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Editorial |
Cardiothoracic Surgery, University Hospitals, Coimbra, Portugal
Received 13 August 2009; received in revised form 13 August 2009; accepted 17 August 2009.
* Corresponding author. Address: Centro de Cirurgia Cardiotorácica, Hospitais da Universidade, 3000-075 Coimbra, Portugal. Tel.: +351 239400418; fax: +351 239829674. (Email: antunes.cct.huc{at}sapo.pt).
Key Words: Aortic valve replacement • Risk-score • Euroscore
In this issue of the journal, Di Giammarco et al., from Chieti, Italy [1], report their evaluation of the performance of the EuroSCORE calculator in the prediction of the 30-day outcome after isolated aortic valve replacement (AVR), ‘in order to assess its absolute reliability and usefulness as selection criteria to percutaneous aortic valve implantation (PAVI).’ With this aim, they carried out a retrospective statistical analysis on 379 of their patients consecutively submitted to isolated AVR in the past 10 years of surgical activity. Their observed mortality was 5.2%, significantly lower than the 9.4% expected mortality by the logistic EuroSCORE. The discrepancy was particularly significant in the latter 5-year period. They conclude that the ‘EuroSCORE appears to be a not validable model in absolute and relative risk prediction for isolated AVR. On this basis its use in selecting candidates to PAVI should be carefully weighted.’
The emergence of PAVI has resulted in an unprecedented use of the EuroSCORE to predict the results of conventional aortic valve replacement, especially in the high-risk groups, which would, thus, become the candidates for PAVI. Large series with mean logistic scores above 20% suddenly appeared, where they were not suspected before. Most surgeons had not seen so many patients considered too high a risk for surgery. I certainly had not. This, in turn, triggered many retrospective analyses of series with patients who were recently submitted to AVR, which, invariably, found that the EuroSCORE overestimates the risk of isolated AVR [2,3]. This is the main message of the article by Di Giammarco et al., but only this year there have been another half a dozen papers with identical conclusions.
The group from Bad Oeynhausen, Germany, is about to publish one based on 2757 patients submitted to AVR recently in their centre [4]. Similarly, concluding that ‘patient selection for interventional AVR cannot be based on the EuroSCORE, because it lacks discrimination and centre-specific calibration.’ These authors thus recommend ‘individual, surgical judgement that weighs institutional expertise of high risk patients against possible reduction of mortality by using interventional techniques.’ Although not usually recognised, we all know that expertise, hence the results thereof, vary from group to group and, within these, from surgeon to surgeon. No risk score can cover all these differences. Similarly, an analysis of a subgroup of 6305 patients submitted to isolated AVR registry of the German Society of Thoracic and Cardiovascular Surgery from 2006 and 2007 revealed an overall hospital mortality of 3.9% whereas the logistic EuroSCORE predicted 7.3%, which supports ‘the substantial lack of predictive value of the EuroSCORE [5].’
Some other articles also recently published were directed at validating the EuroSCORE in parts of the world other than Europe and their conclusions are that the EuroSCORE does not apply there [6–9]. However, I believe, it also does not apply in Europe. For three main reasons: firstly, the EuroSCORE is already outdated, as it was developed from data on patients operated on almost a decade and a half ago, and the results of surgery have improved significantly since, especially in the elderly. Secondly, because the data originated from only eight European countries and, from each one of these, only few centres contributed. As with any type of statistical analysis, it generated mean values which may even not serve all these centres. As stated recently [10], ‘the logistic EuroSCORE risk stratification system was developed and validated within the European population. There should be caution in the utilisation of any particular risk stratification system outside the countries of origins, and it is important to carefully evaluate the validity of such system amongst foreign population,’ which means that it may even not be applicable to all European countries. Thirdly, and most important, the EuroSCORE was especially developed for cardiac surgery in general, especially for coronary re-vascularisation procedures, the majority of data belonging to this group of patients, and not specifically for AVR.
Hence, it is now generally recognised that the EuroSCORE does not reflect current results of cardiac surgery, including coronary re-vascularisation, but especially AVR. Curiously, the additive model of the EuroSCORE, initially published in 1999 [11], was modified in 2003 by the introduction of the logistic model [12], which is now the most widely used, but whose values are even higher than those of the additive score. Furthermore, it is important to stress that the model would not apply, in any case, in any situation, before validation, to each particular surgical group. We, in Coimbra, have recognised that and have, recently, developed our own scores for prediction of the risks of mortality and morbidity after coronary surgery in our population and are about to do the same for valve surgery. Others have gone in a similar path. Alternatively, The Society for Cardiothoracic Surgery in Great Britain and Ireland, and others, has proposed recalibrations of the model by multiplying the EuroSCORE-derived risk values by procedure-specific coefficients. These shortcomings have been recognised by the EuroSCORE group and have led to a revision of the EuroSCORE, which is currently under way.
Other risk scores were developed, which are also widely used internationally. The Society of Thoracic Surgeons (STS) score, based on the enormously large database of this Society, has recently been hailed as a more accurate predictor of the operative results. Roughly, the STS risk-score-predicted mortality rates are about half of those predicted by the EuroSCORE for all levels of risk. Comparative studies have demonstrated a closer relationship between predicted and observed mortality with the STS score than with the EuroSCORE [13]. Yet, in some studies, the STS score still overestimates the mortality risk somewhat.
Hence, why is the logistic EuroSCORE, which by all accounts gives the highest values and is the furthest away from observed rates, used almost exclusively by the groups performing PAVI, when it has been conclusively proven to be inaccurate, unreliable and difficult to validate for all groups of patients? Will it be because there is a pressing need to push forward a technique which, however promising for the future, currently still underperforms conventional AVR? Recent reports of early failure of valves implanted percutaneously appear to indicate that currently available devices for use in PAVI are not as durable as those used in conventional AVR, which justifies the word of caution against wider use of the procedure recently raised by the most prominent European cardiac medical and surgical societies [14]. It is very informative that almost every report on PAVI published in recent years includes patients initially thought to constitute a prohibitive risk for conventional AVR, on the basis of a high EuroSCORE, who were subsequently considered inappropriate for the percutaneous procedure and submitted to surgery, generally with better results than those of the patients who underwent PAVI.
Obviously, risk evaluation systems are needed for adequate planning of cardiac surgery, including these newer procedures, but currently available models need to be rebuilt or perfected to be able to appropriately fulfil their role. Until then, I have to support the conclusion derived by Di Giammarco et al. that ‘each single Institution involved in PAVI procedures should weigh each independent predictor of death in evaluating local surgical results in terms of absolute and relative risk.’
References
This article has been cited by other articles:
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  M. Pasic, A. Unbehaun, S. Dreysse, T. Drews, S. Buz, M. Kukucka, A. Mladenow, T. Gromann, and R. Hetzer Transapical Aortic Valve Implantation in 175 Consecutive Patients: Excellent Outcome in Very High-Risk Patients J. Am. Coll. Cardiol., August 31, 2010; 56(10): 813 - 820. [Abstract] [Full Text] [PDF]
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