New protocol can rule out MIs in 90 minutes

Triage combined with point-of-care blood test

Using a simple, inexpensive blood test and a critical pathway for triage, researchers at the U.S. Department of Veterans Affairs (VA) in San Diego have developed a protocol that can rule out heart attacks in 90 minutes, compared with six to 24 hours for existing methods. The protocol combines a new, Food and Drug Administration-approved "point-of-care" blood test for three cardiac enzymes with an electrocardiogram and patient history.

Over a period of nine months, from July 1998 to April 1999, the researchers analyzed the diagnoses, triage patterns, and medical outcomes of 1,285 patients. The critical pathway used the cardiac markers, as well as the clinical criteria, to triage patients either to the intensive care unit (ICU), the direct observation unit (DOU), the ward, or home. (To see pathway from the U.S. Department of Veterans Affairs, San Diego, click here.)

"Patients who had chest pain were directed into one of five pathways based on history, electrocardiogram, and clinical suspicion of MI [myocardial infarction]," the authors explained. "A cardiac marker algorithm was incorporated into this pathway, which tested myoglobin, cTnI [cardiac troponin I], and CK-MB [creatine kinase-MB] at time of presentation (time 0), and at 30, 60, and 90 minutes to help determine patient diagnosis."1 When indicated, the researchers subsequently measured the cardiac enzymes at three and six hours to establish a final diagnosis of MI. In most cases, they report, the emergency department (ED) physicians were able to complete the evaluation process and determine patient triage destination within 90 minutes.

The researchers were seeking a balance between the "excessive and often unnecessary costs" created by admissions of patients who are at low risk for acute coronary syndromes and "strategies that are too liberal," which can lead to large numbers of patients released with undiagnosed MI.

"We began our research initially as part of a performance improvement project at our hospital," explains Alan S. Maisel, MD, director of the coronary care unit at the VA San Diego Health Care System, professor of medicine at the University of California at San Diego and one of the paper’s co-authors.

"We didn’t have enough beds and were actually sharing them. We had previously done research on the three markers. We got hold of this new point-of-care machine and decided to look at our earlier research and at sequential testing, using the algorithm and taking into account history or EKG findings. The marker elevation or lack thereof would then determine where the patients should go and what meds they should receive."

ED physician makes the call

Per the protocol, the ED physician, after consultation with the cardiac care unit (CCU) team, made the call as to whether the patients could be sent home. The critical pathway dictated that patients who were not sent to the CCU on admission or not sent home after the first negative set of markers would be re-evaluated after 90 minutes. The physicians were allowed to make triage decisions (CCU, DOU, ward, home, or further testing) at the 90-minute point. Of the 1,285 patients who presented with chest pain, 508, or 40%, were discharged home. Of this group, 13 returned to the ED within 30 days. One patient subsequently was diagnosed with MI, and 12 others were admitted for unstable angina.

"This critical pathway decreased CCU admissions by 40% while triaging the sickest patients to the CCU," the authors write. "This decrease, along with its likely associated cost savings with regard to intensive care unit costs, may even be underestimated, because at several time points during our study, a shortage of DOU beds may have falsely elevated the CCU admission rate."1 They estimate that about 10% of the CCU patients would have been sent to the DOU had space been available.

Maisel notes that "Early rule-outs and rule-ins are becoming pretty mainstream," noting other recent examples in the literature where it was determined that MIs could be ruled out within 90 minutes.

"What we want to do is move people out of the ED as quickly as possible — not only to save space, but because we also know that with the myocardium involved, time is money," Maisel adds. "If we can start treatment with the newer meds within 90 minutes instead of six hours, it can do a lot of good. For example, the II-3 platelet inhibitors (i.e., aggrastat) are found to be very effective in acute coronary syndrome, and the earlier you give it the better."

The exact nature of a critical pathway for ruling MI in or out must of necessity vary from hospital to hospital, Maisel notes. "Some hospitals have chest pain observation units," he points out. "They could use the algorithm and quickly rule out MI to see if the patient should go there."

Reference

1. Ng SM, Krishnaswamy P, Morissey R, et al. Ninety-minute accelerated critical pathway for chest pain evaluation. Am J Cardiol 2001; 88:611-617.

Need more information?

For more information, contact: Alan S. Maisel, MD, VA Hospital, 3350 La Jolla Village Drive, San Diego, CA 92161. E-mail: amaisel@ucsd.edu.