By ANDREW P. MARDELL
Your medic unit responds to a 45-year-old man with 30 minutes of rapid onset chest pain. The patient has a history of hypertension but no previous history of myocardial infarction (MI). He is also taking ramipril.
You perform a 12-lead electrocardiogram (ECG), which demonstrates a three- to four-millimeter (mm) ST segment elevation in leads V1-V6 and no Q waves present (Figure 1). On examination, you find a regular pulse of 90 bpm, a blood pressure of 105/60 mm/hg, clear lungs, and normal heart sounds with no murmurs. You interpret the ECG as an impending anterior STEMI (ST-Elevation myocardial infarction) (anterior current of injury) and activate the catheterization laboratory en route to the hospital.
ECG Anterior ST Elevation Myocardial Infarction
On arrival, the patient goes directly to the catheterization laboratory. Coronary angiography demonstrates an occlusion to the proximal left anterior descending coronary artery, which is successfully treated with balloon angioplasty and stent deployment.
Prehospital EMS systems have three major components: emergency medical dispatch, public safety (fire/law enforcement), and EMS ambulance response.1Each of these operates within a broader emergency care system, which includes acute care facilities.
Early EMS access is promoted through the 911 system, available in most of the United States and Canada. Dispatchers have a variety of training, depending on location; this varies for minimal medical training from EMTs and paramedics to certified emergency medical dispatchers. Prearrival instructions are important to cardiac care outcomes.
Dispatchers can instruct bystanders to administer aspirin in suspected MI cases. Use other prescribed medications, such as nitroglycerine, for patients with unstable angina; perform cardiopulmonary resuscitation (CPR); and use an automated external defibrillator (AED), if one is available, while awaiting emergency personnel arrival.
To minimize time with lifesaving treatment, many communities have first response systems consisting of volunteer or paid firefighters and law enforcement officers capable of administering basic cardiac care, including oxygen, aspirin, CPR, and early defibrillation with AEDs, until EMS arrives. The goal is to get personnel and equipment to the patient’s side within five minutes of the call.
An EMS ambulance’s staffing range depends on geographic location in North America. Most urban and suburban ambulances are staffed with paid or volunteer firefighters, third-service EMS, and private- or hospital-based and volunteer rescue squad personnel. Ambulances may be staffed and equipped at the basic life support level (EMT) or by paramedics and intermediate-level EMTs. A minority of systems provide only advanced life support ambulance service.
Approximately four to five percent of EMS patients with chest pains are having an acute STEMI.2Prehospital 12-lead ECG acquisitions are critical for determining which chest pain patients need transport to a percutaneous coronary intervention (PCI)-capable facility.3-6In a recent survey of EMS systems serving the 200 largest United States cities, 84 percent of EMS systems reported that 12-lead ECGs were “available” in their system.7However, the National Registry of Myocardial Infarction reported a prehospital 12-lead ECG was recorded in less than 10 percent of STEMI patients.8-9
Traditionally, most community-based protocols direct EMS teams to bring chest pain patients to the nearest hospital, presuming that most hospitals provide fibrinolysis if the patient has a STEMI. The increasing primary PCI reperfusion strategy use is prompting many communities to bypass the closest facility in favor of the nearest primary PCI-capable and -available hospital.
Prehospital-initiated fibrinolysis was explored because of a demonstrated benefit in starting fibrinolytic therapy as early as possible after the onset of STEMI symptoms.10A meta-analysis of prehospital-initiated fibrinolytic trials suggests that there is a 17-percent relative improvement in outcome associated with prehospital (vs. ED) fibrinolysis.11Most of these trials were conducted in Europe, where physicians staff ambulances.
