The test measures blood levels of a molecule called CD40 ligand in patients who come to an emergency room complaining of chest pain. Using that test and giving quick treatment with a drug that prevents blood clots cut the death rate for those high-risk patients by more than half, says a report in the March 20 issue of The New England Journal of Medicine.
CD40 ligand is a protein released by blood platelets, which play a major role in formation of clots that can block a heart artery, explains Dr. Christopher Heeschen, a professor of internal medicine at the University of Frankfurt and leader of the research group. High levels of CD40 ligand indicate the platelets have been activated and clots are likely to form, so the patients "can have a heart attack in the next few hours," he says.
The CD40 ligand test is unique because it can give a preview of a heart attack, says Dr. Jane E. Freedman, an associate professor of medicine at the Boston University School of Medicine and author of an accompanying editorial in the journal. Existing tests given to emergency room patients with chest pain look for molecules that are released when a heart attack is under way.
"This test could potentially reflect the state of platelets before, rather than after, damage is done," she says.
The German study is a landmark in research on CD40 ligand as a heart attack predictor because "it is the first big trial to look at it," Freedman says. "But it needs to be evaluated in other patients and other settings."
The Frankfurt trial included 626 emergency room patients with severe chest pain and a history of artery disease. They were all given a standard electrocardiogram, a test that measures the electrical activity of the heartbeat. They were also given the CD40 ligand test, which showed elevated levels in 221 of them. Some of those with elevated levels were given abciximab, an anti-platelet drug, while others got a placebo, an inactive substance.
One result of the study showed that CD40 ligand levels are a good indicator of heart attack risk, Heeschen says. Nearly 20 percent of patients with the highest suffered a heart attack or died in the next six months, compared to less than 5 percent of those with the lowest levels. And just 5.5 percent of those getting abciximab suffered cardiac events, compared to 13.3 percent of those getting a placebo.
The CD40 ligand test isn't available for general use now, Heeschen says. It still needs approval by regulatory agencies such as the U.S. Food and Drug Administration. Meanwhile, he says, "we are talking with pharmaceutical companies to verify that the marker can be measured and to define the upper limits of a normal value."
The larger-scale trials of the test and the treatment needed for government approval can be done easily, Freedman says. "They can be built into ongoing trials of platelet inhibitors," she says.