Several Factors Behind False-Positive STEMI Activations

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More than one-third of patients referred for primary percutaneous coronary intervention (PCI) from the emergency department do not have ST-segment elevation myocardial infarction (STEMI), according to a study published online May 7, 2012, ahead of print in the Archives of Internal Medicine. The researchers found several patient-level characteristics associated with increased odds of false-positive STEMI activation of the cath lab.

James M. McCabe, MD, of Brigham and Women’s Hospital (Boston, MA), and colleagues analyzed consecutive patients referred to the cath lab for possible STEMI at 2 San Francisco-area centers from October 2008 to April 2011. They defined false-positive STEMI activation as “lack of a culprit lesion by angiography or by assessment of clinical, electrocardiographic, and biomarker data in the absence of angiography.” Both hospitals were found to have similarly frequent use of angiography and subsequent false positives.

Erring on the Side of Primary PCI

Of 411 patients with suspected STEMI, 146 (36%) were adjudicated as false-positive. A total of 352 patients (86%) underwent diagnostic angiography: 101 (29% of those tested) had no culprit lesion and 39 (9.5%) had no atherosclerotic stenosis greater than 20%. Among the 59 patients who did not receive angiography for various reasons, 75% were considered false-positives.

Among those who went on to receive PCI for a culprit lesion, 1% would have been labeled as false-positive in the absence of angiography because of troponin values lower than 0.2 ng/mL and absence of STEMI criteria by ECG.

Patients with the following characteristics were more likely to have been unnecessarily referred to the cath lab for primary PCI:

• Less frequently white or Asian (P = 0.002)
• Lower mean BMI (P < 0.001)
• Less apt to present with typical angina symptoms (P = 0.004), cardiac arrest (P = 0.006), or hypotension (P = 0.005)
• More frequently diagnosed during standard working hours (P = 0.048)
• Used more illicit drugs (P < 0.001)
• More often had a known or reported history of CAD (P < 0.001)

Multivariate analysis found that left ventricular hypertrophy on ECG, a history of CAD, and illicit drug use all were independently associated with increased odds of false-positive activation. Conversely, a chief complaint of chest pain or pressure appeared to reduce the odds of false-positive activation (compared with all other presentations), and each unit increase in BMI above the mean of 26.5 was associated a 9% reduction in the likelihood of a false-positive activation.

True-positive STEMI diagnoses were triaged to the cath lab more quickly (P < 0.001) but had longer hospital stays (P = 0.05), had lower mean LVEF on echocardiography (P = 0.001), and were more often biomarker positive (P < 0.001). There were also numerically more deaths during the index hospitalization among true-positive activations (11% vs. 6%; P = 0.07).

The Specifics Matter

“The more we got into this particular issue of false-positive STEMI diagnoses, the more we realized that defining [what constitutes false-positive] is actually pretty difficult,” Dr. McCabe told TCTMD in an e-mail communication. “What surprised us was how similar the populations of ‘true’ and ‘false’ [STEMIs] were—underscoring how challenging it can sometimes be to sort out the true transmyocardial infarctions from everyone else.”

In a telephone interview with TCTMD, Jeffrey W. Moses, MD, of Columbia University Medical Center/Weill Cornell Medical Center (New York, NY), said it is really a question of context.

“I’m not sure what they are driving at because when you look at the diagnoses that didn’t have STEMIs, it doesn’t necessarily mean that it was wrong to cath them,” he said. “With many of these people, you could not get a definitive diagnosis without a catheterization. With cases like Takotsubo cardiomyopathy, myocarditis, known coronary disease, it’s hard to keep those out of the cath lab, nor would you want to.”

In addition, Harlan M. Krumholz, MD, SM, of the Yale School of Medicine (New Haven, CT), told TCTMD in a telephone interview that the language used in the study makes it different and “a little backward.”

Prior studies have looked at ‘false activations,’ which occur when a patient with no or little indication for STEMI is wrongly sent to the cath lab, and those studies have reported lower rates, he said. This study looked at ‘false positives,’ which are different because not all false positives are false activations, thus resulting in a higher rate.

J. Lee Garvey, MD, of the Carolinas Medical Center (Charlotte, NC), was the lead investigator of a study published in the January 17, 2012, issue of Circulation that looked at ‘false activations.’ He told TCTMD in a telephone interview that he would like to compare the methods of both papers, adding, “I bet the discrepancies would be less than what it looks like at first glance.

“[Is a STEMI] considered to be a false-positive because there’s no intervention to be done even though there’s still probably some significant cardiac disease?” he said, adding that patients whose culprit lesions could not be identified had relatively high troponin levels irrespective of whether they were diagnosed with coronary disease. “So there’s some other issue going on other than an acutely occluded coronary artery that needed an intervention with angioplasty and stent placement.”

In an accompanying editorial, Fouad Bachour, MD, and Richard Asinger, MD, both of the University of Minnesota, Minneapolis (Minneapolis, MN), write that “the quality of acute reperfusion therapy should be judged not only on the basis of door-to-door treatment time but also the ratio of ‘appropriate’ vs. ‘inappropriate’ activation of reperfusion therapy.”

Steps to Improve Care

Dr. Garvey urged that “we need to have agreed upon definitions for appropriate versus inappropriate cath lab activation and then a standard flow of what happens to patients who go to the cath lab.” Even so, there will always be an “accepted false-positive rate because you don’t want any false negatives,” he said.

Dr. Krumholz added that clinicians should make efforts to ensure patients who need to go to the cath lab are actually the ones who get there.

“[McCabe et al] are trying to identify some factors that might help do this, but they stop short of being able to create a predictive instrument that might be used by practitioners to make better decisions,” he commented. “We have yet to be able to identify that cluster of factors that gives us confidence that we aren’t missing anyone but we’re able to avoid taking people emergently to the cath lab who don’t need it.”

According to Dr. Moses, performing echocardiograms in the emergency department could add another level of certainty before sending a patient to the cath lab. He also suggested testing to see if catheterization is helpful in a global population.

“Just because it’s not a STEMI doesn’t mean the cath doesn’t add to the care,” he concluded.

Dr. McCabe agreed. “Our findings will need to be corroborated in larger studies of real-world patients with an emphasis on diverse hospital systems. As noted, it can be very difficult to define ‘false-positive’ STEMI diagnoses and perhaps equally hard to reproducibly record the decision-making in the emergency department without the patina of angiographic or other forms of reclassification bias.”  

Drs. Bachour and Asinger note in their editorial that adhering to the “criteria of clinical symptoms” reported in the paper could potentially reduce inappropriate activations.

“Most important for any program is a systematic protocol for the diagnosis and emergent treatment of STEMI including pivotal medical history for comorbid features, patient preference, continuous review of clinical experience, and direct feedback,” they advise, noting that an acceptable rate of inappropriate activation would likely fall in the 15% to 20% range.

 

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Sources:
1. McCabe JM, Armstrong EJ, Kulkarni A, et al. Prevalence and factors associated with false-positive ST-segment elevation myocardial infarction diagnoses at primary percutaneous coronary intervention-capable centers: A report from the Activate-SF registry. Arch Intern Med. 2012;Epub ahead of print.

2. Bachour F, Asinger R. Activating primary percutaneous coronary intervention for STEMI that is not: The collateral damage of improving door-to-balloon time. Arch Intern Med. 2012;Epub ahead of print.

 

 

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• Most Cath Lab Activations by Emergency Personnel for Suspected STEMI Appropriate
• Reducing D2B Time Alone Not Enough to Improve Overall STEMI Care
• AHA Database: Door-to-Balloon Times Improve, Still Not Ideal

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