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The British Cardiovascular Intervention Society was founded in 1988 and represents cardiologists and allied health care professionals with an interest in interventional cardiovascular procedures in all countries of the United Kingdom. The Society promotes education, training and research in cardiovascular intervention and develops and upholds clinical and professional standards to try to ensure that all patients being treated by PCI get the best possible care. We have therefore collected data about the way in which PCI is performed, and outcomes for patients following PCI, for many years. The data are publicly available on the Society’s web site and have focused on the performance of individual PCI centres. In recent years BCIS has collaborated with the National Institute of Cardiovascular Outcomes Research (NICOR) to collect and analyse these data.
While the main focus has been on the practice of PCI in different hospitals, in recent years we have also presented analyses of the practice of individual PCI consultant operators. In reading these analyses it is important to understand how they were generated so that their strengths and limitations can be recognised and the information seen in context.
These data have been provided by each centre and their PCI consultant operators. It is not possible for BCIS or NICOR to validate these data; their accuracy, therefore, rests with the PCI operators and the data collection personnel in the hospital where the PCI was performed.
For each PCI procedure over 100 data items are recorded. These include:
a) Information about the patient such as their age, sex and other conditions that they might be suffering from such as diabetes and hypertension.
b) The reason a patient needs to be treated by PCI. For example this might be for symptoms of stable angina or because they have presented to a hospital with sudden onset of chest pain due to a heart attack.
c) The way the PCI was performed, including the techniques employed and the equipment, stents and medications used.
d) How the patient got on after the PCI and whether there were any adverse events before they were discharged home.
| List of abbreviations | |
| ACS | Acute Coronary Syndrome |
| BCIS | British Cardiovascular Intervention Society |
| CABG | Coronary Artery Bypass Grafting |
| CHD | Coronary Heart Disease |
| ECG | Electrocardiogram |
| MACCE | Major Adverse and Cerebrovascular Event |
| NSTEMI | Non ST elevation Myocardial Infarction |
| PCI | Percutaneous Coronary Intervention |
| STEMI | ST elevation Myocardial Infarction |
| UA | Unstable Angina |
All PCI procedures performed over a three year period are included in the analysis of numbers, case mix and outcomes (a rolling three year program). For analyses of delays to treatment (STEMI and NSTEMI), radial rates and interhospital transfer rates, only the most recent year’s data are included to ensure the results are as contemporaneous as possible
Clearly only data sent to NICOR can be analyzed. Almost all UK NHS hospitals have uploaded data, and some (but not all) private hospitals.
To assess survival after PCI, the Office of National Statistics provides us with independently assessed life status, by linkage using the NHS number. This analysis is therefore limited to England and Wales. The data are presented as 30 day survival. Patients who present with out of hospital cardiac arrest and require mechanical ventilation prior to PCI are excluded from the survival analyses, but there are no other exclusions (see section ‘split by syndrome’ for an explanation).
Further details are given under ‘Risk Adjusted Outcomes’.
The aim is to include all consultant PCI operators in the UK who performed PCI at any time during the 3 year period
Survival to 30 days after PCI is reported, using life status data provided by the Office of National Statistics. Factors that determine survival after PCI are often not related to the treatments given and procedures performed, but are influenced by the patient’s general state of health and the condition with which they present. For example some patients admitted with a heart attack may die because of extensive damage to the heart and in spite of excellent care including PCI. Most heart attacks are associated with a mortality of about 5%. If a patient presents with a very big heart attack and is in a state of ‘cardiogenic shock’, then in spite of excellent care and a high quality PCI procedure there is about a 50% risk of death (see below)
Nevertheless outcome will also depend on the quality of care given and the timeliness of treatment. For this reason the analysis attempts to account for the differences in how sick patients are when they present, so that what remains of the variation in outcomes might be explained by the care received.
The data are shown both for each operator and also for each PCI hospital. A skilled interventional cardiologist requires a combination of good clinical judgment and technical ability. Skills can only be maintained by performing a procedure regularly. However, there is no definite cut off below which an operator’s ability to perform high quality PCI will be reduced. BCIS recommends a minimum of 75 PCI procedures in a year (but encourages activity of over 150 procedures a year).
