Prognostic Value of the Residual SYNTAX Score on In-Hospital and Follow-Up Clinical Outcomes in ST Elevation Myocardial Infarction Patients Undergoing Percutaneous Coronary Interventions

Aims We investigated the prognostic significance of residual SYNTAX score (RSS) in patients undergoing PCI due to STEMI and relationship between RSS and in-hospital and long-term ischemic cardiac events. Methods Between June 2015 and December 2018, 538 patients who underwent primary PCI were evaluated for in-hospital events and 478 patients were evaluated for clinical events during follow-up. Primary and secondary endpoints for both in-hospital and follow-up periods were cardiac death and major adverse cardiac events (MACE). Results 538 patients were included the study. RSS values of 131 patients were 0, and RSS values of 407 patients were >0. The median value of the RSS > 0 group was 7. According to this value, the RSS > 0 group was divided into 2 groups as R-ICR (RSS < 7, N = 188) and ICR (RSS ≥ 7, n = 219). In the RSS ≥ 7 group, during in-hospital and follow-up period, both mortality and MACE rates were higher than the other two groups. Area under the curve (AUC) for RSS for in-hospital death was found to be higher than SS (p=0.035) but similar to Grace Score (GS) (p=0.651). For MACE, RSS was higher than SS (p=0.025) and higher than the GS (p=0.041). For follow-up cardiac mortality, the AUC of the RSS was found to be higher than SS (0.870/0.763, p=0.02) and GS (0.870/0.733, p=0.001). For MACE, the AUC of RSS was higher than SS (p=0.03) and GS (p=0.004). Conclusions High RSS values in STEMI patients are associated with increased risk of ischemic cardiac events. RSS may help determine revascularization and level of additional PCI to improve prognosis by reducing the risk of ischemic cardiac events after P-PCI.


Introduction
ST-elevation myocardial infarction (STEMI) is known as a life-threatening complication of coronary artery disease (CAD) and it is one of the leading causes of death all over the world. Primary percutaneous coronary intervention (P-PCI) of the culprit vessel in patients with STEMI is standard clinical practice [1]. At the time of P-PCI, 4065% of the patients exhibit one or more concomitant coronary lesions (i.e., multivessel disease (MVD)). e presence of narrowed coronaries other than those related to index ischemia in patients with STEMI is suggested as a feature associated with adverse clinical outcomes [2]. e presence of MVD is strongly associated with higher 30-day mortality, reinfarction ratio, reduced myocardial reperfusion success, and occurrence of major adverse cardiac events (MACE) at 1 year compared with single-vessel CAD [3,4].
Complete revascularization (CR) of all diseased segments is a desirable goal in patients undergoing P-PCI. Despite major advances in PCI technology and technique, CR is often not achieved (e.g., the diffuse disease in small vessels, complex calcified lesions, and chronic total occlusions). Also, CR has always been an important topic of discussion. Indeed, incomplete revascularization (ICR) may be unavoidable and detrimental in patients with complex coronary artery disease [5][6][7][8]. In cases where CR is not possible, PCI can be made to ensure a minimum level of ischemia to prevent ischemic cardiac events. e concept of reasonable ICR, defined as a reasonable amount of coronary lesion burden after revascularization, is on the agenda because it gives similar results with patients who underwent CR. e effect of residual SYNTAX score (RSS) for the determination of a reasonable ICR level was investigated in patients with MVD who underwent PCI [5,9,10]. e RSS was developed to quantitatively assess the degree and complexity of residual stenoses, based on recalculating the SYNTAX score from coronary angiography after PCI [11]. Systematic characterization and quantification of residual atherosclerosis after PCI may be important to standardize and improve the prognostic utility of ICR. Higher RSS has been associated with worse outcome in patients undergoing angiography-mediated PCI [12]. In a post hoc analysis of the ACUITY trial including patients with moderate-high-risk non-ST elevation (NON-STEMI) acute coronary syndromes, RSS > 8.0 was an independent predictor of mortality and ischemic events at one year [13].
In this study, we investigated the prognostic significance of RSS in patients undergoing PCI procedures due to STEMI and its relationship with ischemic cardiac events during hospitalization and follow-up period.

