Dec. 7, 2010 -- A newer, more sensitive version of a blood test used to help diagnose heart attacks may have a much wider application as a screening tool for early heart damage, new research suggests.
The test looks for a protein released by injured heart muscle cells called troponin T, and it is typically ordered when patients come to the emergency room with chest pain to help doctors discriminate heart attacks from heartburn and other copycat complaints.
But years before such a serious event occurs, troponin T may be present at much lower levels than are seen after heart attacks, a quiet sign of a heart under stress.
And two studies published on Wednesday in the Journal of the American Medical Association, which screened thousands of adults with the so-called highly sensitive cardiac troponin T test, found 1 in 4 between the ages of 30 and 65, and in 2 out of 3 who were over age 65, had measurable levels of the protein.
The studies also found that people with detectable troponin T had significantly greater risks of developing heart failure or dying, compared to those in whom the protein couldn’t be found.
“It’s a pretty remarkable association,” says James A. de Lemos, MD, a cardiologist at the University of Texas Southwestern Medical Center in Dallas who led one of the studies. “It’s way more powerful than CRP [C-reactive protein] or more powerful than other tests that we’ve looked at for sure.”
The new test, which is used in Europe but is not yet available in the United States, can measure troponin T at levels 10 times lower than labs can currently detect, and some experts think it may one day help doctors catch ailing hearts years before symptoms appear.
“That’s the promise of this,” says Robb D. Kociol, MD, a cardiology fellow at Duke University Medical Center in Durham, N.C., who was not involved in the study. “If we can find the damage before it becomes advanced, perhaps we can prevent overt heart failure.”
But other experts caution that more research is needed before the test becomes widely used, largely because there’s very little information to help doctors and patients know what to do with their results.
“We don’t know, for example, if a patient at higher risk for heart failure as identified by troponin testing may benefit from additional medications or a certain kind of clinical workup,” says Willibald Hochholzer, MD, of Brigham and Women’s Hospital in Boston, who was not involved in the study. “There is still much to be learned.”
Many Middle-aged Adults Test Positive for a Marker of Heart Damage
For the first study, researchers performed so-called highly sensitive troponin T tests on blood samples taken from some 3,500 people between the ages of 30 and 65 who were enrolled in the Dallas Heart Study. Participants were then followed for an average of about six-and-a-half years. During that time there were 151 deaths, and 62 of those were caused by heart disease.
When researchers analyzed the results, they found that 25% of participants had detectable troponin T levels at the beginning of the study.
Perhaps more surprising, however, was that when they narrowed their results to people without medical conditions known to contribute to heart disease, like diabetes, high blood pressure, or chronic kidney disease, 1 in 6 still had detectable levels of the protein.
And the higher a person’s level, the greater their risk of dying, even if they had no other known risk factors. About 2% of the group with the lowest troponin T levels died during the study compared to 28% of the group with the highest levels.
But de Lemos says troponin testing is likely to complement, rather than replace, other kinds of heart checks because the protein seems to be picking up a “different family of risk.”
“This looks like not a marker of heart attacks in the sense of myocardial infarction, which is a problem of atherosclerosis or thrombosis, but rather a marker of heart failure, which is typically problems with either weakening or thickening of the heart,” he says.
“These are changes in the heart muscle before people develop frank heart failure. It’s reading early heart damage caused not by heart attacks but by chronic stress on the heart, be it from hypertension or kidney disease, or other factors,” de Lemos adds.
Lowering Troponin T Levels May Lower Heart Risks
In the second study, of more than 4,000 adults over age 65, two-thirds had detectable levels of troponin T on the highly sensitive test, even though they had no history of heart failure.
“There are very low levels of troponin in seemingly normal people,” says study author Christopher R. deFilippi, MD, a cardiologist and associate professor at the University of Maryland School of Medicine in Baltimore. “That’s the scary thing about this scenario. Our study participants were older, but they had none of the traditional risk factors.”
And as in the previous study, deFilippi and his team found that the higher a person’s troponin T level, the greater their risk of developing heart failure or dying from heart disease.
Over an average follow-up of about 12 years, people with the highest levels had a fourfold greater risk of developing heart failure and a threefold greater risk of dying of cardiovascular problems, compared to those with undetectable levels.
In contrast to the previous study, deFilippi and his team repeated the troponin T test every two to three years, so they were able to see how study participants fared if their levels changed over time. Those whose levels were detectable at the beginning and increased by 50% or more had about a 60% increased risk of developing heart failure or dying compared with those whose levels remained stable.
Study participants who saw their levels drop by at least 50%, on the other hand, had about a 30% drop in their risk of heart failure or death, suggesting that there may be ways people can change their troponin T levels and influence their fate.
If further research confirms his results, deFilippi says he thinks the highly sensitive troponin tests would be a cost-effective, patient-friendly way to catch chronic disease.