Here are some highlights from Larson, Menssen, Sharkey et al False-Positiveâ€ Cardiac Catheterization Laboratory Activation Among Patients With Suspected ST-Segment Elevation Myocardial Infarction.Â JAMA 2007;298(23):2754-2760.
The false positive rates (suspected STEMI patients with ST-segment elevation but no clear culprit coronary artery, no significant coronary artery disease, and negative cardiac biomarker results) were analyzed at the Minneapolis Heart Institute at Abbott Northwestern Hospital in Minneapolis, Minnesota (a tertiary cardiovascular center with referral relationships with community hospitals throughout Minnesota and western Wisconsin).
First the authors note:
â€œTime to reperfusion is a major determinant of outcome in patients presenting with an ST-segment elevation myocardial infarction (STEMI). The American College of Cardiology/American Heart Association STEMI guidelines recommend that the emergency department physician make the decision regarding reperfusion therapy within 10 minutes of interpreting the initial diagnostic ECG, which may be challenging because clinical decisions are often made without a previous ECG result for comparison or time to observe evolutionary ST-segment changes or cardiac biomarker resultsâ€¦â€œ
Hereâ€™s the bombshell:
Of the 1335 patients who underwent angiography, 187 (14%) did not have a clear culprit coronary artery, 10 patients (0.7%) had multiple potential culprit arteries (severe 3-vessel disease and positive cardiac biomarker results), and 1138 (85.3%) had a clear culprit artery. Patients with a culprit artery were treated with percutaneous coronary intervention (94%), coronary artery bypass surgery (4%), or medical management (2%). Retrospective review of the index ECG indicated that 24 atients (1.8%) did not have diagnostic ST-segment elevation but instead had ST-segment depression, T-wave inversion, or nonspecific ST-T changes, including 3 patients with positive biomarker results (2 with non-STEMI and 1 with a drug overdose) and 21 with negative cardiac biomarker results. These patients were included in the no-culprit artery group. The prevalence of false-positive catheterization laboratory activation with the no-culprit coronary artery criteria was 14%â€¦â€œ
The authors then pose a difficult question:
â€œAchieving door-to-balloon times in less than 90 minutes is an important quality metric that is tied to pay for performance and has been the focus of recent quality improvement initiatives such as the American College of Cardiology’s D2B Alliance and the American Heart Association’s Mission: Lifeline. Upstream activation of the cardiac catheterization laboratory by the emergency department physician is one of the key strategies to reducing door-to balloon times. A major challenge for the emergency department physician is the patient who presents with nonspecific symptoms or subtle ST-segment elevation or QRS repolarization abnormalities that obscure or mimic ST segment elevation. In these cases, is it best to immediately activate the catheterization laboratory, considering the consequences of a false alarm, or take the time to obtain additional data, such as from serial ECGs, biomarkers, or an echocardiogram?â€œ
One final note that I found interesting:
â€œPatients 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 results.â€
It would be interesting to know whether or not the false positive LBBB patients met Sgarbossaâ€™s criteria. The authors donâ€™t say it, but I canâ€™t help but wonder if the patients with previous MI â€œand abnormal baseline ECG resultsâ€ had persistent ST segment elevation similar to (what we think of as) left ventricular aneurysm.