Heart attack misdiagnosis: What role for cardiac markers?
Those methods include the 3 primary cardiac markers measured in the ER setting: creatine kinase (CK-MB) isoenzyme, myoglobin, and cardiac troponins T and I. The qualitative tests of both troponin T and troponin I may be of particular use in the ER or chest pain unit when given serially, for example at presentation and 6 hours later. Results from a study in 1997 indicate that the 30-day risk of nonfatal MI or cardiac death was extremely low in patients with negative results on the troponin T or, particularly, the troponin I test. Positive results on this test could be used to select patients for further quantitative testing. Other rapid tests for CK-MB and myoglobin have been developed and are still being tested. The results are promising, however, in that more widespread use of these rapid cardiac marker tests as screening devices might prevent some misdiagnoses.
Why, however, are young or middle-aged women and black patients more frequently misdiagnosed? Does this reflect gender and racial bias within healthcare systems, or are there reasons for these differences? Several researchers have been investigating this issue.
The problems start even during triage. In one survey, ER triage nurses admitted that MI is not the first diagnosis considered for middle-aged women. Severe chest pain is absent more often in women than men; in fact, only about 25% of cardiac patients display the classic, severe chest pain so often portrayed in the popular media.
Another study found that symptoms of impending acute coronary events in women are dramatically different than symptoms reported by men. In the preacute MI stage, women are more likely to experience unusual fatigue, discomfort in the shoulder blade area, and chest sensations than men. Women who experienced an acute event more frequently reported chest sensations, shortness of breath, feeling hot and flushed, and unusual fatigue with a gradual progression in the number and severity of symptoms.
The high rate of heart attack misdiagnosis in women seems to be largely due to the established symptom profile of MI being nonrepresentative of what women experience. On the issue of higher misdiagnosis rates in blacks, the researchers in the Pope study suggest that the black patients included in this study tended to be younger in general and were more often women.
Overall, there are 1500 chest-pain units in the US, and each has its own protocol in the emergency room--most measure CK-MB, about one-third measure myoglobin, and another two-thirds measure cardiac troponins, according to Robert H. Christenson, PhD, DABCC, director of the clinical chemistry and rapid response labs at the University of Maryland. The challenge to ER physicians is knowing what cardiac markers to measure, which comes back to recognizing the associated symptoms in different patient populations.
"Once a patient is identified as being at high-risk for an acute coronary event, he or she is put onto a care path or protocol, and cardiac markers are tested periodically," said Christenson. "It is the identification of high-risk patients that is difficult unless the varying symptoms of different patient populations is recognized," he continued.
Many hospitals continue to include chest pain as part of their standard protocol used to choose the type of cardiac marker laboratory test. Using quick, qualitative tests to measure cardiac troponins as a screening device, in addition to better recognition of nontraditional symptoms, could improve the identification of patients in need of treatment and save lives--in all patient populations.
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|Publication:||Medical Laboratory Observer|
|Date:||Jul 1, 2000|
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