TPA PREHOSPITAL USE STUDY: 6% OF 2,100 PATIENTS EVALUATED
TPA PREHOSPITAL USE STUDY: 6% OF 2,100 PATIENTS EVALUATED were suitable for prehospital thrombolytic treatment, study investigator W. Douglas Weaver reported Nov. 14 at the American Heart Association's 61st scientific meeting in Washington, D.C. "Of all those patients with possible cardiac pain, 27% met the criteria for the electrocardiogram, and about one in five of the electrocardiograms shows ST segment elevation, so that we're left with about 6% of patients who meet the criteria for prehospital initiation of TPA," Weaver stated. Weaver presented preliminary results from the first phase of the project. In the first seven months of the study, over 2,100 patients with chest pain were evaluated by paramedics, Weaver noted. Nearly three-fourths of those patients were excluded as a result of exclusionary criteria listed in a checklist, leaving 587 eligible for electrocardiograms. Of that group, approximately 23% (135) were not evaluable due to technical problems; 89 of the remaining 452 ECGs, or about one in five, showed ST segment elevation. The investigators arrived at the 6% TPA eligibility figure by assuming that one in five of the nearly 30% of patients receiving ECGs would show elevated ST segment. The three-year Myocardial Infarction, Triage and Intervention (MITI) Project is evaluating the feasibility of prehospital administration of TPA (Genentech's Activase) by paramedics. The project consists of two phases. The objective of the first phase, which began last January, is focused on determining optimal selection criteria for patients to receive TPA. Phase two, which started Nov. 2, will attempt to determine whether any benefit is derived from prehospital administration of thrombolytic therapy. The endpoints to be evaluated include left ventricular function, residual infarct size, and mortality. The MITI project involves 19 hospitals and is being administered by investigators at the University of Washington in Seattle. During phase one, paramedics evaluate patients complaining of chest pain. Through the use of a checklist with inclusion/exclusion criteria, a history and physical exam and an electrocardiogram, a determination of MI patients eligible for prehospital TPA administration is made. Paramedics also use a cellular transmitted electrocardiogram to send results to a base station physician for consultation. Weaver also ran through the time characteristics of the selected patients. The median time from onset of chest pain to calling the ambulance was 27 minutes, Weaver said. The paramedics arrived eight minutes after the 911 call on average and it took the paramedics 18 minutes on average to evaluate whether the patient met the treatment criteria. Preparation of the patient for transport and transportation to the hospital took 20 minutes, and another 61 minutes elapsed on average from the patient's admission to the time he received treatment. This 81-minute period, Weaver said, "represents a potential time-saving that could be achieved with prehospital initiation of thrombolytic therapy." Comparison of patients that received prehospital ECG with those who did not, but were also transported by paramedics, showed "that there was a 20 minute time saving of hospital admission to actual delivering of therapy," Weaver noted. The project also sets up a registry of all myocardial infarctions treated by the 19 hospitals, Weaver pointed out. The registry will also include acute myocardial infarction patients that arrive at the hospital by means other than by paramedics. Data from this registry shows that acute myocardial infarction patients "on the average received treatment 1.8 hours after the onset of chest pain," Weaver said. The investigator hypothesized that if "the remote physician and paramedic had been equipped during phase one to treat...the average time to treatment [would have been] 50 minutes."
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