The accelerated diagnostic protocol consists of three elements: TIMI score risk assessment, electrocardiography (ECG), and cardiac troponin I (cTnI) levels at presentation and two hours later. All three elements have to be negative for the ADP to be considered negative and for the patient to be identified as low short-term risk for a cardiac event.
This ADP performed well in a large prospective observational study involving 1,975 consecutively enrolled patients presenting to two urban EDs in Brisbane, Australia and Christchurch, New Zealand between November 2007 and February 2011.
This ADP “should be applied as a ‘screen-out’ process in patients that clinicians would otherwise investigate using a delayed (six hour or later) second cardiac troponin,” Dr. Martin Than from Christchurch Hospital who worked on the study told Reuters Health by email.
According to a report published June 5 in the Journal of the American College of Cardiology, 302 of the 1,975 patients (15.3%) had a major adverse cardiac event (MACE) within 30 days (the primary end point). Most were myocardial infarctions that occurred in the first 10 days after discharge.
The ADP classified 392 patients (20%) as low risk and only one of these patients (0.25%) had a MACE during initial hospital attendance and follow-up, giving the ADP a sensitivity and negative predictive value of 99.7%. It had a positive predictive value of 19.0% and specificity of 23.4%.
The one patient who had a MACE was a 52-year-old Caucasian male who presented after 3.5 h of chest pain. He was previously healthy, with no risk factors for ischemic heart disease. He had a normal ECG and his cTnI was less than 0.01 1mcg/L at presentation, 0.03 mcg/L at two hours and 16.8 mcg/L after 12 hours.
In the United States alone, more than six million ED visits annually involve chest pain patients, who often undergo lengthy assessment. “The reduction in time required for observation for some patients through application of this ADP could have significant benefits for health services, even in those centers with chest pain observation units,” the authors say.
“This study also demonstrates that central laboratory troponin assays currently in use have sufficient sensitivity at an early time point to negate the need for additional biomarkers (such as myoglobin and creatine kinase-MB) as components of the ADP. These other biomarkers do not improve the sensitivity, and reduce the proportion of patients defined as low risk (due to a greater number of patients with a positive biomarker result), as was shown in the ASPECT study,” they point out.
Briefly, the ASPECT (A 2-h Diagnostic Protocol to Assess Patients with Chest Pain Symptoms in the Asia-Pacific region) study used zero and two-hour biomarker testing with a point-of-care multimarker panel, ECG and TIMI score. In that study, the ADP identified 9.8% of patients with suspected ACS who could have been discharged early from the ED, with a sensitivity of 99.3% for 30-day MACE.
Dr. Than noted that “intervention studies of diagnostic processes are uncommon, as are widespread external validations of such processes (before clinical uptake) so a study like this is sometimes the best evidence one has to call upon before deciding about implementation at one’s own hospital. As it happens, we are just finishing a well powered randomised controlled trial of this diagnostic process, which we call the Chest Pain ‘Fast-Track’ study, and the results will be available soon.”
This ADP, Dr. Than said, “is not for patients already so low risk that the judgment of the clinician is that they do not require workup for possible acute coronary syndrome involving troponin testing at all. Only use it in a ‘screen-out’ manner, in patients already identified as needing serial troponins and prolonged observation. The ADP does not rule-out unstable angina and further investigation are recommended to look for coronary disease (e.g. stress test/imaging) if this has not already occurred.”