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The SYNTAX Score for Chronic Total Occlusions: Building a Better Mousetrap
Patients with coronary artery disease (CAD) are frequently found to have occluded arteries during coronary angiography. The prevalence of coronary chronic total occlusions (CTOs) varies from 18%-54% in contemporary practice.1 The optimal treatment strategy for CTOs has yet to be defined and is a topic of much debate. Percutaneous coronary intervention (PCI) for CTOs is infrequently attempted because it is deemed to be technically challenging, time consuming and costly, associated with high failure and complication rates, and of questionable benefit to the patient even if successful. As a result, patients with CTOs are typically referred for coronary artery bypass graft (CABG) surgery when symptomatic, or treated medically if the disease burden is low or surgery is not an option.2 However, technical refinements and improvements in equipment have led to higher success rates with fewer complications for CTO-PCI.3 There is evidence now to suggest that successful revascularization improves quality of life (QOL) for many patients.4
A major challenge in the treatment of CTOs is the lack of a dedicated decision-making tool to guide physicians in choosing the most appropriate revascularization strategy for such patients. The Synergy between PCI with Taxus and Cardiac Surgery (SYNTAX) score (SS) is an angiographic grading system that is commonly used to define CAD complexity and to help guide therapy for patients who have multivessel CAD.5 In this scheme, points are awarded for anatomic characteristics such as the number and location of vessels with an angiographically significant stenoses (>50% narrowing in vessels with a diameter of >1.5 mm), involvement of the left main artery, bifurcation or trifurcation disease, and presence of CTOs. In the original SYNTAX trial, patients with low scores (SS ≤22) were seen to do equally well with PCI or CABG, whereas patients with intermediate (SS 23-32) or high scores (SS ≥33) did better with CABG in terms of major adverse clinical event (MACE) rate.6 The SS has since been validated in various clinical settings, and has been endorsed by multiple professional societies as a tool to guide therapy in patients with complex CAD.7
The SS for CTOs is based on the likelihood of technically successful PCI. All CTOs are weighted higher (x5) than non-CTO lesions (x2), and additional points are awarded for angiographic features that have been associated with CTO-PCI failure. Patients with CTOs typically have much higher scores than those with non-CTO lesions for similar disease distribution. In the SYNTAX trial, patients with intermediate and high scores were more likely to have CTOs present than those with low scores. Interestingly, a significant proportion of occlusions went untreated in both treatment arms: 51% in the PCI cohort (mostly after a failed attempt) and 32% in the surgical arm (not attempted for various reasons).8 Nevertheless, the high prevalence of CTOs in patients with high scores has bolstered the idea that surgery is the best option for CTOs.
The SS has several shortcomings that make it less than ideal. The criteria used to determine technical success for CTO-PCI are based on interventional techniques that are outdated by at least two decades.9 Furthermore, the score was validated using trials in which few CTO lesions were treated according to contemporary techniques. Outcomes after CTO-PCI have improved markedly and success rates approach 90% or greater with very low complication rates in dedicated centers.3 This calls into question the rationale for weighting CTOs more heavily than non-CTOs by a factor of 2.5 in the SS, and raises the concern that the SS may be inherently biased against PCI for the treatment of CTOs that: (1) may be amenable to PCI; and (2) are frequently left untreated at the time of surgery.
In this issue of the Journal of Invasive Cardiology, Redfors et al10 use data from the quantitative coronary angiography (QCA) substudy of the prospective Acute Catheterization and Urgent Intervention Triage StrategY (ACUITY) trial to better understand the contribution of CTOs to the SS, and to evaluate the utility of a simplified scoring system in which CTO and non-CTO lesions were weighted equally (x2).11 The authors analyzed angiograms from 4356 patients who presented with a moderate-risk or high-risk non-ST segment elevation MI and were treated with medical therapy, PCI, or CABG. They divided the study population into those with CTOs and those without CTOs, and they calculated the standard SS as well as the simplified SS (sim-SS) for each cohort. They found that on average, CTOs accounted for two-thirds of the standard SS score and were associated with worse outcomes at 1 year regardless of the treatment strategy. A higher SS was associated with an increased risk of death or MACE for patients treated conservatively or with PCI but not with CABG. Use of the sim-SS lowered the median score in the CTO group from 19.5 to 13 (as opposed to 8 for the non-CTO cohort), and reclassified 31% of the patients in this cohort to the lowest tertile (SS <22). The sim-SS was able to predict the risk of adverse outcomes with similar power to the SS, which suggests that almost one-third of the patients with CTOs would have been potential candidates for PCI. The authors do not specify how many CTOs were actually treated by either PCI or surgery, nor the percentage of patients in whom complete revascularization was achieved.
The authors are to be commended for this well-done analysis, which challenges the notion that patients with CTOs are rarely candidates for PCI. Their observations confirm that the presence of CTOs is associated with worse outcomes, and that patients with the most complex disease do better with CABG than with PCI or medical therapy. Their simple but innovative use of a simplified angiographic scoring system shows that more patients with CTOs may be candidates for PCI, acknowledging that technical success rates with PCI have improved significantly. It also suggests that the SS in its current iteration may not be the ideal tool for evaluation of treatment options for patients with CTOs. This is important considering the inconsistent performance of the SS in predicting outcomes after CABG, and the observation that patency rates after surgical revascularization for CTOs are lower than expected (unless the occlusion is located in the left main or left anterior descending artery).12,13
Despite its widespread applicability and reproducibility, the SS is less than ideal for evaluating patients with CTOs. As the number of CTO-PCIs grows, there is a need to develop a more clinically relevant CTO classification system that incorporates both angiographic and non-angiographic variables for maximum relevancy. The authors have taken an important step in this direction. Their findings suggest that it may be possible to update the SS rather than devise a new scheme from scratch. This is good news for both patients with CTOs and the clinicians who treat them, because if the current trend in outcomes continues to hold, we are not far from a time when PCI for certain CTOs is considered to be the norm rather than the exception to the rule.
References
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9. Hamburger JN, Serruys PW, Scabra-Gomes R, et al. Recanalization of total coronary occlusions using a laser guidewire (the European TOTAL Surveillance study). Am J Cardiol.1997;80:1419-1423.
10. Redfors B, Palmerini T, Caixeta A, et al. Impact of chronic total occlusions on revascularization scores and outcome prediction. J Invasive Cardiol. Epub 2017 March 15.
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12. Lemesle G, Bonello L, de Labriolle A, et al. Prognostic value of the Syntax score in patients undergoing coronary artery bypass grafting for three-vessel coronary artery disease. Catheter Cardiovasc Interv. 2009;73:612-617.
13. Widimsky P, Straka Z, Stros P, et al. One-year coronary bypass graft patency: a randomized comparison between off-pump and on-pump surgery angiographic results of the PRAGUE-4 trial. Circulation. 2004;110:3418-3423.
From the University of Texas Health Science Center at Houston, McGovern Medical School, Houston, Texas.
Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.
Address for correspondence: H. Vernon Anderson, MD, Cardiology Division, University of Texas Health Science Center at Houston, McGovern Medical School, 6431 Fannin, MSB1.246, Houston, TX 77030. Email: h.v.anderson@uth.tmc.edu
