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Neth Heart J. 2010 August; 18(7-8): 365–369.
PMCID: PMC2922783

Evaluation of quality in adult cardiac surgery: let us speak the same language


Over the last years, measurements of quality of care have become more and more a public product, used by providers, purchasers and consumers, and patients. This information serves as an important guide for improvement, as well as a decision support tool for everybody taking part in medical treatment. This evolution can be compared with advertising and as in commercials it is important to use the right information. In this report we focus on the quality of adult cardiac surgery. Honest information is of course essential, but in this article attention is asked for the variables used to evaluate the quality of cardiac surgery. (Neth Heart J 2010;18:365–9.)

Keywords: Cardiac Surgical Procedures, Quality of Health Care, Myocardial Revascularization

The importance of quality control in health care is steadily increasing.1 In issues of referring patients to certain treatment centres, it is often a determining factor. Moreover, patients these days have an enormous amount of information at their disposal, e.g. via the Internet, and are thus more likely to speak up. As a consequence, the patient himself now has an indubitable say in where (and whether) he will be treated.2 However, one should constantly question whether or not the implemented quality control is correct. Are referring physicians, general practitioners, patients and family correctly and responsibly informed? This article does not seek to question whether or not the data employed are correct but rather whether the parameters and variables are suitable to describe the quality. This could easily be compared with the working of the Dutch Advertising Code (Nederlandse Reclame Code).3 Apart from general ethical stipulations, this code also lays down specific norms for specific products. To illustrate the quality of washing powder, for example, it is important to concentrate on the actual power of the product instead of its colour or scent. By determining certain criteria by norm, the code thus tries to ensure that the consumer is appropriately informed.

In the Netherlands, isolated aorta-coronary bypass surgery is still the most common surgical procedure; it constitutes circa 50% of the annual average of 16,000 open heart operations.4 This means that not only a lot of patients, but also their families, GPs, specialists and insurance agents are confronted with such an operation and accordingly that the question of quality control for this operation is of the utmost importance. Partly because of this prevalence, it is important that everyone involved has a clear picture of the most recent views in this field.

Consequently, the goal of this article is to provide a global overview of the variables in use, as well as to give an example of the evaluation of quality, based on the results of isolated CABG operations carried out at the UMC St. Radboud during a period from 1 October 2006 to 30 September 2009.

Data registration as a basis for quality control

An adequate registration of data is essential for the implementation of quality control, as well as for the identification and tracking of possible ways of improvement. Cardiac surgery, a field in which large numbers of patients with a similar pathology are treated in an almost standardised manner, is a prime subject for such registration. So, it should come as no surprise that cardiac surgeons have collected, registered and analysed clinical outcome data of their operations as a means of evaluation for years.5 The most commonly used parameter is hospital mortality, either risk adjusted or not. Ever since the problematic situation in the cardiac surgery department of the St. Radboud Hospital arose, however, the cumulative sum test (CUSUM analysis) has been added to the standard procedure of quality control in Dutch heart centres.6 At this moment, such a CUSUM analysis constitutes one of the most viable methods to safeguard a process.7 Yet, one should not forget that quality control entails more than just an evaluation of mortality. The Agency for Healthcare Research and Quality has defined quality as ‘doing the right thing, in the right patient, at the right time in the patient’s disease process, with the best possible outcome, and which strikes the right balance of services.’8 In other words, quality remains a fluid and abstract concept. Moreover, quality control of medical processes obviously involves more than just the outcome, e.g. hospital mortality, of a certain treatment. In order to describe such an abstract concept of quality, one needs to define a representative combination of factors, all of which are intricately related to the entire concept of quality. Subsequently, these variables are evaluated on a separate basis and combined to reach a total score. In the best case scenario, a measure of comparison – benchmarking – is possible.

In April 2007, the Society of Thoracic Surgeons (STS) published its report on quality control in adult cardiac surgery, and more specifically on aorta-coronary bypass surgery.9 The focus of this STS quality report on CABG surgery is due to its prevalence; CABG is the most commonly performed cardiac surgery, with standardised procedures and well-defined complications. In most cases, the results of CABG surgery are even used as a foundation for postulations regarding all cardiac surgery performed in adults.10,11 Aside from CABG models, there are also high-quality risk models for cardiac valve surgery. Yet, because there is a large diversity within this surgical category – aortic valve, mitral valve, etc. – it is less prone to quality analysis.12 On a side note, the STS report also makes benchmarking possible – a comparison in relation to STS norm values.

