Transcatheter aortic valve implantation (TAVI) has emerged as a less invasive treatment alternative for patients with severe symptomatic aortic stenosis at high or very high surgical risk.1,2 Surgical risk scores are established tools for assisting in the decision-making process for these patients. The Society of Thoracic Surgeons Predicted Risk of Mortality3 (STS) score and the European System for Cardiac Operative Risk Evaluation4 (EuroSCORE II) are the most commonly used.

A multiparametric risk score for early mortality prediction has recently been derived based on a TAVI population from a French registry (FRANCE-2).5 In this registry, early mortality after TAVI was mainly related to age, severity of symptoms, comorbidities and access (transapical or other). The FRANCE-2 score is a simple additive score (ranging from 0 to 21) that can be used to predict early mortality after TAVI. In the internal validation, it showed only moderate discriminative ability,5 reflecting limited accuracy in the identification of high-risk patients.

In this study, we sought to externally validate the STS, EuroSCORE II and FRANCE II scores and to compare their performance in a TAVI population.

The mean age of the study population was 81±7 years, 57% were female and 72% presented with New York Heart Association class III or IV. Mean aortic gradient and valve area were 51.3 ± 15.7mmHg and 0.68±0.18cm2, respectively, 53 patients (22%) had reduced left ventricular ejection fraction (LVEF) (<40%), 65 (27%) had previous cardiac surgery and 58 (24%) had moderate to severe renal failure (six were on dialysis). The baseline characteristics are shown in Table 1. Transfemoral access was chosen in two-thirds of patients; alternative approaches were transapical, and less commonly transaortic and subclavian. Four types of devices were implanted: the balloon-expandable Sapien (Edwards Lifesciences®), the first-generation self-expandable CoreValve (Medtronic®), Portico (St. Jude Medical®), and Lotus (Boston Scientific®).

Performance of mortality prediction scoresDiscriminative power

The median EuroSCORE II, STS and FRANCE-2 scores were 5.0 (IQR 3.2-8.3), 5.1 (IQR 3.6-7.1) and 2.0 (IQR 1.0-3.0), respectively, with a corresponding 30-day mortality prediction of 8%.

EuroSCORE II and STS discriminated patients who died from those who did not numerically but not statistically better than FRANCE-2 (C-statistic for EuroSCORE II: 0.67, p=0.029; C-statistic for STS: 0.67, p=0.029, C-statistic for FRANCE-2: 0.53, p=0.724; p=0.26 for the comparison between areas under the curve using the DeLong method) (Figure 1).

Figure 1.

Receiver operating characteristic curves of the three models for the prediction of 30-day mortality. AUC: area under the curve; CI: confidence interval; STS: Society of Thoracic Surgeons.

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Calibration

Overall, EuroSCORE II, STS and FRANCE-2 overestimated early mortality ([expected percentage-observed percentage]/observed percentage) by 11.2%, 7.2% and 38.8%, respectively. The calibration plots for EuroSCORE II, STS and FRANCE-2 in quartiles are shown in Figure 2. Despite the higher discordance for FRANCE-2, all scores showed adequate calibration (calibration-in-the-large for EuroSCORE II -0.03, p=0.51; STS -0.25, p=0.54; and FRANCE-2 -0.38, p=0.29) (Figures 3-5).

Figure 2.

Calibration plots for EuroSCORE II, STS and FRANCE-2 (in quartiles). STS: Society of Thoracic Surgeons.

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Figure 3.

Predicted and observed 30-day mortality (%) for EuroSCORE II in quartiles. Q: quartile.

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Figure 4.

Predicted and observed 30-day mortality (%) for Society of Thoracic Surgeons score in quartiles. Q: quartile.

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Figure 5.

Predicted and observed 30-day mortality (%) for FRANCE-2 in quartiles. Q: quartile.

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In our study, all scores showed low discriminative power for prediction of early mortality, though with adequate calibration.

The early mortality rate of our population (5.8%) is within the range of other contemporary multicenter registries and one recent meta-analysis of more than 16 000 procedures (5.4-12.4%).7-11

There are conflicting data regarding the role of surgical risk scores for early mortality prediction in TAVI patients. In a Swiss study,12 EuroSCORE II performed better in predicting short- and long-term mortality compared with STS and logistic EuroSCORE. A French study showed that EuroSCORE II had moderate discrimination for 30-day mortality after TAVI.13 Watanabe et al.,14 in another French study, demonstrated that EuroSCORE II had low accuracy in predicting 30-day mortality in 435 patients undergoing TAVI.

The low accuracy of the STS score in predicting short-term mortality after TAVI was also demonstrated in a Canadian study involving 399 patients15 and in an Italian study that assessed 663 patients.16 The STS score was an independent predictor of mortality after surgical aortic valve replacement but not after TAVI in the PARTNER trial.17 In addition, in a real-world Brazilian registry, the surgical risk scores were also inaccurate in predicting mortality after TAVI.18 However, in a German registry19 including 36% transapical procedures, the STS score proved to be a good predictor of 30-day mortality after TAVI.

Major differences between the FRANCE-2, EuroSCORE and STS scores in terms of included comorbidities are shown in Table 2. New prediction scores aim to improve their accuracy by including features specific to TAVI, as in the FRANCE-2 score, which was derived from a large TAVI population and is designed to predict 30-day mortality by combining nine variables (age, body mass index, functional class, previous pulmonary edema, pulmonary hypertension, respiratory insufficiency, critical hemodynamic state, dialysis and approach). Nevertheless, FRANCE-2 had the worst performance of the three scores in our population. This may be because, being derived from a registry, it does not take in account prognostically important variables like LVEF, mitral regurgitation, obstructive pulmonary disease, cerebrovascular disease, chronic kidney failure, pulmonary hypertension, coronary artery disease or frailty.20–23 Additionally, procedural success indicators that influence prognosis, particularly perivalvular regurgitation and thrombotic and bleeding events, are not included, which limits its predictive ability. In our population, left ventricular function and mean gradient were independent predictors of death at 30 days (odds ratio [OR] 0.95, 95% CI 0.90-1.00; p=0.039 and OR 0.89, 95% CI 0.83-0.96; p=0.001). These variables are directly or indirectly included in the EuroSCORE II and STS scores.

These results suggest that risk prediction tools should not be used in isolation, although they can help in deciding on the best therapeutic options for the individual patient, as procedural success still has a major role in this complex, albeit increasingly simple, technique. The role of heart teams is crucial, as they offer a better kind of collaboration between cardiologists and cardiac surgeons in many centers, from screening to procedural planning and success.24

To our knowledge, this is the first study to compare the performance of the FRANCE-2, EuroSCORE II and STS risk scores in predicting 30-day mortality after TAVI. It is also one of the first external validations of the FRANCE-2 score.

A score derived from a TAVI registry, FRANCE-2, did not improve early mortality prediction after TAVI in comparison to the EuroSCORE II and STS surgical scores. Prospective studies are needed for further validation.

The authors have no conflicts of interest to declare.