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Am J Cardiovasc Dis. 2012; 2(3): 216–222.
Published online 2012 July 25.
PMCID: PMC3427976

Impact of SYNTAX score on 1-year clinical outcomes in patients undergoing percutaneous coronary intervention for unprotected left main coronary artery

Abstract

SYNTAX score is an angiographic scoring system that was developed to quantify the number, complexity, and location of lesions in patients undergoing coronary revascularization. Up to now, the impact of SYNTAX score on clinical outcomes in patients undergoing percutaneous coronary intervention (PCI) for unprotected left main coronary artery (LMCA) lesions has not been fully examined. Therefore, we evaluate the usefulness of the SYNTAX score and identify the cutoff value of this score to predict 1-year clinical outcomes in patients undergoing PCI for unprotected LMCA lesions. This was a single-center retrospective study that included 49 consecutive patients undergoing elective PCI for unprotected LMCA lesions. We calculated the SYNTAX score and examined the correlations between this score and 1-year clinical outcomes. Major adverse cardiac events (MACE) occurred in 12 patients (24%): target lesion revascularization in 9 patients (18%), myocardial infarction in 2 (4%), and cardiac death in 1 (2%). The frequency of MACE was significantly higher in the intermediate (47%) or high score group (50%) than in the low score group (4%). Furthermore, the SYNTAX score was significantly higher in the MACE group than in the non-MACE group (31 vs. 22, p = 0.008). Receiver-operating characteristic curve showed that the SYNTAX score exhibited 83% sensitivity and 76% specificity for predicting the development of MACE at a cutoff value 26. These results demonstrate that the SYNTAX score could be a useful tool to predict 1-year clinical outcomes in patients undergoing elective PCI for unprotected LMCA lesions.

Keywords: Coronary artery disease, left main coronary artery, percutaneous coronary intervention, SYNTAX score

Introduction

SYNTAX score is an angiographic scoring system that was developed to quantify the number, complexity, and location of lesions in patients undergoing coronary revascularization [1,2]. The SYNTAX score has been used to assist in deciding the optimal revascularization strategy for patients with complex coronary artery disease (CAD), because patients with a high SYNTAX score treated by percutaneous coronary intervention (PCI) have been shown to be at a high risk of adverse cardiac events [3,4].

Contemporary treatment guidelines recommend coronary artery bypass grafting (CABG) as the most appropriate revascularization strategy for patients with unprotected left main coronary artery (LMCA) disease [5]. However, since the introduction of PCI with coronary stents, particularly drug-eluting stents (DES), interventional cardiologists have been expanding the application of coronary stenting to include patients with complex lesions, including unprotected LMCA disease. The predictive value of the SYNTAX score was recently validated in patients undergoing PCI for 3-vessel CAD in the Arterial Revascularization Therapies Study Part II [6]. Although the 1-year clinical prognosis in LMCA patients was similar for CABG and PCI, patients with higher baseline SYNTAX scores had significantly worse outcomes for PCI [7].

The aim of our study was to evaluate the usefulness of the SYNTAX score and identify the cutoff value of this score to predict 1-year clinical outcomes in a single center population of patients undergoing PCI for unprotected LMCA lesions.

Materials and methods

Patients population

This single-center, retrospective, observational study included 49 consecutive patients who underwent elective PCI for de novo unprotected LMCA disease at Yokohama Sakae Kyosai Hospital, between January 2002 and December 2008. The LMCA lesion was defined as unprotected if there was no patent bypass graft to the left anterior descending coronary artery or left circumflex coronary artery. PCI was performed in patients who preferred PCI rather than CABG and in patients for whom CABG was considered too risky. Interventional strategies, including optional techniques, types of stents and intravascular ultrasound use, were left entirely to the discretion of the operators. An intravenous bolus of heparin was administered at a dose of 100 U/kg immediately before PCI. Before the procedure, patients received both 100 mg of aspirin and thienopyridines (75 mg of clopidogrel or 200 mg of ticlopidine daily). After the procedure, all patients were prescribed aspirin for lifetime and thienopyridines therapy for at least 12 months irrespective of the type of stent used. Angiographic follow-up was performed at 6-12 months after PCI unless the patient had earlier clinical indications.

