Comparison of two models of risk stratification in patients submitted to elective coronary artery bypass surgery

Abstracts

OBJECTIVE: To compare the Cleveland Clinical Score and EuroSCORE when evaluating patients submitted to CABGS electively in Rio Grande do Sul. METHODS: Cohort study with 202 patients submitted to CABGS between January 2006 and March 2007. Surgical risks were categorized by the Cleveland Clinic and EuroSCORE as low, medium and high risks. The incidence of deaths was measured in a 60 days interval. RESULTS: The average age of patients was 62±10 years and 134(66%) were men. A correlation was observed between both scores to classify patients at different levels of risk. Patients were categorized using the Cleveland Clinic and EuroSCORE respectively: 142(70.3%) and 155(76.7%) as low, 56(27.7%) and 43(21,3) as medium and 4(2%) and 4(2%) as high risks, with a Kaplan correlation coefficient of 0.432; p0.001. In the first sixty days after surgery, 13(6.4%) patients had died. A correlation between the higher incidences of death with increased category of risk was observed in the Cleveland Clinic and EuroSCORE. Deaths occurred respectively in the Cleveland and EuroSCORE: 6(4.4%) and 7(4.5%) in the low; 5(8.9%) and 5(11.6%) in the medium and 2(50%) 3 1(25%) in the high risks. Noted sensitivity in surgical mortality forecast was of 72.5% and 66.5% Cleveland and EuroSCORE respectively. CONCLUSION: The Cleveland Clinic and EuroSCORE risk scores have proven effective to evaluate risk of death in patients electively submitted to CABGS.

Risk; Myocardial revascularization; General surgery

OBJETIVO: Comparar o Cleveland Clinical Score eo EuroSCORE na avaliação de pacientes submetidos eletivamente à CRM no Rio Grande do Sul (RS). MÉTODOS: Coorte com 202 pacientes submetidos à CRM entre janeiro de 2006 e março de 2007. O risco cirúrgico foi determinado por meio dos escores da Cleveland Clinic e do EuroSCORE como de baixo, médio e alto risco. A incidência de óbito foi aferida no intervalo de 60 dias. RESULTADOS: A idade média dos pacientes foi 62 (± 10) anos, 134 (66%) eram homens. Houve correlação entre os escores da Cleveland Clinic e EuroSCORE em categorizar, respectivamente os pacientes em baixo: 142 (70,3%) e 155 (76,7%); médio 56 (27,7%) e 43 (21,3); e alto risco 4 (2%) e 4 (2%) conforme o coeficiente de concordância de Kappa 0,432; P 0,001. No pós-operatório de 60 dias, 13 (6,4%) pacientes morreram. Observou-se uma correlação com percentual crescente da incidência de óbitos com o aumento da categoria de risco em ambos os escores, 6 (4.4%) e 7 (4,5%) no baixo; 5 (8,9%) e 5 (11,6%) no médio; 2 (50%) e 1 (25%) no alto risco nos escore de Cleveland e EuroSCORE respectivamente. Observou-se sensibilidade na previsão de mortalidade cirúrgica de 72,5% e 66,5% para o Cleveland e EuroSCORE respectivamente. CONCLUSÃO: Ambos os escores de risco, da Cleveland Clinic e EuroSCORE, mostraram-se eficazes em prever mortalidade de pacientes submetidos eletivamente à CRM de forma moderada.

Risco; Revascularização miocárdica; Cirurgia

ORIGINAL ARTICLE

Comparison of two risk stratification models in elective coronary artery bypass patients

Rosane Maria Nery^I; Rosa Cecília Pietrobon^II; Mahmud Ismail Mahmud^III; Maurice Zanini^IV; Juarez Neuhaus Barbisan^V

^IMestrado em Ciências da Saúde e Cardiologia; educadora física e doutoranda do programa de pós-graduação da Universidade Federal do Rio Grande do Sul – UFRGS, Porto Alegre, RS

^IIMestrado em Ciências da Saúde, Cardiologia; psicóloga

^IIIMestre em Epidemiologia e fisioterapeuta do Hospital de Clínicas de Porto Alegre – HCPA, Porto Alegre, RS

^IVGraduação em Educação Física; educadora física da Universidade Federal do Rio Grande do Sul – UFRGS, Porto Alegre, RS

^VDoutor em Medicina – Cardiologia e chefe do serviço de Tilt Test do Instituto de Cardiologia do Rio Grande do Sul RS/ Fundação Universitária de Cardiologia-FUC, Porto Alegre, RS

Correspondence

ABSTRACT

OBJECTIVE: To compare the Cleveland Clinical Score and EuroSCORE when evaluating patients submitted to elective CABGS in Rio Grande do Sul, RS, Brazil.

