Relationship Between the Angiographically Derived SYNTAX Score and Outcomes in High-Risk Patients Undergoing Percutaneous Coronary Intervention

Author(s): 

Sorin J. Brener, MD, Ashok J. Prasad, MD, Raushan Abdula, MD, Terrence J. Sacchi, MD

ABSTRACT: Numerous risk scores have been designed to predict the outcome of percutaneous coronary intervention (PCI). The Synergy between Percutaneous Coronary Intervention with Taxus and Cardiac Surgery (SYNTAX) score has been shown to predict outcome in patients with severe coronary artery disease (CAD) randomized to PCI or bypass surgery, but its utility in patients with less severe CAD is less well established. Methods. We calculated the SYNTAX score in 482 patients with diabetes mellitus or chronic kidney disease (serum creatinine > 1.5 mg/ml) undergoing non-emergency PCI. The study endpoint was 3-year all-cause mortality or repeat revascularization. Results. The mean age was 69 ± 11 years, 44% were women, 82% had diabetes and they had 1.82 ± 0.78 diseased vessels. The mean creatinine clearance was 67.3 ± 37.2 ml/min. The mean SYNTAX score was 11 ± 8, median of 9 (5–15), tertiles < 7, 7–12 and > 12. There was good interobserver concordance (0.784 and 0.816, p < 0.01, respectively among two pairs of observers). The 3-year estimated survival rate was 0.85 (95% confidence interval [CI] 0.82–0.88). By multivariable analysis, creatinine clearance (hazard ratio [HR] 0.82 per 10 ml/min, p < 0.001), ejection fraction (HR 0.82 per 10%, p = 0.004) and prior infarction (HR 1.7, p = 0.03) were the only predictors of death. The SYNTAX score did not predict mortality. The incidence of repeat PCI by increasing tertiles of SYNTAX score was 19.2%, 32.2% and 33.2%, respectively, p < 0.001. Conclusion. In patients at high risk for ischemic events without severe CAD, the SYNTAX score is not associated with mortality at 3 years.

J INVASIVE CARDIOL 2011;23:66–69

Key words: percutaneous coronary intervention; mortality;
SYNTAX; predictive score

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Numerous scores have been designed to predict outcomes of percutaneous coronary intervention (PCI).1–6 These scores include clinical, demographic and angiographic parameters and are particularly helpful to predict in-hospital events. Recently, the investigators of the Synergy between Percutaneous Coronary Intervention with Taxus and Cardiac Surgery (SYNTAX) trial developed and validated a score for severity of coronary artery disease (CAD) based entirely on angiographic characteristics (presence of total occlusion, bifurcation or trifurcation, angle and involvement of branch vessels, calcification, lesion length, ostial location, tortuosity and presence of thrombus).7,8 The SYNTAX score can be calculated using an interactive Web program and is the summation of the individual scores for each lesion with > 50% diameter stenosis by visual estimation in a vessel > 1.5 mm in diameter. It was used predominantly in patients with very complex CAD, such as left main coronary stenosis or 3-vessel CAD in clinical trials or registries comparing PCI to coronary artery bypass grafting (CABG)9–11 and it was found to reliably predict major adverse cardiac events (MACE).

Since the SYNTAX score was designed to characterize risk in patients with very severe CAD, but not in those with less critical CAD, we set out to evaluate the relationship between the SYNTAX score and mortality or repeat revascularization in patients with less severe CAD treated in routine clinical practice. In order to increase the rate of observed events, we chose a population of patients considered at high risk for ischemic events because of the presence of diabetes mellitus or chronic kidney disease.12

Methods

Data for patients undergoing PCI at our institution are prospectively entered into a computerized database based on the reporting system of the American College of Cardiology National Cardiovascular Database Registry (ACC NCDR). We included for this analysis all patients undergoing their first PCI between 1/1/2006 and 12/31/2007. In order to select a population with higher risk for cardiovascular death, only patients with diabetes mellitus or chronic kidney disease (CKD; serum creatinine ≥ 1.5 mg/dl) were included. Patients with previous CABG or those undergoing primary PCI for ST-elevation myocardial infarction (MI) were excluded. The authors separately evaluated the SYNTAX score and concordance was evaluated in a subset of 160 patients, for which paired assessments were performed (SJB and RA, SJB and AJP). The study endpoint was all-cause mortality or repeat revascularization, assessed by the Social Security Administration Death Index (SSDI, updated on 4/14/2010)13 and local electronic medical records.