Materials and Methods
is was a single-center, retrospective, observational cohort study that enrolled consecutive unselected nonrandomized eligible patients who were hospitalized for STEMI and underwent P-PCI at our institution from June 2015 to December 2018. To determine adequate sample size, G * Power 3.1.9 was used [14]. Effect size was determined as w � 0.291. With the 95% power and 0.05 alpha, the minimum sample size to be included in the study was calculated as n � 183. A total of 697 patients were screened for involvement in study. 159 patients were excluded from the study. After angiography, 45 patients were given medical treatment, and 35 patients were given CABG decisions. In addition, patients with severe concomitant noncardiac diseases were excluded from the study.
is is shown in Figure 1. A total of 538 patients were included to the final study population. Clinical events of patients, which developed in-hospital and after discharge until June 2019, were recorded and retrospective analysis was performed. Ischemic cardiac events that developed in-hospital and after discharge were evaluated separately. Our local ethics committee approved the study protocol by the Declaration of Helsinki and all patients provided written informed consent.
Demographic, clinical, and laboratory data at admission were collected from our hospital electronic database. Patients who were previously diagnosed with diabetes or newly diagnosed according to ESC Diabetes Guideline were classified as diabetic [15]. Patients who were previously diagnosed with hypertension and those with values above 140/ 90 mm·Hg in serial blood pressure measurements after STEMI were categorized as hypertensive. Dyslipidemia was defined as a low-density lipoprotein cholesterol level of 130 mg/dl or more at fasting [16]. However, patients who were previously diagnosed with dyslipidemia or who used lipid-modifying agents were also included in this category. Patients who smoked within 12 months before the index event were classified as smokers. Patients who had undergone PCI before and who had ≥50% stenosis in major coronary arteries and side branches, larger than 1.5 mm, on coronary angiography were defined as having coronary artery disease. e diagnosis of STEMI was made according to current guidelines [17].
In our study, biochemical and hemogram data were obtained from blood samples taken at admission. Cardiac enzymes, creatinine levels, and hemogram parameters were studied daily during hospitalization. Peak troponin levels during hospitalization were evaluated in the study. Since troponin values above 50000 are given as >50000 in laboratory results, this situation was taken into consideration in our study. Contrast-induced nephropathy (CIN) was defined as a 25% increase in creatinine level compared to baseline or as an absolute increase of at least 0.5 mg/dl in the first 48 hours after P-PCI [18]. Major bleeding was defined according to the Bleeding Academic Research Consortium (BARC) definition (BARC type 3-5) [19]. Grace Score (GS) was calculated by using clinical, laboratory, and electrocardiographic data at admission [20]. All patients underwent echocardiography within 48-72 hours after P-PCI and after discharge at the first month. e modified Simpson method was used to calculate the left ventricular ejection fraction (LVEF).

Invasive
Procedures. P-PCI was undertaken according to the European Society of Cardiology Guidelines and the operator's routine practice. In the centers where the patients are referred or in our emergency department since clopidogrel or ticagrelor was given as a P 2 Y 12 inhibitor, the rate of use of these drugs was high. e exchange between the molecules of interest was left to the operator's preference. In patients who did not receive clopidogrel and ticagrelor before coronary angiography, prasugrel was also given before P-PCI depending on operator preference. e selection of the specific type of revascularization, procedural devices, and stent types was based on the decision of the operator. After the successful procedure, in line with the current STEMI guidelines, the patient's clinical characteristics were taken into consideration and their treatments included aspirin, P 2 Y 12 inhibitor, beta-blocker, statin, angiotensinconverting enzyme inhibitor-angiotensin receptor blocker, mineralocorticoid receptor antagonists, and furosemide [17]. e coronary arteries were divided based on anatomical criteria. e following vessels were considered as major coronary arteries: left main coronary artery (LMCA), left anterior descending (LAD), circumflex (CX), and right coronary artery (RCA). Isolated intermediate and isolated diagonal artery lesions were classified as other coronary vessels (if there is no critical stenosis in the three major coronary arteries). MVD was defined as at least one lesion in a major non-infarct-related artery deemed angiographically significant (≥50% luminal narrowing diameter). Ischemia time was defined as the time between symptom onset and reperfusion (after balloon angioplasty or direct stent implantation in the culprit artery during P-PCI). rombolysis in myocardial infarction (TIMI) flow grade at the start and end of the procedure was determined from the angiographic films as previously described in previous studies [21]. Stent diameter refers to the maximal stent diameter, and stent length is the sum of the lengths of all implanted stents. Multivessel PCI was defined as revascularization of at least one non-culprit lesion during the index procedure, before discharge or planned in the following 30-45 days without ischemic symptoms. Treatment of non-culprit artery during P-PCI was left to the operator's preference. e decision to revascularize the non-culprit coronary artery after P-PCI was made by the heart team.

