BACKGROUND
T4 is the main thyroid hormone secreted from the thyroid gland. T4 is converted to T3, the active hormone, in many tissues outside the thyroid. There is a strong association between thyroid hormones and the heart in both health and in disease. In particular, in patients with congestive heart failure, T3 levels are often low and are associated with worse outcomes. T3 levels are also low in patients admitted with heart attack and after heart surgery. This is known as the low T3 syndrome and has led to studies using T3 therapy in patients acutely sick with heart problems and with the low T3 syndrome. The goal in these studies has been to increase T3 levels back to normal to try to improve outcomes. To date, studies have been unclear of any benefit; importantly no bad effects of T3 therapy has been shown in these studies.

The degree to which the low T3 syndrome represents a protective or harmful response to acute heart injury and whether treatment with thyroid hormones will improve patient outcomes remain uncertain. This study was aimed to evaluate the effect of high-dose liothyronine (LT3) shortly after a heart attack.

THE FULL ARTICLE TITLE
Pantos CI et al 2022 Effects of acute triiodothyronine treatament in patients with anterior myocardial infarction undergoing primary angioplasty: Evidence from a pilot randomized clinical trial (ThyRepair Study). Thyroid. Epub 2022 May 5. PMID: 35297659.

SUMMARY OF THE STUDY
This trial was conducted in two clinical centers in Greece and included adult patients diagnosed with anterior or anterolateral ST-elevation myocardial infarction (STEMI) presenting within 12 hours of the onset of chest pain.

Patients were randomly assigned to receive intravenous (IV) LT3 treatment or no hormone. The IV infusion of LT3 or no hormone was given by continuous infusion for 48 hours.

A total of 52 patients were enrolled. There were no significant differences in baseline characteristics between the two groups. After accounting for participants who did not complete follow-up, a total of 16 patients in the no hormone group and 21 patients in the LT3 group were analyzed. As expected, total T3 levels were higher in the LT3 group than in the no hormone group during the initial 72 hours. There was no significant difference in overall heart function at discharge, although a trend favoring LT3 therapy was noted. A trend toward a decrease in the size of the damaged heart muscle was noted in the LT3 group at 6 months. No serious lifethreatening adverse effects related to LT3 treatment were reported. Patients in the LT3 group had higher heart rates during the initial 72 hours than the no hormone group, but no significant difference was found at discharge or during follow-up. There was a trend of increased incidence of atrial fibrillation (AF) in the LT3 group during the 48 hours of drug infusion and responded to medical management.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study shows treatment with IV T3 in the setting of an acute heart attack resulted in a trend toward improved heart function. Importantly, no serious life-threatening adverse events were noted; however, there was a trend toward a higher incidence of AF in the LT3 group. This study sets the parameters for future larger studies.

—Alan P. Farwell, MD

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