Continuous and categorical variables were summarized with means and proportions, respectively. The concordance correlation coefficient (Lin) was determined for the two pairs of observers. Survival analysis was performed using Kaplan-Meier methodology with log-rank testing. A multivariable Cox proportional hazard model was developed to assess the impact on all-cause mortality, or revascularization, of the following variables: age, gender, extent of CAD (number of diseased vessels), SYNTAX score, ejection fraction, prior MI, diabetes mellitus, CKD (defined as serum creatinine ≥ 1.5 mg/dl, or as creatinine clearance < 60 ml/min [calculated from the Cockcroft-Gault formula with adjustment for gender]), smoking (current or past), arterial hypertension, hyperlipidemia, family history of CAD and PCI priority, using definitions of ACC NCDR v3.0. P-values < 0.05 were considered statistically significant. All analyses were performed with STATA SE 9.0 (College Station, Texas).

The institutional review board (IRB) approved the local PCI registry and allowed the use of aggregate data for clinical research.

Results

We identified 482 patients who underwent elective or urgent PCI in the specified period and fulfilled the inclusion and exclusion criteria. We had excluded 102 patients with previous CABG and 19 because of STEMI. During the study period 2,404 PCI procedures were performed. The baseline characteristics of the cohort are shown in Table 1. The mean duration of follow up was approximately 3 years (1,027 ± 311 days, median 1,070 days). The mean SYNTAX score was 11 ± 8, median of 9 (5–15), tertiles < 7, 7–12 and > 12. The maximum score was 63. The score was not normally distributed (p < 0.001) with marked left skewness (Figure 1). The concordance coefficient between observers in each pair was 0.784 and 0.816, p < 0.01 for both, respectively. The maximal interobserver difference was 4 points.14

The estimated 1-, 2- and 3-year survival rates and 95% confidence intervals (CI) were 0.94 (0.91–0.96), 0.88 (0.85–0.91) and 0.85 (0.82–0.88), respectively. There were 79 deaths overall (16.4%), including 3 periprocedural deaths prior to hospital discharge. The mortality rate was 13.3% and 19.7% in patients with scores below and above the median (i.e., 9), respectively, p = 0.04. The mortality rate according to tertiles of SYNTAX scores is shown in Figure 2 (p = 0.60). Using the multivariable regression model described above (c-statistic 0.70), the strongest independent predictor of death was creatinine clearance (hazard ratio [HR] 0.82 [0.74–0.90], p < 0.001 per 10 ml/min). Ejection fraction (HR 0.98 [0.73–0.91], p = 0.004 per 10%) and prior MI (HR 1.7 [1.1–2.7], p = 0.03) were the other independent predictors of death. The SYNTAX score as a continuous variable or as an ordered value by tertile or median values did not independently predict outcome. Substitution of creatinine clearance with a dichotomous definition of CKD (creatinine ≥ 1.5 mg/min or creatinine clearance < 60 ml/min) yielded very similar results.

Repeat PCI was performed in 113 patients (23.4%). The estimated cumulative rate at 3 years was 19.2%, 32.2% and 33.2%, in increasing tertiles of score, p < 0.001 (Figure 3). In 70 patients (62%) repeat PCI was a planned procedure to complete revascularization. Using the same multivariable model as above, the SYNTAX score was not associated with repeat PCI. Excluding patients with staged PCI, only the extent of CAD (HR 1.8 per vessel, p = 0.04), and prior MI (HR 2.0, p = 0.05) were independently predictive of repeat PCI for de-novo or restenotic lesions. None of the patients underwent surgical revascularization after their initial PCI.

Discussion

In this single-institution experience, we report the use of the SYNTAX score outside randomized clinical trials in patients who had less than critical CAD (involving the left main coronary artery or all 3 vessels) but had high-risk clinical features and underwent non-emergency PCI. We found that at a median follow up of 3 years, all-cause mortality was predominantly predicted by the degree of renal dysfunction, ejection fraction and previous myocardial infarction. The SYNTAX score, which could be reliably and consistently calculated by the investigators, did not independently predict outcome. The mortality rate in our cohort was approximately 5% per year. A higher SYNTAX score was associated with a higher rate of repeat PCI, but this association became insignificant after adjustment for important baseline characteristics.


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