Baseline and Residual SYNTAX Score.
Coronary angiograms were recorded to digital media for quantitative analysis. e SS and RSS were derived from the summation of the individual scores for each lesion (defined as ≥50% stenosis in vessel ≥1.5 mm) on angiograms obtained before and after the procedure, respectively, as previously described [22]. All angiographic variables pertinent to SS and RSS calculations were computed by two of the experienced cardiologists who trained for SS assessment and they were blinded to procedural data and clinical outcomes. In case of disagreement, the opinion of the third observer was obtained and the final decision was made by consensus. All data were assessed for quality and entered a dedicated computerized database. In our study, RSS score calculated after the procedure was evaluated in the results of the hospital, which was calculated after the intervention to IRA or after additional coronary vascular interventions outside IRA before discharge. If additional vascular intervention was not planned after discharge, the same RSS value was used for follow-up results. In patients who underwent additional vascular intervention after discharge, RSS value calculated after PCI during the hospital was recorded in the in-hospital results. RSS calculated after additional planned PCI in the follow-up was used for the results in the follow-up period. e author evaluating the result was blind to the SS and RSS score.

Follow-Up, Clinical Endpoint Definitions.
We divided endpoints into two groups as in-hospital and follow-up. Information about in-hospital outcome was obtained from an electronic centralized clinical database. In-hospital clinical results were collected by a physician who was unaware of the initial clinical, laboratory, and angiographic results. In-hospital primary endpoint was defined as incidence of cardiac death considered as any death with a demonstrable cardiac cause or any death that was not attributable to a noncardiac cause. In-hospital secondary endpoint was MACE, the combined endpoint of cardiac death, reinfarction, heart failure, and arrhythmic events. Reinfarction in acute post-P-PCI phase was defined as clinical signs of reinfarction with recurrent or persistent symptoms and ST-segment changes and requiring repeat P-PCI and/or second peak in CK-MB mass or troponin-T increase to ≥3 times the upper limit of normal, not related to an interventional procedure and new pathological Q waves in 2 or more contiguous electrocardiograph leads [8]. Heart In-hospital mortality (n : 47) Decided on CABG a er P-PCI (n : 13) Cardiology Research and Practice failure was defined as presence of signs or symptoms of congestion, mainly shortness of breath, and signs of fluid retention. Arrhythmic events during hospitalization were defined as documented sustained ventricular tachycardia (VT) and ventricular fibrillation (VF). Safety endpoints were defined as combined endpoints of CIN and bleeding.
After discharge, at follow-up, clinical evaluation was made with 478 patients because 47 patients died in hospital and 13 patients decided to undergo surgical treatment after P-PCI ( Figure 1). All patients were contacted for follow-up to assess the presence of primary and seconder endpoints. After discharge, all clinical follow-up data were prospectively collected by scheduled clinic evaluations, in-hospital records of the rehospitalized patients, and direct telephone interviews. In cases of the unavailable information, we obtained information from the local citizen's registration office and medical charts. Follow-up clinical events were investigated and recorded by a physician unaware of RSS score and inhospital events.
Follow-up primary endpoint is cardiac death and secondary endpoint is MACE, which consists of combined endpoints of cardiac death, non-fatal reinfarction, heart failure, and recurrent revascularization. Cardiac death was defined as death caused by myocardial infarction, heart failure, sudden cardiac death, and cardiac procedures. Nonfatal reinfarction was defined as a new elevation of cardiac biomarkers associated with symptoms or new Q waves at 12-lead electrocardiogram or ST-T variation during symptoms [23]. Patients hospitalized with the diagnosis of decompensated heart failure were evaluated as clinical endpoint of heart failure. Any repeat revascularization was defined as any ischemia-driven target or non-target vessel revascularization by either PCI or CABG [24].

