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Impact of the residual SYNTAX score on clinical outcomes after percutaneous coronary intervention for patients with chronic renal insufficiency

Abstract Objectives This study demonstrated the prognostic value of the residual SYNTAX score (rSS) for patients with chronic renal insufficiency (CRI). Background The rSS has been proposed as a useful tool for quantifying and stratifying the degree and complexity of residual stenosis and predicting long‐term clinical outcomes following percutaneous coronary intervention (PCI). However, it has never been validated for patients with CRI. Methods A total of 2,468 consecutive patients with an estimated glomerular filtration rate <90 ml/min/1.73 m2 who underwent PCI were retrospectively enrolled. Patients with rSS >0 were defined as having incomplete revascularization and were stratified into the reasonable incomplete revascularization (RICR; 0 < rSS ≤ 8) group or the incomplete revascularization (ICR; rSS >8) group. Their outcomes were compared to those of the complete revascularization (CR) group. Results During follow‐up (median, 3 years; range, 1.5–5 years), the ICR group had the highest incidence of all‐cause death, cardiac death, myocardial infarction (MI), unplanned revascularization, stroke, and major adverse cardiovascular and cerebrovascular events (MACCE). Despite having higher rates of unplanned revascularization and MACCE, RICR group had comparable all‐cause mortality, cardiac mortality, MI, and stroke with CR group. A multivariable Cox analysis indicated that rSS was an independent predictor of cardiac death, MI, unplanned revascularization, stroke, and MACCE. Furthermore, compared with baseline SYNTAX score, rSS had stronger prognostic accuracy when predicting the risk of unplanned revascularization, stroke, and MACCE at the 3‐year follow‐up. Conclusions The rSS is a powerful indicator of clinical outcomes and may help determine reasonable levels of revascularization for patients with CRI following PCI.


| INTRODUCTION
Chronic kidney disease (CKD) is a common high-risk comorbidity that increases cardiovascular mortality and morbidity rates. 1 Furthermore, CKD has been confirmed to be associated with lower procedural success rates, more complications, and worse clinical outcomes, including restenosis or stent thrombosis following percutaneous coronary intervention (PCI). 1,2 Percutaneous coronary intervention has become an important option for treating patients with coronary artery disease (CAD), and achieving complete revascularization (CR) is a desired goal of PCI. Previous studies suggested that CR was more advantageous than incomplete revascularization (ICR) and that residual disease was associated with adverse clinical outcomes after PCI. [3][4][5][6] However, for patients with more complex lesions, CR is not always achieved. Recent studies have shown that patients with an acceptable burden of obstructive CAD after revascularization have outcomes similar to those of subjects who achieved CR. [7][8][9] Therefore, the concept of reasonable incomplete revascularization (RICR) has been proposed. [7][8][9] The residual SYNTAX score (rSS), which was recently proposed as an objective, quantitative measure of the degree and complexity of residual stenosis after PCI, has been validated as an independent predictor of worse clinical outcomes after PCI in different population cohorts. 5,[10][11][12][13][14][15][16][17][18][19] However, no previous study assessed the utility of rSS for patients with chronic renal insufficiency (CRI). The purpose of this study was to assess the prognostic value of rSS for patients with CRI at the 3-year (median) follow-up. Among them, 2,529 consecutive cases with an estimated glomerular filtration rate (eGFR) <90 ml/min/1.73 m 2 were retrospectively enrolled.
The eGFR was calculated using the following simplified modification of  20 Because the SYNTAX score has been validated only for patients with native CAD, nine cases with a history of previous coronary artery bypass grafting (CABG) were excluded. After excluding another 28 cases with staged PCI and 24 cases with unplanned PCI during the second admission, 2,468 patients were finally analyzed in this study ( Figure 1).
The baseline SYNTAX score (bSS) was assessed visually by two of three experienced interventional cardiologists who were trained to perform SYNTAX score assessments and blinded to the treatment assignment and clinical outcomes. In the case of disagreement, the opinion of the third observer was obtained and the final decision was made by consensus. Each lesion with stenosis >50% in diameter in vessels >1.5 mm in diameter was scored using the SYNTAX score algorithm (fully described elsewhere). 21 The intraobserver variability of the calculated bSS (quartile partitioning) based on reanalyzing 50 cases every 3 months indicated a high level of agreement (k statistic = 0.88; 95% confidence interval [CI], 0.78-0.98; p < .001). 22 The rSS was calculated based on the other obstructive coronary disease cases after treatment with PCI. 10 In the case of staged PCI procedures (defined as a second planned PCI procedure after the initial intervention), the final planned procedure was used as the entry point for this study. All data were entered into a dedicated computer database. The study protocol was approved by the ethics committee of Cangzhou Central Hospital, Hebei Medical University, and all patients provided written informed consent.

| Endpoints and definitions
Clinical follow-up was scheduled at 1, 3, 6, and 12 months, and then annually thereafter via clinical visit or telephone contact. The primary endpoints were all-cause mortality and cardiac mortality. Death that could not be attributed to a noncardiac cause was considered cardiac T A B L E 2 Anatomical and procedural characteristics of lesions according to the residual SYNTAX score  to patients with CR and ICR, patients with RICR had more target vessels (p < .001) and more implanted stents with longer lengths (p = .005). However, the ICR group had the lowest delta SYNTAX score (p < .001). p = .798), MI (4.8% vs. 3.0%; p = .020), and stroke (6.5% vs. 6.6%; p = .644) rates that were similar to those of the CR group (Table 3 and Figure 4).  (Table 4).  Figure 6).

