EARLY CARDIAC CATHETERIZATION LABORATORY ACTIVATION BY PARAMEDICS FOR PATIENTS WITH ST-SEGMENT ELEVATION MYOCARDIAL INFARCTION ON PREHOSPITAL 12-LEAD ELECTROCARDIOGRAMS Christopher H. Lee, MD, Carin M. Van Gelder, MD, David C. Cone, MD Prehosp Emerg Care Downloaded from informahealthcare.com by 64.134.180.52 For personal use only. ABSTRACT tion laboratory activation protocol based on our initial data. Conclusion. Important reductions in time to reperfusion seem possible by activation of the catheterization laboratory by EMS from the scene, with an acceptably low false-positive rate in this small sample. This type of clinical research can inform multidisciplinary policies and bring about meaningful clinical practice changes. Key words: STEMI; emergency medical services; electrocardiogram; heart catheterization Background. Prompt reperfusion in ST-segment elevation myocardial infarction (STEMI) saves lives. Although studies have shown that paramedics can reliably interpret STEMI on prehospital 12-lead electrocardiograms (p12ECGs), prehospital activation of the cardiac catheterization laboratory by emergency medical services (EMS) has not yet gained widespread acceptance. Objective. To quantify the potential reduction in time to percutaneous coronary intervention (PCI) by early prehospital activation of the cardiac catheterization laboratory in STEMI. Methods. This prospective, observational study enrolled all patients diagnosed with STEMI by paramedics in a mid-sized regional EMS system. Patients were enrolled if: 1) the paramedic interpreted STEMI on the p12ECG, 2) the Acute Cardiac Ischemia TimeInsensitive Predictive Instrument (ACI-TIPI) score was 75% or greater, and 3) the patient was transported to either of two area PCI centers. Data recorded included the time of initial EMS “STEMI alert” from the scene, time of arrival at the emergency department (ED), and time of actual catheterization laboratory activation by the ED physician, all using synchronized clocks. The primary outcome measure was the time difference between the STEMI alert and the actual activation (i.e., potential time savings). The false-positive rate (patients incorrectly diagnosed with STEMI by paramedics) was also calculated and compared with a locally accepted false-positive rate of 10%. Results. Twelve patients were enrolled prior to early termination of the study. The mean and median potential time reductions were 15 and 11 minutes, respectively (range 7–29 minutes). There was one false STEMI alert (8.3% false-positive rate) for a patient with a right bundle branch block who subsequently had a non–ST-segment elevation myocardial infarction. The study was terminated when our cardiologists adopted a prehospital catheteriza- PREHOSPITAL EMERGENCY CARE 2010;14:153–158 INTRODUCTION In the United States, more than 1 million people have heart attacks every year, and the majority of the heart attacks occur outside of the hospital. Public health efforts have focused on educating the public to call emergency medical services (EMS) at the first sign of chest discomfort, as it is well established that prompt recognition and early treatment of myocardial infarction save lives. In patients with ST-segment elevation myocardial infarction (STEMI), rapid reperfusion of myocardium with either fibrinolytic therapy or percutaneous coronary intervention (PCI) significantly decreases morbidity and mortality.1,2 Current American College of Cardiology/American Heart Association (ACC/AHA) guidelines for the management of STEMI recommend “door-to-drug” times of less than 30 minutes for fibrinolytic therapy and “door-to-balloon” times of less than 90 minutes for PCI.3 Although there have been substantial improvements in the overall care of STEMI patients in recent years, door-to-balloon times continue to lag behind national benchmarks.4–6 Much effort has been put into identifying potential delays in treatment, and PCI centers have incorporated successful strategies to improve door-to-balloon times.7,8 Many of these strategies are currently in place across the nation, where the cardiac catheterization laboratory is activated by an emergency physician immediately upon recognition of a STEMI. Upon activation, a multidisciplinary team approach involving both emergency department (ED) and cardiology staff is utilized to rapidly treat and transport the patient to the catheterization laboratory. However, despite streamlining many in-hospital processes to shorten the doorto-balloon interval, many systems are now focusing Received June 21, 2009, from Section of EMS, Department of Emergency Medicine, Yale University School of Medicine, New Haven, Connecticut. Revision received September 9, 2009; accepted for publication October 26, 2009. The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this paper. Address correspondence and reprint requests to: Dr. Christopher H. Lee, Section of EMS, Department of