices; Hypothyroidism; Heart rate

Figure

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  Fig. 1 Study design and flow. Blood tests included a thyroid function test and other biochemical tests. LT4, levothyroxine; LT3, liothyronine; RAI Tx, radioactive iodine (I131) therapy; F/U, follow-up; rhTSH, recombinant human thyrotropin.

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  Fig. 2 Change of (A) serum free thyroxine (T4) levels, (B) Zulewski’s clinical score, (C) On-site resting heart rate (rHR), (D) rHR from wearable device (WD-rHR), (E) HR during sleep from wearable device (WD-sleepHR), and (F) HR from 2:00 AM to 6:00 AM from wearable device (WD-2to6HR) during the study period. Error bars represent 95% confidence interval of the means. The symbols indicate two groups.

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