| Clinical outcomes
F I G U R E 5 Independent predictors of clinical outcomes at 3 years. CI, confidence interval; eGFR, estimated glomerular filtration rate; MACCE, major adverse cardiovascular and cerebrovascular events; rSS, residual SYNTAX score Abbreviations: AUC, area under the curve; MACCE, major adverse cardiovascular and cerebrovascular events; ROC, receiver-operating characteristic.

| DISCUSSION
In this study, we assessed the impact of the rSS on long-term clinical outcomes of a large cohort of patients with CRI after PCI. During this study, we validated the prognostic value of the rSS for patients with CRI. We found that an rSS >8 was associated with progressively increasing rates of all adverse clinical outcomes, and that an rSS <8 indicated comparable risks of all-cause death, cardiac death, and stroke with CR for patients with CRI. We also found that the rSS had stronger accuracy than the bSS for predicting the risk of unplanned revascularization, stroke, and MACCE.
Patients in our study were stratified according to the rSS after PCI.
CR, defined as an rSS value of 0, was achieved in only 24.1% patients, this rate was obviously lower than that reported by other studies. 5,10-17 F I G U R E 6 Comparison of receiver-operating characteristic curves of the residual SYNTAX score and baseline SYNTAX score for the predictability of long-term outcomes. AUC, area under the curve; CI, confidence interval CKD is a common comorbidity with cardiovascular diseases, and it increases mortality and morbidity. 1 Patients with CKD have clustering of significant cardiovascular risk factors and comorbidities and are more likely to have anatomically complex disease (e.g., calcification, bifurcation, long lesions, and multivessel disease). [25][26][27] Furthermore, CKD is known to be associated with higher rates of complications related to invasive procedures, including stent thrombosis and restenosis, and lower procedural success rates. 1,2 Patients with CKD are at increased risk for the development of contrast-associated acute kidney injury after PCI. 28 Therefore, interventional cardiologists may encounter more potential difficulties when treating highly complex CAD with CKD, and they tend to perform ICR treatment for these patients.
The concept of rSS was first developed by Stone and colleagues.
The rSS was assessed in a large cohort of patients with moderate-risk and high-risk acute coronary syndrome undergoing PCI. This study demonstrated that the rSS was useful for quantifying and stratifying the degree and complexity of residual stenosis after PCI. Specifically, an rSS >8.0 after PCI was associated with poor 30-day and 1-year prognoses for patients with moderate-risk and high-risk acute coronary syndrome. 10 Farooq validated the prognostic impact of the rSS on adverse outcomes in the SYNTAX trial, which showed that the rSS is a powerful indicator of 5-year mortality. 5 The prognostic value of the rSS has also been confirmed for patients with multivessel CAD, 13 not have a negative impact on long-term adverse cardiac events. Consistent with a previous study, we found that the ability of the rSS to predict mortality and MI was comparable with that of the bSS. 16 However, in contrast to that previous study, the rSS significantly improved the ability of the bSS to predict unplanned revascularization, stroke, and MACCE. 16 Despite the greater anatomic complexity in the ICR group, the delta SYNTAX score from baseline to post-PCI, which represented the burden of coronary disease removed by PCI, did not significantly vary according to the rSS. These results suggest the potential difficulties that physician may encounter with highly complex CAD. Therefore, ICR is more likely because the anatomy is unfavorable for PCI.
Advances in PCI technology developed to ensure that major epicardial vessels have been fully revascularized and aggressive secondary prevention may improve the long-term prognosis of patients with substantial ICR after PCI.

| LIMITATIONS
This study was limited by its post hoc nature. Validation was restricted to patients with CRI, the proportion of patients with CKD was small (11.9%), and the proportion of patients with Stages 4 or 5 renal insufficiency was even smaller (0.97%). We evaluated kidney function using the eGFR derived from serum creatinine rather than direct measurements of renal function such as iothalamate clearance. Additionally, the creatinine level might have been influenced by medications or clinical conditions. Third, rSS cannot fully represent coronary artery function. A previous study demonstrated that only 35% of lesions visually estimated to represent angiographic stenosis were functionally significant when tested by the fractional flow reserve, and low rates of clinical events were observed for lesions with normal fractional flow reserve. 30 Finally, participants in our study were enrolled at a single center. Further prospective, multicenter, randomized trials are required for better quantification of these findings.

| CONCLUSIONS
For a large cohort of patients with CRI after PCI, the rSS was an independent predictor of cardiac death, MI, unplanned revascularization, stroke, and MACCE at the 3-year follow-up. ICR (rSS >8) was associated with progressively increasing rates of adverse clinical outcomes, and RICR (rSS <8) was associated with similar risks of all-cause death, cardiac death, and stroke with CR despite its higher risks of MI, unplanned revascularization, and MACCE. The rSS may aid in determining a reasonable level of revascularization for patients with CRI after PCI.

ACKNOWLEDGMENT
We are grateful to all of the study participants whose work made this study possible.