Exercise ECG Testing in Chest Pain Units
Abstract & Commentary
By Michael H. Crawford, MD. Dr. Crawford is a Professor of Medicine, and Chief of Clinical Cardiology, at the University of California, San Francisco; and he is the Editor of Clinical Cardiology Alert.
Synopsis: If a policy of invasive management is implemented for patients with positive exercise test results, the clinical risk score constitutes the main prognostic predictor of 1-year outcome.
Source: Sanchis J, et al. Usefulness of Early Exercise Testing and Clinical Risk Score for Prognostic Evaluation in Chest Pain Units without Preexisting Evidence of Myocardial Ischemia. Am J Cardiol. 2006;97:633-635.
Controversy exists concerning the usefulness of stress testing for low-risk patients held for observation in a chest pain unit. Thus, this group from Barcelona, Spain, evaluated their experience with 340 consecutive patients held in an Emergency Department Chest Pain Unit for chest pain suspicious for angina, no ST segment deviation, normal troponins X2, the ability to exercise, and no prior evidence of ischemic heart disease using a clinical score vs standard ECG treadmill exercise testing (Bruce protocol). The clinical score was a simplification of the TIMI score, which considered age > 67 years, ≥ 2 episodes of chest pain in 24 hours, and the presence of diabetes. Each of these variables was given one point, so the maximum score was 3.
A negative stress test was found in 68%, and these patients were sent home. Those with a positive stress test (16%) were admitted and recommended for cardiac catheterization. In the 16% with inconclusive tests, clinical judgement resulted in the admission of 80% of them. The patients were then followed for one year, and the primary end point of all cause mortality and myocardial infarction assessed. Secondary end points included a composite of the above plus readmission for unstable angina. Of those hospitalized, 74% had cardiac catheterization and 48% were revascularized.
At one year, the primary end point was achieved in 7.4% of those with a positive stress test and 2.1% of the negatives (P = .06); the secondary end point was found in 9.3 vs 2.8%, respectfully, P = .04. The higher the clinical risk score, the more likely was a primary or secondary end point (0 to 12%; P < .03 for both). Among those with a positive or negative stress test, the clinical score further stratified their risk of an event (OR = 2.0; 95% CI =1.2-3.2; P = .004). Sanchis and colleagues concluded that in a protocol in which low risk chest pain patients with a positive exercise ECG test were referred for cardiac catheterization, a simple clinical risk score is the most powerful predictor of outcome at one year.
Perhaps the most interesting aspect of this study is the clinical risk score. It is a simplification of the TIMI score which eliminates the TIMI variables, which we now know makes a patient high risk (positive biomarkers, known coronary disease, ST transients). This simplified score which uses only historical factors is the most powerful predictor of one-year outcomes in this aggressive Chest Pain
Unit protocol. Since 31% of those with a risk score of 3 had a negative stress test, yet 12% of those with a score of 3 had events, the study raises the question of whether those with a high score should be admitted and stress testing eliminated. This makes sense since clinical judgement should always trump testing, in my opinion. One difference between this study and others that may have come to different conclusions is that revascularization is a management strategy in this study, rather than an end point. This study builds on previous studies showing the value of certain strategies, and tests the relative value of a simple clinical assessment as compared to a testing driven strategy. Despite these protocol-driven constraints, simple clinical historical variables are still valuable.