Risk Assessment for Transcatheter Aortic Valve Replacement
Understanding STS score, EuroSCORE, and frailty indices.
During the past decade, transcatheter aortic valve replacement (TAVR) has advanced from a treatment option in symptomatic patients with severe aortic valve stenosis and extreme or high surgical risk to recently also being indicated in patients with intermediate surgical risk.1,2 In addition, several ongoing randomized clinical trials are comparing TAVR with surgical aortic valve replacement (SAVR) in patients with low surgical risk (NCT02675114, NCT02701283, NCT02825134).
According to the American College of Cardiology/American Heart Association (ACC/AHA) and European Society of Cardiology/European Association for Cardio-Thoracic Surgery (ESC/EACTS) guidelines for the management of valvular heart disease, a central component for considering treatment for severe symptomatic aortic valve stenosis with TAVR is assessing the underlying risk of SAVR, partly guided by Society of Thoracic Surgeons (STS) score or European System for Cardiac Operative Risk Evaluation (EuroSCORE) II.1,2 The STS scores are conveniently categorized as low (< 4%), intermediate (4%–8%), or high (> 8%) surgical risk in the ACC/AHA guidelines, whereas the ESC/EACTS guidelines use low (STS score or EuroSCORE II < 4%) or increased (STS score or EuroSCORE II > 4%) surgical risk.1,2 Similar definitions re-emerge in major randomized controlled trials, but show significant differences in predicted and observed 30-day mortality after TAVR (Figure 1).3-9
Risk models are invaluable measures for objectifying something as complex as risk assessment, as they aid in the clinical decision-making and comparison of study populations. However, the STS score and EuroSCORE II are based on 67,292 patients from the United States and 22,381 primarily European patients undergoing open heart surgery, respectively.10,11 The risk models are designed to give an accurate estimate of the observed average mortality rate within 30 days of SAVR but have been found to be limited in risk assessment among patients being considered for TAVR.
CONVENTIONAL RISK SCORES
The original additive EuroSCORE was developed almost 2 decades ago based on a patient population that underwent cardiac surgery (primarily coronary artery bypass grafting) and proved to be a valuable tool for risk assessment in relation to cardiac surgery.12 In 2003, the logistic EuroSCORE followed, and Michel et al13 found both risk models to be accurate with an area under the receiver operating characteristic curve (AUC) of 0.78. A subsequent meta-analysis including data from surgical valve operations concluded that the additive and logistic EuroSCORE performed poorly in isolated valve surgery and overestimated the risk of 30-day mortality.14 Meanwhile, TAVR had emerged, and the logistic EuroSCORE and STS score were used for risk assessment in these study populations. As a consequence, the logistic EuroSCORE is mentioned in the recently published ESC/EACTS guidelines, but is only suggested to be used for comparison, as it was applied in many previous TAVR studies and is no longer recommended for risk assessment of SAVR or TAVR.2
The STS score and EuroSCORE II have fair accuracy in predicting 30-day mortality risk after SAVR.10,11 However, a meta-analysis of 24 studies including 12,346 TAVR patients concluded that discrimination of 30-day mortality based on the STS score, logistic EuroSCORE, and EuroSCORE II was weak to modest, as all risk models reached an AUC of 0.62.15 Further, the logistic EuroSCORE substantially overestimated 30-day mortality, the EuroSCORE II marginally overestimated 30-day mortality, and the STS score both underestimated 30-day mortality at lower predicted mortality scores and overestimated 30-day mortality at higher predicted mortality scores.15 Despite the recommend use of STS score and EuroSCORE II, the guidelines stress that the risk models have significant limitations in concordance with the aforementioned factors and the lack of consideration of important risk factors such as frailty.1,2
Factors other than clinical comorbidities need to be considered when predicting the risk of death and morbidity after TAVR; otherwise, the very elderly patient with no comorbidities could be classified as a low surgical risk candidate according to the STS score or EuroSCORE II. The typically elderly patient population indicated for TAVR is very heterogeneous with regard to (sub)clinical risk factors such as nutritional status, physical and cognitive impairments, and psychosocial status. A reduced homeostatic reserve and decreased resiliency to stressors accompanying impairment of such factors has been termed frailty.16
