Troponin POCT in the emergency cardiac pathway

Time to treatment is crucial in acute events when patients present with chest pain and other symptoms of cardiovascular disease (CVD). They need to receive fast and effective care. 

 

Yet, we recognise that a quick and definitive means of ruling in acute myocardial infarction (AMI) is still an area needing improvement. 

 

In England and Wales, acute chest pain is responsible for around 700,000 emergency department attendances and 350,000 emergency admissions per year. Of these, approximately 114,000 people in the UK alone are admitted to hospital with an acute coronary syndrome (ACS) each year. Most cases occur in people aged over 50 and risk rises with age. The challenge for today’s cardiologist or emergency physician is to deliver the best diagnosis and treatment in a short period of time. 

 

Having access as quickly as possible to clinically significant information is therefore critical to effective and safe patient management. When the diagnosis is clear-cut, treatment is straightforward, ‘time is muscle’. However, diagnosis is not clear in the majority of people who present with chest pain. If we had the tools to rule in or rule out ACS more quickly, patients can be more quickly prioritised for treatment or safely discharged or referred back to their GP. 

 

Need to integrate point-of-care testing (POCT) into acute care pathways

In vitro diagnostics at the point of care could potentially address the lack of timely diagnostic information, leading to an overall improvement in the quality of patient care and levels of satisfaction with their treatment. It also offers the means of improving operational efficiency, reducing overcrowding and the length of stay in acute care. However, to realise the full potential of POCT, it must be integrated into hospital procedures and may involve fundamental changes to clinical pathways and services. Further, new guidelines are needed for determining what constitutes a clinically relevant POCT system within the emergency care pathway. 

 

Existing studies into the effectiveness of point of care support this view. They indicate that a fundamental review and reengineering of operational processes within the emergency department would be required to take full advantage of the rapid availability of results that POCT makes possible.¹ This demands the type of workflow improvement analysis that hospital laboratories worldwide are already expected to carry out to meet current workload demands (Figure 1).

 

The guiding principle underlying POCT measurement must be to reduce turnaround time without compromising the quality of information on which clinical decisions for patients are based. Initiatives that could potentially reduce the length of stay are of considerable clinical interest. 

 

This article looks at evidence for the integration of POCT into the emergency cardiac pathway, discusses its benefits, and suggests benchmarks for realising its potential. It focuses on the role of the measurement of the cardiac biomarker troponin but also indicates the potential role for other acute care markers such as BNP. 

 

Fig. 1: POCT workflow improvement.

 

Differentiating ACS from other causes of chest pain

It can sometimes be difficult to distinguish between ACS and other causes of chest pain. The pain may be similar to a bout of stable angina, but it is usually more severe, lasting longer than 15 minutes – sometimes for several hours.

 

Alongside knowing a patient’s medication, comorbidities, family history, previous test results, we look to the severity and nature of the symptoms being presented. Is the patient reporting heavy pain-like pressure onto the chest, does the pain travel up into the jaw and down the left or both arms? Is the patient sweating, feeling nauseous and faint, with shortness of breath?

 

However, some people with ACS may not have any chest pain, particularly those who are elderly or those who have diabetes. And symptoms of ACS in women often differ from those in men, which may lead to misdiagnosis. Several studies²   have shown that, compared with men, women were more likely to have absence of chest pain or discomfort with ACS. Women with ACS are also more likely than men to have middle or upper back pain, neck pain, jaw pain, shortness of breath, paroxysmal nocturnal dyspnoea, nausea or vomiting, indigestion, loss of appetite, weakness or fatigue, cough, dizziness, and palpitations.

 

Reduce turnaround time without compromising quality of care

Cardiac biomarker measurement currently addresses two key questions in patient management. The first is the differential diagnosis of chest pain, in particular, is the chest pain caused by an AMI? The second question is the differential diagnosis of the patient with breathlessness, and we need to identity if the patient has heart failure requiring a different treatment protocol.

 

From a cardiology perspective, having access to troponin test results at the point of care shows significant potential in the emergency care pathway. The management of patients presenting with chest pain takes up a significant amount of emergency care resources and remains challenging. Therefore, the introduction of POCT for cardiac troponin has the potential to reduce turnaround time (TAT) for assay results, compared with central laboratory testing, and make better use of hospital resources.

 

With patient care and the quality of the patient experience already under pressure from escalating healthcare costs, there are ethical as well as financial imperatives encouraging us to explore new pathways. Bringing in vitro diagnostics to the acute care cardiac patient is potentially one of these key solutions. 

