Curriculum in Cardiology
Integrating the Synergy between percutaneous coronary intervention with Taxus and Cardiac Surgery (SYNTAX) score into practice: Use, pitfalls, and new directions

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Risk stratification is key in optimizing care of patients undergoing percutaneous coronary intervention (PCI). Score algorithms, in particular, are useful prognostic tools to select the most appropriate strategy of treatment and help patients and their families to get a better understanding of issues relevant to treatment strategies and subsequent risks. Most scores tested in the setting of PCI focus on clinical variables. The SYNTAX score is a semiquantitative angiographic score developed to prospectively characterize the disease complexity of the coronary vasculature. This scoring system has recently been assessed in numerous cohorts of patients undergoing coronary revascularization by PCI or bypass surgery. When using the SYNTAX score, however, physicians are still challenged with a labor-intensive calculation and conflicting results from validation studies. Understanding how the SYNTAX score works, for which patients it works best, and whether it predicts accurately enough for its purpose is of paramount importance to get the maximum benefit from its application. The present article provides an overview of the background and the currently available evidences on the use of the SYNTAX score in patients undergoing coronary revascularization along with its limitations.

Section snippets

SYNTAX score calculation

The SYNTAX score is calculated based on the American Heart Association classification of the coronary artery tree modified by the ARTS investigators.1, 3, 4 This classification scheme divides the coronary tree into 16 segments that are differently depicted based on the presence of a right or left dominant coronary system. Each of these segments is attributed a multiplicative weighting factor similar to the Leaman score5 according to the relative blood flow supplied to the left ventricle.

Issues relevant to the real-world validation of the SYNTAX score

Validating and investigating the predictive accuracy of a prognostic model requires careful consideration of a number of variables. First, open issues include the optimal cutoff to distinguish the subgroup of patients at highest risk and the number of strata to be considered. Second, the use and cutoff values of the score may be different in patients with 1- and 2-vessel disease, 3-vessel disease, or left main disease. Third, there are no evidence demonstrating that the SYNTAX score is linearly

SYNTAX score in left main and multivessel disease

Table I summarizes the results of studies assessing the SYNTAX score in left main patients, treated either percutaneously or surgically.7, 8, 9, 10, 11, 12, 13, 14, 15 In the SYNTAX trial, the 24-month risk of major adverse cardiovascular and cerebrovascular events (MACCE) among patients treated with PCI in the left main cohort indicated differential survival rates in the anticipated order across tertiles (SI = 0.142), with a balanced rapport between those at intermediate risk and those at low

Combinations of SYNTAX score and clinical variables

A limitation of the SYNTAX score relies in the fact that the score algorithm does not entail any clinical variable. Comorbidities are known to impact early outcomes of patients undergoing CABG, but a role in worsening the operative morbidity of patients undergoing PCI cannot be ruled out.18, 19 For example, it is reasonable that patients with similar SYNTAX score may experience very different procedural outcomes according to their diabetes or chronic kidney disease status, emergent

SYNTAX score for aiding patients selection in left main revascularization

The above data corroborate the understanding that clinical outcomes of PCI patients vary appreciably, with incremental impact across SYNTAX score tertiles. Conversely, CABG seems less susceptible to the SYNTAX score variations (Figure 1). This is in line with the observation that CABG bypasses the lesion rather than directly treats it; hence, lesion complexity does not represent per se a reason for higher risk of clinical events.26 Another consideration that may be drawn from the data provided

SYNTAX score in randomized clinical trials

The SYNTAX score offers an attractive opportunity for stratifying patients included into randomized controlled trials of novel revascularization options. By prospectively dividing patients into categories of angiographic risk, comparisons of different devices may generate hypotheses to be tested in subsequent, adequately powered trials. For example, the forthcoming Evaluation of Xience Prime versus Coronary Artery Bypass Surgery for Effectiveness of Left Main Revascularization (EXCEL) trial

Pitfalls and issues relevant to SYNTAX score application in clinical practice

Several issues have emerged that need to be addressed in the forthcoming versions of the SYNTAX score. First, the score algorithm does not include subsets of lesions frequently observed in the growing population of patients with previous revascularization submitted to the catheterization laboratory such as in-stent restenosis and stenotic bypass grafts. Patent bypass grafts, coronary anomalies, muscular bridges, and aneurysms also make the calculation of the SYNTAX score less obvious. In the

Conclusions

Risk stratification by means of risk scores denotes a simplicistic approach if criteria for selecting the appropriate strategy do not also include a broad array of considerations dealing with the so-called Heart Team approach, including a comprehensive overview of PCI results, CABG results, preference of the patient, comorbidities, social, economic, cultural conditions and, last but not least, lesion characteristics. In this context, the semiquantitative SYNTAX score helps in prospectively

Disclosures

Conflict of interest: none reported.

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