Age, kidney function index, ACS presentation, diabetes, LVEF, culprit coronary artery, heart rate, sex, cerebrovascular disease, Killip class, ST-segment deviation, PVD, hypertension, prior CABG, cardiogenic shock, smoking status, CLD, elevated cardiac markers, cardiac arrest, TIMI flow grade, BMI, prior PCI, and BNP/NT-proBNP were the most widely applied variables in the risk prediction scores/models for patients after PCI. Moreover, our results show that variables are often used variously by researchers and participants, which suggests that ethnicity or geographical considerations influence how these variables are used. These results complement and expand on recent guidelines 1,11 that prognostic risk assessment may contribute to further precise secondary prevention after PCI.
Even after PCI, patients with CHD require precise risk assessment and secondary prevention, which can significantly improve patient outcomes. Guidelines recommend risk scores/models used to identify risk stratification to guide therapeutic decision-making and help physicians improve the prognosis of patients.1,11,12 Several scoring systems have been developed to evaluate the prognosis of patients with CHD within the last two decades,5–10,13−16 but few have been unanimously recognized as being suitable specifically for prognosis assessment of patients after PCI. Risk scores/models use covariates (each variable is assigned relative weights) to estimate the probability that a certain outcome (e.g., death or readmission) will occur in the future.17–19 Therefore, variables are the basic elements of risk scores/models, and different variables may play different roles in different risk scores/models. Hence, it is necessary to conduct a detailed analysis of the variables contained in the risk scores/models to identify suitable candidates for further study and discussion.
In risk prediction scores/models, some variables, such as demographics, personal history, comorbidities, physical examination, and test results, have relatively stable predictive performance and universal applicability.18,19 Our results showed that age, sex, sex, BMI, diabetes, hypertension, smoking, and SBP are representative of these variables (Table 2). We found that age, as a well-known prognostic predictor, was treated as a continuous variable (e.g., per year, per 10 years, or 30 years) in some scores/models,5,6,10,13 whereas in other scores/models, it was applied as a categorical variable (e.g., > 40 years, > 50 years, > 60 years, > 65 years, > 70 years, > 75 years, or > 80 years).7,9,20–26 Similarly, SBP and some scores/models regard per mmHg, per 10 mmHg, or per 20 mmHg as a continuous variable,5,6,27,28 while more scores/models used it as a categorical variable based on < 100 mmHg or not.7,29–31 At present, there is no uniform regulation on whether it is better to define such variables as continuous or categorical predictors, and researchers tend to favor their own needs for building models (e.g., increasing the discrimination power), which will cause a certain degree of selection bias. However, the guidelines 1,11,32 and several well-known risk scores 7,9,33 seem to favor age and SBP as categorical variables to assess risk and assist in the treatment of patients with CHD, which is also preferred by our panel to construct a score/model for patient prognosis assessment after PCI.
Diabetes, hypertension, and smoking have long been established as risk factors for CHD and used as predictors to assess patient outcomes after PCI.11,22,24,34 Similar to CHD, CVD, and PVD are both arterial diseases, and the pathogenesis is both atherosclerosis, which leads to vascular stenosis or blockage and, in turn, causes ischemia of the target organ.35 Therefore, CVD and PVD are also often included as variables in the risk scores/models of patients.36,37 CLD (including COPD) is also a common concomitant disease of CHD.38 CLD is closely related to the prognosis of patients with CHD, and is often selected as an important variable in the prognostic scoring system of PCI patients.24,25,37,39 Perhaps it would be a good idea to construct a scoring system where all risk variables are comorbidities.
Regarding sex in predicting the prognosis of patients after PCI, there is still a matter of controversy among different scores/models. In general, if other factors are not considered, women with CHD have worse prognosis than men. However, there is now growing evidence that differences in adverse outcomes for women after PCI in different situations, compared to men, either no longer present or are significantly reduced after adjusting for confounding factors.40 Specifically, some scores/models took female as the risk variable of the prognosis score after PCI (e.g. ATRIA risk score, EuroSCORE, EuroSCORE II, SYNTAX score II, and STS score) 2,9,41,42, while others took male as the risk variable of the prognosis score after PCI (e.g. CHIP score, COAP risk model, and Framingham Risk Score).24,34,43 Sex/gender, in any case, is a very important variable in the risk assessment scores/models for patients after PCI, and whether men or women are more at risk depends on the situation.
