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Vasim Farooq, Yvonne Vergouwe, Lorenz Räber, Pascal Vranckx, Hector Garcia-Garcia, Roberto Diletti, Arie Pieter Kappetein, Marie Angèle Morel, Ton de Vries, Michael Swart, Marco Valgimigli, Keith D. Dawkins, Stephan Windecker, Ewout W. Steyerberg, Patrick W. Serruys, Combined anatomical and clinical factors for the long-term risk stratification of patients undergoing percutaneous coronary intervention: the Logistic Clinical SYNTAX score, European Heart Journal, Volume 33, Issue 24, December 2012, Pages 3098–3104, https://doi.org/10.1093/eurheartj/ehs295
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Abstract
The SYNTAX score (SXscore), an anatomical-based scoring tool reflecting the complexity of coronary anatomy, has established itself as an important long-term prognostic factor in patients undergoing percutaneous coronary intervention (PCI). The incorporation of clinical factors may further augment the utility of the SXscore to longer-term risk stratify the individual patient for clinical outcomes.
Patient-level merged data from >6000 patients in seven contemporary coronary stent trials was used to develop a logistic regression model—the Logistic Clinical SXscore—to predict 1-year risk for all-cause death and major adverse cardiac events (MACE). A core model (composed of the SXscore, age, creatinine clearance, and left ventricular ejection fraction) and an extended model [incorporating the core model and six additional (best performing) clinical variables] were developed and validated in a cross-validation procedure. The core model demonstrated a substantial improvement in predictive ability for 1-year all-cause death compared with the SXscore in isolation [area under the receiver operator curve (AUC): core model: 0.753, SXscore: 0.660]. A minor incremental benefit of the extended model was shown (AUC: 0.791). Consequently the core model alone was retained in the final the Logistic Clinical SXscore model. Validation plots confirmed the model predictions to be well calibrated. For 1-year MACE, the addition of clinical variables did not improve the predictive ability of the SXscore, secondary to the SXscore being the predominant determinant of all-cause revascularization.
The Logistic Clinical SXscore substantially enhances the prediction of 1-year mortality after PCI compared with the SXscore, and allows for an accurate personalized assessment of patient risk.
Comments
Dear Editor
We read with interest the editorial comment related to our study, Combined Anatomical and Clinical Factors for the Long Term Risk Stratification of Patients Undergoing Percutaneous Coronary Intervention: The Logistic Clinical SYNTAX Score. Whilst we welcome constructive criticism and debate, this should be based on having a complete understanding of the scientific and epidemiological reasoning. We cannot leave inaccurate views unchallenged, as it will give your readership an unbalanced, distorted view of our study.
1) The Logistic Clinical SYNTAX Score was externally validated, and should therefore legitimise the application of the Logistic Clinical SYNTAX Score in clinical practice. This is contrary to the views expressed in the editorial. As clearly specified in our study, a cross-validation process was used to evaluate the generality of the Logistic Clinical SYNTAX Score across the 7 trials in the dataset (n=6309). This has been referred to as an 'internal-external cross-validation' procedure. (1) We omitted each of the 7 trials in turn, with the prognostic model parameters being estimated from the remaining studies, and validated in the omitted study. This process was undertaken to control for any possible 'trial effects' (from each of the 7 trials in the dataset) potentially confounding the results, and is well accepted in the medical and epidemiological literature, as a form of external validation. (1-8) Of course, we encourage further validation of the Logistic Clinical SYNTAX Score to support its future clinical use.
2) The purpose of the Logistic Clinical SYNTAX Score was to move away from the category based assessment (i.e. "low", "intermediate," or "high" risk) and instead to rely on an individualised assessment of risk. The previously adopted category based assessment of risk has recently been shown to be potentially detrimental to the individual patient, where a cohort of patients with lower SYNTAX Scores were found to have a prognostic advantage to undergoing cardiac surgery, rather than percutaneous coronary intervention. (9) Individualised risk predictions are a move to eliminate these issues. Relying on arbitrarily defined cut- offs, as suggested in the editorial, is therefore potentially misguided. Although we do agree that a cut-off for the score to support decision- making may be necessary, this can either be done by subject experts, or left to the discretion of the treating physician, where they may, for example, weigh the long-term outcomes of undergoing PCI, against the short -term operative risks in undergoing CABG. We have previously shown that high clinical risk patients are potentially more suitable for CABG compared to PCI, provided an acceptable threshold of operative risk is not exceeded. (9)
3) The editorial claims about differences between an 'additive' or 'logistic' Clincial SYNTAX Score seems to make no sense, since we use the mathematical property of the logistic regression model, i.e. we can simply add scores at the logistic scale to formulate the final score. (10) An online calculator will soon be made available to make the process of calculating the Logistic Clinical SYNTAX Score simpler.
Future work will now attempt to produce a single risk score that can be applied to patients undergoing either CABG or PCI, to aid the Heart Team in objectively selecting the most appropriate revascularization modality. This will incorporate the principles of the Logistic Clinical SYNTAX Score, and its surgical counterpart, the ACEF Score. (11, 12)
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Conflict of Interest:
None declared