ORLANDO, Fla. -- Two different multi-hospital studies have demonstrated that a blood test can indicate which heart attack patients may be in danger of dying from a heart attack, Duke University Medical Center researchers reported Monday.
The original version of the test takes one to two hours in a laboratory for results, while a newer version can identify the highest-risk patients in as little as 10 minutes. That time difference can literally mean life or death for these heart attack patients, said Duke cardiologist Dr. E. Magnus Ohman, leader of one of the studies.
Both tests measure the presence of "troponin T," a regulatory protein that helps heart muscle contract. Once this muscle starts dying, as in a heart attack, cell membranes break down and internal cellular material, including proteins, are released and are carried away by the blood.
"Anything that can help us make quick treatment decisions about patients with myocardial infarctions (heart attacks) is invaluable," Ohman said. "We studied this test prospectively on more than 12,000 patients, making this the largest such trial ever conducted."
Ohman was principal investigator in a study published Oct. 31, 1996 in the New England Journal of Medicine demonstrating that troponin T was the best indicator yet of which heart attack patients are at greatest risk of dying of another attack within 30 days. His new study looked at the rapid test for the first time.
The rapid version of the test, which is administered at the patient's bedside, detects only the presence or absence of troponin T, while the laboratory version indicates how much of the protein is in the blood, Ohman said.
"Our study indicates convincingly that merely the presence of troponin T is a strong predictor of further cardiac events or death," Ohman said in an interview.
Duke cardiologist Dr. Kristin Newby led the second study, which looked at the patients one year after treatment.
"We knew that a positive troponin T finding is a strong predictor of 30-day mortality or in patients suffering from another heart attack," she said. "After following up one year later with 855 heart attack patients, we found that the test's ability to predict risk remained the same."
Specifically, after one year, 14.2 percent of the patients with a positive troponin T finding had died, while only 5.8 percent with a negative troponin T finding died. The earlier study showed a 10.4 percent vs. 3.3 percent mortality at the 30-day endpoint.
"This test is a powerful diagnostic tool to help us identify the highest-risk patients," Newby said. "The challenge for cardiologists is now to determine which of the many therapies available to us should be used to reduce the future risks for these patients."
Ohman and Newby prepared the results of their studies for presentation Monday at the 70th scientific session of the American Heart Association (AHA).
Ohman's study followed 12,635 patients at 600 hospitals in the United States and abroad enrolled in the GUSTO-III (Global Utilization of Strategies to Open Occluded Arteries in Acute Coronary Syndromes) trial, which compared the benefits of clot-busters reteplase and alteplase.
Overall, 8.9 percent of the GUSTO-III patients tested positive for troponin T, and 6.9 percent of them died within 24 hours, compared to 2.1 percent for troponin T-negative patients, Ohman said. The in-hospital death was 14.4 percent for troponin t-positive patients and 5.5 percent for the negative patients.
"Importantly, this test was a potent indicator independent of other risk factors such as age and location of infarction," Ohman said. "Also, the test is very easy to perform."
"We expect that the use of this test will continue to grow because it is so specific in detecting cardiac troponin T in the blood," Newby said. "We can detect very low levels of the protein, which makes it a valuable prognostic tool for cardiologists."
The AHA estimates that in one year as many as 1.5 million Americans will have a heart attack and 500,000 of them will die. Thousands of those who die will have been prematurely released from the hospital because their heart attack was not diagnosed, researchers said.
The test can give cardiologists a head start in initiating immediate heart care, Newby said.
"Most of the negative events that happened to these patients occurred in the first 30 days," Newby explained. "Between 30 days and one year, the mortality rates were about the same. So it is important to initiate treatment very early in patients who have positive troponin T levels.
The cardiologists said that further studies are needed to determine exactly which of the many treatment options ? whether procedure or drug based ? will work the best for troponin T-positive patients.
Newby and colleagues analyzed data from a sub-study of a larger clinical trial known as GUSTO IIa. That trial was supported by Ciba-Geigy Corp., Advanced Cardiovascular Systems, and the German pharmaceutical company Boehringer Mannheim, which manufactures the troponin T test.
The trial involved 855 patients in the U.S. and Canada, and involved physicians from both small community hospitals and large research centers.
Joining Newby in the study, from Duke, were, Ohman and Steven Peck; Robert Christenson, University of Maryland; Dr. Hugo Katus, University of Heidelberg, Germany; Dr. Christian Hamm, University Hospital Epperdorf, Hamburg, Germany; and Dr. Paul Armstrong, University of Alberta, Edmonton, Canada.
The Duke Clinical Research Institute (DCRI) directed the rapid troponin T test study, which included the following researchers, Dr. Paul Armstrong, University of Alberta, Edmonton, Canada; Dr. W. Douglas Weaver, Henry Ford Hospital, Detroit; Dr. W. Brian Gibler, University of Cincinnati; Dr. Eric Bates, University of Michigan Medical Center; Amanda Stebbins, DCRI; and Dr. Judith Hochman, St. Luke's Roosevelt Hospital Center, N.Y.
Journal
New England Journal of Medicine