The figures presented here are for the consultant responsible for the PCI procedure, but under certain circumstances a lower volume operator may work with a high volume colleague (a ‘buddy’ or ‘mentor’), and that information is not captured in the data presented.
There are several possible reasons why operators maybe recorded with low procedural volumes. It may genuinely reflect their practice. They may have only been appointed as a consultant part way through the year in question (and so only a subset of their cases will be included). They may have suspended their work due to pregnancy, or by taking a sabbatical. In some cases an operator may have retired part way through the data collection period. There may be an error with data submitted, with missing procedures, or missing consultant GMC numbers associated with procedures.
If an operator has worked on multiple sites, then all data from those sites will be ascribed to that one operator. However some private hospitals have not submitted data electronically to NICOR, and these cases will not be included.
Patients need PCI for a variety of different reasons called ‘syndromes’ and these are called the ‘Indications for PCI’. The indications for PCI in each operator’s practice are shown. Below is an explanation of each of these indications.
Stable
Stable angina occurs when a coronary artery becomes progressively narrowed and blood supply to the heart muscle becomes restricted. People usually experience a tight constricting feeling across the chest which may be associated with breathlessness. It is brought on by physical exertion or stress. Patients with stable angina will have been admitted from home for a planned procedure and usually return home the same day or the following day.
Primary PCI (for ST Elevation Myocardial Infarction or STEMI)
Patients presenting with a complete blockage causing ST elevation on the ECG need immediate treatment. If the blockage persists the region of the heart muscle supplied by that artery will progressively die (myocardial necrosis). In the past patients were treated with a drug that dissolved the occlusive clot (thrombolysis), but now the majority are treated by PCI. This emergency treatment is called Primary PCI, and the number of these cases by each consultant (or hospital) is shown (in these data we have also included ‘facilitated PCI’ – where primary PCI is immediately preceded by treatment with certain other medications).
ACS (Non STEMI)
All other acute coronary syndromes (unstable angina and NSTEMI) are usually caused by a partial or intermittent blocked of the coronary artery and do not usually need to be treated immediately. Recommendations are that they are treated during the initial hospital presentation, preferably within 72 hours. These have been grouped together in this category, and labelled ‘ACS (non STEMI)’.
Shock (Patients in cardiogenic shock before the start of the PCI procedure)
In some patients, the damage caused to the heart muscle by a heart attack is so extensive that the pumping function of the heart is profoundly compromised. If the amount of blood pumped around the patient’s body falls too low, it may be insufficient to sustain the normal function of vital organs, and they begin to shut down (for example kidneys, brain and the liver). When this happens a patient is described as being in ‘cardiogenic shock’. The chances of a patient surviving this critical condition are low, even when the best possible care is provided by the cardiac team. Approximately a third to a half of all such patients will succumb. An operator who works in a hospital that sees a relatively large number of such patients will have a higher mortality irrespective of how skilled the teams are in treating such patients. These factors need to be taken into account when interpreting outcome data. The risk adjustment models attempt to correct for these differences, but all such mathematical methods have limitations (see below)
Ventilated Pre op (patients who have sustained out of hospital cardiac arrest)
Another group of patients whose mortality is high, are those whose hearts stop before they can be brought to hospital. They are said to have suffered an ‘out of hospital cardiac arrest’. While such patients often die before reaching hospital, some can be resuscitated by trained bystanders or paramedics. In this case they are usually brought into hospital by ambulance unconscious and attached to a machine to help them breathe (a ventilator). This group are described as ‘Ventilated Pre-Op’. Even if they are successfully brought to hospital the chance of survival remains poor at about 50%. It is also very difficult to predict survival at the time they arrive. For example it is not possible to know if they have already sustained irreversible brain damage (which is the organ most susceptible to damage at the time of cardiac arrest). If this is the case then even after a successful PCI to treat their heart attack, they may never regain consciousness. These cases are listed in the chart, but as there are no mathematical models yet developed to predict outcomes they have not been included in the assessment of risk adjusted outcome.
Other
There are a few other less common reasons for performing PCI which are grouped here.