Calculation of SYNTAX score

SYNTAX score was calculated retrospectively based on diagnostic angiograms obtained before the PCI by two experienced interventional cardiologists using the SYNTAX score calculator (available at http://www.syntaxscore.com). In case of disagreement, the opinion of a third observer was obtained, and the final decision was made by consensus. The total SYNTAX score was composed of the individual scores for each separate lesion with a diameter stenosis of ≥50% in a vessel of ≥1.5mm in diameter by visual assessment, as previously reported [1].

Correlation between SYNTAX score and clinical outcome

The major adverse cardiac events (MACE) were cardiac death, nonfatal myocardial infarction (MI), and target lesion revascularization (TLR) within 1-year after PCI. MI was defined according to the definition given in the Arterial Revascularization Therapy Study [8]. TLR was defined as either PCI or CABG to treat restenosis within the stent, or within the 5-mm borders of the stent, or the ostium of the side branches.

To examine the correlations between SYNTAX score and clinical outcomes, we divided the patients into 3 groups: high score group (SYNTAX score ≥33), intermediate score group (23 to 32), and low score group (0 to 22) [3]. One-year clinical outcomes were compared among the 3 groups. Furthermore, we examined the difference in SYNTAX score between the MACE and non-MACE group and determined the cutoff value of SYNTAX score for predicting 1-year clinical outcomes.

Data on clinical, angiographical, and procedural characteristics were obtained from medical records. Follow-up information was obtained either from a review of the hospital records, by telephone call, or from the primary care physician.

Statistical analysis

Statistical analyses were performed using Stat-View version 5.0 (SAS Institute Inc., Cary, North Carolina). Results are expressed as the mean ± SD. Differences in continuous variables between the 2 groups were compared using the unpaired t-test. One factor analysis of variance (ANOVA) was used to compare mean values among the 3 groups and Fisher’s Protected Least Significant Difference was used to compare between the 2 groups. Categorical variables among groups were compared using the chi-square test. The receiver-operating characteristic (ROC) curve was used to determine the cutoff value of SYNTAX score for predicting 1-year clinical outcomes. Statistical significance was set at p < 0.05.

Results

Baseline clinical characteristics in the 3 groups are shown in Table 1. No significant differences were observed among the 3 groups.

Table 1
Baseline clinical characteristics of subjects.

Angiographical and procedural characteristics are shown in Table 2. The frequencies of LMCA plus 2-vessel or 3-vessel disease were significantly higher in the intermediate (18% and 6%, respectively) and high score group (50% and 17%, respectively) than those in the low score group (0%, p = 0.002). The number of stents used and stent length were significantly greater in the intermediate and high score group than those in the low score group. Whereas, the frequencies of single stenting and single stenting plus kissing balloon technique for bifurcation treatment were significantly lower in the intermediate (24% and 29%, respectively) and high score group (33% and 17%, respectively) than those in the low score group (54% and 35%, p = 0.04).

Table 2
Angiographical and procedural characteristics.

MACE occurred in 12 patients (24%): TLR in 9 (18%), MI in 2 (4%), and cardiac death in 1 (2%). The frequency of MACE was 50% in the high score group and 47% in the intermediate score group, and this frequency was significantly higher than that in the low score group (4%) (Figure 1). Furthermore, the SYNTAX score in the MACE group was significantly higher than in the non-MACE group (31 vs. 22, p = 0.008) (Figure 2). ROC curve showed that the SYNTAX score exhibited 83% sensitivity and 76% specificity for predicting the development of MACE at a cutoff value 26 (Figure 3).

Figure 1
Frequencies of MACE in the 3 groups. The frequency of MACE was 50% in the high score group and 47% in the intermediate score group, and in both group it was significantly higher than that in the low score group. MACE, major adverse cardiac events.
Figure 2
SYNTAX score in patients with and without MACE. SYNTAX score in the MACE group was significantly higher than in the non-MACE group (31 vs. 22, p = 0.008). MACE, major adverse cardiac events.
Figure 3
Cutoff value of SYNTAX score for predicting the development of MACE within 1 year after PCI. ROC curve showed that the SYNTAX score exhibited 83% sensitivity and 76% specificity for predicting the development of MACE within 1 year after PCI at a cutoff ...

Discussion

The main finding of this study was that the SYNTAX score was useful as a predictor of 1-year clinical outcomes in patients undergoing elective PCI for unprotected LMCA lesions. Furthermore, the cutoff value of this score to predict the development of MACE was 26. This suggests that the SYNTAX score is a suitable tool to stratify late outcomes after PCI for LMCA disease.

