Patients who test positive for the presence of a specific biochemical marker of heart-cell death in their blood but who do not exhibit other risk factors for future heart attack should be treated as higher-risk patients, according to a new analysis by cardiologists at Duke Medical Center.
The researchers found that troponin, a protein that is released into the bloodstream as heart muscle cells die, can be a reliable indicator of future risk even when other traditional measures of heart health are negative. This is important, the researchers say, in light of the recent recasting of the definition of heart attack by the major cardiology organizations to place more emphasis on the results of troponin testing, in addition to the presence of chest pain and electrocardiogram abnormalities.
"Our analysis shows that patients who test positive for troponin but not for creatine kinase-MB (CK-MB) should still be treated as if they tested positive for both," says Duke cardiology fellow Sunil Rao. "This is important because in the past these patients would usually not be treated aggressively." Rao prepared the results of his study for presentation during the annual scientific sessions of the American Heart Association.
Both troponin and CK-MB are proteins within cells that spill out into the bloodstream as the cell wall breaks apart during cell death. The difference between the two is that troponin is only released by heart muscle, while CK-MB can be released by both dying heart and skeletal muscle.
"We believe that even low levels of troponin in the bloodstream indicate the presence of tiny heart attacks, or infarctlets," Rao explains. "The question is, does the death of a few heart cells matter, and can they be a reliable predictor of larger infarctions, or heart attacks, in the future?" According to the Duke analysis, it does matter.
The researchers say the troponin test, which is an extremely specific and sensitive indicator of cardiac cell damage, can help physicians detect those patients who would be described as low-risk, but who actually are at a higher risk of future cardiac events. They would even argue that troponin levels should be used instead of CK-MB in the definition of heart attack.
Other members of the Duke team were Vic Hasselblad, Robert Christenson, W. Brian Gibler, Christopher Granger, and Magnus Ohman. The data analysis was supported by the Duke Clinical Research Institute.