perform 12‐lead ECGs broadly (e.g., everyone over the age of 30 with any of the following characteristics: chest pain, shortness of breath, abdominal pain, diabetes, or cardiac history), the prevalence of actual STEMI is between 0.5% and 5%. The positive predictive value of a “STEMI positive” prehospital 12‐lead ECG may approximate 50% [57]. Such an approach could result in more false positive than true positive activations of the PCI team.
When patients have a reasonable likelihood of STEMI based on their clinical presentations and 12‐lead ECG findings, prehospital cardiac catheterization PCI team activation has consistently been shown to shorten the time to definitive treatment. For example, Nestler et al. showed that prehospital activation of the catheterization laboratory reduced the median door‐to‐balloon times from 59 to 32 minutes [58]. Cone et al. found that field activation of the catheterization laboratory was associated with 37‐ and 35‐minute shorter door‐to‐balloon times than ED activation for walk‐in STEMI patients or STEMI patients arriving by EMS without field activation, respectively [59]. In addition, field activation of the catheterization laboratory was associated with improved performance relative to 90‐minute STEMI treatment benchmarks. Finally, Horvath et al. found similar reductions in the door‐to‐balloon times (44 vs. 57 minutes) in EMS‐transported STEMI patients who had prehospital activation of the cardiac catheterization laboratory compared to those who had the laboratory activated after ED arrival [60].
Field activation of the cardiac catheterization laboratory when a prehospital ECG shows evidence of STEMI is strongly supported by published data. However, in one published study of 27,840 patients with STEMI, where field activation could have occurred, only 41% of the time did field activation happen [61]. EMS systems should work with their PCI‐capable hospitals to establish and promote cardiac catheterization laboratory prehospital STEMI activation protocols and quality improvement monitoring.
EMS transport
Despite the benefits of EMS for chest pain patients, many patients misinterpret their symptoms, delay calling EMS, or use personal transportation to go to the hospital. Public education campaigns have not shortened the overall time interval from symptom onset to hospital arrival, but they have increased the proportion of ACS patients who use EMS [62].
Destination protocols
Almost 80% of the adult population of the United States lives within 60 driving minutes of a PCI‐capable center [63]. Of those patients whose closest hospital is not capable of PCI, 74% require additional transport time of less than 30 minutes to reach a PCI‐capable institution. Many states and communities have developed protocols to facilitate EMS transport of STEMI patients directly to hospitals with 24/7 capability to perform PCI. In a study of 19,287 patients, comparing states that allowed EMS to bypass closer non–PCI‐capable institutions and transport directly to a PCI‐capable institution, it was found that in bypass‐approved states, 57% of people exhibiting myocardial infarction received PCI in <90 minutes and 82% underwent PCI within 120 minutes of EMS contact. In states with no bypass policies, only 45% of people received PCI within 90 minutes and 77% within 120 minutes [64]. In Ottawa, a STEMI bypass protocol for EMS was implemented in May 2005 [65]. Paramedics performed a 12‐lead ECG, and if STEMI was identified in a hemodynamically stable patient, the patient was transported directly to the region’s single cardiac center catheterization laboratory with prehospital notification of the impending arrival of the STEMI patient. To do so, EMS often bypassed one of the four other EDs in the city. The median first door‐to‐balloon time was 69 minutes for patients brought to the catheterization laboratory directly by EMS, compared with 123 minutes for those needing interhospital transfer. In the Netherlands, prehospital identification of patients with STEMI and transport to a PCI‐capable center, bypassing other EDs, was associated with improved left ventricular function [66].
Some systems are directing EMS to take STEMI patients directly to the heart catheterization lab, bypassing the ED. The strategy reduces door‐to‐balloon time up to 60 minutes [67]. In rural settings without available PCI centers, coordinated programs with regional STEMI receiving centers can achieve remarkable door‐to‐balloon times, even when measuring from the first door (i.e., the door of the rural ED). Two reports from Minnesota show that excellent treatment times can be achieved. In the Minneapolis area, the median first door‐to‐balloon time was 95 minutes if the referring hospital was less than 60 miles from the PCI center and 120 minutes if the referring hospital was farther away [68]. In the Mayo Clinic STEMI system, patients were transferred from 28 regional hospitals up to 150 miles away from the PCI center. The median first door‐to‐balloon time for the transferred patients was 116 minutes [69].
Air medical evacuation of STEMI patients
A key to a successful regional STEMI system is ready access to air medical transport. Rapid patient transport by highly skilled teams available in medical helicopters can save significant time from the first door‐to‐balloon. Some air medical programs are working closely with referring hospitals and ground EMS systems to dispatch helicopters before arrival of a STEMI patient at a referring hospital [70]. In terms of quality improvement, a recent national assessment of quality programs in EMS showed that air medical agencies are more likely to track quality measures compared to fire‐based agencies [71].
Expanding the role of basic life support (BLS) clinicians
Many 9‐1‐1 prearrival instructions already direct callers to take aspirin if they have chest pain. Allowing BLS clinicians to administer aspirin, if not contraindicated and if permitted by EMS laws and regulations, seems the next logical step. One reason stated for the lack of aspirin administration to eligible ACS patients is the inability of BLS clinicians to administer it based on local protocols or regulations [72].
BLS clinicians can be taught to acquire and transmit 12‐lead ECGs. This approach may be particularly beneficial in rural areas, with scant ALS coverage and long transport times to definitive care. Using the 12‐lead ECG to triage STEMI patients to air transport from the scene may lead to improved cardiac care in rural areas and more efficient use of available resources [73].
Other common causes of chest discomfort
Although most of the available prehospital interventions for chest pain are focused on the identification and treatment of ischemic cardiac disease, the majority of EMS chest pain patients will have other causes for their symptoms, some of which are also immediate threats to life (Box 9.3). A chest pain protocol should focus on treatments that may benefit the ACS/STEMI patient while considering the effects of these treatments on other causes of chest pain.
Box 9.3 Causes of chest discomfort that are immediate life threats
Acute coronary syndrome
Pericardial tamponade
Pulmonary embolism
Tension pneumothorax
Thoracic aortic dissection
Aortic dissection
Acute aortic dissection classically causes sudden pain in the chest, sometimes radiating to the back. The dissection is caused by a tear in the intimal lining of the aorta with entry of high‐pressure blood into the wall of the aorta. The dissection propagates distally and sometimes proximally. If the dissection extends around the origin of a peripheral artery, then that vessel can be partially or completely occluded, creating a >15‐ to 20‐mmHg difference in blood pressures between patient arms. If the origin of a carotid or vertebral artery is occluded, then the patient may develop neurologic signs suggesting a stroke. Occlusion of a spinal artery from the aorta can cause acute paralysis of both legs. Most patients with dissection have long‐standing hypertension, but the problem can occur in