A new, faster screening protocol can identify patients at a very low risk of cardiovascular events when they present to the emergency department with chest pain, allowing them to be safely discharged in 2 hours instead of the usual 6 or more, a New Zealand–based team of researchers has found.
The "accelerated diagnostic protocol," or ADP, evaluated in the study consists of three widely available measures: a patient’s thrombolysis in myocardial infarction, or TIMI, score; an electrocardiograph; and a biomarker panel of troponin, creatine kinase MB, and myoglobin. The current standard of care consists of serial sampling of cardiac troponin over 6 hours from the onset of symptoms.
In an article published March 23 in The Lancet (doi:10.1016/S01406736(11)603103), the Christchurch, New Zealand, team, led by Dr. Martin Than of Christchurch Hospital, investigated the protocol in the Asia-Pacific Evaluation of Chest Pain Trial (ASPECT), which included 3,582 consecutive patients presenting with chest pain suggestive of acute coronary syndromes at hospitals in nine countries in the Asia-Pacific region. All patients were followed up for a month. Study participants were mostly older, men, and either white or Chinese, they wrote.
Of the study subjects, just under a tenth (352) qualified for early discharge under the protocol. This meant that they had a TIMI risk score of 0 (out of 7), no ischemic ECG changes, and normal pointofcare triplemarker panels at presentation and 2 hours later.
The study’s primary end point was a major adverse cardiac event within the 30 days of follow-up, including death that was not clearly noncardiac, myocardial infarction, cardiogenic shock, and arrhythmia or atrioventricular block requiring intervention. A major adverse cardiac event occurred in three (0.9%) of the ADP-screened patients, Dr. Than and colleagues reported, giving the protocol a sensitivity of 99.3%, a negative predictive value of 99.1%, and a specificity of 11%.
"The near 10% possible reduction in patients needing prolonged assessment in this large patient group could reduce overcrowding in hospitals and emergency departments and provide earlier reassurance and greater convenience for patients," Dr. Than and colleagues wrote in discussing their findings.
They acknowledged as among the trial’s weaknesses its observational design and the protocol’s low specificity, which they described as commensurate with that of other diagnostic instruments to exclude acute coronary syndromes.
They also pointed out that "patients without chest pain but who presented with atypical symptoms (fatigue, nausea, vomiting, diaphoresis, faintness, and back pain) were not included in this trial," and that the researchers could not tell how many presented with those symptoms. "Thus," they wrote, "the applicability of the ADP is limited to the selected cohort of patients with chest pain (or discomfort) suggestive of acute coronary syndromes for whom the attending physician planned to investigate for these syndromes."
Dr. Than and six of his 26 coauthors disclosed having received grants and supplies, speaking honoraria, travel expenses or a combination of these from Alere Medical, a maker of diagnostic tests and equipment and the major funding source of the study. Eight other investigators received travel support from Alere to attend meetings.
In an editorial comment (Lancet 2011 March 23 [doi:10.1016/S01406736(11)603929]) accompanying Dr. Than and colleagues’ article, Dr. Richard Body of the Cardiovascular Research Group at the University of Manchester (England), noted that "the need for an effective rapid rule-out strategy to facilitate early discharge from the emergency department has been appreciated for over 20 years," and yet none has been widely adopted.
Dr. Body praised Dr. Than and colleagues’ study as "well designed to achieve its objectives," and showing "that it is possible to achieve an acceptably high sensitivity when triplemarker testing is used in the appropriate population."
However, he cautioned, the triple-marker testing alone had a sensitivity of only 82.9%. The overall sensitivity of the protocol "increased to an acceptable level because of the application of Bayesian principles, with biomarker testing only in patients with a low pretest probability of disease."
Most people "will probably consider this net risk to be statistically acceptable," Dr. Body wrote. "However, if properly informed, low-risk patients might feel differently about the relative merits of waiting for definitive 6h laboratory-based troponin testing or going home after 2 h on the basis of results from a test that correctly identifies serious coronary disease, when present, in just over eight of ten occasions."
Dr. Body advised that Dr. Than and colleagues’ findings be considered in light of other diagnostic tools. One newer troponin assay can detect with 90% sensitivity for acute myocardial infarction at presentation, he pointed out, and other "promising" biomarkers are being studied. "It therefore remains important that triplemarker testing is compared with some of these more recent alternatives," Dr. Body wrote.