New Handheld Device Rapidly Identifies Heart Damage at Patient Bedside.
The blinded study evaluated the new assay in comparison with the clinical standard for diagnosis of myocardial infarction, including measurement of the enzymes creatine kinase (CK) and creatine kinase MB fraction (CK-MB) in a central hospital laboratory. Blood samples from 100 patients with chest pain were tested at admission.
"The current methods for diagnosing damage to the heart, including a history of chest pain, changes on the electrocardiogram, and measurement of traditional cardiac enzymes are often inconclusive. Since the cardiac troponin T protein is found only in the heart, the assay proved to be an accurate method for diagnosing damage to the heart at the patient's bedside," said Elliott Antman, MD, lead author and director of the Coronary Care Unit at BWH.
The study found that the rapid cardiac troponin T assay's accuracy in detecting acute heart injury increased significantly when a progressively greater number of hours elapsed after the onset of chest pain. One out of three heart attack patients had a positive test as early as two hours after the onset of chest pain and four out of five were positive by eight hours after the development of chest pain. Of note, patients with a positive rapid troponin T assay on admission were significantly more likely to die or experience a second heart attack during the same hospitalization.
"Once the results from the test are known it enables physicians to triage patients with chest pain to appropriate courses of treatment more effectively," says David B. Sacks, MD, co-author of the study and medical director of the Clinical Chemistry Laboratory at BWH. "The rapid cardiac troponin T assay helps physicians to ensure that patients receive the care they need."
Sufficient blood was drawn from 84 of the 100 patients to measure CK-MB and also perform the rapid cardiac troponin T assay. Test results agreed in 86 percent of patients, however, nine of the patients with positive rapid troponin T rapid assays had normal CK-MB levels (< 6 ng/ml). Four of these nine patients who were missed by the CK-MB assay were ultimately confirmed to have experienced myocardial infarction. In addition, three of 84 patients had elevated CK-MB levels at admission, but were not recognized as having troponin T present in their blood. Of these three patients, two were ultimately diagnosed with myocardial infarction.
Another potential benefit of the new bedside assay is that it can be used to diagnose patients who have experienced symptoms several days before seeking treatment. Cardiac troponin T starts to be released in the blood within a few hours after myocardial injury occurs, and it remains elevated for up to 14 days. Other available blood tests used to detect cardiac damage, such as CK-MB, return to normal levels within two to three days after myocardial infarction.
However, before adopting such new point-of-care diagnostic tools into routine clinical practice, further investigation is needed to determined how they should be integrated with other laboratory data and also to evaluate their impact on the clinical management of patients with chest pain.
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