Taking Ambulance Cuts Time to Cath Lab 26%


Major Finding: After adjustment for multiple risk factors, severity of illness and extent of ECG changes, patients with suspected STEMI who did not arrive by ambulance at the emergency department spent 62% more time in the emergency department before undergoing catheterization.

Data Source: A study of 356 consecutive patients referred for emergent cardiac catheterization for a suspected STEMI by emergency physicians at a tertiary care hospital and a county hospital in San Francisco in 2009.

Disclosures: Dr. McCabe and Dr. Wright reported no relevant conflicts of interest.

NEW ORLEANS – Patients with suspected ST-elevation myocardial infarction who called an ambulance received lifesaving care in half the time as patients who got to the hospital by other means, according to a study conducted at two San Francisco hospitals.

“Patients who take an ambulance get a prehospital ECG,” said lead investigator Dr. James M. McCabe of the University of California, San Francisco, at the meeting. “These patients move through the emergency room and get to the cath lab much faster.”

“We found that almost half of patients referred for a potential heart attack don't take an ambulance but come in on their own, and it turns out they are doing themselves a great disservice,” Dr. McCabe said.

The study analyzed 356 consecutive patients referred for emergent cardiac catheterization for a suspected STEMI by emergency physicians at a tertiary care hospital and a county hospital in 2009. Of the 356 patients, 199 (56%) arrived by ambulance and 157 (44%) did not.

Variables affecting the time interval from the inciting ECG to STEMI pager activation, and door-to-balloon time, were analyzed in univariate and stepwise multivariate regression models.

All components of care were affected.

“The ultimate metric, door-to-balloon time, was reduced by 26% in patients taken by ambulance,” Dr. McCabe reported. This highly significant finding is important because studies show mortality risks are higher when door-to-balloon times exceed 90 minutes, he added.

The investigators then broke down the door-to-balloon time into its various components and compared the groups. After adjusting for demographic factors, traditional cardiovascular risk factors, severity of illness and extent of ECG changes, merely not presenting by ambulance to the emergency department (ED), and therefore not receiving a prehospital ECG, significantly lengthened by 62% the total time in the ED before undergoing catheterization.

Among patients arriving by ambulance, “each interval that occurred within the emergency room was reduced by more than 50%,” he reported.

The procedural time for revascularization, however, did not vary based on how the patient arrived at the hospital. This finding supports the conclusion that care was made more efficient prior to the catheterization itself, he said.

The one observable difference was that patients arriving by ambulance were more critically ill. They had more cardiac arrests, and required more cardiopulmonary resuscitation and intubation. “While these patients are sicker and require more care in the ER, they are still getting through the ER faster, after adjusting for multiple risk factors and elements in the decision-making process,” Dr. McCabe noted. “Taking the ambulance results in efficiency, and this translates into faster ER throughput and shorter door-to-balloon times.”

Of some concern to the researchers was that calling 911 did not ensure that patients with suspected STEMI arrived at the hospital with ECG results in hand. Among the 356 patients in the study, 68% did not receive an ECG, either because they did not travel by ambulance or because, in 43% of the cases, they were not given an ECG en route.

Dr. McCabe suspects that patients who did not receive an ECG in the ambulance may have had vague presenting symptoms when paramedics arrived. Of patients with symptoms more indicative of an MI, 78% got an ECG in the ambulance, he said.

“Our community is diverse, and we feel that barriers in communication with non–English speakers may also have played a role,” he added.

He further noted that in San Francisco, paramedics did not have the technology to forward the ECGs electronically to the receiving hospital. San Francisco will be implementing citywide remote transmission of ECGs soon, and the investigators plan to study whether this makes for even more efficient transfer of STEMI patients to the cath lab.

“These data suggest better triage systems may be necessary for patients with likely STEMIs, particularly for [more than] 40% of patients who do not arrive by ambulance,” Dr. McCabe concluded.

Dr. Janet Wright, ACC senior vice president of science and quality, said that “This is a safety message for patients: 'Your local ER wants you to come by ambulance!' And for physicians and health care systems, the message is that there are critical intervals within the overall pattern of care that need scrutiny,” said Dr. Wright, a cardiologist in Chico, Calif. “The person who arrives by private transportation may languish within those time intervals,” she said. “The message is to focus on every handoff. They accumulate in precious minutes.”


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