Introduction

The capability for advanced cardiovascular life support (ACLS) crews to perform a 12-lead ECG in the prehospital setting has been expanding throughout healthcare worldwide over the past several decades. This has been helped along by several organizations including the American College of Cardiology Foundation (ACCF), American Heart Association Task Force (AHA), and the European Society of Cardiology (ESC). These have all released policies recommending that a 12-lead ECG per performed at the point of first medical contact (FMC) for patients with signs or symptoms consistent with acute ST-elevation myocardial infarction (STEMI).[1][2] This is defined as a 12-lead ECG that is performed by a paramedic on an ACLS unit that is either interpreted in the field or transmitted to a hospital emergency department or coronary care unit (CCU) for interpretation.

The ultimate goal of the prehospital ECG is to generate an early diagnosis of STEMI and ensure that the patient is managed appropriately given the location of the patient and the capability of local healthcare facilities. Preferably, patients should be transported to a percutaneous coronary intervention (PCI)-capable center with a goal of FMC of a definitive intervention in 90 minutes or less. This can mean bypassing closer, non-PCI capable hospitals. However, if it is impossible to reach FMC to a device in less than 120 minutes, the patient will require fibrinolytic therapy, if eligible. AHA and ACCF recommendations leave this decision to the discretion of the emergency medical service (EMS) providers to make it to a PCI-capable hospital promptly or to head to the nearest hospital for fibrinolytic therapy. Early fibrinolytic therapy has been shown beneficial in reducing morbidity and mortality in patients with acute STEMI who cannot reach a PCI-capable center. In the United States, this is primarily performed at rural, non-PCI-capable facilities. Several European countries including the United Kingdom have produced numerous studies showing that fibrinolytic therapy performed in the field, by a trained paramedic, with a physician or in conjunction with a physician at a nearby facility reviewing the prehospital ECG can be safe and significantly decrease reperfusion time in an acute STEMI. This is not widely adopted in the United States due to the lack of funding and training in rural areas where this would see the most benefit.[2]

Therefore, the prehospital, 12-lead ECG is an important tool that can be considered in triaging a patient with symptoms concerning for an acute STEMI and transport the patient either to the nearest non-PCI capable hospital, directly to a PCI-capable hospital, or directly to the nearest cardiac catheterization laboratory (CCL).

Issues of Concern

The main goal of the prehospital ECG is to identify a STEMI more quickly, leading to a more timely intervention in the appropriate candidates. Several studies have shown that decreased FMC-to-device times have improved morbidity and mortality. An effective way of decreasing the time to PCI is activating the cardiac catheterization lab from the prehospital setting and bypassing the emergency department in qualified facilities. This is a large undertaking for any health system, requiring an interprofessional effort between the EMS services, emergency department staff, interventional cardiologist, and the CCL staff.  There have been some reservations about “false positive” ECGs from the field. The fear is that there will be an unnecessary utilization of resources involved with activating the CCL, as well as the possible iatrogenic injuries and adverse outcomes associated with the procedure itself.[1][2]

Clinical Significance

Prehospital 12-lead ECGs can significantly reduce to time to definitive treatment for STEMI when performed on those with symptoms concerning for acute STEMI.

Patients who have an ECG performed prehospital may bypass a hospital without PCI capabilities to significantly reduce time to definitive intervention. One study with 344 patients demonstrated that a median door to balloon time was 69 minutes for those who had an ECG performed in the field, interpreted by paramedics, and taken directly to a PCI-capable facility. This compared to a median of a 123-minute door to balloon in patients referred from an emergency department physician at a non-PCI capable facility. This study also demonstrated that 80% versus 12% of patients met the 90-minute door-to-balloon time goal when first arriving at a non-PCI capable center.[3]

Patients who bypass the emergency department based on a prehospital ECG have significantly decreased FMC to reperfusion. This was demonstrated in a study by the American Heart Association with 12,581 STEMI patients. In this study, 10.5% of patients were able to bypass the emergency department based on a prehospital ECG and go directly to the CCL. These patients had a median FMC to definitive treatment of 68 minutes versus 88 minutes. While ideally, the 10.5% emergency department bypass rate would be higher, this study found the bypass rate significantly varied in different health systems depending on their resources, training, and system protocols. The study did demonstrate that the emergency department was more likely to be bypassed during the daytime when more staffing and resources are present in the hospital.[4]

Reduction in Mortality in STEMI Patients  

A study based on Britain’s Myocardial Ischemia National Audit Project (MINAP), 288,990 patients were documented to come to the Emergency Department between 2005 and 2009 by EMS and were ultimately admitted with a diagnosis of STEMI on NSTEMI.  Analysis showed that there was reduced 30-day mortality in patients who had a prehospital ECG performed at 8.6% versus 11.4%. A 30-day mortality reduction was also seen in patients with NSTEMI with a prehospital ECG at 5.9% versus 6.5%. Multiple studies have reproduced findings that decreasing time to reperfusion has a significant decrease in 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 a great deal from the health system to health system and from study to study with rates anywhere from 9% to over 50%. Over the past 2 decades, with an emphasis on increased FMC to reperfusion time, there appears to be an overall trend upward in false-positive activations. One retrospective study in Los Angeles showed that there was a 7.8% higher rate of false-positive activations from the prehospital setting. However, another study showed a 5% decrease in false-positive CCL activations with successful transmission of the ECG to the PCI-capable facility.[6][7][8]

A study with 485 patients, including 77 false-positive CLL activations, showed 7 cases of transient acute kidney injury without other major complications. This also showed that the hospital cost was relatively minor in false activation cases. The largest concern was a cardiac catheterization delaying 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 to triage patients with STEMI-like symptoms to enhance their transport to the appropriate facility, and ultimately, reperfusion. While some studies have shown that a prehospital ECG can cause a short delay from time on the scene to hospital arrival, the prehospital ECG ultimately enhances FMC to reperfusion greatly and has an associated mortality benefit. While there is concern about possible false-positive CCL activations, the overall benefits of the ECG outweigh issues from these activations.  This overall benefit leads to multiple interprofessional and international organizations promoting prehospital 12-lead ECGs. Health systems should work closely with their emergency departments, CCL team, interventional cardiologists, and EMS services to implement a program to screen patients with potential acute, STEMI-like symptoms with a prehospital 12-lead ECG.