 

Defining new diagnostic pathways

In the initial assessment of a patient presenting with acute chest pain and other clinical symptoms, an ECG showing consistent ST-elevation leads to their immediate transfer to the catheterisation lab. However we know that the majority of patients with suspected ACS do not present with such a clear diagnosis on the ECG. In the case of these patients, non-ST elevation myocardial infarction (NSTEMI) is suspected and different diagnostic protocols are required.³

 

It still takes the centralised hospital laboratory 60 minutes (or more) to provide troponin blood test results. This delay presents the opportunity for new diagnostic pathways to be defined incorporating POCT. On-the-spot access to POC tests, which reliably measure troponin levels for a patient suffering acute chest pain would lead to faster diagnosis and improved patient outcomes. 

 

A new pathway offering the potential of a faster rule-in for NSTEMI would enable treatment to be safely started more quickly. For less urgent patients where we are waiting for blood tests to help us rule out NSTEMI, we can significantly reduce their waiting time and, at the same time, reduce the overcrowding this causes. The availability of a sensitive and accurate POCT of their blood cardiac marker levels would allow us to reduce the standard six-hour requirement to a safe three-hour rule-out protocol, and possibly even less.

 

Current recommendations identify the importance of cardiac biomarker measurement, primarily troponin, in the differential diagnosis of both acute chest pain and unstable angina when a patient presents at the emergency department. In fact, studies⁵  confirm that troponin alone, rather than a panel of cardiac markers, is sufficient for an accurate diagnosis. Troponin, therefore, remains the gold standard blood test and is clinically significant when ruling in or ruling out ACS. 

 

Measurement performance of troponin POCT

Although some POC cardiac troponin tests may be less sensitive than cardiac troponin tests developed for the automated laboratory, numerous studies have shown their effectiveness within accelerated protocols for ruling out acute coronary syndromes, without increasing subsequent re-admission for ACS.⁶ The Randomised Assessment of Treatment using Panel Assay of Cardiac Markers (RATPAC) study, published in 2012, was the first of several recent studies investigating POCT and how its performance in emergency cardiac care compared with the hospital laboratory.⁵

 

The main RATPAC trial demonstrated that POCT allowed for safe and accurate diagnosis, with no difference in the number of adverse outcomes between patients randomly assigned to conventional lab testing or to POCT.⁵ In addition, a sub study assessed the diagnostic measurement performance of troponin and whether this was dependent on the marker being used within a point- of-care panel of cytoplasmic markers, such as myoglobin or the MB isoenzyme of creatine kinase (CK-MB), or was effective in its own right. This confirmed that troponin measurement alone by POCT was sufficient and that additional markers made no clinically significant difference.  

Fig. 2: Triage and management of patients in the emergency pathway. Reproduced from Hamm et al., with the permission of Oxford University Press.⁴

 

Lab2Go study assesses analytical performance of POCT system

The European Union is currently funding the Lab2Go project, a multicentre study into the clinical effectiveness of POCT, which is set to report its findings next year. From the UK, Sheffield Teaching Hospitals NHS Foundation Trust and St George’s University Hospitals NHS Foundation Trust are taking part − with St George’s providing analytical expertise while the team at Sheffield provide clinical patient recruitment. The other participants are Stichting Catharina Ziekenhuis Eindhoven, Hôpital de la Pitié-Salpêtrière Paris, Medizinische Universitaet Innsbruck and Klinikum Nürnberg), Philips and industrial partners Conworx Technology GmbH, MicroSystems (UK) Limited and Scienion AG.

 

Started in 2014, Lab2Go was designed to assess the analytical performance of POCT in the emergency department and its ability to speed up identifying patients at high risk of acute cardiac events.  The POCT system under investigation offers the potential of lab comparable results of the cardiac marker troponin I within 10 minutes, from a minimal quantity of blood.

 

If changes to emergency clinical pathways are required for the full integration of POCT, then what are the benchmarks for determining the future use of POCT in the hospital? The Lab2Go study defines system usability and analytical performance as critical to success. It takes into account the need for built in quality control, as well as confidence in making clinically significant diagnostic decisions based on results from just a drop of blood. We are also investigating how easy a POCT system is to use by staff outside the lab, including paramedics, noting that acceptance comes more quickly when the concept of transferring a minimal amount of blood to the cartridge is better understood.  A POCT platform that has the flexibility of delivering its result from either a droplet of blood directly loaded from a finger prick or a venous sample tube, if protocols still require this, would therefore be an advantage. 