To perform PCI, a tube (catheter) needs to be inserted into the patient’s arterial system (see ‘The PCI procedure’). This can be inserted into the artery at the top of the leg (called the femoral artery), or in the wrist (called the radial artery). During the early development of PCI, before full miniaturisation of equipment, large bore tubes had to be used, and so could only be inserted into a large artery (such as the femoral). Through advances in engineering, equipment has become ever smaller, and is now thin enough to be inserted into the smaller, radial artery.
There are several advantages to using the radial artery for access. For example, unlike the femoral artery it does not have other critical structures close by that could be damaged (the femoral artery on the other hand is surrounded by the femoral vein and nerve). It is easier to compress the radial artery to stop bleeding after the tubes are removed, and if any bleeding does occur it is more obvious and so can be corrected more quickly. Furthermore the use of the radial route enables quicker mobilisation after the procedure.
Complications are lower if it is possible to use the radial rather than the femoral route, and radial access results in better long term outcomes and lower mortality. Nevertheless, the radial route is technically more challenging especially if the operator’s previous training and experience has been limited to transfemoral access.
In the public reports we give radial versus femoral access rates for all operators and PCI hospitals. However it is not possible to treat all patients using a radial approach. Some patient’s radial arteries are still too small, and some PCI techniques still require large bore equipment that cannot fit into a an average radial artery. As a result operators who attempt to use a radial route in all appropriate patients will not have 100% radial rates, but rather rates that are likely to be between about 80% and 95%.
If a patient develops an ST Elevation myocardial infarction (STEMI) and is to be treated by primary PCI, then speed is of the essence. A STEMI occurs when a blood vessel supplying the heart muscle blocks completely. In the absence of oxygen and nutrients this part of the heart muscle starts to die. The longer the vessel is blocked, the more heart muscle will die, and so this blockage must be opened as quickly as possible.
The ‘Door to Balloon’ time is a measure of how long it takes a PCI centre to treat such patients. It measures the delay between the arrival of a patient at the hospital, and the re-opening of the blocked artery using PCI. An audit standard is for this to be less than 90 minutes, aiming for less than 60 minutes in higher risk cases. The data are therefore presented as the percentage of patients who were treated within 90 minutes of arrival.
Breakdown by of route of admission
Patients experience longer delays to treatment if the first hospital to which they are admitted does not have the capability to perform PCI. It is therefore best for patients with symptoms of a possible heart attack to be taken directly to a hospital that can perform this treatment. Higher ‘direct admission’ to a PCI centre reduces delays to treatment and reduces overall time the patient needs to spend in hospital.
Data quality
Assessment of predicted outcomes is dependent on the accuracy and completeness of certain key data submitted to NICOR for analysis. This section starts with a measure of the data completeness of these key fields, which are those in the equation used to predict survival (example below).
Thirty Day Survival post PCI (ONS Tracked)
Accurately reporting mortality following PCI can be difficult for some centres, particularly those that treat patients and then transfer to another hospital before they are discharged. The Office of National Statistics holds extremely accurate records of all deaths in England and Wales, and was therefore used to provide an independent source of information regarding life status.
A risk model in a contemporary cohort of patients was developed to measure risk adjusted survival at 30 days.
(reference: McAllister KSL, Ludman PF, Hulme W, de Belder MA, Stables R, Chowdhary S, Mamas MA, Sperrin M, Buchan IE. A contemporary risk model for predicting 30-day mortality following percutaneous coronary intervention in England and Wales. Int J Cardiol. 2016;210:125–132)
A risk calculator has been created and is accessible at this link.
In previous years we have been able to provide a statistical analysis to determine if the observed survival was significantly outside the range predicted by the model. The statistical methodology behind these analyses is complex and evolving. NICOR have partnered with the statistical team at UCL under Professor Rumana Omar to developed this methodology further and this methodology has now been published: Pavlou et al. Outlier identification and monitoring of institutional or clinician performance: an overview of statistical methods and application to national audit data. BMC Health Services Research (2023) 23:23. The full manuscript is available as an open access paper that can be downloaded from this link: https://rdcu.be/c29Lo
Using the previous methodology, no individual operator was identified as performing significantly less well than predicted in the years 2014 to 2016. However, until the new statistical team have completed their assessment and possible modification to those methods we decided not to include any confidence intervals.
