Adoption of high-sensitivity cardiac troponin for early rule out of Acute Myocardial Infarction (AMI) at the Royal Wolverhampton National Health Service (NHS) Trust

The aims of this project were to:

• Safely reduce the number of ‘low risk’ patients being admitted to hospital unnecessarily
• Rule out AMI faster
• Reduce length of stay
• Reduce cost
• Assess safety of new pathway

The learnings presented in the editorial from Ford, C (2017) Benefits of High Sensitivity Cardiac Troponin I at Admission. Medical Lab Management Vol 6, No 6 have been used to supplement the content of this case study.

Emergency departments (ED) face increased pressure to improve performance, reduce overcrowding, and shorten wait times. Patient wait times within the ED that exceed four hours from arrival to discharge, trigger substantial institutional penalties. Faster triage must not supersede the need for accuracy. For these reasons, it is critical to develop optimised clinical pathways that ensure high levels of patient safety while maximising speed to diagnosis and care management.

The Royal Wolverhampton NHS Trust (RWT) is one of the largest acute and community providers in the West Midlands. Around 10% of the emergency department (ED) population at the RWT is people experiencing chest pain. It was decided that the chest pain pathway should be reviewed to improve their triage through the ED.

Before the change in pathway, all patients attending RWT with possible cardiac chest pain were admitted to the acute medical unit where a blood sample was collected, 12 hours post onset of pain, for cardiac troponin T testing to aid in the confirmation or exclusion of acute myocardial infarction. Pressure from the commissioners to reduce hospital admissions coupled with a need to increase patient discharge rates from the ED (which had experienced a large increase in patient numbers following the overnight closure of a neighbouring unit) led to a review of the Trust’s chest pain pathway by a consultant acute care physician.

A baseline assessment conducted in July 2012 showed that 60.9% of people presenting with chest pain were admitted and the mean length of time between admission to ED and discharge was 23 hours.

Introduction of the ARCHITECT STAT high-sensitive Troponin-I (hs-cTnI) assay in April 2013, following a tendering for new automated laboratory equipment, afforded clinical practitioners the opportunity to implement a novel and radically different pathway. The team hypothesised that a new clinical pathway for patients with suspected ACS may improve patient flow within the ED. Clinical assessment and a multifactorial algorithm using hs-cTnI would enable an earlier rule out (discharge) which in turn would reduce length of stay and associated costs, improve emergency triage, while maintaining high levels of patient safety.

The new pathway implemented at the RWT uses the ARCHITECT STAT hs-cTnI assay to test blood samples taken on arrival at ED. If hs-cTnI is ≤1.9ng/L (the limit of detection of the assay) the patient may be discharged. Discharge does not occur if the patient is assessed to be at high risk of ACS on clinical grounds or if the arrival hs-cTnI sample is collected within one hour after the onset of chest pain.

With the new pathway, high-risk patients are admitted to the acute medical unit and low-risk patients with an hs-cTnI >1.9ng/L are transferred to a clinical decision unit within the ED to await the hs-cTnI result from a second sample. Initially, the second sample was collected at 6 hours post arrival but following the publication of the NICE guidance on the use of high sensitivity troponin for the early rule out of myocardial infarction in October 2014 (DG15) the time between samples was reduced to 3 hours.

The pathway is presented in detail in the online editorial by Clare Ford (2017).

A cross-disciplinary team comprised of cardiology, emergency medicine, acute medicine, and pathology collaborated to align on safe and effective patient pathways that included clinical assessment and strategic use of cardiac biomarkers. A key challenge with any new algorithm is physician compliance. This is especially true in emergency situations where physicians had personal experience with previous pathways. To alleviate these concerns and maintain the cadence of the new program, laboratory medicine partnered with emergency medicine and cardiology for educational forums and grand rounds on the evidence-based safety and benefits of the new process.

Development and implementation of the novel chest pain pathway involved cross-functional collaborative efforts that included – adoption of new technology, assessment of patient flow throughout the ED, creation of a Clinical Decision Unit (CDU) within the ED, application of core lab instrumentation, as well as Thrombolysis In Myocardial Infarction (TIMI) based screening criteria for ED physicians to use. Patient safety was considered the foremost important goal and after verification, testing, education, and audits the new algorithm was deemed safe and effective.

Patient safety

To assess the safety of the pathway, consecutive patients presenting to ED with chest pain were prospectively studied over 6 months between July 2013 and January 2014. Patients <16 years old, from trauma calls and who self-discharged, were excluded. Patients with an arrival hs-cTnI of ≤1.9ng/L were followed up at 30 days and then at 9 months for major adverse cardiac events (MACE). MACE includes: death, myocardial infarction, symptom-driven revascularisation, and readmission for ACS.

Thirty-day review of all 849 patients identified 3 MACE: 2 deaths (1 unrelated malignancy and 1 peri-arrest sample) and 1 percutaneous coronary intervention (PCI). Nine-month follow-up showed a further 11 MACE: 9 deaths (8 unrelated malignancies, 1 pulmonary fibrosis) and 2 PCIs. There were no myocardial infarctions or ACS re-presentations. One discharged patient had a MACE with elective PCI following ED referral to cardiology.

Patient pathway

Over the study period, 3,853 patients presented to ED with chest pain, ACS was ruled out clinically in 1,280 patients, and the remaining 2,573 patients had an admission hs-cTnI collected. Eight hundred and forty-nine (849) patients (32% of those with possible ACS) had an admission hs-cTnI ≤1.9ng/L and 688 (27%) were immediately discharged.

The new chest pain pathway resulted in reduced hospital admissions and length of stay. The percentage of chest pain patients admitted to the hospital declined from 60.9% to 38.4% and the mean length of stay reduced from 23 hours and 2 minutes to 9 hours and 36 minutes.

Cardiologist input for all patients attending ED with chest pain in October 2013 was also assessed. Of the 529 patients, attending physicians clinically ruled out ACS in 257. The remaining 272 patients had hs-cTnI samples collected, which were interpreted by acute care physicians based on clinical findings and RWT’s hs-cTnI algorithm. Forty-eight patients had a final diagnosis of ACS, 35 of which required cardiology input.

• Rapid rule out strategies for low risk patients with suspected ACS and hs-cTnI values less than the limit of detection using the ARCHITECT STAT hs-cTnI assay can be safe and effective
• Implementing a system-wide, cross disciplinary educational strategy is vital to ensure understanding of and adherence to new clinical pathways.
• Patient experience was improved through the safe discharge of over 25% of low risk patients without the need for serial measurements of hs-cTnI and time to discharge for some low risk patients was reduced by approximately 6-fold.
• No ACS related deaths were associated with using single hs-cTnI values to discharge low risk patients after ED presentation
• Use of the stringent hs-cTnI algorithm meant that there were no unwarranted increase in Cardiology consultations (false positives).
• Implementation resulted in reduced unnecessary admissions that saved the Trust approximately £788,000