By Nathan Seppa, Science News
A new blood test might reveal hidden heart damage in some people that puts them at increased risk of heart failure or death, researchers report in the Dec. 8 Journal of the American Medical Association.
Although factors such as obesity, diabetes or high blood pressure hike a person’s risk of heart disease, many people have a heart attack without these problems. Efforts to identify other early warning signs have largely focused on two compounds, C-reactive protein and B-type natriuretic peptide, which have been tested as potential tip-off biomarkers. But only blood levels of BNP have shown some predictive ability (SN: 1/7/06, p. 13).
Two new studies, led by teams in Texas and Maryland, suggest that measurements of another blood compound called cardiac troponin T might outperform the others as a heart risk indicator, says cardiologist Christopher deFilippi of the University of Maryland School of Medicine in Baltimore. “Troponin T may actually have real value in determining which people asymptomatically have underlying heart disease,” he says.
Jay Cohn, a cardiologist at the University of Minnesota Medical School in Minneapolis, concurs. “Most heart attacks occur in the absence of any prior symptoms,” says Cohn, who was not involved in the new research. “This work proves these diseases can be detected long before people get sick.”
Cohn says that, under stress, muscle cells in the heart release BNP and troponin T, signaling that subtle changes are happening before any problem can be diagnosed. He and other doctors currently use BNP as one of their heart-screening tools. Based on these new data, he says, doctors might eventually add troponin T.
In the Maryland analysis, deFilippi and his colleagues used blood samples obtained from more than 5,000 people nationwide who were age 65 or older and had no history of heart failure. Volunteers provided the samples when they enrolled in a study from 1989 to 1993. The researchers used the new blood test to measure cardiac troponin T levels. During nearly 12 years of follow-up, on average, people with the highest levels of cardiac troponin T at the study outset were at least 51 percent more likely to develop heart failure and 70 percent more apt to die from cardiovascular causes than were those with the lowest levels. The researchers accounted for other factors such as blood pressure, previous heart disease and smoking.
In the Texas study, researchers evaluated blood obtained from nearly 3,500 people without coronary heart disease, age 30 to 65, between 2000 and 2002. The scientists measured the subjects’ initial troponin T levels with the new test. By 2007, people with the highest levels were at least 40 percent more likely to have died of any cause compared with those with the lowest levels. A statistical range shows the risk could actually be much higher in both analyses. The Texas group also accounted for differences among the participants.
Using magnetic resonance imaging, the researchers linked high levels of the biomarker with an abnormal buildup of tissue in the largest chamber of the heart, a sign that the heart is struggling to pump blood.
Combining cardiac troponin T measurements with BNP as a cardiac test “definitely would make sense,” says cardiologist James de Lemos of the University of Texas Southwestern Medical Center at Dallas, who coauthored both papers.
Troponins are structural proteins found in muscle tissue throughout the body. Cardiac troponin T is specific to the heart muscle, deFilippi says, and shows up in the blood when heart tissue is damaged. A less specific measurement of cardiac troponin T is currently a standard test for diagnosing a heart attack in emergency rooms, having outperformed several other tests. High cardiac troponin T cinches the diagnosis.
The new blood test for cardiac troponin T is up to 10 times more sensitive than that older one, de Lemos says. About two-thirds of the people in the Texas study with the highest levels of cardiac troponin T would have had undetectable levels using the older test.
The biomarker showed up in 16 percent of people who had no signs of cardiovascular disease or other clear risk factors, according to the Texas report. Older people were more likely than the young to make the protein, and men were three times as likely as women. Reasons for those differences remain unclear, de Lemos says
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