Rate of False-Positive STEMI Diagnoses

More than one third of patients referred from the emergency department (ED) for percutaneous coronary intervention (PCI) do not have ST-segment elevation myocardial infarction (STEMI), according to results of a recent study. For patients with STEMI, rapid activation of the cardiac catheterization laboratory for PCI, when readily available, has been recommended. Autonomous activation of the STEMI team by ED physicians may decrease time to reperfusion, but may also increase the rate of false-positive activations [Arch Intern Med. 2012;172(11):864-871].

To determine the prevalence of false-positive STEMI diagnoses among emergency physicians at primary PCI-capable centers, the researchers analyzed 411 consecutive patients with a clinical diagnosis of STEMI admitted to EDs of tertiary care hospitals and an urban trauma center between October 2008, and April 2011. Clinical and electrocardiographic variables associated with false-positive STEMI activation were also analyzed. False-positive STEMI activation was defined as lack of a culprit lesion on angiography or, in absence of angiography, on basis of clinical, electrocardiographic, and biomarker data.

Among the 411 consecutive ED STEMI diagnoses, 146 (36%) were deemed to be false positive. A total of 352 patients underwent diagnostic angiography (86% of total): 101 (29%) had no culprit lesion and 39 (9.5%) had no atherosclerotic stenosis >20. Of the 59 patients who did not receive angiography, 45 (75%) were considered to be false-positive STEMIs: 7 of 9 patients (78%) refused catheterization and 38 of 42 patients (88%) were declined by the cardiology service. Patients in the false-positive STEMI activation group had a lower mean body mass index (BMI); less often presented with typical angina symptoms, cardiac arrest, or hypotension; were more frequently diagnosed during standard working hours; and used more illicit drugs.

Factors independently associated with false-positive activation were electrocardiographic left ventricular hypertrophy (adjusted odds ratio [AOR], 4.28; 95% confidence interval [CI], 1.94-9.42; P<.001), a history of coronary artery disease (AOR, 2.05; 95% CI, 1.02-4.12; P=.04), or illicit drug use (AOR, 2.73; 95% CI, 1.06-7.07; P=.04). By contrast, the likelihood of false-positive STEMI activation was lower in patients with increased BMI (AOR, 0.91; 95% CI, 0.85-0.98; P=.01); and those with angina at presentation (AOR, 0.28; 95% CI, 0.14-0.57; P<.001).

Over the study duration, the percentage of false-positive STEMI activations rose slightly per year (P=.03 for trend) without considerable change in door-to-door balloon times (P=.54 for trend), or the percentage of false-positive STEMI activations were stopped by the interventional cardiology team (P=.13 for trend).

The researchers acknowledged limitations to the study. For instance, the Activate-SF registry is composed of a diverse, urban patient population. The data may not reflect processes of care in other settings. The researchers also chose a conservative strategy for defining false-positive STEMIs to underscore the value of diagnostic sensitivity.

In summary, the investigators stated, “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.”