The Myocardial Infarction Triage and Intervention study in Seattle, Washington, failed to demonstrate a statistically significant overall mortality benefit for prehospital vs. ED fibrinolysis. Although there are isolated areas in the United States and Canada that have instituted prehospital fibrinolytic programs,12-13the strategy has not been widely instituted, most likely because of high costs, difficulty in maintaining paramedic skills for an infrequently used treatment, short transport times, and potential litigation from complications if fibrinolysis is administered to a patient who does not need it.14-15
The American College of Cardiology/American Heart Association (AHA) STEMI guidelines do not support prehospital fibrinolytic therapy. However, they do support prehospital fibrinolysis in special settings where physicians are present in the ambulance or transport times are less than 60 minutes in high-volume EMS systems. (2)
A recent AHA-released scientific statement on the “Implementation and Integration of Prehospital ECGs into Systems for Acute Coronary Syndrome” may cause you to review the handling of patients presenting with STEMI.16Despite national guidelines and consensus statements recommending the use of prehospital ECGs to evaluate patients with suspected acute coronary syndrome, fewer than 10 percent of STEMI patients receive an ECG. (8)17
The primary reason to perform an ECG is to determine if coronary blood flow is at risk to advance the timeliest solution of coronary reperfusion. Many times the acquisition of prehospital ECGs does not contribute to increased reperfusion time because of insufficient coordination with receiving hospitals.
Multiple studies show that decreased door-to-drug and door-to-balloon times benefit patients by decreasing morbidity and mortality. (8,16,17)18Prehospital ECGs can also decrease revascularization time by 10 to 20 minutes. (8,17) Further reductions in door-to-balloon time are realized when prehospital ECGs are used to activate the catheterization laboratory while the patient is en route to the hospital.19-20
According to the AHA, time from symptom onset to reperfusion is measured in four time intervals (for patients transported by EMS): symptom onset to EMS arrival, EMS arrival to hospital arrival, hospital arrival to ECG, and ECG to reperfusion. With effective coordination of prehospital ECG implementation and coordination, a decrease in the latter three time intervals would be recognized (Figure 2). A STEMI diagnosis might cause EMS personnel to behave with more urgency, thus lessening the second interval. A prehospital ECG essentially eliminates the third time interval. Decrease the fourth interval or time to reperfusion in hospital by early/advanced catheterization laboratory activation.
Ting, H. H. et al. Circulation 2008;118:1066-1079
In a recent study, Scholz et al., reported on the effect of time intervals and prehospital ECG collection from 114 STEMI patients in an integrated system of care.21Emergency responders collected prehospital ECGs and faxed them to the cardiac intensive care unit of the nearest PCI-capable facility, activating the catheterization laboratory en route if STEMI was diagnosed, bypassing the emergency department when the catheterization laboratory team was on-site. The results, compared with a control group (performance for one quarter before protocol was implemented), showed that the time spent on-scene decreased from 25 to 19 minutes, the time spent in the ED decreased from 14 to three minutes, the time from arterial access to balloon decreased from 21 to 11 minutes, door-to-balloon time decreased from 54 to 26 minutes, and first medical contact to balloon time decreased from 113 to 74 minutes.
Collaboration, quarterly review, and feedback of all cases by cardiology, ED, and EMS stakeholders were important components in improving prehospital and hospital care systems (Figure 3).
Current vs. ideal processes to integrate prehospital ECGs into systems of care.
EMS providers can rapidly acquire diagnostic prehospital ECGs with an average increase of five to six minutes in the on-scene time interval.22A recent survey found that 90 percent of EMS systems serving the 200 largest United States cities had 12-lead ECG equipment available in their ambulance systems. (7) Studies show that despite increased on-scene times, there is no prolongation of interval 2 (EMS arrival to hospital arrival). (17) This may be related to selection biasi.e., patients with longer transport distances to the receiving facility might have received a higher rate of prehospital ECGs when compared with shorter transport distances.
The feasibility of prehospital ECG interpretation identifying STEMI, with or without wireless telemetry, has been undertaken. Options may be limited by a specific resource available in the community or local geography. The pros and cons for three modelscomputer algorithm interpretation, paramedic interpretation and wireless transmission, and physician interpretationare outlined in Table 1.
