Describing Activity in Primary Percutaneous Coronary Intervention: An Exploration of Denominators. From the HEAT Trial – A Systematic Evaluation of PPCI Activations in Liverpool, Explaining Denominators (HEAT-SEALED)

Abstract: Background. The provision of primary percutaneous coronary intervention (PPCI) in the emergency management of ST-elevation myocardial infarction (STEMI) is expensive and resource intensive. Accurate data collection is essential not only for outcomes analysis but also to characterize activity and performance for regions, centers, and operators. Inconsistency in the use of denominators currently creates problems in data interpretation. Objective. To establish a system of denominator groupings, seeking to better describe the range of clinical activity resulting from an unselected series of PPCI activations. Methods. The HEAT-SEALED pathway designates a key denominator group (n1-n9) to each phase of PPCI activity and identifies a final “destination category” for each patient leaving the pathway. HEAT-PPCI (How Effective are Antithrombotic Therapies in Primary Percutaneous Coronary Intervention) is a true “all-comers” trial and provides an ideal platform to collect data for prospective validation of the pathway. We report data from all PPCI activation events for the HEAT-PPCI trial. Results. Our findings demonstrate important differences between the sizes of key PPCI denominator groups and hence the potential for variation in reported outcomes depending on the denominator category selected. The main figures are: all activations (n1 = 2490); all suspected MI cases (n4 = 1940; 77.91%); patients in whom angiography was performed (n5 = 1904; 76.46%); cases in which diagnosis was confirmed with a probable culprit lesion (n6 = 1657; 66.54%), and cases with complete PCI success (n9 = 1441; 57.87%). Conclusion. The HEAT-SEALED pathway offers a practical and comprehensive solution to the problem of describing denominators in STEMI and PPCI. Routine application would facilitate a more consistent and precise description of activity and outcome.

J INVASIVE CARDIOL 2016;28(6):247-252. Epub 2016 April 15.

Key words: ST-elevation myocardial infarction, STEMI

Primary percutaneous coronary intervention (PPCI) is now considered the gold-standard treatment for ST-elevation myocardial infarction (STEMI).^1,2 PPCI activity is expanding as this becomes the dominant treatment modality for emergency reperfusion. In the 12 months between April 2011 and March 2012, a total of 32,439 patients in the United Kingdom were recorded as having a STEMI event.³ Reperfusion treatment was delivered to 70% of these patients and of these, 95% had PPCI as their index therapy³ (approximately 330-380 PPCI procedures/million⁴). In the United States, according to the CathPCI registry, the number of STEMI patients receiving PPCI is exceeding 100,000 per year^5-9 (estimated 300-350 PPCI procedures/million^2,7,10).

The provision of a high-quality PPCI service is a complex and demanding task. This involves public health education and a number of different aspects of emergency care provision – with several, otherwise disparate, agencies and teams involved in delivery. Public health education seeks to encourage an earlier “call for help” to reduce the time interval between the onset of symptoms and presentation. Improvements in the response of emergency medical services (EMS) and the receiving medical teams should help reduce the delays associated with the move to an appropriate facility and the provision of reperfusion therapy.⁴ There appears to be a relationship between the quality of service and more favorable outcomes.^2,3,11-15 This has prompted great interest in improving systems and performance with audits and analysis, often coordinated at a national level.^3,16,17 

There is a self-evident need to record accurate data to facilitate clear reporting of patient risk profiles, presentation characteristics, procedural data, and outcomes. There is also a need for consistency in reporting the performance and activity levels of different regions, PPCI centers, and individual operators.

Currently, there is no consistent and agreed system to describe denominators for STEMI. For instance, of all those suffering STEMI, a proportion will die of cardiac arrest and never reach the hospital. Those who do reach the hospital may be unsuitable for reperfusion therapy, and those who are suitable may be taken to the cardiac catheterization laboratory, but may not require PPCI for clinically appropriate reasons. It is therefore difficult to analyze PPCI activity and outcomes, as authors may choose to use different denominators for reported figures. To demonstrate high-volume activity, one might choose to quote the total number of PPCI activations at a center. To reflect more favorable mortality figures, one might restrict the patient population to those with successful reperfusion. These “floating denominators” can make it difficult to interpret and compare reports of PPCI activity and outcome.