In the SYNTAX trial, CABG was associated with a lower rate of major adverse cardiac and cerebrovascular events at 1 year in patients with 3-vessel disease or LMCA disease as compared with PCI [3]. As a result, contemporary treatment guidelines recommend CABG as the most appropriate revascularization strategy for patients with unprotected LMCA disease [5]. However, recent studies showed that in patients with LMCA disease PCI was associated with a lower rate of periprocedural adverse events and long-term event-free survival was similar to that obtained with CABG [9-11]. Furthermore, in the SYNTAX trial, subgroup analysis of patients with LMCA disease showed that PCI had safety and efficacy outcomes comparable to those attained with CABG at 1 year [7]. However, in another previous study that examined the usefulness of SYNTAX score in patients undergoing PCI for LMCA disease, high SYNTAX score was significantly associated with cardiac mortality and MACE [12]. Consistent with previous reports, our findings showed that high SYNTAX score was associated with the development of MACE.

Capodanno et al. reported that score 37 was the optimal cutoff value to distinguish between patients at low and high risk of MACE [12]. Nevertheless, a SYNTAX score 26 was associated with the development of MACE in this study. This difference between the previous study by Capodanno et al. and the present study was due to a difference in the number of patients with LMCA plus multivessel disease. Patients with LMCA plus 2-vessel or 3-vessel disease accounted for 31% (79/255) and 22% (55/255) of the study population in Capodanno’s study and for 12% (6/49) and 4% (2/49) in our study. The present results are in agreement with a recent study showing a SYNTAX score 28 as the optimal cutoff value for predicting MACE in patients undergoing PCI for unprotected LMCA disease [13].

PCI for patients with LMCA disease showed safety and efficacy outcomes comparable to those with CABG at 1 year, whereas the rate of repeat revascularization was significantly higher in the PCI arm [7]. Furthermore, some nonrandomized trials have also shown significantly higher revascularization rates for PCI than for CABG in LMCA disease [10,14,15]. Our findings showed that a high SYNTAX score was associated with the development of MACE, particularly with repeat revascularization. These findings indicated that lesion complexity had a greater effect on the outcomes of PCI. In contrast with excellent long-term angiographic and clinical outcomes of LMCA ostial or shaft lesions treated by PCI with stenting, distal LMCA bifurcation lesions are still challenging to the treating physician and show less favorable outcomes with PCI. Cumulative evidence suggests that results are less favorable when distal LMCA lesions are treated by two-stent complex techniques as compared to a single-stent cross-over technique [16,17]. Moreover, in a large observational study comparing the outcomes between ostial/shaft and distal bifurcation lesions with LMCA disease, distal LMCA bifurcations were associated with a 50% excess risk for adverse outcomes, which was mainly driven by bifurcation lesions that were treated with complex stenting [18]. Consensus treatment guidelines continue to recommend CABG as the “gold standard” for revascularization of unprotected LMCA lesions but note that PCI is feasible and may be a promising strategy in selected patients [19]. In patients with a low or intermediate SYNTAX score, particularly under 26, and ostial or shaft lesions, PCI is a useful strategy to treat the unprotected LMCA lesions.

The most recent guidelines on myocardial revascularization have recommended the SYNTAX score as a risk stratification score to be used in candidates for PCI (class IIa, level of evidence B) but not in those for CABG (class III, level of evidence B) [20]. This ability to identify patients at a high risk for the occurrence of adverse events has important clinical implications. It enables physicians to adequately inform their patients regarding the potential risk of adverse events and the selection of a revascularization procedure (PCI vs. CABG). Consequently, this may leads to act as a trigger for more aggressive lipid-lowering therapy as well as lifestyle modification in patients at a very high risk of adverse events.

Study limitations

This study has several limitations. First, it was a retrospective single center study and the sample size was too small to evaluate clinical endpoints. Second, the SYNTAX score was retrospectively evaluated in a population with a known history of unprotected LMCA stenting. Third, we included patients who were treated with bare metal stent and DES. The difference in the stents used may affect the results of this study. Finally, patients with surgical revascularization were not included, thus there was a potential bias in patient selection that may confound the interpretation of the results.

Conclusions

In the current observational, relatively small study, the SYNTAX score could be a useful tool to predict 1-year clinical outcomes in patients undergoing elective PCI for unprotected LMCA lesions.

References

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