As “zero-miss” philosophies for chest pain proliferated, so did the “early objective testing” phenomenon. Chest pain presentations of all colors and ages, following an initial evaluation in the Emergency Department, have been invariably referred for inpatient observation and stress testing. The problem? Most of these tests are performed in patients for whom the pretest likelihood of coronary artery disease is low, and the incidence of false-positives outweighs that of true-positives.
This rehash of prior observational data aims to address this issues – specifically deriving a prediction rule for those who are so low risk any follow-up testing ought be obviated. Based on cohorts enrolled for two previous studies of potential acute coronary syndrome presentations in New Zealand and Australia, these authors track 2,396 patients for 30 days. Following an initial negative ED evaluation, 5.6% were diagnosed with acute coronary syndrome within 30 days – mostly “unstable angina”, and mostly based on follow-up objective testing. Using standard statistical bootstrapping techniques, the authors partition out 31.1% of this cohort as having a <1% risk of ACS within 30-days: age <50, <3 risk factors, and no prior CAD or MI. The authors suggest patients meeting these criteria, following a negative ED evaluation, need not be referred for any objective testing.
The puzzle here is in the outcomes measured: 30-day AMI, cardiovascular death, unstable angina, or revascularization. The leap, then, involves associating a lack of these outcomes with the disutility of provocative or anatomic testing. It is probably true there is colinearity between clinically important coronary artery disease and incidence of major adverse cardiac outcomes, but this is a bit tenuous of a foundation for their conclusions. A lack of 30-day adverse event does not exclude benefit from cardiac imaging, and, vice versa, the presence of a 30-day adverse event does not imply a benefit from cardiac imaging. However, given the lack of other useful evidence, this is as valid a proxy as we have to inform practice.
Finally, what tends to disappoint me most in these sorts of articles is something of a disconnect between the study design and the clinical questions relevant in practice. Chest pain presentations lay somewhere on a bell curve. At the low end, a subset of young and healthy folks are mostly harmed by overdiagnosis and additional resource utilization. Then, at the high end, patients with multiple risk factors and known disease can no longer be substantially helped by additional invasive interventions. Each of these cohorts is appropriate for early discharge from the Emergency Department without additional cardiac imaging, yet the focus is persistently on only the very low-risk end of the spectrum. I hope future study is able to provide a more sophisticated analysis of the features of moderate- and high-risk patients to identify the individuals within these cohorts who do benefit from cardiac imaging, and which specific testing best informs downstream care.
“A Clinical Decision Rule to Identify Emergency Department Patients at Low Risk for Acute Coronary Syndrome Who Do Not Need Objective Coronary Artery Disease Testing: The No Objective Testing Rule”
http://www.ncbi.nlm.nih.gov/pubmed/26363570