Statistical
Methods. Statistical analysis was made by using IBM SPSS Statistics for Windows, Version 23.0 (IBM Corp., Armonk, NY). e normality assumptions were controlled by the Shapiro-Wilk test. Descriptive analyses were presented by using mean ± SD, median (0.250.75 percentiles), or n (%), where appropriate. Categorical data were analyzed by Pearson chi-square. e Kruskal-Wallis test was used for comparison of non-parametric variables between groups and the Bonferroni-Dunn test was used as a post hoc test for significant cases while One-Way ANOVA with post hoc Tukey HSD test was used for parametric variables.
e receiver operating characteristic (ROC) analysis was applied to evaluate the predictive performance of SS, RSS, and GS for MACE and cardiac death and area under the curve (AUC), sensitivity, and specificity were calculated and reported with 95% confidence intervals. e optimal cutoff point of measurements was determined as the value of the maximum Youden index. Survival curves were generated by the Kaplan-Meier method, and the log-rank test was used to evaluate differences between groups. Univariate and multivariate analyses of independent predictors of cardiac death and MACE were performed with a Cox proportional hazard regression model. e variables which showed significant association with cardiac death and MACE in the univariate analyses were further tested in the multivariate model. Hazard ratio (HR), with corresponding 95% confidence intervals (95% CIs), was reported. A p value of less than 0.05 was considered statistically significant.
Baseline demographic, clinical, and laboratory data were analyzed and compared between the groups (Table 1). Patients with RSS ≥ 7 were older and had a higher prevalence of CAD. In the RSS ≥ 7 group, the number of admissions with Killip ≥2 heart failure, need for intravenous diuretic, inotropic therapy, and intra-aortic balloon pump was higher than the other groups; moreover, duration of hospitalization was longer in this group. Blood glucose, HbA1C, creatinine, leukocyte, CRP levels, and GS were higher in the RSS ≥ 7 group, and systolic and diastolic blood pressure, creatinine clearance, and LVEF were lower than the other groups. e ratio of hypertensive, diabetic patients and neutrophil levels in the RSS ≥ 7 group was higher than the RSS � 0 group. Peak troponin levels and ischemia time were significantly different between all groups. ere was a positive correlation between basal SS values and RSS values of the patients included in the study (r � 0.727; p < 0.001). We show this correlation in Figure 2. e angiographic and procedural characteristics of the patients included the study are presented in Table 2. In the RSS ≥ 7 group, pre-PCI TIMI-0 flow, and post-PCI TIMI-2 flow rates were higher than the other groups. Post-PCI TIMI-3 flow, the rate of infarct-related artery as LAD, and additional vessel intervention rates were low. Post-PCI TIMI-1 flow and infarct related artery (IRA) RCA ratios were higher in RSS ≥ 7 group than RSS � 0 group. e rate of two-vessel disease was higher in the RSS < 7 groups than the other groups. Single-vessel, three-vessel, and multivessel disease rates and SS and RSS levels were significantly different between the groups. 478 patients were evaluated for long-term cardiac events. Baseline demographic, clinical, laboratory, angiographic data, scores, and medications given at discharge of those 478 patients are presented in Table 3. Age, IRA RCA ratio, stent length, CRP, peak troponin levels, GS, and furosemide use were higher in the RSS ≥ 7 group than the other groups; on the other hand, IRA-LAD ratio, CrCL, and LVEF were lower. e rates of hypertensive and diabetic patients, number of stents used, and HbA1c level were higher in the RSS ≥ 7 group than the RSS � 0 group. e rate of two-vessel disease was higher in the RSS < 7 groups than the others. Clopidogrel usage was low and ticagrelor usage was high in RSS � 0 group. e single vessel and three-vessel disease rates and SS and RSS levels were significantly different between the groups. In-hospital mortality, cumulative MACE, and subgroups of MACE were higher in the RSS ≥ 7 group than the other groups. One of the common safety endpoints was CIN and the common safety endpoint was more in the RSS ≥ 7 group than the other groups. Long-term clinical events were investigated and cardiac death, MACE, and recurrent revascularization rates were higher in RSS ≥ 7 than the other groups. In RSS ≥ 7 group, reinfarction rate was higher than RSS � 0. Table 4 shows the ratio of in-hospital and long-term clinical events. Patients with ≥7 RSS score showed higher cardiac mortality and MACE rates compared with the other two groups with Kaplan-Meier analysis (p � 0.044, p < 0.001, respectively). e Kaplan-Meier survival curves stratified according to RSS groups are presented in Figures 3(a) and 3(b).
Regardless of endpoints, all-cause mortality occurred in 35 patients. All-cause mortality occurred in 6 patients (4.6%) in the RSS � 0 group, 10 patients (5.5%) in the RSS < 7 group, and 19 (11.7%) patients in the RSS ≥ 7 group, and it was higher in the RSS ≥ 7 group than the other groups (p � 0.031).
Univariate and multivariate Cox proportional hazards model was performed to define the factors independently influencing cardiac death and MACE and the risk factors are shown in Tables 5 and 6. On a multivariate model for SS, independent predictors for cardiac death were age and SS.   e cutoff values for in-hospital mortality were found to be 10, 18.8, and 136, respectively. For in-hospital mortality, AUC of RSS was similar to GS but higher than the Cutoff values for cardiac death were found as 13, 22, and 126, respectively. AUC of RSS was higher than AUC of the SS and GS. Cutoff values for MACE were found as 11.5, 17, and 119, respectively. AUC of RSS was higher than the SS and GS.