Guidelines for the management of patients with aortic valve stenosis recommend objectively assessing frailty in addition to the general risk scores and discourage relying on the “eyeball test,” as this tends to be subjective and inconsistent.1,2 However, to date, there is no standardized method for frailty assessment, although many different general and TAVR-specific frailty scales have been developed, repeatedly showing an association between frailty and increased risk of mortality and morbidity after TAVR (Table 1).16-19 The AHA/ACC guidelines recommend using a simple questionnaire including six activities of daily life and evaluation of ambulation for assessing no, mild, or moderate-to-high frailty correlating to a low, moderate, or high surgical risk, respectively. However, it is specified that other frailty scales can be applied.1
Afilalo et al compared seven frailty scales in patients undergoing SAVR or TAVR and found that the Essential Frailty Toolset scale consisting of four items (time to stand five times, cognitive assessment, and hemoglobin and serum albumin levels) was the most robust predictor of 1-year mortality, leading to an increase in AUC of 0.071 (from 0.713 to 0.784) when combined with the STS score.16 Still, there is no consensus on the optimal frailty scale to use for potential TAVR candidates, limiting its use in clinical practice.
NEW RISK MODELS
The addition of frailty to conventional risk scores such as the STS score or EuroSCORE II could increase their value for risk assessment after TAVR but would still lack other potentially relevant clinical risk factors (eg, expected access route for TAVR). Further, adding extra variables to a risk model is not necessarily beneficial, as this could increase the risk of overfitting and make assessment more cumbersome to complete.20 The development of a TAVR-specific risk model could be a valuable tool for risk prediction. Edwards et al recently developed a Transcatheter Valve Therapy (TVT) Registry risk model predicting in-hospital mortality based on TAVR patients and found it to have favorable discrimination and calibration indices when compared with the STS score, EuroSCORE II, or the TAVR-specific FRANCE-2 model.21 The TVT Registry model consists of nine covariates, but is subject to change as more data are gathered, with planned evaluation of the impact of frailty as a covariate and the capabilities of predicting of 30-day and 1-year mortality and, importantly, quality of life after TAVR.21 As a minority of patients continue to have poor quality of life after TAVR, predicting the absence of symptom improvement could also be an important aspect to help prepare patients with realistic expectations.
The risk of death and morbidity related to the procedure has to be assessed as favorable compared with the risk of the natural history of severe aortic valve stenosis before recommending SAVR or TAVR. The STS score and EuroSCORE II were developed for risk prediction after cardiac surgery and do not include potential important variables such as frailty or TAVR-specific factors such as access route or valve type. Consequently, the conventional risk models have subpar accuracy for risk prediction after TAVR. Adapting the existing STS score or EuroSCORE II or developing new a TAVR-specific risk model could separate the expected results of SAVR versus TAVR (eg, intermediate risk for SAVR and low risk for TAVR) in an almost completely objective manner, aiding the decision-making process.
1. Nishimura RA, Otto CM, Bonow RO, et al. 2017 AHA/ACC focused update of the 2014 AHA/ACC guideline for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. Circulation. 2017;135:e1159-e1195.
2. Baumgartner H, Falk V, Bax JJ, et al. 2017 ESC/EACTS guidelines for the management of valvular heart disease. Eur Heart J. 2017;38:2739-2791.
3. Thyregod HG, Steinbrüchel DA, Ihlemann N, et al. Transcatheter versus surgical aortic valve replacement in patients with severe aortic valve stenosis: 1-year results from the all-comers NOTION randomized clinical trial. J Am Coll Cardiol. 2015;65:2184-2194.
