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Faster results, earlier treatment July 2000 Point-of-care assays for troponin have extended the clinical value of this marker beyond its initial utility. "Bedside markers, especially troponin, have enabled us to reduce the time to treatment in the 50 percent of patients who come in with ischemic heart disease who do not have a telltale sign," says Dr. Raymond Bahr, medical director of the Paul Dudley White Coronary Care System at St. Agnes Health Care, Baltimore. Bert Morton, MD, director of the clinical chemistry laboratory at St. Agnes Health Care, has been collaborating with Dr. Bahr on bedside troponin assays. "In mid-1999, we elected to study how the use of bedside cardiac markers would affect patient care, particularly in the ED," Dr. Morton says. Over the ensuing five to six months they used simultaneously a Spectral Diagnostics point-of-care device for troponin I, myoglobin, and CK-MB and routine laboratory assays for the same markers, and they compared them. "The data is very impressive from the standpoint of being able to identify very rapidly those patients who have myocardial injury, or frank MI, and in some instances those who had suspected myocardial injury," Dr. Morton told CAP TODAY. "Suspected myocardial injury" refers to clinical evidence of ischemia, such as chest pain, but not elevated CK-MB and not clearcut ECG changes. "These are the patients we are really looking for," Dr. Morton says. "They probably have unstable angina or non-Q-wave MI and from all other studies will benefit from further followup and intervention." In this and other clinical trials, handheld troponin devices have been proven reliably to detect acute coronary syndromes (ACS), being positive in more than one-third of patients eventually found to have unstable angina or non-Q-wave MI. Says Dr. Bahr, "It used to be when you drew blood and did markers, results would come back two hours later, when the ED physician and nurse were not present to make a decision. They were off stopping a GI bleed. So the advantage of bedside markers is that they have been proven to be accurate and to correlate well with serum markers, and we can get results in 10 to 15 minutes at the bedside with the caregivers still there. Now if we get a positive marker," Dr. Bahr continues, "especially troponin, that makes that patient a high-risk patient. That patient can be given low-molecular-weight heparin and platelet inhibitors to cool off the event. And we can do cardiac catheterization a short time later." Dr. Robert Christenson, director of clinical chemistry laboratories, professor of pathology, and director of point-of-care testing at the University of Maryland School of Medicine, concedes it may be "trite," but one study suggested that "time is muscle" for interventions in ACS patients just as for thrombolytic therapy. "If these data hold up and an intervention can be started earlier in the ED, then it should be," Dr. Christenson says. "That will be a key driver for point-of-care testing for ACS patients." He adds, "It would be untenable to not obtain ECG data on presentation, and the same would be true for troponin." Early and other studies, he says, may provide evidence that will drive the need for the troponin result immediately in the ED. Dr. Christenson used a troponin T rapid assay, on which he has published papers on performance characteristics of the first- and second-generation assays. Director of POC testing at his hospital, he says there was no problem with his oversight of cardiac POC testing. "Clinicians are aware of regulatory issues on POC testing, so they are glad to have the help," Dr. Christenson has found. "They want a reliable, fast result in their hands. The turf war over who controls testing is not an issue. What is an issue," he says, "is if you are viewed as an obstructionist, if you give the impression that the service is not offered because of the extra bother involved or if you question whether clinicians really need an immediate result." Now that earlier test results are possible, earlier therapy is being evaluated. In an ongoing study, investigators are looking at whether treatment with a Gp IIb/IIIa inhibitor in the ED is better than waiting until the patient is moved to the cardiology unit, a difference of one hour versus three to five hours. William Check, PhD |
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