Cardiology Research and Practice
Comparative results of ROC analysis related to inhospital and follow-up clinical endpoints are presented in Table 7. All ROC analyses are shown in Figure 4.

Discussion
e main findings of our study are as follows. (1) Rates of inhospital death, MACE, safety endpoint, and CIN were higher in the RSS ≥ 7 group. (2) In the RSS ≥ 7 group, longterm cardiac death and MACE were more than the other groups. During the study follow-up, the time spent without cardiac death and MACE was shorter in the RSS ≥ 7 group than the other groups. (3) When evaluated together with other risk factors, SS, RSS, and age were independent predictors of death during follow-up. SS and RSS were found as independent determinants for MACE in follow-up. (4) Predictive value of RSS was higher than SS for in-hospital death and higher than SS and GS for MACE. Predictive value of RRS was higher than SS and GS for long-term cardiac death and MACE.
Patients with STEMI are susceptible to significant morbidity and mortality, even when an early revascularization strategy such as P-PCI is performed. us, an appropriate risk stratification after P-PCI is essential to estimate the short-and long-term prognosis of these patients. Risk stratification in patients with STEMI is a major feature in real clinical practice, as it provides a broad perspective of patient outcomes based on patient characteristics and optimal treatment. e GS is considered the most robust score for evaluating the risk of patients with STEMI at the initial presentation. In addition to clinical risk assessment, angiographic characteristics that have additional independent prognostic significance include IRA, patency of the IRA, presence of multivessel disease, and lesion characteristics [25,26]. In our study, RSS and GS showed similar efficacy for determining in-hospital mortality and in RSS ≥ 7 group, GS was higher than the other groups. Also, the ROC analysis for GS showed that AUC for in-hospital events was higher than AUC for the long-time period. In COX regression analysis, no correlation was found between GS and clinical events developed in long-time period. In our study, role of GS for predicting in-hospital events in STEMI patients treated with P-PCI was more significant than followup cardiac events. Since the GS is not based on severity of coronary artery disease, based on clinical findings at admission, it may be poor for predicting ischemic burden after P-PCI and clinical events in chronic phase.
In patients with STEMI, severity of coronary artery disease and extent of myocardial tissue under threat of ischemia are predictors of adverse cardiac events that may develop after P-PCI in hospital and follow-up period [27].
erefore, presence and extent of additional coronary lesions are important for detection of myocardial tissue under threat of ischemia [28]. Reducing ischemic burden of patient would undoubtedly improve long-term prognosis, as exemplified by previous studies associating a short-and longterm survival benefit in patients with moderate to large amounts of inducible ischemia who were revascularized [5].
To address the question of the intervention of nonculprit vessel PCI in those with STEMI patients, scoring systems already used in clinical practice may be utilized. It is well accepted that amount of myocardium at risk at baseline and complexity and extent of CAD are directly correlated with occurrence of adverse events after revascularization [29].  SS has been recently developed as a combination of several previously validated angiographic classifications aiming to grade coronary anatomy concerning number of lesions and their functional impact, location, and complexity [30]. SS has proved to be useful in risk stratification of NON-STEMI and STEMI patients who underwent urgent PCI as an independent predictor of mortality, MACE, and stent thrombosis up to one-year follow-up. In patients undergoing P-PCI for STEMI, quantification of the presence, severity, and complexity of coronary vessel disease by SS is a useful tool in determining short-term and long-term outcomes independently of any other clinical, angiographic, and procedural characteristics. Patients with higher SS are at high risk and may need more intensive supportive and interventional management to improve their event-free survival [31].
CR seems to be a legitimate aim for patients with STEMI patients treated by PCI, whenever it can be safely achieved. In current practice, achieving CR is not always possible, and whether it is necessary for favorable outcomes is still a matter  of debate. For patients presenting with NON-STEMI acute coronary syndromes, about 40% of patients have MVD and they are treated by PCI [32]. Indeed, whereas ICR may be unavoidable and detrimental in patients with complex coronary artery disease, in other cases (e.g., low CAD burden) the long-term prognosis may be reasonable with optimal medical therapy [8]. However, little is known about whether the specific vessels that are incompletely revascularized or degree of stenosis in those vessels are associated with different mortality rates [33]. erefore, determining a reasonable level of revascularization in patients with STEMI undergoing P-PCI is of great importance. Number of untreated or unsuccessfully treated vessels was considered an indicator of ICR in many other studies. e concept of reasonable ICR has been proposed. erefore, it is very important to determine a reasonable level of revascularization [13,34].