Methods

The HEAT-SEALED (HEAT Trial – Structured Evaluation of Activations in Liverpool, Explaining Denominators) pathway was initially designed in Nov 2010, from first principles, on the basis of accumulated clinical experience. It became a part of the documentation of the integrated care pathway for PPCI patients at Liverpool Heart and Chest Hospital (LHCH) in 2011. In the HEAT-SEALED pathway, the first column of the flow chart (Figure 1) designates a key denominator group (n1-n9) to each phase of the PPCI pathway. The second column describes the flow of clinical activity associated with each step. The last column identifies a possible final destination category for each patient leaving the pathway and operators must choose the option that best characterizes their patient.

HEAT-PPCI (How Effective are Antithrombotic Therapies in Primary Percutaneous Coronary Intervention) is a randomized controlled trial comparing unfractionated heparin and bivalirudin in the treatment of patients with a clinical diagnosis of STEMI for planned management with PPCI.¹⁸ HEAT-PPCI is a true “all-comers” trial and all PPCI pathway activations are assessed for eligibility and documented by trained research staff. The trial therefore provides an ideal platform to collect data for this prospective study. For HEAT-PPCI, patients were recruited from February 7, 2012 to November 20, 2013. In this paper, we report data from all activation events of the LHCH-PPCI pathway during this period (n1 = 2490). 

The PPCI service was activated at the host institution either directly by ambulance services or by local referring hospitals. This regional hospital referral network comprised 11 hospitals located in the Merseyside and North Wales serving a catchment area of 2.5 million people. In the peripheral centers, doctors working in the emergency department were responsible for the diagnosis of STEMI and activation of the PPCI pathway. For direct ambulance admissions, paramedics were responsible for this process. Both services were independent in decision making and did not require input from the on-call team at the host institution. 

The diagnoses of inappropriate catheterization laboratory activations (CLAs), such as non-cardiac diagnosis, non-ischemic cardiac diagnosis and acute coronary syndromes suspected but not ST-elevation, were made by the attending cardiologists at the host institution. This was based on the patients’ clinical history, examination, and electrocardiographic (ECG) and echocardiographic findings. STEMI was defined as ongoing cardiac sounding chest pain along with the following ECG changes: ST-segment elevation measured at the J point, found in two contiguous leads and ≥2 mm in precordial leads or ≥1 mm in limb leads. Posterior STEMI was defined as new-onset ST-segment depression in leads V1-V3 along with positive R-wave in leads V1-V3 (or concomitant ST-segment elevation ≥1 mm recorded in leads V7-V9). New-onset persistent left bundle-branch block was also considered as one of the criteria to activate the PPCI pathway. Pericarditis was defined as a combination of two or more of the following: (1) retrosternal or left precordial chest pain (may be radiating to the trapezius ridge, pleuritic in nature and/or varying with posture); (2) presence of pericardial rub on auscultation; (3) ECG showing concavely shaped ST-segment elevation (± PR segment depression); and (4) evidence of pericardial effusion on echocardiography.

HEAT-PPCI study records have been compared against the data collected by the hospital clinical quality and audit department. The audit team is responsible for the submission of data to the United Kingdom national registries for PCI and acute myocardial infarction. We have carefully scrutinized all data for any mismatches between HEAT-PPCI case record form and hospital audit system records. In the event of such a mismatch between the two datasets, or if the data were not available in the audit department records, the data were validated against the patient’s case notes.

Results

Figure 1 shows the HEAT-SEALED pathway, along with a summary of the results. Of all PPCI activations, 2377 (95.46%) were considered “genuine” (n2) – representing confirmed activations for the planned provision of index, emergency reperfusion in cases of suspected STEMI. The cases that were not classified as genuine mainly comprised non-PPCI emergencies (eg, rescue PCI) using the PPCI activation system. The total number of cases arriving at the PPCI center (n3) was 2341 (94.01%). “Dropouts” before arrival resulted mainly from a change in the patient’s clinical status or from a change in the suspected initial diagnosis, resulting in cancellation of the activation call. 

