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- ↵∗Address for correspondence:
Dr. Marie-Claude Morice, Institut Cardiovasculaire Paris Sud, 5 rue du Théâtre, 91300 Massy, France.
In line with the ongoing debate regarding the actual prognostic value of the SYNTAX (Synergy Between Percutaneous Coronary Intervention With Taxus and Cardiac Surgery) score based on angiographic anatomical criteria and its accuracy compared with functional criteria of lesion severity as a guide for the revascularization decision process, the residual SYNTAX score is also being challenged in view of the results of recent studies (1,2) showing the superiority of fractional flow reserve (FFR)–guided functionally complete revascularization in predicting the outcomes of patients with stable coronary artery disease.
Against this backdrop, and as a complement to the previous study that they performed in patients with stable coronary disease (3), Kobayashi et al. (4) report in this issue of the Journal a post hoc analysis of the predictive value of the residual SYNTAX score based on data from 3 randomized trials encompassing a total of 547 patients with acute coronary syndromes who underwent FFR-guided complete revascularization. In keeping with their previous findings, they observed a consistent predictive superiority of complete revascularization of functionally significant stenoses in terms of ischemic events compared with the residual SYNTAX score in a population of patients with acute coronary syndromes.
The SYNTAX score was developed as an angiographic stratification tool (5) initially used in the eponymous study to grade the complexity of coronary lesions and establish evidence-based guidelines for determining the most appropriate revascularization strategy in patients with complex multivessel and left main disease.
This score proved extremely useful in the context of the SYNTAX trial, because it enabled the stratification of a very heterogeneous population of patients into 3 distinct tertiles: low risk (SYNTAX score <22), intermediate risk (>23 and <32), and high risk (>32).
Based on this score, the trial demonstrated that, in the group of patients with multivessel coronary disease, only those in the <22 tertile had similar noninferior outcomes after percutaneous coronary intervention (PCI) compared with coronary artery bypass grafting (CABG), whereas patients in the intermediate- and high-risk groups had better outcomes when treated by CABG. Quite unexpectedly at the time, patients with left main lesions in both the low and intermediate tertiles had equivalent outcomes with PCI and CABG indiscriminately, thus widening the role of PCI in this setting.
A few years later, the residual SYNTAX score (6) was introduced as an objective, quantitative measure of the degree and complexity of any remaining obstructive coronary disease after PCI and was divided into 3 tertiles: 0 to <4, >4 to 8, and >8. In the PCI cohort, the mean RSS was calculated at 4.5. This measurement tool of incomplete revascularization was found to be a powerful indicator of 5-year mortality in the SYNTAX trial population, with the >8 tertile being associated with the highest mortality rate at 5 years.
More recently, in the NOBLE (Percutaneous Coronary Angioplasty Versus Coronary Artery Bypass Grafting in Treatment of Unprotected Left Main Stenosis) and EXCEL (Evaluation of XIENCE Versus Coronary Artery Bypass Surgery for Effectiveness of Left Main Revascularization) trials (7,8), the SYNTAX score was shown to be poorly predictive in terms of treatment selection and outcomes between PCI and CABG for patients with left main disease. It was also unanticipated that in the NOBLE trial, in contrast with the findings of SYNTAX, the group of patients in the lowest tertile undergoing CABG had significantly better outcomes than those treated by PCI. In the EXCEL trial, the outcomes were similar in all 3 tertiles.
There are, indeed, limitations inherent in the SYNTAX score that have been repeatedly underlined. It has been clearly shown that one of its major shortcomings is its low intraobserver and interobserver reproducibility (9). Incidentally, Kobayashi et al. (4) should be commended for their excellent results in terms of intraobserver variability. It is, however, less than certain that such results may be universally replicated in all centers in a “real life” setting. Another limitation of the score is that it takes into account the presence of lesions in very small vessels (1.5 mm), which are almost always functionally insignificant and in which the benefit of revascularization is uncertain.
Before driving the final nail in the coffin of the SYNTAX score, we may want to consider that this stratification tool was originally designed to predict the outcome of patients with complex multivessel and left main disease and high scores of lesion severity, and not for the purpose of determining the prognosis of those with low scores (6.7 in the study reported here by Kobayashi et al. ). Furthermore, in the EXCEL trial, post hoc analysis of the outcomes by tertiles may constitute a methodological bias, given that patients with a high score were excluded from the study per protocol.
At a time when the debate is ongoing as to whether complete revascularization of ST-segment elevation myocardial infarction, either based or not based on functional criteria, should be preferred to revascularization of the culprit vessels alone, the authors should be praised for providing new and consistent data collected in patients with acute coronary syndromes in favor of revascularization prompted by functional criteria.
Their findings may help tip the balance in favor of systematic FFR-guided complete functional revascularization as the most appropriate strategy for predicting optimal outcomes despite the presence of potentially “active” residual lesions, even in patients with unstable coronary disease.
Even though its value is currently being questioned, the SYNTAX score can be credited with having paved the way for the stratification of the huge undifferentiated mass of patients with multiple vessel disease.
Finally, although we have intuitively assumed that complete revascularization is a predictor of good outcomes in stable patients, it is reassuring to know that this also holds true for unstable patients with a less predictable prognosis.
↵∗ Editorials published in the Journal of the American College of Cardiology reflect the views of the authors and do not necessarily represent the views of JACC or the American College of Cardiology.
Dr. Morice has reported that she has no relationships relevant to the contents of this paper to disclose.
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