Cath Labs Get False Alarms in Up to 14% of Suspected STEMI

By Charles Bankhead
MINNEAPOLIS, Dec. 18 -- False alarms for ST elevation myocardial infarction make up a sizable proportion of alerts for cardiac catheterization labs, investigators here reported. Data from a prospective registry of transfers from community and rural hospitals showed that 14% of patients had no culprit coronary artery and 11.2% had negative cardiac enzyme tests, Timothy D. Henry, M.D., of the University of Minnesota, and colleagues wrote in the Dec. 19 issue of the Journal of the American Medical Association.
"The frequency of false-positive cardiac catheterization laboratory activation for suspected STEMI is relatively common in community practice, depending on the definition of false-positive," the authors concluded. "Recent emphasis on rapid door-to-balloon times must also consider the consequences of false-positive catheterization laboratory activation."
Time to reperfusion figures prominently in the outcome of patients with STEMI. The American College of Cardiology and American Heart Association recommend that emergency department physicians make a decision about reperfusion therapy within 10 minutes of seeing the initial ECG result.
Activation of the cardiac cath lab by the emergency department physician represents a key component of strategies to reduce door-to-balloon time. However, the potential clinical and financial consequences of false alarms also should enter into the discussion.
Dr. Henry and colleagues sought to determine the frequency, origin, and outcomes of false-positive activation of cardiac cath labs. They reviewed data from a regional system for management of STEMI. The system provides management for patients transferred from community and rural hospitals in Minnesota and western Wisconsin to the Minneapolis Heart Institute.
They reviewed the 1,335 patients with suspected STEMI enrolled from March 2003 through November 2006. All patients had coronary angiography, which showed that 187 patients (14%) had no culprit coronary artery and that 127 (9.5%) did not have significant coronary artery disease.
Cardiac enzyme tests were negative in 11.2% of patients, and 9.2% of the patients had neither a culprit artery nor diagnostic enzyme levels. Thirty-day mortality was 2.7% in patients without a culprit artery versus 4.6% with a culprit artery.
The authors noted several sub-populations with a higher prevalence of false-positive cath lab activation.
"Women had a higher prevalence of false-positive catheterization laboratory activation based on no culprit artery or no significant coronary artery disease, but there was no sex difference when negative cardiac biomarker results were used. Stress cardiomyopathy that occurs predominantly in women accounts for much of this discrepancy."
"Patients with new or presumably new left bundle-branch block had an inordinately high prevalence of false-positive catheterization laboratory activation (almost half did not have a culprit artery)."
"Patients with a previous myocardial infarction or previous coronary bypass surgery had a significantly higher prevalence of no culprit artery, likely because of abnormal baseline ECG result."
"The issue of false-positive catheterization laboratory activation remains a significant concern because unnecessary emergency coronary angiography is not without risk to the patient and may impose a burden on limited human and physical catheterization laboratory resources," the authors said. "This critical decision process must balance the risk of a false alarm with the consequences of delaying myocardial reperfusion."
The findings suggest that "false-positive catheterization laboratory activation may be another quality metric to monitor for a STEMI program," they concluded.
In an accompanying editorial, Frederick Masoudi, M.D., of Denver Health Medical Center, said "the view of quality should extend beyond the time to treatment and include patient selection, and ultimately to outcomes. While efforts to improve the quality of care will -- and should -- continue, the science of improvement must advance so that clinicians can be increasingly confident that efforts to deliver the right care to the right patient at the right time are improving and extending patients' lives."
Dr. Henry and co-authors and Dr. Masoudi reported no disclosures.

Primary source: JAMASource reference:Larson DM, et al "'False-positive' cardiac catheterization laboratory activation among patients with suspected ST-segment elevation myocardial infarction" JAMA 2007; 298: 2754-2760. Additional source: JAMASource reference: Masoudi FA, "Measuring the quality of primary PCI for ST-segment elevation myocardial infarction: time for balance" JAMA 2007; 298: 2790-2791.