Chest Pain but MI Rule-Out? Further Noninvasive Testing Usually Unhelpful, Says Analysis

January 29, 2015

HERSHEY, PA — Patients admitted to the emergency department with chest pain who are ruled out for an MI are at a low risk for having an MI in the short- and longer-term follow-up even if they receive no further diagnostic testing, according to the results of a new study[1].

Most important, the analysis showed that compared with the outcomes of individuals who received no further diagnostic tests, noninvasive testing with exercise ECG, myocardial perfusion scintigraphy, and computed tomography coronary angiography (CTCA) did not appear to prevent subsequent MIs but did lead to more procedures and tests.

"We found that having an early cardiac stress test was not associated with a lower odds of having an MI in the future, but it was associated with significantly higher odds of downstream invasive tests and procedures, namely cardiac catheterization and revascularization," lead investigator Dr Andrew Foy (Penn State Milton Hershey Medical Center, Hershey, PA) told heartwire .

The study is published January 26, 2015 in the JAMA: Internal Medicine.

Protocol Depends on ED Physician's Concern

When a patient presents to the emergency department with chest pain that might be the result of an acute coronary syndrome, the protocol typically involves serial ECGs and serial cardiac-enzyme testing, with at least two sets of cardiac troponin tests performed over 4 to 6 hours, explained Foy.

"If the patient rules out for an MI and the electrocardiogram is unremarkable, they will usually recommend noninvasive cardiac testing either prior to discharge or within 72 hours of discharge," said Foy. "But this really depends on the physician's concern for acute coronary syndrome."

At present, the American Heart Association endorses the safety and usefulness of noninvasive testing to provoke ischemia or to detect anatomical coronary artery disease before or within 72 hours of discharge. Such testing is done to identify patients who might benefit from more aggressive therapy, such as coronary revascularization.

To heartwire , Foy said the protocol has never been studied in a randomized clinical trial, one where patients would be randomized to cardiac stress testing vs conservative management (no testing). The purpose of their analysis, he said, was to analyze patients who underwent further testing, including exercise stress testing, and to report downstream invasive tests, procedures, and hospitalizations for MI.

They performed a retrospective analysis of health-insurance claims data from a national sample of privately insured patients, including individuals with a primary or secondary diagnosis of chest pain in the emergency department. They examined the downstream benefits of five treatment strategies: no follow-up noninvasive testing, exercise ECG, stress echocardiography, myocardial perfusion scintigraphy, or CTCA.

In total, 421 774 individuals were included in the analysis. Of these, 293 788 underwent no further testing, 82 954 underwent myocardial perfusion scintigraphy, 24 101 underwent stress echocardiography testing, 18 206 exercise ECG testing, and 2725 underwent CTCA. The mean length of follow-up after the test was just over 6 months.

Following the index test after their emergency-department visit for chest pain, just 0.11% of patients were hospitalized within 7 days of follow-up for an MI. At 190 days, 0.33% were hospitalized for MI. There were no significant differences in the rate of hospitalizations for MI among any of the testing groups when compared with the no-testing strategy.

In total, 3.0% and 5.3% of patients underwent a subsequent cardiac catheterization at 7 and 190 days of follow-up, respectively. At 7 and 190 days follow-up, 0.7% and 1.3% of patients underwent coronary revascularization.

At 190 days, the revascularization rate among untested patients was 0.8%. Conversely, the revascularization rates were 1.3% among stress-echocardiography patients, 1.9% among exercise-ECG patients, 3.0% in the myocardial-perfusion-scintigraphy group, and 2.4% in the CTCA group. Regarding catheterizations at 190 days, the rates were 3.4% in the no-testing group, 4.7% in the stress-echocardiography group, 6.0% in the exercise-ECG group, 12% in the myocardial-perfusion-scintigraphy group, and 6.8% in the CTCA group.

Compared with the no-testing group, individuals receiving any of the invasive tests were significantly more likely to undergo subsequent cardiac catheterization or coronary revascularization by day 7 of follow-up. At 190 days, the results were the same, although the association between testing and catheterization/revascularization was not evident among those who underwent an initial strategy of stress echocardiography.

"There's a population of patients with a not-so-great story," said Foy. "They don't have any electrocardiographic changes; therefore they're safe for cardiac stress testing. I think what people believe is that if you identify a blockage in these patients . . . they have unstable angina. I think a lot of people would say that's an oversimplification, and you might just be finding unrelated disease. There is a concern that might be what's driving the revascularization. The question is, 'Is it really helping?' "

To heartwire , Foy said that if the noninvasive tests identified patients with unstable angina, by definition, the subsequent revascularization procedures should lead to a reduction in the future downstream MI rates, which it did not.

Attempt to Deal With Bias

The researchers are aware of the limitations of their analysis, particularly the criticism that patients undergoing no testing were significantly younger and had less comorbidities than those undergoing noninvasive testing. Selection bias and the potential for unmeasured confounding variables is a drawback. However, they did attempt to control for these variables in their analysis.

Foy pointed out that the cohort of patients who did not undergo further testing was large, and while they had fewer comorbid conditions, they included many older patients with comorbidities, given that it included nearly 300 000 individuals (which was twice as large as the testing cohorts). "I think we got rid of bias as much as we could have and that large numbers were a huge help," he said.

Regarding the overall findings, Foy said that chest pain in the emergency department is a big public-health issue and, given the extent of the problem and the resources devoted to rule-outs and stress testing, there is a need for a prospective clinical trial to determine whether there is a benefit.

"I think the findings from this study really cast some doubt on the benefit of early noninvasive testing in this patient population," said Foy. "Our results are certainly not definitive, and I wouldn't want anybody to have the impression that this is the final word. But I do think it should facilitate a clinical trial to address this question."

The authors have reported no relevant financial relationships.

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