Emergency Medicine, Yale University School of Medicine, 464 Congress Avenue, Suite 260, New Haven, CT 06519. E-mail: [email protected] doi: 10.3109/10903120903537213 153 Prehosp Emerg Care Downloaded from informahealthcare.com by 64.134.180.52 For personal use only. 154 PREHOSPITAL EMERGENCY CARE on reducing the “first-medical-contact-to-balloon” interval, which often starts with evaluation at the scene by EMS. Important reductions in time to reperfusion can be achieved by earlier activation of the cardiac catheterization laboratory by EMS through the use of a prehospital 12-lead electrocardiogram (p12ECG).9,10 The acquisition and interpretation of a p12ECG by EMS can have a large impact on improving door-to-balloon times, and studies have shown that paramedics can reliably interpret STEMI on p12ECGs.11,12 Studies have also shown that the use of a p12ECG is associated with a shorter time to reperfusion therapy and decreased mortality in the management of STEMI.10,13–19 Reductions ranging from 10 to 50 minutes in door-to-balloon time have been documented in the literature, but catheterization laboratory activations by EMS have not yet gained widespread acceptance in hospital protocols. One potential hurdle to prehospital activation may be the reluctance of interventional cardiologists to amend their protocols with an aspect of EMS they perceive to be unproven. In fact, our own cardiology colleagues did not want to change our STEMI care protocol based on the existing prehospital activation studies in the literature; rather, they requested to see first-hand quantitative data specific to our local system. The use of prehospital activation as an adjunctive strategy for reducing door-to-balloon time has been supported by a qualitative analysis of the methods employed by the most successful PCI centers.7 Our research study serves as an effort to add quantitative data to the existing qualitative research and to continue to grow support in the literature for the implementation of EMS cardiac catheterization laboratory activation. In the first phase of our multiphase project, the paramedics staffing the diverse EMS systems in our area demonstrated that they can reliably identify STEMI on p12ECG.20 The primary objective of the current phase of the project was to quantify the potential reduction in time to reperfusion by prehospital activation of the catheterization laboratory. The present study was also designed to determine the feasibility of early catheterization laboratory activation by paramedics in our system and to estimate a falsepositive rate, i.e., the percentage of paramedic activations in which the attending emergency physician and/or interventional cardiologist did not feel activation was warranted. METHODS This was a prospective, observational study conducted in a mid-sized regional EMS system consisting of 21 EMS agencies covering 12 cities and towns, with a total population of approximately 400,000. Inclusion criteria APRIL/JUNE 2010 VOLUME 14 / NUMBER 2 FIGURE 1. Study inclusion criteria. ACI-TIPI = Acute Coronary Ischemia Time-Insensitive Predictive Instrument; p12ECG = prehospital 12-lead electrocardiogram; ED = emergency department; PCI = percutaneous coronary intervention; STEMI = ST-segment elevation myocardial infarction. (Fig. 1) were as follows: 1) the paramedic interpreted STEMI on p12ECG, 2) the p12ECG printout included an Acute Coronary Ischemia Time-Insensitive Predictive Instrument (ACI-TIPI) score of ≥75%, and 3) the patient was transported to either of the two 24-hour PCI centers in the area. Data collection began on July 13, 2008, and continued until the study was terminated on December 1, 2008. The ACI-TIPI is a mathematical algorithm on the p12ECG that calculates the probability of acute coronary ischemia based on patient risk factors and ECG rhythm recognition,21 and it can be used as an adjunct to aid the paramedic’s diagnosis of prehospital STEMI. Figure 2 shows an ECG from a study patient; the ACI-TIPI score is shown to be 97%. At the time of the study, the standard clinical protocol for STEMI on p12ECG involved the paramedic’s calling the receiving hospital for a “chest pain alert.” However, while the receiving hospital took steps in preparation to receive the patient, the cardiac catheterization laboratory was not activated until the patient had been transported and assessed by an attending emergency physician in the ED. In this study, standard clinical care was not changed; however, upon recognition of a prehospital STEMI, the paramedic called the receiving ED for a STEMI alert. On a data-collection form (Fig. 3), the triage nurse receiving the STEMI alert call by telephone or radio recorded the following: 1) the time the STEMI alert was received, 2) the time of patient arrival at the ED, 3) the time of cardiac catheterization laboratory activation by the ED attending physician, and 4) the time the patient left the ED for