Structure, process and outcome variables

In order to describe the quality of care, a triad of structure, process and outcome variables is employed. This triad was initially presented by Donabedian and later expanded on by Birkmeyer.13,14

Structure variables deal with organisation, which entails, among other things, the number of actions (operations, catheterisations), the ratio nurses/doctors/patient, and the participation in large systems of data registration. There is no exceptionally strong relationship between such structure variables and quality of care, however. The relation between volume and quality, for example, is quite open to discussion. While the relation is remarkably weak in the case of frequently performed surgery such as CABGs, it is quite strong when it comes to less frequent operations such as surgery of the oesophagus. Ultimately, structure variables appear to only be important when good outcome and process variables are absent. The more adequate the outcome and process variables are, the less important structure variables turn out to be.15

Process variables provide information regarding the course of a certain process and its testing by a predetermined guideline. The correlation of these variables to the results of the process at hand has already been established. There is, for example, a verified relation between the outcome of coronary surgery and the use of aspirin, or that of an arterial graft. Doubtlessly, it is important to appreciate that process variables take into account the entire process, instead of only part of it. In the case of CABG, it is thus important to consider all pre-, per- and post-operative variables. Yet, one should realise that individual patients can also show counter-indications or may not be suitable for certain guidelines. For example, some patients cannot tolerate β-blockers, or one cannot demand for a new arterial graft to be put in during a second operation, when one was already used in the first. In the case of these process variables, a certain dispersal is thus acceptable.16

Outcome variables, which provide information on the results of treatment and care, are the best known and most commonly used variables. The best known outcome variable is without a doubt ‘death after treatment’, but information on complications or length of hospital stay, for example, equally counts as an outcome variable. It is important to relate these variables to the quality of care and to examine them within the right context, especially considering mortality rates and the number of complications. Therefore, it is essential to clearly and concretely define not only the variables themselves but also the group in which they are registered. It is in this way that a certain form of ‘risk adjustment; is considered.17

Quality variables for aorta-coronary bypass surgery

The selected variables, as well as their respective definitions, are shown in table 1. These variables encompass the entire CABG process – pre- as well as per-operative, and risk-adjusted hospital mortality as well as postoperative, risk-adjusted morbidity. The correlation between all of these variables and the quality of the performed CABG has already been demonstrated.9-11,18 Apart from, and on the basis of these variables, an extra, combined variable such as ‘perioperative medical care, ‘operative care’ and ‘risk-adjusted severe postoperative morbidity’ can be deduced.

Table 1
Domains of the STS composite quality score with definitions.

The set does not comprise any structure variables because, as noted before, their relevance is limited when large numbers are involved and adequate process and outcome variables are available. Although all of these variables are easily registered in a general database, some problems may arise in the definition of operative mortality. The STS defines operative mortality in the first place as all postoperative hospital mortality, no matter how long after the operation, but also incorporates mortality within 30 days postoperatively, even if the patient has already been discharged, with the exception of mortality unrelated to the operation. The problem resides in the second part of the definition, as there is a recognised problem in the availability of follow-up data regarding mortality.19,20 In the Netherlands it is, at this time, impossible to obtain patient mortality rates in a systematic manner, while those numbers that are available are the result of institution-related initiatives.19,20 For now, the Netherlands thus must take comfort in registering general hospital mortality.

Additionally, table 2 shows the results of the CABGs performed in Nijmegen between 1 October 2006 and 30 September 2009 (n=1435). A major advantage is that the values provided by STS can immediately function as benchmarks and thus that the surgery performed can be evaluated according to those values. These charts, often drafted on a yearly basis, can thus immediately confront a department with deteriorating results regarding one or more variables. To avoid such surprises, the UMC St. Radboud presents the results of the different variables on a tri-monthly basis. Apart from this tri-monthly evaluation, risk-adjusted CUSUM curves of all performed adult cardiac surgery for process control (figure 1) are generated on a monthly basis.7,21

Table 2
Domains of the STS composite quality score with STS median and interquartile range (IQR) and the Radboud percentage for 1435 isolated CABGs.
Figure 1
Risk-adjusted CUSUM analysis of adult cardiac surgery at the Radboud University Nijmegen Medical Center between 1 October 2006 and 30 September 2009 (n=2081). The basic principle of a CUSUM analysis is that of reward or punishment in function of the risk. ...


This article provides an overview of the situation regarding quality control of cardiac surgery, and more specifically the CABG operation. Talking about the quality as experienced by the patient and his social network, factors outside the actual operation do, of course, play a part. Consider, for example, the treatment by physicians, nursing care, and support from the patient’s family and friends, to name but a few. Yet, despite the influence of such external factors, we are convinced that the quality of the operation performed, as well as a correct way of evaluating it, are of the utmost importance in the global issue of quality control. Too often, however, vague and badly defined criteria, such as ‘cardiovascular complication’ lacking in any scientific background and proven correlation with the quality of surgery, are employed. The use of this STS quality score does not only have the benefit that the variables used have a proven relation with quality of care, but also the possibility of benchmarking. Dutch cardiac surgery centres should consider using this quality score. Standard use in annual reports will not only result in benchmarking, but in the first place in more standardised, scientific-based information.


Elise Noyez is thanked for her correction of the English text.


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