The number of patients who reached the PPCI center, but were considered as incorrect activations on clinical grounds was 401 (16.1%). The breakdown for these cases comprised non-cardiac diagnoses (eg, pulmonary embolism, chest infection, musculoskeletal chest pain, and gastrointestinal-related problems), non-ischemic cardiac diagnoses (mainly pericarditis), and cases in which an acute coronary syndrome was suspected but the ECG did not fulfill the criteria for STEMI. 

The total number of cases deemed appropriate to proceed to the catheterization laboratory was 1940 (77.91%) (n4) and coronary angiography was performed in 1904 (76.46%) (n5). The reasons for patients not being able to proceed to angiography were mainly clinical (3 patients died before entering the lab, 16 were too unwell to have angiography, 10 had already completed the infarct, and 2 had failed access to coronaries). The breakdown for the 16 patients considered to be too unwell to have angiography is as follows: 11 had acute left ventricular failure; 2 had acute respiratory system pathology; and 3 were deemed very frail for the procedure. The diagnoses and final decisions were made by the attending cardiologists.

Of the patients who had angiography, 247 (9.91%) did not have any angiographic evidence of acute myocardial infarction. Thus, the diagnosis of myocardial infarction was supported by an angiogram with identification of a probable culprit lesion in 1657 total activations (66.54%) (n6). PCI was attempted in 1564 cases (62.81%) (n7). The main reasons for not having PCI were the presence of surgical disease or PCI being judged impractical. The total number of patients who had reperfusion success with TIMI III flow in the culprit vessel was 1464 (58.79%) (n8). Despite achieving TIMI III flow, 23 cases (0.92%) were deemed to have suboptimal PCI result. The reasons for this include presence of residual stenosis of 30% or more following stent implantation or 50% or more following balloon angioplasty, or if further revascularization of the culprit lesion was planned. Complete PCI success (n9) was achieved in 57.87% of cases. 

Discussion

Data collection for PPCI patients. There has been considerable and rapid growth in PPCI activity over the last decade. Developing standards has been difficult as, until recently, only limited data have been available. Currently, there are two national systems collecting data for STEMI patients in the United Kingdom: the British Cardiovascular Interventional Society Central Cardiac Audit Database (BCIS-CCAD) and the Myocardial Infarction National Audit Programme (MINAP). For BCIS-CCAD, data are collected mainly for patients who undergo a coronary intervention,²⁰ whereas MINAP is responsible for collecting data for all acute coronary syndrome events, including STEMI patients.³ There are variations between the two systems in the ways data are collected and analyzed. Currently, neither system includes any robust mechanism for identifying the outcome of all PPCI pathway activations. To the best of our knowledge, other large registries in the European Union and United States also lack a comprehensive structure to interpret and demonstrate the outcomes of all PPCI activations.^6,21-24 

Potential variation in PPCI reporting. The results of this study show a considerable absolute difference between various PPCI denominators. Patient numbers are eroded at each step. The number of successful PCI cases (n9) is only 57.87% of the total number of activations (n1). The potential for the presentation of misleading or inconsistent data is obvious.

Using the results of our study, one could potentially report on PPCI performance using n8/n7 (achieving TIMI III flow in all patients in which PCI was attempted), which would give a success rate of 93.6% (1464/1564 x 100). However, if n9/n7 (achieving complete success in all patients in which PCI was attempted) was used, the success rate would be 92.1%, and this would fall further to 86.9% if n9/n6 (achieving complete success in all patients in which a culprit lesion was confirmed) was used. This problem of selective rate reporting can only be solved by using the correct and appropriate denominator.

