Discussion
The high proportion of patients with chest pain in ED means that prompt assessment is essential to flow within the department. The LACPP has improved LOS in the ED without compromising patient safety.
The LACPP was adapted from the ESC 3-hour rule-out pathway. Patients in the 2011 cohort were a higher-risk population than the 2018 cohort. Unsurprisingly, there were more type 1 MIs at index presentation, higher rates of MACE and all-cause mortality at 30 days. Despite this, in patients who were discharged from ED, rates of MACE, type 1 or type 2 MI at 30 days were similar between groups. This suggests non-inferiority with regard to safety of rule out between the two cohorts. In a similar study Sandeman et al4 analysed 10 315 consecutive patients presenting with symptoms suggestive of ACS. Patients who presented prior to June 2016 were managed using the standard protocol. This involved hs-TnT sampling on presentation, with a repeat at 6 hours and potentially a further repeat at 12 hours. The earliest point of rule-out was 6 hours. Patients presenting after June 2016 were managed using a rapid 3 hour rule-out pathway. In these two cohorts they found that there was no difference in all-cause mortality or cardiovascular mortality at 30 days or 1 year.
Use of the LACPP significantly reduced patients’ total LOS. The most obvious explanation is that blood sampling is done at a shorter interval. It also has the capacity to rule out MI with one hs-TnT measurement. It is widely appreciated that LOS is also influenced by how busy ED departments can be, impacting on time to assessment, treatment and discharge. Despite this, improvements were still seen with the LACPP.
Similar results were found by Sandeman et al.4 They found a significantly lower LOS for patients on a 3-hour rule-out pathway as opposed to the previous 6-hour pathway. In a stepped-wedge cluster RCT in Scotland,20 31 492 consecutive patients were analysed; 14 700 in the standard care arm and 16 792 in the intervention arm. The standard care involved hs-TnI (Abbot Architect troponin I) sampling at presentation and then repeated at 6–12 hours if required. The intervention arm had a single sample rule out if initial hs-TnI was <5 ng/L and symptom onset was >2 hours prior. Samples were repeated at 3 hours with the potential to rule out MI if the delta values were met. In this trial, the intervention arm reduced LOS from 10.1±4.1 hours to 6.8±3.9 hours (p<0.001). Discharge rates from the ED were increased from 50% to 71% (OR 1.59 (95% CI 1.45 to 1.75%). There was no significant difference in MI or cardiac mortality between the groups at 30 days and 1 year.
The LACPP was introduced following endorsement in the 2015 ESC guidelines for management of patients without persistent ST-elevation on ECG.7 This project provides an insight into the practice of the hospital trusts it was undertaken in. However, it must be recognised that these recommendations are somewhat historic. The two most recent guidelines in 2020 and 2023 have endorsed and now recommend 0/1-hour and 0/2-hour rule out algorithms.21 22 At the time of data collection, these more rapid rule out algorithms were in their infancy.
The ability for the LACPP to reduce LOS and burden on EDs is dependent on reduced intervals to repeat sampling. With the newly endorsed 0/1-and 0/2-hour algorithms, this interval is further reduced. This is an exciting prospect but not exempt from wider ED pressures. It relies on timely sampling and prompt action once the result is available. There are various points in the process where there could be delays.
An observational implementation study by Twerenbold et al23 assessed the effect of the 0/1-hour rule out algorithm on ED LOS. In 2296 patients with suspected ACS, the median LOS in the ED from admission to either transfer or discharge was 150 min. There was no comparator group in this study but given that average time to discharge was less than 3 hours, it is likely that this would be superior to a 0/3-hour algorithm. This study, however, was conducted in private healthcare systems so these results are not directly applicable to public healthcare systems like in the UK. Further research is required to assess feasibility of the 0/1-hour algorithm in this setting.
A randomised controlled trial of 3378 patients compared the 0/1-hour rule out algorithm with a masked, non-high sensitive 0/3-hour algorithm.24 Patients managed with the 0/1-hour and the 0/3-hour algorithm had a median ED LOS of 4.6 hours (IQR 3.4–6.4) and 5.6 hours (IQR 4.0–7.1) respectively (p=0.001). Interestingly, the median LOS of patients managed in this trial’s 0/3-hour arm was very similar to those in our QIP, 5.6 hours and 5.5 hours, respectively. This indicates that a similar improvement may be possible with a 0/1- hour algorithm.
Time to blood sampling improved following LACPP implementation, the median time was still 90 min. This could be improved with staff training in triage of suspected ACS patients, including timely troponin sampling at the front door. In addition, phlebotomists present in ED may ease the pressure on other clinical staff. The time to initial ECG was longer following the introduction of the LACPP and was much longer than the recommended 10 min by the ESC.7 Dedicated ECG technicians based in ED will lead to improvements here.
The introduction of the LACPP reduced the number of patients having multiple troponins. This was in part due to the inclusion the single sample rule out pathway for patients with pain >3 hours and an initial hs-TnT of <5 ng/L, the LOD of the assay.
A meta-analysis of 11 cohorts with a pooled study of population of 9241 patients, by Pickering et al5 revealed that an initial hs-TnT<5 ng/L (LOD) and a non-ischaemic ECG gave a pooled sensitivity of 98.7% (95% CI 96.6% to 99.5%) and negative predictive value of 99.3% (95% CI 97.3% to 99.8%). These were favourable results but below the consensus goal of 99.5% for negative predictive value. In this study, of the 14 false negatives in the population, 7 were in patients whose chest pain onset was <3 hours to troponin draw. This highlights the challenges of early presenters with rapid rule-out strategies. Careful consideration is needed to discharge based on a single sample, particularly if the onset is <2 hours before blood draw. Therefore, the LACPP advocates a repeat troponin sample at 3 hours even if the initial is below the LOD.
Reduced need for repeat sampling has economic benefits. Not only does it reduce ED LOS, but it reduces work load in the biochemistry laboratory. It avoids unnecessary testing, which may in turn reduce burden and have a positive effect on lab result turnaround time.
Limitations
The data collected are not randomised. There were differences in patient complexity and demographics between the two cohorts. The 2011 cohort was higher risk, and therefore, comparing discharge rates will be confounded by these differences. Clinical practice changes over time, including discharge decision-making. Given the difference in patient population risk factors, the ADP may not be the only factor influencing discharge. Discharge from ED did almost double, however.
We do not have data regarding rates of angiography and intervention in either cohort. Therefore, we cannot draw conclusions regarding the appropriateness of invasive intervention in those ruled-in based on troponin results.
The 2011 data for this QIP were collected retrospectively. Therefore, not all the recorded information was available and documented for each patient and not all patients were included in analysis for every variable.
The study analysed data up to 30 days post admission. Therefore, we are unable to comment on the safety of the LACPP beyond this period.
Strengths
Data from 3003 patients across two cohorts constitutes a large sample of real-world practice. It is an accurate representation of a busy ED. Patient inclusion was also consecutive with a 100% follow-up rate, nationally in the 2011 cohort and regionally in 2018 cohort. The size of this sample and the unselected, consecutive nature of data collection indicates generalisability of these findings. Patients diagnosed with MI were adjudicated by two physicians, to ensure accuracy of diagnosis. This level of quality control is something rarely seen in QIPs.