Negative Stress Test May Not Rule Out Acute Coronary Syndrome

From Medscape Emergency Medicine > Viewpoints Posted: 03/17/2011

Amal Mattu, MD

Introduction

Cardiac stress testing is an important element in risk stratification of patients and prediction of future cardiac events.
However, the utility of a recent negative stress test (ST) is limited when it is used to determine the risk for acute coronary syndrome (ACS) in a patient presenting to the emergency department with symptoms of angina.
Almost every experienced emergency physician has cared for patients with true ACS or even primary cardiac arrest despite having a recent negative ST.
Unfortunately, overreliance on negative tests, especially STs, is a common reason for misdiagnosis or delays in diagnosis in patients with ACS.
The study by Walker and colleagues has provided us with a nice reminder that negative STs are certainly not a guarantee of cardiac health.

Coronary Disease in Emergency Department Chest Pain Patients With Recent Negative Stress Testing

Walker J, Galuska M, Vega D
West J Emerg Med. 2010;11:384-388

The authors performed a retrospective chart review of adult patients who presented to their community-based teaching hospital with a chief complaint of chest pain and who had a negative or inconclusive most-recent ST within the preceding 3 years. Various types of STs were included (treadmill ECG study, treadmill echocardiogram, treadmill nuclear study, pharmacologic echocardiogram, pharmacologic nuclear study).
Patients were excluded if they had undergone cardiac catheterization or coronary artery bypass graft surgery between the time of their most recent ST and their emergency department visit.
Patients were then evaluated for significant coronary artery disease (CAD) within 30 days of the emergency department visit.
Significant CAD was defined as an acute myocardial infarction with positive cardiac biomarkers, subsequent positive ST (of any type), cardiac catheterization requiring intervention, coronary artery bypass graft surgery, or death as a result of medical cardiac arrest.

A total of 164 patients were evaluated; 34 (20.7%) of these patients had CAD. There was no significant difference between the patients with true negative ST vs inconclusive ST: 122 patients had negative ST, of which 25 (20.5%) had CAD, and 42 patients had inconclusive STs, of which 9 (21.4%) had CAD.
Of the 34 patients who had CAD, 16 (47.0%) had their most recent ST within 6 months of admission, and 8 (23.5%) had their most recent ST within 1 month of admission.

Viewpoint

The key takeaway point from this study is very simple and provides confirmation of the anecdotal experience of seasoned emergency physicians: a recent negative ST does not exclude ACS in patients presenting with anginal symptoms.
It is critical to remember that cardiac tests (ECGs, troponins, STs, and even coronary angiography) are useful for risk stratification, but no test is capable of stratifying a patient's risk to zero.
Patients presenting with a history of a present illness that is strongly suggestive of ACS should be treated conservatively with a repeat workup if necessary -- that recent negative ST should never obviate your concern!