the catheterization laboratory; synchronized clocks were used for all time points. Our primary outcome measure, the potential time reduction with EMS activation of the catheterization laboratory, was assessed by subtracting the time of the STEMI alert notification from the time of the actual catheterization laboratory activation by the emergency Prehosp Emerg Care Downloaded from informahealthcare.com by 64.134.180.52 For personal use only. Lee et al. 155 PREHOSPITAL CATHETERIZATION LABORATORY ACTIVATION FIGURE 2. Sample patient electrocardiogram (ECG), illustrating automated Acute Coronary Ischemia Time-Insensitive Predictive Instrument (ACI-TIPI) calculation and printout. MI = myocardial infarction. physician. This difference can be characterized as the amount of time that could have been saved had the cardiac catheterization laboratory been activated immediately upon the paramedic’s STEMI alert to the ED. We also calculated a false-positive rate (proportion of patients incorrectly diagnosed with STEMI by paramedics, as judged by either the attending emergency physician or the responding interventional cardiologist) and compared it with a locally accepted false-positive rate of 10%. Our criterion standard for STEMI diagnosis was the diagnosis of both the attending emergency physician and the interventional FIGURE 3. Sample data-collection form. ED = emergency department; EMS = emergency medical services. 156 PREHOSPITAL EMERGENCY CARE cardiologist, as determined by review of the ED and inpatient charts. A sample size of 25 patients was planned, based on the assessment of our cardiologists that this would be an adequate number of patients to assess the potential time reduction and the false-positive rate. The institutional review boards (IRBs) of both of the PCI hospitals approved this research, and the requirement for written consent was waived by the IRBs for this observational study. Prehosp Emerg Care Downloaded from informahealthcare.com by 64.134.180.52 For personal use only. RESULTS Twelve patients were enrolled prior to early termination of the study. The time data are summarized in Table 1. The mean and median potential time reductions were 15 minutes (standard deviation 7.4 minutes) and 11 minutes (range 7–29 minutes), respectively. There was one incorrect STEMI alert (false-positive rate = 8.3%) for a patient with a right bundle branch block on p12ECG who was diagnosed with a non–ST-segment elevation myocardial infarction during his hospitalization. The study was terminated when our cardiologists adopted a prehospital catheterization laboratory activation protocol based on the review of the first five months of data, preventing further data collection. DISCUSSION There is much interest in implementing successful strategies for improving the care of STEMI patients and reducing the time to reperfusion therapy. The ACC/AHA has endorsed the concept that faster times to reperfusion therapy and better systems of care are associated with important reductions in morbidity and mortality in STEMI patients.3 The acquisition and interpretation of a prehospital ECG have been identified as an important step in reducing the transport time to a PCI center and in earlier activation of the catheterization laboratory.3,17 There is also much discussion regarding the visual transmission of p12ECG images from the field to the ED physician for review, but significant financial and technologic limitations currently limit widespread utilization of wireless image transmission. In this study, we observed important potential reductions in reperfusion time by EMS activation of the catheterization laboratory. Our findings of reductions up to 29 minutes, with mean and median time reductions of 15 and 11 minutes, respectively, correlate well with existing studies in the literature.18 We can translate our findings to clinical significance, particularly if we consider the time of day and EMS transport time of the cardiac catheterization laboratory activation. It is reasonable to conclude that prehospital activation will have more of an impact on nights and weekends when the PCI staff is called in from home. Currently, if APRIL/JUNE 2010 VOLUME 14 / NUMBER 2 a STEMI patient arrives during these off-hours, the patient is treated in the ED until cardiac catheterization resources are prepared to receive the patient. This process can take up to 30 minutes. However, if a prehospital activation precedes patient arrival, mobilization of the cardiac staff can occur simultaneously with the patient en route to maximize efficiency. Ideally, this could enable EMS to essentially transport the patient directly to the catheterization laboratory upon their arrival at the hospital. In general, it seems reasonable that rural areas with long transport times would benefit the most from earlier prehospital activation. Over the past several years at our institution, the median times to primary