Rapid rule out of MI in the Emergency Department: a politically inconvenient innovation?
Chest pain: there’s a lot of it about
Chest pain accounts for 6% of all Emergency Department (ED) attendances in England and Wales, representing approximately 700,000 visits annually1, a figure that continues to increase2. A 2011 study showed that although 80% of chest pain patients were admitted to hospital, less than 25% eventually received a diagnosis of myocardial infarction (MI)3. Traditionally, patients with chest pain have been risk-stratified using initial history and examination, followed by 12-lead electrocardiogram (ECG). Those with ST-elevation myocardial infarction (STEMI) were referred for immediate percutaneous revascularisation. Those without obvious ST-elevation underwent troponin testing at presentation and again after 12 hours, to further stratify into a cohort of non-ST elevation MI (NSTEMI) versus unstable angina (UA): known collective as acute coronary syndrome (ACS). These patients were typically admitted from the ED under the medical or cardiology team, not only to facilitate the 12-hour Troponin sampling but also for further risk stratification. As we now know, the traditional Troponin T and I assays, although relatively specific for MI, were not particularly sensitive (roughly 70-80%4) with the potential for early falsely reassuring results. This further emphasised the need for admission and repeat sampling to identify a potential late rise in the biomarker. Our understanding of its limitations led us to label patients with other markers of risk – such as a raised GRACE5 or TIMI6 score – as high-risk patients potentially requiring urgent intervention, even with an unremarkable serum troponin level.
The death of ‘unstable angina’
Patients with high-risk features as defined by GRACE or TIMI (such as ongoing pain, biochemical abnormalities or surrogate markers of ischaemia or heart failure) represented a cohort of patients with a poor prognosis5–7, even in the absence of a raised troponin level. We, as a specialty – as we didn’t want these patients to be missed – emphasised the importance of holistic patient assessment and not to rely on the troponin level as the single arbiter for diagnosis and management.
Further developments in biomarker technology, with the advent of high-sensitivity troponin assays, have shifted the landscape. The high-sensitivity assay is almost 100% sensitive (with use of appropriate cut-off values, timing and with slight variations between assays) for diagnosing MI8. The cohort of patients who may have previously been diagnosed as high-risk UA are likely to demonstrate a raised high-sensitivity troponin and thus be correctly diagnosed and managed as for MI. We now know that those with a normal high-sensitivity troponin do very well9,10, so those high-risk, poor-prognosis patients previously labelled as UA probably just reflected the inadequacies in our previous generation of troponin testing. The diagnosis of UA therefore, arguably has little utility in risk stratifying today’s patients.
Negative troponin as a reliable rule-out
Due to the significant burden of chest pain on emergency care services in the UK and elsewhere, there has been considerable interest in developing a single test, available acutely, to safely discharge patients in such settings.
Two recent landmark studies9,10 trialled the use of a single negative high-sensitivity troponin value as a tool to safely discharge patients with a suspected ACS directly from the ED. They both found that, using a low cut-off value for the assays, a single negative troponin value at presentation is associated with an extremely high negative predictive value of >99.6% for MI and that with a normal value, a discharged patient is likely to have an excellent outcome up to one year. Using this strategy, between one- to two-thirds of all chest pain presentations can be safely discharged directly from the ED. The troponin value must be interpreted in the clinical context and an abnormal ECG, unstable symptoms or signs must also be taken into consideration, as confirmed by a recent validation study11.
Conflicting priorities in the Emergency Department
The National Health Service (NHS) in England and Wales is under unprecedented pressure to find hospital beds, partly fuelled by recent cuts to social care funding12. The number of patients ready to be discharged medically but still occupy a medical bed has increased markedly by 15% over the past year13. These so-called ‘delayed transfers of are’ are a key driver for high bed-occupancy rates within hospitals. The news that we may now be able to discharge up to two-thirds of all chest pain patients from the ED, after a history, examination and single blood test, is a significant development for those who work at the coalface in emergency and acute medical areas. This should have significant downstream benefits in the form of reduced admissions to medical and cardiology bed-bases.
However, EDs are subject to intense performance monitoring, and the ED 4-hour target (<4 hours from patient presentation to discharge or transfer) is a key metric by which NHS Trusts are measured and accordingly rewarded or penalised. As a result, this culture permeates down to the clinical level where there is a strong emphasis on rapid decision-making. Studies of this target showed that initially, it did improve the speed with which patients were moved through the emergency setting, although with a majority of patients admitted in the 30-60 minutes before breaching14 and with reports of inappropriate patient transfers and even threats to patient safety and a culture of bullying in imposing these targets15,16. While there were without doubt improvements to the patient experience and reduced waiting times in ED as a result of this target, with increasing pressure came reduced time for patient-doctor interaction in the ED and a reduced sense of patient ownership17,18. Due to intense pressure to meet these targets, medical admission has been seen by some as a “route of least resistance” with less likelihood of the patient breaching than if they were fully worked up and discharged directly from the ED19,20.
Chest pain – new tools, new decisions
Previously, patients presenting with chest pain often represented a relatively straightforward cohort of patients who, if suspected for an ACS, would warrant automatic admission. The advent of high-sensitivity troponin now permits the risk-stratification, decision-making and discharge of these patients from the ED rather than downstream under medical or cardiology teams. While an opportunity for improved patient care and reduced unnecessary admissions, EDs in England and Wales are under unprecedented pressure with dramatic recent increases in the total number of ED attendances as well as 4-hour target breaches21,22. Coupled with staffing issues21 and a rise in temporary or locum staff, emergency physicians may feel they have neither the time nor the training to take such decisions, for fear of making mistakes or adding time onto the patient’s journey within the ED.
A need for clinical leadership and interdepartmental cooperation
The rapid recent advances in high-sensitivity troponin testing allow an exciting opportunity for rapid assessment and discharge of low-risk chest pain patients from the ED, potentially with a single presentation blood test. In order to harness such innovations we must ensure our emergency physician colleagues are adequately resourced to implement this. The presence of chest pain nurses within the ED and other training provided by cardiology departments will promote the uptake of this new approach, with likely benefits for patients and professionals alike.
Conflict of interest: I perform medical registrar on-call shifts and receive a high volume of referrals for low-risk chest pain. No funding sources to declare.
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