Multiple "Marker" Test Quickly Identifies High-Risk Heart Attack Patients
AMSTERDAM - Quick, simultaneous testing for three different chemical markers of heart damage at the bedside of patients with a suspected heart attack could potentially tailor treatment and save lives, according to researchers from Duke University in Durham, N.C.
Their study, prepared for presentation Sunday at the 22nd annual congress of the European Society of Cardiology, found that combining tests seldom used together, and analyzing them much more quickly than is typical, identified many more high-risk patients significantly earlier than standard laboratory testing.
Of about 1,000 patients who came into six different emergency rooms complaining of chest pain, the standard laboratory test conducted by the hospitals identified 44 patients at risk, none of whom later died. The average time to detection of positive results was about three hours. Comparatively, when researchers ran multiple tests simultaneously on the same patients, they found much shorter times to detect positive results:
- A test of two different markers, completed in about 15 minutes, identified 114 patients with evidence of heart damage (two of whom died within a month).
- An even more sensitive combination test of three markers found 149 positive patients, including three who soon died. There were no deaths among patients with negative results.
The combination tests were experimental and therefore physicians decided how to treat the patients based on results from the standard laboratory tests. But the study shows that standard tests did not identify heart damage in the three patients who died, researchers said. Furthermore, many patients who had negative standard tests but positive combination tests later went on to have second heart attacks and such aggressive treatment as angioplasty or bypass surgery.
"This multi-marker strategy can help us identify earlier and more effectively high-risk patients who need immediate care, and it may help save lives," said Dr. Kristin Newby, a cardiologist at the Duke Clinical Research Institute, who, along with Dr. Magnus Ohman, led the study.
The research was conducted at Duke, the University of Cincinnati; Carolinas Medical Center in Charlotte, N.C.; St. Luke's Medical Center in Milwaukee, Wisc.; Stanford University Medical Center in California; and St. Luke's Roosevelt Hospital in New York. It was funded by Dade-Behring Corp., manufacturer of the FDA-approved "Stratus CS STAT" device used in the study.
Duke proposed studying testing of multiple cardiac markers in patients to determine whether it would provide emergency room physicians with better, more rapidly available information upon which to base treatment for patients complaining of chest pain, Newby said.
Only about 10 percent of patients who come into the emergency room with chest pain actually show changes consistent with a heart attack on an electrocardiogram - the first diagnostic test physicians use to find evidence of heart trouble. Those patients clearly need immediate help, and they often receive either a clot-busting drug or an angioplasty procedure to open clogged arteries, Newby said.
But for the remaining patients, many have only minor heart disease that can be treated later, or no heart disease at all. But some are at high risk of dying. To pick out those patients, hospitals commonly use one of several blood tests that include creatine-kinase MB (CK-MB), a cardiac troponin, or a test of myoglobin. Both CK-MB and cardiac troponin tests look for cellular chemicals released when muscle is damaged. The troponin tests, which are newer, are more sensitive to only those chemicals that come from the heart, while CK-MB can test positive for damage in skeletal muscles as well. But it takes six to eight hours for such chemicals to reliably appear in the blood stream when there is a heart attack, and if a patient receives either of these tests before then, results may be negative.
Myoglobin is a protein also released by dying heart muscle, as well as other traumatized tissues, but it appears in blood much faster than CK-MB or troponin, and so can assess early heart damage. Unfortunately, it also is cleared rapidly from the blood, so cannot detect damage hours after a heart attack, Newby said.
Some hospitals use two of these tests, but most only use one, and so a positive test depends on when a patient has a heart attack and when he or she comes into the emergency room, Newby said. Further complicating the picture is the fact that hospital labs can often take 1-2 hours to analyze the tests and report the results, thus potentially delaying time-sensitive treatment. Hence, development of machines like the Stratus CS STAT device can prove to be valuable because it can analyze results at a patient's bedside within 15-20 minutes.
The researchers concluded that combining all three tests - CK-MB, troponin and myoglobin - and quickly analyzing them is the best potential strategy to find evidence of heart damage and determine risk for complications, but rapidly testing for CK-MB and troponin can also pick up more patients at risk than did single tests.