'False-Positive' Cath Lab Activation for STEMI Up to 14%


The prevalence of unnecessary activation of a cardiac catheterization laboratory for suspected ST-segment elevation myocardial infarction ranged from 9.5% to 14% in one Midwestern coronary intervention network, depending on the diagnostic criteria used, researchers reported.

“Upstream” activation of a coronary catheterization lab by the emergency department physician is a key strategy to reducing door-to-reperfusion times in cases of suspected MI.

However, in the press to speed this process, the medical community may have overlooked one adverse conse-quence: false-positive referrals to percutaneous coronary intervention (PCI) centers, according to Dr. David M. Larson of the Minneapolis Heart Institute, Abbott Northwestern Hospital, and his associates.

This is “a significant concern” because unnecessary coronary angiography is a risk to the patient and “may impose a burden on limited human and physical catheterization laboratory resources,” they noted.

The investigators assessed such false-positives in a study of 1,345 consecutive patients suspected of having ST-segment elevation MI (STEMI) and referred to their regional catheterization lab between 2003 and 2006. The lab covers a network of about 30 medical centers within a 200-mile area, “representing a wide range of hospital sizes and emergency department volumes” in a real-life setting.

The rate of false-positive cath lab activations was 14% in patients who showed no clear “culprit” artery on angiography. Review of their initial ECGs showed that 24 of these patients (1.8%) did not have ST-segment elevation but instead had ST-segment depression, T-wave inversion, or nonspecific ST changes.

A total of 127 patients with no clear culprit artery also had negative results on tests of cardiac biomarkers and were therefore considered to be free of significant coronary artery disease, for a false-positive rate of 9.5%.

However, 64 patients with no clear culprit artery proved to have positive biomarker tests and were found to have MI due to emboli or spasm, myocarditis, stress cardiomyopathy, or STEMI with no angiographic lesion.

The rate of false-positive cath lab activations was 11.2% in patients who had negative biomarker results. However, 26 of these patients (17%) showed a clear culprit artery on angiography and were diagnosed as having either aborted STEMI or unstable angina.

“Our results indicate that a wide spectrum of etiologies may lead to false-positive catheterization laboratory activation. Many of these include high-risk patients who may benefit” from angiography even if they don't proceed to PCI, Dr. Larson and his associates said (JAMA 2007;298:2754–60).

In an editorial comment accompanying this report, Dr. Frederick A. Masoudi of the Denver Health Medical Center said that prior to this “important” study, little had been known about false-positives in PCI systems, and they were assumed to be “relatively rare.”

According to any of the diagnostic criteria in this study, “no fewer than 1 in 11 referrals were considered false positives,” a proportion that certainly is not trivial, he said (JAMA 2007;298:2790–1).

In some of the cases in this study, such as those for whom the electrocardiogram was seemingly misinterpreted, the risks of unnecessary angiography clearly outweighed any potential benefits.

However, in others, “such as those ultimately diagnosed with stress cardiomyopathy or coronary artery spasm, coronary angiography was likely an appropriate diagnostic test even though PCI was ultimately not performed,” Dr. Masoudi noted.

“False-positive catheterization laboratory activation may be another quality metric to monitor for a STEMI program.” the study investigators concluded.

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