Obesity is an independent risk factor for CHD onset and development. Interestingly, a large body of literature has shown that overweight and obese patients with CHD have a better prognosis than the lean patients, which is known as the "obesity paradox".44 For example, in models such as KORMI score,45 MVD score,46 and TIMI score,7 body weight/BMI less than a certain cut-off value is considered to be a risk factor for poor prognosis of patients after PCI, while in models such as NCDR CathPCI risk score 36 and Logistic Clinical SYNTAX score,47 BMI higher than a certain cutoff value is a predictor of poor prognosis in patients after PCI. In addition, some researchers have suggested that either a higher or lower BMI is a risk variable for long-term mortality after PCI,37 with a U-shaped association. We are in favor of the last view; however, the conclusion needs to be verified by more high-quality, multicenter, and large-sample risk score/model studies with long-term follow-up.
Some indicators related to cardiac function, such as variables in the risk scores/models, also influence the prognosis of patients after PCI. Cardiogenic condition is a serious condition. In Mayo Clinic Risk Score,10 NERS score II,48 NCDR CathPCI risk score,36 PPCI risk score,41 and Toronto score,49 cardiogenic shock was used to predict the in-hospital and 30-day mortality of AMI patients after PCI (patients with AMI are more prone to cardiogenic shock). More risk scores/models are needed to explore the impact of cardiogenic shock on long-term prognosis after PCI. As we all know, LVEF and Killip class are the criteria used to evaluate cardiac function, BNP and NT-proBNP are important biomarker for diagnosis and evaluation of HF in many clinical settings, and their level represents whether HF has occurred and the severity of HF.50,51 For patients with CHD, the level of cardiac function indicates the clinical consequences of coronary ischemia. Therefore, cardiac function-related indicators can be used as indispensable variables in the construction of prognosis scores for post-PCI patients.
Additionally, prior PCI,36,52,53 prior CABG,52,53 ACS presentation,54 ST-segment deviation,5–7,55 elevated cardiac markers,5–7 culprit coronary artery,10,20,24,48,56 and TIMI flow grade 20,54,57,58 are directly related to an increased risk of poor prognosis after PCI. Studies have shown that previous revascularization (PCI or CABG) is associated with adverse cardiac events of patients with repeat PCI.59,60 ACS presentation, ST-segment deviation, and elevated cardiac markers represent an unstable state of CHD, even AMI, which means greater and more variable risk.61 As variables, they occupy an important place in the prognostic scoring model of patients after PCI. The culprit coronary artery and TIMI flow grade are two factors that are directly related to PCI. Left main, multi-vessel, and chronic occlusive diseases are more complex and high-risk stratified coronary vascular lesions. They not only pose risks to PCI itself but also to the prognosis after PCI.10,20,24,48,56,62 The TIMI flow grade indicates whether the coronary blood supply is adequate, and pro- or post-procedural TIMI flow grade can affect the clinical outcome of PCI patients.20,54,57–59 Therefore, this type of risk variable is essential for creating a score/model to predict the outcome of patients after PCI.
Another variable worth discussing when constructing prognostic scores for patients after PCI is kidney function index. The kidney function index, measured by serum creatinine level, includes indicators such as AKI,63 CKD,22,64 eGFR,48,64 kidney insufficiency,65,66 and dialysis,24,26 excluding contrast-induced nephropathy, and has different degrees of influence on the clinical outcomes of patients with stable CHD or ACS after PCI. The heart and kidney are both important organs in the human body, and their simultaneous onset of the two organs can affect each other, resulting in a series of pathophysiological changes known as cardiorenal syndrome, which increases the incidence of adverse prognosis. For AKI or CKD, mild kidney insufficiency, or end-stage kidney disease requiring dialysis, the serum creatinine level was the final evaluation criterion. Similarly, serum creatinine level was used as either a categorical variable 22,24,48,64–66 or a continuous variable 8,9,13,20,28 in the risk score/model after PCI.
However, another issue is worth noting: The proportion of the above variables applied differed in the risk scores/models built for different ethnic groups (Table 2). In other words, many variables differ between Caucasians and non-Caucasians; some variables may be more suitable for Caucasians (e.g., kidney function index and ACS presentation), whereas other variables may be more suitable for non-Caucasians (e.g., SBP and heart rate). Even for the same variables, the cut-off values differed across ethnic groups. For example, Asians generally have lower BMIs than Caucasians.67 Therefore, when constructing relevant scores/models, the selection of variables should also fully consider the ethnic background of the study population.