BACKGROUND
In critically ill patients, especially those being treated in an intensive care unit, thyroid hormone levels are often altered, with low T3 and TSH values frequently observed. These abnormalities occur because of the response of the thyroid to the severe illness and not because of any specific thyroid function abnormality. This is called the nonthyroidal illness syndrome (NTI) and is seen in ~80% in of patients in intensive care units. In the vast majority of these patients, thyroid hormone therapy is not indicated.

While low T3 and TSH levels are common in NTI, low FT4 levels often indicate a bad prognosis, particularly when they persist after the acute period of the disease. There is still a large debate over the possible benefits of treatment of these NTI patients with low FT4 levels with thyroid hormones. One area where thyroid hormone therapy may have some benefit is in patients with heart failure or in heart donors before heart transplantation.

In this study, the association between thyroid status and heart transplantation was explored in patients with end-stage heart failure. The benefit of administering thyroid hormone replacement, as advocated by a standard donor protocol and treatment in the recipients, was also evaluated.

THE FULL ARTICLE TITLE
Szécsi B et al. The perioperative period of heart transplantation is affected by thyroid hormone status. Thyroid 2024;34(6):774-784; doi: 10.1089/thy.2023.0628. PMID: 38613807.

SUMMARY OF THE STUDY
This was a prospective single-center study of 283 patients who received heart transplantation (HTx) between February 2013 and November 2020 at the Heart and Vascular Center of Semmelweis University in Hungary.

Thyroid status according to FT3, FT4, and TSH serum levels was evaluated before and after HTx. The effect of levothyroxine (LT4) administered to a subgroup of heart donors and recipients on death before transplantation and after 30 days (short-term) and 1 and 2 years (long-term) was assessed. The Index for Mortality Prediction After Cardiac Transplantation (IMPACT) score, a numerical measure to predict the risk of dying after HTx, was determined. Death was the primary outcome of this study.

The average age of the 283 patients was 54 years. Overt hypothyroidism was found in 12.4% and subclinical hypothyroidism in 2.1%, and 6.7% were diagnosed with thyrotoxicosis. Thyroid replacement was indicated in 37.8% of donors. Of recipients, 11.3% received levothyroxine prior to surgery and 19.4% received levothyroxine after surgery. Thyroid hormones and TSH significantly decreased after HTx except in patients who received levothyroxine. Short-term survival was higher if the donor had received levothyroxine. Long-term and short-term survival was higher in recipients who also received levothyroxine after transplantation.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study confirmed that thyroid tests after heart transplantation are consistent with NTI. Overt and subclinical hypothyroidism also occurred and was treated with levothyroxine. The study suggests that the use of levothyroxine in both donors and recipients improved survival after hear transplantation, especially in patient with pre-existing hypothyroidism. It is unclear how many patients were treated on the basis of NTI and not hypothyroidism. Even so, this is an important study that should result in larger studies to clarify the indications for treatment of these critically ill patients.

— Alan P. Farwell, MD

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