Reperfusion time goals for patients with ST-segment-elevation myocardial infarction.
Paramedics with specific ECG training can reliably interpret prehospital ECGs without transmitting to a hospital or physician. Trained paramedics can identify STEMI with sensitivity of 71 to 97 percent and specificity ranging from 91 percent to 100 percent, with good agreement between paramedics and ED physicians.
Prehospital ECG acquisition has historically been limited to paramedics. The initial draft revision (released June 2007) of the national standard curricula for EMS includes 12-lead ECG interpretations as a required competency for paramedics.23
There are various models of integrating prehospital ECGs, including paramedic interpretation (seen in Boston, Ottawa, and Calgary),24-27computer algorithm interpretations (Los Angeles County),28and wireless transmission and physician interpretation. There are no data to compare the effectiveness of these different approaches for diagnostic accuracy or quality of reperfusion therapy delivered to STEMI patients.
It has been proposed that prehospital ECG acquisition be extended to EMT-basic and EMT-intermediate levels. (1) A preliminary study showed that EMT-basic personnel could acquire, but not interpret, ECGs in a comparable amount of time compared with paramedics.29This requires significant changes in training and protocol revision.
Prehospital ECG programs can potentially improve quality of care and affect STEMI patients’ morbidity by decreased door-to-balloon (or pain onset to balloon) time. Although guidelines direct prehospital personnel to acquire 12-lead ECGs, (2) the primary challenge uses and integrates the diagnostic information from a prehospital ECG into the system of emergency cardiac care. This being the challenge, there are still many issues to overcome in meaningfully adopting nationwide prehospital ECG acquisition.
Logistics include increased patient use of EMS; increased EMS capacity; improved education and quality assurance for EMS providers; improved collaboration among EMS, emergency departments, and cardiology; and improved regional hospital network coordination to provide the ideal patient care rather than optimize market share. (16)
There are also financial barriers, including reimbursement and cost-effectiveness, of this diagnostic technology. Technology is evolving to allow new and innovative means of sending prehospital ECGs. One proposal uses camera phones with multimedia messaging service, which obtains a digital picture of the prehospital ECG paper printout and wirelessly transmits it to an e-mail account, which is then retrieved and viewed on a device such as a computer or smartphone.30
Implementation barriers are not insurmountable as new and less expensive technology becomes available and with ongoing collaboration among stakeholders from patient to cardiologist. The AHA has taken a lead in prehospital ECG implementation with “Mission: Lifeline,” a national initiative launched in 2007 to improve systems of care for STEMI patients.31
Effective measurement and integration of prehospital 12-lead ECGs must be addressed when assessing prehospital ECG use in your system. How does your service use and integrate 12-lead ECGs to reduce onset of pain-to-balloon times? How can you improve this time when caring for your patients?
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2. Antman, EM; Anbe, DT; Armstrong, PW; et al. American College of Cardiology/American Heart Association Task Force on Practice Guidelines; Canadian Cardiovascular Society. “ACC/AHA guidelines for the management of patients with STelevation myocardial infarction: A report of the ACC/AHA Task Force on Practice Guidelines” (Committee to Revise the 1999 Guidelines for the Management of Patients with Acute Myocardial Infarction). Circulation. 2004; 110:e82-e292.
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30. Scholz, KH; Hilgers, R; Ahlersmann, D; et al. “Contact-to-balloon time and door-to-balloon time after initiation of a formalized data feedback in patients with acute ST-elevation myocardial infarction.” Am J Cardiol.2008;101:46-52.
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ANDREW P. MARDELL, RN, BSCNN, CNCC(C), is a firefighter with the Rocky View Fire Service in Calgary, Alberta, Canada. He is also a nurse clinician in cardiac electrophysiology at Foothills Medical Centre in Calgary. He has worked in critical care, emergency, trauma, and air medical services and is actively involved as an educator for Canadian firefighters, paramedics, nurses, and physicians.