4. Leon MB, Smith CR, Mack MJ, et al. Transcatheter or surgical aortic-valve replacement in intermediate-risk patients. N Engl J Med. 2016;374:1609-1620.
5. Leon MB, Smith CR, Mack M, et al. Transcatheter aortic-valve implantation for aortic stenosis in patients who cannot undergo surgery. N Engl J Med. 2010;363:1597-1607.
6. Smith CR, Leon MB, Mack MJ, et al. Transcatheter versus surgical aortic-valve replacement in high-risk patients. N Engl J Med. 2011;364:2187-2198.
7. Reardon MJ, Van Mieghem NM, Popma JJ, et al. Surgical or transcatheter aortic-valve replacement in intermediate-risk patients. N Engl J Med. 2017;376:1321-1331.
8. Popma JJ, Adams DH, Reardon MJ, et al. Transcatheter aortic valve replacement using a self-expanding bioprosthesis in patients with severe aortic stenosis at extreme risk for surgery. J Am Coll Cardiol. 2014;63:1972-1981.
9. Adams DH, Popma JJ, Reardon MJ, et al. Transcatheter aortic-valve replacement with a self-expanding prosthesis. N Engl J Med. 2014;370:1790-1798.
10. Nashef SA, Roques F, Sharples LD, et al. EuroSCORE II. Eur J Cardiothorac Surg. 2012;41:734-744; discussion 744-745.
11. O’Brien SM, Shahian DM, Filardo G, et al. The Society of Thoracic Surgeons 2008 cardiac surgery risk models: part 2—isolated valve surgery. Ann Thorac Surg. 2009;88(1 suppl):S23-S42.
12. Roques F, Nashef SA, Michel P, et al. Risk factors and outcome in European cardiac surgery: analysis of the EuroSCORE multinational database of 19030 patients. Eur J Cardiothorac Surg. 1999;15:816-822; discussion 822-823.
13. Michel P, Roques F, Nashef SA; EuroSCORE Project Group. Logistic or additive EuroSCORE for high-risk patients? Eur J Cardiothorac Surg. 2003;23:684-687.
14. Parolari A, Pesce LL, Trezzi M, et al. EuroSCORE performance in valve surgery: a meta-analysis. Ann Thorac Surg. 2010;89:787-793.
15. Wang TKM, Wang MTM, Gamble GD, et al. Performance of contemporary surgical risk scores for transcatheter aortic valve implantation: a meta-analysis. Int J Cardiol. 2017;236:350-355.
16. Afilalo J, Lauck S, Kim DH, et al. Frailty in older adults undergoing aortic valve replacement: the FRAILTY-AVR Study. J Am Coll Cardiol. 2017;70:689-700.
17. Shimura T, Yamamoto M, Kano S, et al. Impact of the clinical frailty scale on outcomes after transcatheter aortic valve replacement. Circulation. 2017;135:2013-2024.
18. Arnold SV, Afilalo J, Spertus JA, et al. Prediction of poor outcome after transcatheter aortic valve replacement. J Am Coll Cardiol. 2016;68:1868-1877.
19. Stortecky S, Schoenenberger AW, Moser A, et al. Evaluation of multidimensional geriatric assessment as a predictor of mortality and cardiovascular events after transcatheter aortic valve implantation. JACC Cardiovasc Interv. 2012;5:489-496.
20. Ranucci M, Castelvecchio S, Menicanti L, et al. Accuracy, calibration and clinical performance of the EuroSCORE: can we reduce the number of variables? Eur J Cardiothorac Surg. 2010;37:724-729.
21. Edwards FH, Cohen DJ, O’Brien SM, et al. Development and validation of a risk prediction model for in-hospital mortality after transcatheter aortic valve replacement. JAMA Cardiol. 2016;1:46-52.
Troels Højsgaard Jørgensen, MD
Department of Cardiology
Copenhagen University Hospital
Lars Søndergaard, MD, DMSc
Department of Cardiology
Copenhagen University Hospital
+45 35458693; firstname.lastname@example.org