Low levels of heart protein now linked to future heart-related illness, death
With the use of a newly developed, highly sensitive assay or test, researchers at Baylor College of Medicine have linked low levels of a protein made by the heart called cardiac troponin T, normally detected during and after heart attacks, to a higher likelihood of coronary heart disease, heart failure and death in people with no previous heart problems.
The findings appear in the current edition of the journal Circulation.
"In emergency rooms, doctors test for this protein to diagnose a heart attack, but in those cases, it is found in much higher levels than what we detected in the current study," said Dr. Vijay Nambi, assistant professor of medicine – section of cardiovascular research at BCM and co-first author on the study. "The highly sensitive assay can detect levels 10 fold lower that what is normally seen. These levels go undetected with the traditional test."
Determining risk of hospitalization
Researchers found that with this test, they could detect some of these very low levels of cardiac troponin T in almost 65 percent of the people. What is interesting, Nambi said, is that the protein usually leaks into the blood stream after some kind of heart muscle injury. However, this test detected low levels in people with no known heart problem.
"We had thought that since this protein is found in heart attack patients, finding the lower levels would help us predict the likelihood of future heart attacks. However, it is more strongly associated with future risk of hospitalization for heart failure and death," said Nambi, who is also with the Center for Cardiovascular Disease Prevention at the Methodist DeBakey Heart and Vascular Center.
Study participants were part of the Atherosclerosis Risk in Communities study, a large-scale, long-term study designed to investigate the etiology and natural history of atherosclerosis. This allowed researchers to follow their progress over many years.
"We had follow up for about 20 years, so we were able to see that these low levels were associated with those specific outcomes while taking into account traditional risk factors," said Dr. Christie Ballantyne, chief of cardiovascular research and professor of medicine at BCM. He is also senior author of the study. "This is the most powerful marker in the ARIC study that we have found."
Next: Preventive treatments
What causes the presence of cardiac troponin T at these low levels is still unknown. Researchers have found that it is more common in certain groups of people, such as men and diabetics.
The next step is to use this information to work on preventive treatments, Ballantyne said.
"We have to see what it means in these different groups and what other mechanisms are associated with having these very low levels of cardiac troponin T. We can then begin to investigating ways to address these risks," said Ballantyne, who is also director of the Center for Cardiovascular Disease Prevention at the Methodist DeBakey Heart and Vascular Center.
"It is believed preventive therapies such as healthy diet, exercise, weight loss, control of blood pressure, lipids and diabetes would help, but at this time there is no definitive information on how targeting individuals with low levels of cardiac troponin T could prevent the development of heart attacks, heart failure or death."
Others who contributed to the study include: Dr. Justin T. Saunders, formerly of BCM and currently with the University of Michigan, Ann Arbor; Dr. Salim S. Virani, BCM and Michael E. DeBakey VA Medical Center; Dr. Ron C. Hoogeveen, BCM; Dr. James A. de Lemos, University of Texas Southwestern Medical Center; Drs. Lloyd E. Chambless and Gerardo Heiss, and Xiaoxi Liu, University of North Carolina, Chapel Hill; Dr. Eric Boerwinkle, University of Texas Health Science Center School of Public Health; Drs. Brad C. Astor and Josef Coresh, Johns Hopkins Bloomberg School of Public Health; Dr. Thomas H. Mosley, University of Mississippi Medical Center, Jackson; and Dr. Aaron R. Folsom, University of Minnesota School of Public Health, Minneapolis.
The ARIC study is a collaborative study supported by the National Heart, Lung and Blood Institute. Nambi is supported by a National Heart, Lung, and Blood Institute grant and Virani is supported by a Department of Veterans Affairs Health Services Research and Development Services Career Development Award. Astor and Coresh are supported by the National Institute of Diabetes and Digestiv Kidney Diseases. Roche Diagnostics provided reagents and loan of an instrument to conduct the highly sensitive cardiac troponin T and other assays. Siemens Healthcare Diagnostics also provided reagents and loan of instruments to conduct assays.