False-Positives in the PCI Era: Roughly 1 in 10 Patients Sent to Cath Lab Unnecessarily

Shelley Wood
December 21, 2007 — Having emergency-room physicians diagnose ST-segment-elevation MI (STEMI) and "activate" cardiac cath labs directly — cutting out the delay associated with seeing a cardiologist — is a key recommendation for efforts to trim door-to-balloon times for patients with STEMI. But a new analysis suggests that this strategy may lead to false-positive activation of cath labs anywhere from 9% to 14% of the time.
Writing in the December 19, 2007 issue of the Journal of the American Medical Association, Dr David M Larson (Ridgeview Medical Center, Waconia, MN) and colleagues point out that hospitals planning and budgeting for strategies to cut door-to-balloon times will need to take into account this relatively common and unavoidable consequence of direct cath-lab activation [1].
To heartwire, Larson, an emergency room (ER) physician, commented that he thinks a false-positive rate somewhere in the region of what they found is appropriate. In the thrombolytic era, he notes, the false-positive rate of patients who received lytics and later were found not to have a myocardial infarction (MI; by cardiac biomarkers) was about 10%; false-positive rates in the percutaneous coronary intervention (PCI) era have not previously been reported, with or without door-to-balloon time-saving strategies. Larson also thinks that while hospitals should always strive to reduce the rates of patients being sent to the cath lab unnecessarily, there needs to be a balance.
"There are a lot of cases that are in the gray zone," he said. "If you're more specific, and you decrease the rate of false positives, you're probably going to increase your rate of false negatives. It's a trade-off."
Larson et al reviewed all cases of suspected STEMI patients presenting to the Minneapolis Heart Institute or transferred from one of 30 community hospitals — a total of 1345 patients between March 2003 and November 2006. In all cases, emergency-department staff, on the basis of electrocardiogram (ECG) results, activated the cath lab at the tertiary hospital before transferring patients for angiography. In the authors' subsequent review, however, 14% of patients were found to have no culprit coronary artery and 9.5% had no significant coronary artery disease. Of those with no coronary artery disease (CAD), 38% had positive cardiac biomarkers, pointing to myocarditis (31%), stress cardiomyopathy (31%), or STEMI confirmed by cardiac magnetic resonance imaging (MRI) — in some of these patients, angiography did not pave the way for PCI but was at least an appropriate diagnostic test. In all, just 9.2% of patients had both negative cardiac biomarkers and no culprit artery, which the authors say believe is likely the "true measure" of unnecessary cath-lab activation in this study.
Sometimes you do need to slow down
In an accompanying editorial, Dr Frederick A Masoudi (Denver Health Medical Center, CO) points out that the push in recent years to reduce door-to-balloon times may have the unintended consequence of increasing false-positive rates [2]. "In the case of primary PCI, the view of quality should extend beyond the time to treatment to include patient selection and ultimately to outcomes," he writes. To reduce the number of false positives that arise from overly zealous efforts to shorten door-to-balloon times, false-positive rates could, like door-to-balloon times, be a measure in the overall assessment of hospital performance.
Larson agrees: "There's so much emphasis on door-to-balloon time and time to reperfusion; I think sometimes we have to realize that there are cases where we need to slow down and maybe get another ECG or an echocardiogram and not penalize people for slower door-to-balloon times in those cases. When you're looking at quality, it's not just the process measures like time to treatment, it's patient selection as well. If one hospital has a false-positive rate of 25% and the standard in the community is 10%, you have to take a closer look at that."
But Larson also believes there is "always room for improvement." In his study, roughly 2% of electrocardiograms were "overread," resulting in patients heading to the cath lab unnecessarily. Better education would help reduce this problem, and centers with higher rates of false positives could perhaps be targeted for this kind of education, Larson suggests. He also notes that many patients who undergo an urgent diagnostic catheterization and are not found to have occlusive disease are patients who would likely have ended up undergoing angiography at a later date anyhow and, in some cases, may at least be less at risk from an invasive catheterization than if they underwent unnecessary fibrinolytic therapy: for example, patients having a dissection or who have pericarditis.
Larson also emphasized that the results should not be interpreted to mean that a cardiologist should see each and every patient with presumed STEMI in the emergency room—bypassing the cardiologist has proved key to improving door-to-balloon times. "There should always be the opportunity, on questionable cases, to get more data, get help from a cardiologist if necessary, have someone else look at the ECG, without penalizing somebody for having a slower door-to-balloon time. But I don't think we should change the whole system: most of the cases — 90% — are clear-cut. You don't want to hurt the whole system because of the remaining 10% of patients."
Know your rates
Also commenting on the study for heartwire, senior author and cardiologist Dr Timothy Henry (Abbott Northwestern Hospital, Minneapolis, MN) noted that this study "sets a benchmark."
"Everyone talks about false positives, but no one knows what their rates are or what the rates should be," he said. "If your false-positive rate is 2% or 5%, you're doing something wrong and you're missing patients. But if your false-positive rate is 25%, you need to be talking to people about what you could do differently. . . . The most important thing is that everyone should know what their own rate is. We've been so focused on reducing door-to-balloon times that we've forgotten about some of these other things."
Sources
Larson, DM, Menssen KM, Sharkey SW, et al. "False-positive" cardiac catheterization laboratory activation among patients with suspected ST-segment elevation myocardial infarction. JAMA. 2007;298:2754-2760.
Masoudi FA. Measuring the quality of primary PCI for ST-segment elevation myocardial infarction. Time for balance. JAMA. 2007;298:2790-2791.