Evaluating the performance of a PPCI service. The HEAT-SEALED pathway has given us an efficient mechanism to evaluate the performance of PPCI service provision. Every individual denominator will help us evaluate different parts of the system. The case numbers at n2 (all genuine activations) will provide the denominator for the overall assessment of the service. Any consideration that integrates outcomes associated with the emergency diversion of some patients, with a non-cardiac diagnosis, to a cardiac unit will use this figure.  

We can calculate the dropout rate at each step to identify the discrepancies in practice between operators and institutions. The ratio n4/n2 will inform discussions about the diagnostic performance of the EMS and will be affected by local protocols and thresholds to initiate a PPCI activation.

A consideration of n5/n4 may provide information about the threshold of an institution or an individual operator to perform angiography in this emergency, demanding, and often high-risk setting (perhaps suggesting some cardiologists are too bold or too cautious). Review of n6/n5 may illuminate differences in the use of angiography as a means of ruling out infarction in cases with diagnostic uncertainty.  

The ratio n7/n4 may provide some indication of the willingness of the operators to attempt PCI reperfusion and n9/n7 or n8/n7 will, to some extent, be a reflection of technical skills and other factors related to the performance of PCI. 

More detailed information is of course available at all stages of the pathway. For example, the breakdown of dropout between n5/n4 could help to identify deficiencies in the provision and administrative performance of services (eg, how many patients failed to have a procedure due to unavailability of lab space or staffing issues).

Identifying inappropriate catheterization laboratory activations. A number of other authors have noted a “false-positive” or inappropriate CLA rate of 10%-36%.^25-27 The dropout rate between PPCI pathway activation and patient receiving angiography can be reduced to much lower levels (<1%) if there is communication with the PPCI center prior to activation of the pathway.^25,26,28,29 In contrast, rates are higher if there is no prior contact with the PPCI center.^27,30 In the United Kingdom, the guidelines suggest that the PPCI pathway should be activated in the periphery without involvement of the cardiac center and Liverpool has adopted this approach.³¹

Inappropriate CLAs represent a significant challenge for a PPCI system. Higher rates can lead to misuse of scarce and expensive resources and (in the absence of dedicated staff, working a full shift system) may result in the on-call personnel becoming tired and demoralized. In theory, a patient with a genuine myocardial infarction event may have their reperfusion delayed if the PPCI facility and team are engaged in a procedure being performed mainly to confirm a suspected false activation.

ST-segment elevation on the presenting ECG can be difficult to interpret and can be associated with conditions other than myocardial infarction.^32-39 Correct ECG analysis can reduce the inappropriate CLA rate by 45%.²⁶ In our study, 401/514 (78%) of all inappropriate CLAs were due to incorrect initial ECG interpretation. 

It is important to note, however, that an attempt to minimize CLA events may result in more “false-negative” assessments by referring staff – with genuine STEMI cases being denied optimum reperfusion. The problem of inappropriate CLAs and the extent of their impact on the system are yet to be quantified with precision. Currently, there is no robust system in place to record and analyze the inappropriate CLAs. Use of the HEAT-SEALED pathway could help to address these issues. 

Conclusion 

This prospective validation exercise demonstrates that the HEAT-SEALED pathway offers a practical and comprehensive solution to the problem of describing denominators in STEMI and PPCI. More universal application of this system would help us improve the description, analysis, and interpretation of service provision, to compare different services and facilitate better practice and improved outcomes.

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From the ¹Institute of Cardiovascular Medicine and Science, Liverpool Heart and Chest Hospital NHS Foundation Trust, Liverpool, United Kingdom; ²The Leeds Teaching Hospitals NHS Trust, Leeds, United Kingdom; and ³University Hospital Southampton NHS Foundation Trust, Hampshire, United Kingdom.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Manuscript submitted November 15, 2015, provisional acceptance given December 15, 2015, final version accepted February 16, 2016.

Address for correspondence: Adeel Shahzad, MBBS, MRCP, Liverpool Heart and Chest Hospital, Cardiology, Liverpool Heart and Chest Hospital, Liverpool, United Kingdom. Email: adeelshahzad@hotmail.co.uk