If a heart attack survivor also has an underactive thyroid, treating them with supplemental thyroid hormone probably won't help, new research shows.
The study found that use of the hormonal drug, called levothyroxine, didn't improve heart muscle function in heart attack patients diagnosed with "subclinical hypothyroidism" -- an underactive thyroid.
In fact, "screening for and subsequent treatment of subclinical hypothyroidism in patients who have had a heart attack to preserve or improve heart function is not justified," concluded the study's lead author, Salman Razvi. He's a consultant endocrinologist at Newcastle University and the Queen Elizabeth Hospital in Gateshead, U.K.
Mild or subclinical hypothyroidism -- which affects about 10% of adults -- means that the thyroid doesn't produce enough hormones.
Management of the condition is uneven because there's a lack of good evidence either for or against treatment, Razvi's team noted.
Dr. Satjit Bhusri is a cardiologist at Lenox Hill Hospital in New York City. He wasn't involved in the new research but said that, in the United States, guidelines for heart patients "generally do not recommend checking thyroid function unless there is an indication that's related to an arrhythmia [irregular heartbeat]."
The new British study included 46 heart attack survivors who had received levothyroxine and 49 who received a "dummy" placebo.
A year into treatment, heart function had improved in both groups, the researchers said, but there was no greater improvement in those who'd received levothyroxine.
The findings suggest that levothyroxine does not improve heart function in patients who've had a heart attack and is unlikely to be beneficial, Razvi's group said.
"The results of this trial will help clinicians reconsider offering treatment with levothyroxine to tens of thousands of patients with subclinical hypothyroidism worldwide," Razvi said in a university news release.
"To any patient who has had a heart attack and has been diagnosed with subclinical hypothyroidism, I would advise that they consult their [doctor] on whether levothyroxine is likely to be of benefit," he added. "The results of our trial suggest that all such patients should have their thyroid function rechecked after a few weeks. Treatment with levothyroxine should not be started routinely in such patients."
Dr. Benjamin Hirsh directs preventive cardiology at Northwell Health's Sandra Atlas Bass Heart Hospital in Manhasset, N.Y. Reviewing the new findings, he noted that "subclinical hypothyroidism is a milder form of hypothyroidism that's more common than true primary hypothyroidism." According to Hirsh, subclinical hypothyroidism "affects approximately 5% of the population."
Hirsh said that the study appears to recommend against the use of levothyroxine in heart attack patients with subclinical hypothyroidism. However, he also believes that the study's methodology provided only a "narrow scope" in measuring the benefit of treatment for the heart.
Also, "the sample size of the study is quite small, and it is difficult to make a strong conclusion either way given this limitation," Hirsh said.
The study was published July 21 in the Journal of the American Medical Association.
The U.S. National Library of Medicine has more on hypothyroidism.