Several observations can be made from the point estimates. In the plot above the National (England and Wales) actual and predicted are very similar which confirms that the risk model remains well calibrated. If an operator’s predicted and actual survival are very similar, this means that the operator is performing as the risk model would predict. If the predicted survival of an operator is lower than the National predicted survival (as in this example), that means that that operator is treating higher risk patients than the national average (and vice versa).
Plots of Risk Factor Prevalence and ‘Missingness’
The table at the top of this section gives overall data completeness, but to help identify potential data errors, and to place the data of any one operator or hospital in perspective, two sets of plots have been produced. In each set, the operator (or hospital) is plotted as a coloured dot, against the background of grey dots that represent all other operators (or hospitals). One set of plots shows data completeness, and the other risk factor prevalence. When the risk adjustment analyses are performed, if any risk factor data are missing, the value is assigned to the lowest risk category.
Figure. Example of 3 panels of the Risk Factor Prevalence Plots. Each dot represents a PCI hospital, and the prevalence of a particular feature is ploted against the total number of PCIs performed during the analysis period. In this example this PCI hospital (in yellow) can be seen to have performed about 5000 procedures over the 3 years and is treating patients that are older than those being treated by most other centres (other centres represented by the grey dots), but the sex ratio and prevalence of diabetes are similar.
Discussion
Survival to 30 days after a PCI is dependent on several interacting factors. These include the general well-being of the patient (both the severity of the patient’s presenting condition and their other co-existing medical problems), the risk of the medications given and of the PCI procedure used in their treatment and a variety of aspects of the quality of healthcare provided by the entire team looking after that patient.
Some adverse events may be related to the PCI procedure (such as the need for emergency surgery, or another complication caused by the PCI). Most however occur in spite of excellent care and are due to the serious nature of the condition with which that patient presents. That is, they occur in spite of the PCI, not because of it. In trying to dissect out the relative contributions of these factors to patient outcome, we try to predict what we would expect to be the outcomes in a well-run PCI centre on the basis of the patient’s clinical features and presentation. We compare this with what we observe, and try to see if there is a significant difference between the two. We do this using a technique called ‘risk adjustment’. This requires the use of complex mathematical and statistical techniques. While risk adjustment is an essential tool in trying to understand the quality of PCI treatment, there are many caveats to the methodology and so it can only ever be used to provide a rough guide. For example, some of the features that might predict a good or bad outcome for a patient are not collected (such as if patient is also suffering from a potentially fatal cancer when they have a PCI) or may be very hard to measure (such as ‘frailty’). There will always be random variation in any statistical measure, and so some fluctuation in the apparent risk adjusted outcomes will simply be due to the play of chance.
If we identify a PCI centre or a PCI consultant whose patients appear to have significantly worse outcomes than expected mathematically (called a ‘potential outlier’), we must try to find the correct balance between over reacting (and criticising what may turn out to be a very high standard of care), and missing genuinely poor practice. Other clues can help, such as if apparently poorer outcomes fall back within the expected range in subsequent years and if the operator concerned is treating an unusual case mix that may not be appropriately adjusted for by the mathematical model. The BCIS policy for looking into possible outliers is available from the BCIS web site.
It is also important that though the information here is presented according to the consultant who was responsible for the overall care of the patient during their PCI procedure, they represent part of a larger clinical team consisting of paramedics, emergency medicine doctors, nurses, radiographers and technicians, and the way this teams works together with the hospital facilities available to them may have an impact on the quality of care that can be provided.
One of the most important and worrying aspects of the public reporting of PCI outcomes is the potential for it to generate ‘risk-averse behaviour’. Very sick patients will always have a lower survival rate regardless of PCI or not, be at higher risk of not surviving whether they have a PCI or not, and yet they tend to are those who stand to gain the most from treatment by PCI. If it is felt that the risk model that is used to try to adjust for these patient factors does not work, then there is the potential for a PCI operator to be reluctant to treat the sickest patient who has the most to gain, in case it makes them look as if they have poorer outcomes in spite of them actually providing an excellent quality of PCI. Thus the models for risk adjustment are pivotal to optimising patient care, not only to allow assessment of quality of PCI practice but also to avoid the possibility of risk-averse behaviour.