Recently, the RSS measured after PCI emerged as an independent predictor of long-term clinical outcomes and tools for quantification of after validation by the preexisting clinical trials. e RSS is defined as SS, remaining after completion of PCI, including cases of staged PCI procedure [35,36]. e RSS should be a more accurate marker of residual lesion and residual ischemic burden. High RSS was associated with greater incidence of MACE and conversely, low RSS was linked with a better outcome. Reasonable ICR can be associated with favorable long-term results after PCI. Several observational studies with PCI patients with or without acute coronary syndrome using either cutoff <8 or <5 for RSS found a significant reduction in MACE, death/ MI/stroke, and unplanned revascularization procedures when the RSS after PCI was low. erefore, reasonable ICR as determined by RSS carries better long-term prognosis in terms of clinical outcome than more extensive residual CAD in patients with MVD treated by PCI. RSS may improve the allocation of coronary disease for optimal mode of revascularization [13,36].
Our study showed a relationship between RSS and adverse cardiac events during in-hospital and follow-up and its prognostic significance and role in post-revascularization risk classification in STEMI patients. We found that patients with greater residual coronary lesions and RSS ≥ 7 after PCI had higher clinical risks such as older age, lower LVEF, more comorbidities, bad clinical markers, negative procedural characteristics, and high SS and GS. ese associations reflected a clinical phenomenon that patients at higher risks tend to receive ICR just as prior studies indicated [37]. In our study, RSS ≥ 7 group was associated with higher cardiac death and ischemic adverse events that developed in hospital and the long term. We compared the role of RSS in risk classification with risk parameters with proven efficacy such as GS and SS. In general, RSS was found to be more effective for predicting in-hospital and follow-up clinical events than the other two scores. While the GS and SS scores were associated with ischemia at the time of admission before revascularization, RSS showed the ischemia level associated with residual lesions after PCI. Degree of ischemia, induced by residual coronary lesions after PCI, is associated with early and late adverse cardiac events. is relationship may explain why predictive value of RSS is higher than the other two parameters.
Although no randomized controlled trials are investigating the relationship between RSS and clinical outcomes in the STEMI patient populations, some observational studies have investigated this association. In the study performed by Singbal, relationship between SS and RSS with 1-year mortality was investigated in patients undergoing P-PCI. Median SS value of the study population was 14 (IQR � 8-19.5) and RSS value was 2 (IQR � 2-7). Although SS and RSS were found to be associated with 1-year mortality, it was highly correlated with RSS. RSS > 12 predicted 1-year mortality with 90% specificity [38]. No different evaluation was made for in-hospital and follow-up deaths. In a previous study, Khan investigated the relationship between RSS and in-hospital clinical events in STEMI patients. In the study group, mean SS was 14.1 ± 8.2 and mean RSS was 4.7 ± 7.2. RSS > 8 was shown to be associated with adverse cardiac events [39]. In a study investigating the relationship between RSS, calculated after P-PCI, and clinical events developing in-hospital and follow-up, RSS > 8 was found to be associated with cardiac adverse events developing in hospital and in follow-up. Mean RSS � 4.2 ± 5.4 and median RSS � 2 were found in the study. Study showed that RSS was also an independent predictor of MACE and all-cause mortality during follow-up (OR 2.9 for RSS < 8 and 3.9 for RSS > 8), adding prognostic value over control variables and GS [40]. In a study by Burgess et al., cardiac death and MI were more common in RSS >8 group. RSS was found as an independent predictor of cardiac death, MI, unplanned revascularization, and MACE [41]. We evaluate our results together with current studies; RSS can be used as a reasonable parameter in prognostic evaluation and additional PCI decision after P-PCI. RSS ≥ 7-8 is associated with undesirable clinical events after P-PCI. Consideration of other clinical risk factors when performing additional PCI interventions in these patients may provide prognostic improvement.

