EMS Utilization Of Electrocardiogram In The Field

Issues of Concern

The main goal of the prehospital ECG is to identify STEMI more quickly, leading to timelier intervention in appropriate candidates. Results from several studies showed that decreased FMC-to-device times were associated with lower morbidity and mortality. An effective way to reduce time to PCI is to activate the cardiac catheterization laboratory from the prehospital setting and bypass the emergency department at qualified facilities. Implementing this strategy is a large undertaking for any health system, requiring an interprofessional effort between the EMS services, emergency department staff, interventional cardiologists, and CCL staff. Some clinicians have expressed reservations about false-positive ECG findings from the field. The concern is that unnecessary use of resources may occur with activating the CCL, along with possible iatrogenic injuries and adverse outcomes associated with the procedure itself.[1][2]

Clinical Significance

Prehospital 12-lead ECGs can significantly reduce the time to definitive treatment for STEMI when performed in patients with symptoms concerning for acute STEMI. Patients with a prehospital ECG may bypass a hospital without PCI capabilities to significantly reduce time to definitive intervention. Results from one study of 344 patients showed that the median door-to-balloon time was 69 min for patients who had an ECG performed in the field, interpreted by paramedics, and were transported directly to a PCI-capable facility. This finding compared with a median door-to-balloon time of 123 min in patients referred from an emergency department clinician at a non–PCI-capable facility. Results from this study also demonstrated that 80% versus 12% of patients met the 90-min door-to-balloon time goal upon arrival at a non–PCI-capable center.[3]

Patients who bypass the emergency department based on prehospital ECG findings have significantly decreased FMC-to-reperfusion time. Results from an American Heart Association study of 12,581 patients with STEMI showed that 10.5% were able to bypass the emergency department based on prehospital ECG findings and go directly to the CCL. These patients had a median FMC-to-definitive treatment time of 68 min versus 88 min. Although the 10.5% emergency department bypass rate would ideally be higher, this study found that the bypass rate varied significantly across health systems depending on their resources, training, and system protocols. Results from the study demonstrated that the emergency department was more likely to be bypassed during the daytime, when staffing and resources were higher in the hospital.[4]

Reduction in Mortality in Patients With STEMI

Results from a study based on Britain’s Myocardial Ischemia National Audit Project documented that 288,990 patients presented to the emergency department between 2005 and 2009 by EMS and were ultimately admitted with a diagnosis of STEMI or non-STEMI. Analysis showed reduced 30-day mortality among patients with a prehospital ECG compared with those without (8.6% versus 11.4%). A 30-day mortality reduction was also seen in patients with non-STEMI who had a prehospital ECG compared with those who did not (5.9% versus 6.5%). Results from multiple studies reproduced findings that decreasing time to reperfusion significantly decreases mortality.[1][2][5]

Concern for increased false-positive CCL activation with prehospital 12-lead ECGs used for diagnosis: False-positive CCL activations have been a controversial topic. A true false-positive rate is difficult to obtain because it varies substantially across health systems and studies, with rates ranging from 9% to more than 50%. Over the past 2 decades, with an emphasis on increased FMC-to-reperfusion time, an overall upward trend appears to have occurred in false-positive activations. Results from one retrospective study in Los Angeles showed a 7.8% higher rate of false-positive activations from the prehospital setting. However, results from another study showed a 5% decrease in false-positive CCL activations when ECG transmission to the PCI-capable facility was successful.[6][7][8]

Results from a study of 485 patients, including 77 false-positive CCL activations, showed 7 patients with transient acute kidney injury without other major complications. Findings also showed that hospital costs were relatively minor in false-activation cases. The largest concern was that cardiac catheterization could delay the diagnosis and treatment of another potentially life-threatening pathology, such as pulmonary embolism or aortic dissection.

Summary

A prehospital ECG is an effective tool for triaging patients with STEMI-like symptoms, enhancing transport to the appropriate facility and, ultimately, reperfusion. Although some studies have shown that a prehospital ECG can cause a brief delay from time on scene to hospital arrival, the prehospital ECG ultimately significantly reduces FMC-to-reperfusion time and is associated with a mortality benefit. Although concerns exist about possible false-positive CCL activations, the overall benefits of ECG use outweigh the issues posed by these activations. This overall benefit has led multiple interprofessional and international organizations to promote prehospital 12-lead ECGs. Health systems should work closely with their emergency departments, CCL teams, interventional cardiologists, and EMS services to implement a program to screen patients with potential acute, STEMI-like symptoms with a prehospital 12-lead ECG.