PCI have improved, and many are within the 90-minute benchmark. However, consistently there are patients with times between 100 and 115 minutes. We expect that implementing our protocol for prehospital activation will capture these patients falling just outside the 90-minute mark. Most importantly, decreasing the time to primary PCI will be beneficial to all STEMI patients, regardless of whether or not they fall within the 90-minute benchmark, because “time is myocardium.” The study was terminated after five months when our interventional cardiologists decided to adopt a prehospital catheterization laboratory activation protocol based on our data. While they had initially indicated that 25 patients would be needed to adequately assess the time benefits and false-positive rate, our first interim presentation of data was met with enthusiasm and a request to “start doing it.” Our false-positive rate (8.3%) was deemed appropriate when compared with our cardiologists’ locally accepted false-positive rate of 10%. Currently, a multidisciplinary protocol involving EMS, emergency medicine, and cardiology is being developed at our institution to refine our prehospital STEMI activation process. LIMITATIONS AND FUTURE RESEARCH The major limitation of this study is the small sample size. In our mid-sized system, accumulating enough prehospital STEMI patients who meet enrollment criteria to achieve statistical significance could take several years. Our cardiologists instead wanted to more quickly determine the feasibility of such a program prior to their commitment to changing the current STEMI care protocol. Although our numbers are small, the findings correlate well with existing studies in the literature. Most importantly, we believe that the immediate clinical benefit from this potential reduction in reperfusion time as we implement prehospital catheterization laboratory activation outweighs the years of data collection needed to achieve statistical significance. In addition to the promising results we found, we are greatly encouraged that this EMSdriven research study has helped to foster a mutually Lee et al. 157 PREHOSPITAL CATHETERIZATION LABORATORY ACTIVATION TABLE 1. Summary of Time Data (Hours:Minutes) Date (Mo/Day/Yr) Prehosp Emerg Care Downloaded from informahealthcare.com by 64.134.180.52 For personal use only. 7/13/08 7/27/08 8/4/08 9/2/08 9/10/08 9/27/08 9/28/08 9/29/08 10/25/08 11/12/08 11/13/08 12/1/08 STEMI Alert Time ED Arrival Time 17 : 28 21 : 47 20 : 01 22 : 30 16 : 13 23 : 53 19 : 24 11 : 27 14 : 38 10 : 43 1 : 29 17 : 21 17 : 34 21 : 57 20 : 04 22 : 52 16 : 15 0 : 00 19 : 28 11 : 33 14 : 45 10 : 44 1 : 34 17 : 44 Catheterization Laboratory Activation Time Patient Departure Time 17 : 35 21 : 58 18 : 02 22 : 24 22 : 52 16 : 35 0 : 06 19 : 35 11 : 35 15 : 00 10 : 52 1 : 40 17 : 50 23 : 11 17 : 20 0 : 25 20 : 08 11 : 50 15 : 12 11 : 18 2 : 02 17 : 59 Time Savings (STEMI Alert Time – Activation Time) 0:07 0:11 False positive 0:22 0:22 0:13 0:11 0:08 0:22 0:09 0:11 0:29 Range 7–29 minutes. Mean 15 minutes (SD ±7.4). Median 11 minutes. ED = emergency department; SD = standard deviation; STEMI = ST-segment elevation myocardial infarction. beneficial interdisciplinary collaboration between EMS, emergency medicine, and cardiology. Another limitation inherent in the collection of timedependent data involves ensuring the accuracy of the recorded times. Reasonable efforts were made to minimize the potential bias associated with this type of data collection in a busy ED. The triage nurse receiving the incoming EMS patch was the only person designated to record times on the data sheet. Additionally, there are three large synchronized clocks in the ED that are highly visible from each patient care area. Despite these precautions, it is difficult to ensure the complete accuracy of recorded times as the triage nurse often has multiple duties, particularly during a cardiac catheterization activation. However, the four time points on the data sheet are times that our nurses are required to record for nursing documentation, independent of our research project. In this way, it is our hope that the potential inaccuracies of time documentation were minimized. CONCLUSIONS Important reductions in time to primary PCI in STEMI patients may result from the use of a prehospital ECG and subsequent cardiac catheterization laboratory activation by paramedics in the field. The data from our study directly led to a significant change in clinical practice much earlier than we had anticipated, and demonstrate the significant value of research in fostering multidisciplinary cooperation. References 1. Cannon CP, Gibson CM, Lambrew CT, et al. Relationship of symptom-onset-to-balloon time and door-to-balloon time with mortality in patients undergoing angioplasty for acute myocardial infarction. JAMA. 2000;283:2941–7. 2. 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