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Triiodothyronine (T3) treatment after mild heart attacks is safe but not associated with a clear benefit

CTFP Volume 12 Issue 9

During a major illness, the levels of thyroid hormones (T4 and T3) and thyroid stimulating hormone (TSH) change in most patients. These changes do not represent a problem in thyroid gland, but they are part of a larger hormonal reaction that happens at the time of a significant sickness. The most common finding is a low T3 level, as the body shuts down the production of T3 from T4 during sickness. This may also occur after a heart attack. Indeed, 15-20% of patients have low levels of T3 for several days after a heart attack. Patients with the lowest levels of T3 are usually the sickest and have a higher chance of dying.

While most researchers and physicians believe that the hormonal changes during a sickness are helpful and beneficial for recovery, there is debate on whether treatment with T3 may be helpful when it declines to very low levels. In the past, various animal and clinical investigations have been conducted to answer this question. In this study, the authors tried to evaluate the effect of treatment with T3 on recovery from heart attack; specifically, to assess the potential benefits of T3 on the extent of heart muscle damage and its function.

Pingitore A et al 2018 Usefulness of triiodothyronine replacement therapy in patients with ST elevation myocardial infarction and borderline/reduced triiodothyronine levels (from the THIRST study). Am J Cardiol. Epub 2018 Dec 18. PMID: 30638544.

This study was done in Pisa, Italy. The authors recruited patients with heart attack who were admitted to cardiac intensive unit. The patients were eligible to enter the study if they had a low level of T3 at the time of admission or a 20% drop in T3 level within the first 72 hours after arrival to hospital.

They also had to be treated with a heart procedure to open up the coronary arteries within 12 hours of the onset of their initial symptoms. Patients who were very sick, had history of previous thyroid disease or heart disease and took certain medications were not considered appropriate for the study. A total of 37 patients participated. Patients received either T3 plus standard heart care (19) or just standard heart care (18). The 19 patients who received T3 continued taking it for 6 months. The starting dose was based on patient’s age (lower in older individuals), with later doses based on the results of blood tests for TSH, T4 and T3.

The average age of participants was 68 years and only 16% were female. TSH, T4 and T3 were measured at the time of admission, on daily basis during hospitalization and on regular basis after discharge. MRI was done to assess the extent of heart muscle damage after heart attack as well as its function (ability to pump blood). There was a minimum improvement in the function of heart muscle in patients who received T3 but this was not statistically significant. No side effects were noted from T3.

This study confirmed that after a heart attack, patients who are sicker have a lower level of T3. Although no harm was observed by treating patients with T3 after a heart attack, this study showed that no significant improvement in the function or decrease in the extent of damaged heart muscle was noted from such treatment. At this point, T3 treatment is not recommended after a heart attack based on this study and larger randomized clinical trials are needed.

— Shirin Haddady, MD


Thyroxine (T4): the major hormone produced by the thyroid gland. T4 gets converted to the active hormone T3 in various tissues in the body.

Triiodothyronine (T3): the active thyroid hormone, usually produced from thyroxine, available in pill form as Cytomel™.

TSH: thyroid stimulating hormone — produced by the pituitary gland that regulates thyroid function; also the best screening test to determine if the thyroid is functioning normally.