 

Reducing the time between ordering a test and when those results are actually reviewed in the ED may well be one of the critical factors in determining the impact of point of care on the overall length of stay.  There is a limit to further improvement of laboratory processes. Solutions to improving TAT need to come from a collaborative and integrated approach including implementing new strategies before samples reach the laboratory and downstream review of results. A 2012 UK study into hospital lab turnaround times showed their impact on patient throughput delays in the ED.⁷ Its overall conclusion was that the length of stay was directly dependent on the willingness to adapt the care pathway to capitalise on the faster turnaround time delivered by POCT.

 

Guidelines for POCT initiatives

If clinical pathways within the emergency department start to reorganise to take into account the impact of troponin testing, the potential for other cardiac markers (such as BNP) at the POC also comes into focus. For some time measurement of B-type natriuretic peptide or its N-terminal prohormone, N-terminal pro-B-type natriuretic peptide, has been accepted and recommended by guidelines for diagnosis of congestive heart failure. Confidence in its potential role at the POC is likely to be increased more recent guidelines for acute heart failure. These mandate a single measurement of B-type natriuretic peptide or N-terminal pro-B-type natriuretic peptide in people presenting with new suspected acute heart failure to assist in diagnosis. 

 

An early diagnosis is also associated with improved levels of patient satisfaction. For patients presenting with acute chest pain, the availability of a sensitive and accurate POC troponin test simultaneously with the ECG, would significantly reduce waiting times.  

 

The CRUSADE study in the US provides further evidence that POCT reduces the time before appropriate therapeutic treatment and offers the potential to make better use of hospital resources.⁸ For this to translate into significant operational and cost-saving benefits for the hospital, the clinical pathway needs to be reengineered to incorporate POCT^9,10 practices within its protocols. Clinicians must be willing to adapt and integrate point-of-care testing into overall aspects of their patient management if we are to actively convert a reduced TAT into more rapid discharge and reduce time of stay.¹¹ In practice, this means being open to changing the way cardiology patients are managed in the acute care setting – being willing to receive and act upon POC acute care marker results like troponin as soon as they are available, within 10 minutes of the test being taken.

 

Professor Paul Collinson is a consultant chemical pathologist at St George’s Healthcare and Professor of Cardiovascular Biomarkers. His main clinical interests are in hyperlipidaemia, the primary and secondary prevention of cardiac disease and complex lipid disorders and the use of cardiovascular biomarkers for the diagnosis and treatment of heart disease.

 

1.   Bingisser R et al. Cardiac troponin: a critical review of the case for point-of-care testing in the ED. Am J Emerg Med 2012;30(8):1639–49. 
2.   Canto J et al. Symptom presentation of women with acute coronary syndromes: Myth vs reality. Arch Internal Med 2007;167(22):2405–2413.
3.   Thygesen K et al. Joint ESC/ACCF/AHA/WHF Task Force. Third Universal Definition of Myocardial Infarction. Circulation  2012;126(16):2020–35.
4.   Hamm CW et al. The Task Force for the Management of Acute Coronary Syndromes (ACS) in Patients Presenting Without Persistent ST-Segment Elevation of the European Society of Cardiology (ESC). ESC guidelines for the management of acute coronary syndromes in patients presenting without persistent ST-segment elevation. Eur Heart J 2011;32:2999–3054.
5.   Goodacre S et al. The Randomised Assessment of Treatment using Panel Assay of Cardiac Markers (RATPAC) trial: a randomised controlled trial of point-of-care cardiac markers in the emergency department. Heart 2011;97:190–6.
6.   Reichlin T et al. Early diagnosis of myocardial infarction with sensitive cardiac troponin assays. N Engl J Med 2009;361:858e67.
7.   Gill D et al. Laboratory sample turnaround times: do they cause delays in the ED? J Eval Clin Pract 2012;18:121–17.
8.   Takakuwa KM et al. The usage patterns of cardiac bedside markers employing point-of-care testing for troponin in non ST-segment elevation acute coronary syndrome: results from CRUSADE. Clin Card 2009;32:498–505.
9.   www.usa.philips.com/content/dam/b2bhc/master/case-studies/hts-consulting/westchester/case_study_et_improving_clinical_process_performance_4522_991_05371.pdf. Last accessed April 2016. 
10. www.abbottpointofcare.com/knowledge-center/13-point-of-care-testing-opportunity-to-improve. Last accessed April 2016. 
11.   Rooney KD, Schilling UM. Point-of-care testing in the overcrowded emergency department – can it make a difference? Critical Care 2014,18:692.