While STEMI patients benefit from reperfusion therapy with PCI, a two-center study published May 7 in the Archives of Internal Medicine found than one-third of patients referred for primary PCI from the emergency department (ED) did not have a STEMI and 36 percent were deemed to be false-positive activations. An accompanying editorial questioned the impact of these false-positive activations and concluded that they lead to high costs and increased risk.

“Rapid activation of the cardiac catheterization laboratory for primary PCI improves outcomes for STEMI, but selected emphasis on minimizing time to reperfusion may lead to a greater frequency of false-positive activations,” wrote the study authors.

To better understand the frequency of false-positive STEMI diagnoses among emergency physicians at PCI-capable centers, James M. McCabe, MD, of the Brigham and Women’s Hospital and Harvard Medical School, both in Boston, analyzed 411 STEMI activations by emergency room physicians at two centers from October 2008 and April 2011.  

The researchers defined false-positive STEMI activation as a lack of culprit lesion by angiography or assessment of clinical, electrocardiographic and biomarker data in absence of an angiography.

Of the 411 ED STEMI diagnoses, 36 percent were deemed false-positive. A total of 352 patients underwent angiography. Of those, 29 percent had no culprit lesion and 9.5 percent had no atherosclerotic stenosis greater than 20 percent. Of those patients who did not undergo angiography, 75 percent were considered to be false-positive STEMIs. The authors reported that seven of nine patients refused catheterization and 38 of 42 patients were declined by cardiology services.

Of the patients who received PCI to treat a culprit lesion, 1 percent would have been labeled as a false-positive in the absence of angiography due to troponin values that were lower than 0.2 ng/mL and absence of STEMI by ECG.

The authors reported that patients with false-positive STEMI were less likely to be white or Asian, had lower mean body mass indexes, were less likely to present with typical angina symptoms, cardiac arrest or hypotension and were more likely to use more illicit drugs.

In a univariate analysis, the authors reported that being African-American, having a history of coronary artery disease, illicit drug abuse, among other factors, also increased a patient's odds of obtaining a false-positive STEMI activation.

McCabe et al noted that each millimeter increase in height of STEMI elevations reduced the odds of false-positive activation by 22 percent. Additionally it was noted that method of hospital arrival, patient age and ED experience were not associated with the odds of a false-positive activation.

“By any scheme, false-positive activations are defined relative to clinical outcomes that are unknown at presentation,” the authors noted. “Thus, false-positive activations are not necessarily unwarranted, nor should they suggest a de facto error in judgment.

“A history of coronary disease may lower the diagnostic threshold for interpreting an equivocal presentation or equivocal ECG as consistent with a STEMI,” the authors wrote.

McCabe et al noted that the current data showed that false-positive STEMI team activation rates at primary PCI centers are double what has been reported by previous studies, which showed false-positives to be in the 14 percent range.  

“We have also demonstrated a number of clinical and ECG factors associated with increased rates of false-positive activations,” the authors summed. “While a certain percentage of false-positive STEMI activations are essential to ensuring adequate diagnostic sensitivity, the point of equipoise between necessary diagnostic sensitivity and patient safety requires further investigation, particularly in light of increasing resource limitations.”

In an accompanying editorial, Fouad Bachour, MD, and Richard Asinger, MD, of the University of Minnesota in Minneapolis, wrote: “Prompt and effective revascularization of the infarct-related artery can save myocardium and reduce morbidity and mortality."

Bachour and Asinger noted that while national guidelines have helped to decrease door-to-balloon times, a potential pitfall of this could be that this has led to “more inappropriate CCL [cardiac catheterization laboratory] use.”

“This occurs for multiple reasons including 'misinterpretation' of clinical findings, primarily of the ECG, alternative diagnosis discovered after activation, activation protocol violation, and morbid conditions with ECG changes mimicking myocardial infarction for which a coronary angiogram would be contraindicated,” Bachour and Asinger wrote.

The editorialists noted that this inappropriate activation could increase costs and expose patients to risk. Due to disparities highlighted in the literature, the editorialists said that measures must be established to ensure quality of reperfusion programs, particularly to help stamp out false-positive activations.

“The quality of acute reperfusion therapy should be judged not only on the basis of door-to-treatment time but also the ratio of 'appropriate' vs. 'inappropriate' activation of reperfusion therapy,” Bachour and Asinger summed.