Frequency of False Positive Cardiac Catheterizations in STEMI Patients

Abstract & Commentary

By Harold L. Karpman, MD, FACC, FACP, Clinical Professor of Medicine, UCLA School of Medicine. Dr. Karpman reports no financial relationship to this field of study.

Synopsis: The frequency of false positive cardiac catheterization laboratory activation for suspected STEMI in community practice is relatively common with 14% of patients having no clear-cut culprit coronary artery lesions and 9.5% having no significant epicardial coronary artery disease.

Source: Larson DM, et al. "False positive" cardiac catheterization laboratory activation among patients with suspected ST segment elevation myocardial infarction. JAMA. 2007;298:2754-2760.

The standard 12 lead electrocardiogram (ECG) remains a critically important diagnostic tool for the emergency management of patients with acute myocardial infarctions despite its accepted limitations.1 Time to reperfusion of occluded coronary arteries is a major determinant of outcome in patients presenting with an ST-segment elevation myocardial infarction (STEMI)2,3 and therefore, the STEMI guidelines of the American College of Cardiology/American Heart Association recommend that emergency department (ED) physicians make the decision regarding reperfusion therapy within 10 minutes of interpreting the initial diagnostic ECG.4 Immediate activation of the cardiac catheterization laboratory by the ED physician has been vigorously recommended as a key strategy to reduce door-to-balloon times.5

Because rapid reperfusion of an occluded coronary artery is indeed the most important quality metric in patients with STEMIs, the potential clinical and financial consequences associated with false alarms need to be considered.6 Larson and his colleagues from the Minneapolis Heart Institute Foundation prospectively determined the prevalence, etiology and outcomes of "false positive" catheterization laboratory activation occurring in a consecutive series of transported patients with suspected STEMI.7 The catheterization laboratories were located in a tertiary cardiovascular center in Minneapolis, Minnesota, which serviced 30 community and rural hospitals. A total of 1345 STEMI patients were transferred from various community hospitals located up to 210 miles from the tertiary center for facilitated percutaneous coronary intervention (PCI) according to a standardized protocol. The diagnosis and decision to activate the catheterization laboratory was made by the on-duty ED physician in each community hospital to which the patients had initially been transported. In cases of diagnostic uncertainty, the presenting ECG was faxed to an attending cardiologist for review before the catheterization laboratory was activated. Transferred patients bypassed the ED Department of the tertiary hospital and were taken directly to the catheterization laboratory. The prevalence of false-positive cardiac catheterization laboratory activation was between 9.2% and 14% depending on the definition of "false-positive" based on the anatomy of the coronary arteries determined at the time of catheterization and evaluation of the cardiac biomarker results.

Commentary

Patients were enrolled in the Larson study between March, 2003 and November, 2006.7 The recently published 2007 focused update of the ACC/AHA guidelines for the management of patients with STEMI reaffirms that if a patient is taken to a non-PCI hospital, it is appropriate to consider emergency inter-hospital transfer of the patient to a PCI-capable hospital for mechanical revascularization.8 Among the 1335 patients referred to the tertiary catheterization laboratory, 14% had no clear-cut culprit coronary artery lesions, 9.5% had no significant epicardial coronary artery disease and 11.2% had negative cardiac biomarkers. Or course, it must be recognized that all of these patients were referred from community hospitals and there were not primary admissions to the tertiary hospital where diagnostic accuracy might have been significantly improved.

"False positive" catheterization laboratory activations theoretically should be, of course, unavoidable to some degree because of the necessary trade-offs between specificity and sensitivity since the absence of false positive activations in this study would almost certainly imply that PCI had not been provided to some patients who actually needed the procedure performed. However, in the modern era, it is quite likely that the "false positive" rates may be significantly diminished because so many EDs will likely be improving their diagnostic accuracy utilizing evolving technologies such as 64 slice ultrafast computed tomography on carefully selected STEMI patients presenting with chest pain in whom the diagnosis is not absolutely clear-cut (ie, patients with atypical chest pain and/or who have borderline EKG and/or biochemical abnormalities); however, it should be clearly recognized that patients who demonstrate clear-cut ST segment elevations (especially if associated with enzyme elevations) are certainly not candidates for ultrafast coronary CT angiography (CTA) but rather should be immediately referred to the cardiac catheterization laboratory. CTA would almost certainly have anatomically defined the coronary anatomy in most of the 14% of patients in the Larson study, with no clear culprit of coronary artery lesions, and the 9.5% of patients who had no significant epicardial coronary artery disease but should be considered for use only in atypical chest pain patients in whom the admitting EKG does not demonstrate clear-cut ST segment elevations, and especially if the admitting troponin levels in these patients are normal. However, if any residual uncertainty exists after the ED workup of the STEMI patient is completed, referral to the cardiac catheterization laboratory immediately would be mandatory in most instances. Hopefully, Larson and his colleagues will continue their very important work and will soon be able to report on the diagnostic value of CTA in carefully selected patients in the community ED. However, it should be clearly recognized that, at this time, all chest pain patients with clear-cut ST segment elevations and/or abnormal admitting cardiac enzymes should be sent to the catheterization laboratory and should not be subjected to a diagnostic CTA.

In summary, it is quite clear that the frequency of false positive cardiac catheterization laboratory activation for suspected STEMI patients has been relatively common in community practice. However, current and ongoing improvements in imaging technology and other diagnostic improvements will undoubtedly improve patient selection, will reduce false positives with respect to cardiac catheterization laboratory activation, and ultimately will improve outcomes in the ongoing quest to rapidly open acutely occluded coronary arteries.

References

1. Zinetbaum PJ, et al. Use of the electrocardiogram in acute myocardial infarction. N Engl J Med. 2003; 348(10):933-940.

2. Boersma E, et al. Early thrombolytic treatment in acute myocardial infarction: reappraisal of the golden hour. Lancet. 1996;348(9030): 771-775.

3. Brodie BR, et al. Door-to-balloon time with primary percutaneous coronary intervention for acute myocardial infarction impacts late cardiac mortality in high-risk patients and patients presenting early after the onset of symptoms. J Am Coll Cardiol. 2006;47(2):289-295.

4. Antman EM, et al. ACC/AHA guidelines for the management of patients with ST elevation myocardial infarction: executive summary: a report of the American College of Cardiology/American Heart Association task force on practice guidelines. Circulation. 2004;110(5): 588 at 636.

5. Bradley EH, et al. Strategies for reducing the door-to-balloon time in acute myocardial infarction N Eng J Med. 2006;355(22):2308-2320.

6. Barbagelata A, et al. J Electrocardiol. 2006;39(4);S73-S74.

7. Larson DM, et al. JAMA. 2007;298:2754-2760.

8. Antman E, et al. 2007 focused update of the ACC/AHA 2004 guidelines for the management of patients with ST-elevation myocardial infarction. A report of the ACC/AHA task force on practice guidelines. J Am Coll Cardiol. 2008;51:210-247.