Limitations
e main limitation of our study was undoubtedly its retrospective nonrandomized design. is was a retrospective observational and nonrandomized study conducted at a single hospital and as such has the inherent limitations and bias retrospective single-center studies. Although the multivariable analysis was performed for significant confounders, we cannot exclude the fact that other potential unmeasured confounders may affect the results. is study did not compare the prognostic impact of RSS with newer standardized SYNTAX-II (SS-II) scores that combine angiographic and clinical variables. e addition of these clinical variables to RSS may allow for better prediction of long-term outcomes when compared to the angiographic analysis of residual disease alone. On the other hand, it has been shown that the original SS and SS-II have similar efficacy [42]. We did not measure FFR systematically before and after PCI. Although FFR-guided PCI improved clinical outcomes compared with angiography guided PCI, many PCI procedures are still performed based on coronary angiographic findings. In our study, patients with MVD were not compared separately with or without additional PCI. We did not compare the difference between patients who underwent non-IRA PCI in the same procedure and those in the staged procedure. In addition, leaving the treatment method used to the operator's preference may have affected the results. However, medical treatment applied to patients and patient's compliance with treatment and lifestyle changes are important parameters that affect clinical results.

Conclusion
e present study shows that the RSS, in patients with STEMI undergoing P-PCI, provides important prognostic information with regard to in-hospital and follow-up clinical outcomes, including cardiac mortality and MACE. e RSS is an easy score to calculate the index of residual coronary disease severity and is intuitively more meaningful to apply in this setting. e RSS may improve the determination of an objective level of reasonable revascularization. RSS may help determine the level of revascularization, required to prevent ischemic cardiac events and improve prognosis after P-PCI; however, it can be used to guide additional PCI decisions.

Data Availability
e data used to support the findings of this study are included within the article.

Conflicts of Interest
e authors declare no conflicts of interest.