Researchers at the University of Maryland School of Medicine in Baltimore report that a new, highly sensitive investigative blood test may help predict the risk of heart failure and cardiovascular death much earlier than previously possible in older people who do not have symptoms of heart failure.
Results of a study were presented at the Scientific Sessions of the American Heart Association on November 15, 2010, and simultaneously published online in JAMA, Journal of the American Medical Association.
The new test measures troponin T, a marker for the biological process of cell death that leads to heart failure. Current cardiac troponin T blood tests do not detect troponin in seemingly healthy people and are often used in hospital emergency rooms to clarify whether the source of chest pain is a heart attack or something else. The new test, not commercially available in the United States, detects troponin levels that are 10 times lower than previous tests. The researchers found the marker in two-thirds of people without symptoms age 65 or older whose blood samples were collected and stored for up to 18 years as part of a long-term cardiovascular research project.
"This is a very unique finding," says principal investigator Christopher deFilippi, M.D., associate professor of medicine at the University of Maryland School of Medicine and a cardiologist at the University of Maryland Medical Center. "We found that the higher the level of troponin, the greater the individual was at risk for symptoms of heart failure or death from cardiovascular disease over the next 10-15 years. The meaning of these elevated levels was unknown until this point."
Eighty percent of new cases of congestive heart failure occur in people who are 65 and older. For people in this group with no symptoms, it has been difficult to gauge their risk for heart disease, the number one killer of men and women in the United States.
The study was based on a national research project, the Cardiovascular Health Study (CHS), which began in 1989 and followed more than 4,000 people age 65 and older who were not hospitalized, did not have symptoms of heart failure and were not experiencing an acute medical illness. Blood samples of the study participants, who were ethnically and geographically diverse, were taken when they first entered the study and repeated after two-three years. Each participant was followed for about 12 years to see what, if any, heart-related diseases they developed, with the most recent follow-up visit in 2008.
The blood samples were stored at very low temperatures to stabilize the proteins in the samples for a period of 10-15 years. By preserving the blood samples in this way, researchers such as the University of Maryland team could look back in time with modern testing tools.
"The availability of the blood samples is one of the great strengths of the Cardiovascular Health Study," says senior author and designer of the current study, Stephen L. Seliger, M.D., M.S., assistant professor of medicine at the University of Maryland School of Medicine and a nephrologist at the University of Maryland Medical Center. "Another strength of the CHS is its longstanding and rich database which carefully characterized the participants' risk factors for heart disease as well as the actual outcomes."
The researchers also found that troponin levels can change over time. Troponin levels rose in some study participants between the first and second blood samples, with a corresponding increase in their risk for heart disease. Conversely, the risks dropped in other participants whose blood samples showed a reduction in troponin levels. "These fluctuations suggest that even in people without clinical symptoms of heart disease, we may be able to intervene with lifestyle modifications to lower their risks," says Dr. deFilippi.
"This study may have important clinical implications, since it suggests that physicians need to consider that test results are more dynamic over time and that risk factors are also likely to change over time," says E. Albert Reece, M.D., Ph.D., M.B.A., vice president for medical affairs at the University of Maryland and dean of the University of Maryland School of Medicine.
This study did not take into account the impact of new cardiovascular therapies such as statins that could blunt the predictive value of the troponin level, nor was it possible for the study to explain what was physically happening to the participants to produce detectable levels and the frequent changes over time of troponin in older adults. The researchers say more study is needed to confirm their findings.
The University of Maryland study was supported by grants from the National Institutes of Health, the University of Pittsburgh Claude D. Pepper Older Americans Independence Center and Roche Diagnostics. Roche Diagnostics provided funding and laboratory reagents for the highly sensitive cardiac troponin T assay.
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