METHODS: This was a cohort study of 202 patients given CABGS between January 2006 and March 2007. Surgical risk was categorized according to the Cleveland Clinic Score and the EuroSCORE as low, medium or high. The incidence of deaths was measured over a 60-day period.

RESULTS: The mean age of patients was 62±10 years and 134 (66%) of them were men. A correlation was observed between the scores for classifying patients into different levels of risk. According to the Cleveland Clinic score and the EuroSCORE, respectively, patients were categorized as follows: 142(70.3%) and 155(76.7%) low risk patients, 56(27.7%) and 43(21.3) intermediate risk patients and 4(2%) and 4(2%) high risk patients; with a Kaplan correlation coefficient of 0.432; p0.001. Thirteen (13, 6.4%) patients died during the first 60 days after surgery. There was a correlation between greater incidence of death and higher risk categories for both the Cleveland Clinic score and the EuroSCORE. Deaths occurred in the Cleveland and EuroSCORE risk groups, respectively, as follows: 6 (4.4%) and 7 (4.5%) in the low risk group; 5 (8.9%) and 5 (11.6%) in the intermediate risk group and 2 (50%) 3 1(25%) in the high risk group. Observed sensitivity for surgical mortality prediction was 72.5% and 66.5% for the Cleveland score and EuroSCORE respectively.

CONCLUSION: The Cleveland Clinic and EuroSCORE surgical risk prediction instruments are both moderately effective for predicting mortality among elective CABGS patients.

Key words: Risk. Myocardial Revascularization. Coronary Artery Bypass, Surgery.

INTRODUCTION

Coronary artery bypass surgery (CABGS) is a surgical procedure that is widely studied because of the great clinical interest and because its outcomes are very easily defined. Surgical risk assessment is an important part of preoperative preparation for heart surgery. It gives patients and their families an idea of the real risk of complications and death¹. It is indispensable for the medical team when choosing the procedure, planning postoperative care, predicting prognosis and considering issues of cost against benefit^1-4. The Cleveland Clinical Score was first formulated in 1986 at the Cleveland Clinic Foundation in order to assess the risk of surgery in patients with indications for coronary artery surgery. They identified 13 risk factors that constituted a model that was capable of stratifying patients into three different levels of risk of death from coronary artery bypass graft surgery: low risk (score < 3), intermediate risk (score 3 to 6) or high risk (score > 6)⁴. The EuroSCORE is one of the most up-to-date risk stratification models. It was developed on the basis of data collected from 130 centers in eight different European countries and is designed to predict mortality both for patients who will undergo CABGS and also for heart valve surgery patients². Elective surgery was not therefore considered when comparing the scores. The objective of this study is to compare the applicability of two risk scores, the Cleveland Clinical Score and the EuroSCORE, in patients with stable coronary artery disease (CAD) scheduled to undergo elective CABGS in the Brazilian state of Rio Grande do Sul.

METHODS

This was a prospective cohort study that assessed 215 consecutive, adult, non-hospitalized patients of both sexes who were admitted electively to undergo CABGS with grafts from the saphenous vein and/or mammary artery. These patients were recruited at three public hospitals in Rio Grande do Sul between January of 2006 and March of 2007. Patients were excluded if they were operated on under emergency conditions, had acute coronary syndrome or underwent other surgical procedures at the same time. The primary outcome for this study was mortality, defined as death from all causes while in hospital or within 60 days of hospital discharge.

Ethical considerations

The study was approved by the Ethics Committees and Scientific Committees at the Instituto de Cardiologia do Rio Grande do Sul, the Hospital de Clínicas de Porto Alegre and the Santa Casa de Misericórdia de Porto Alegre. Free and informed consent was obtained from all patients.

Instruments

A structured questionnaire was administered and data were collected on demographic, anthropometric and clinical factors. Each patient was assessed for presence or absence of the 13 risk factors defined by the Cleveland Clinical Score and the 17 risk factors defined by the EuroSCORE, respecting the definitions of each one and attributing the correct scores to them. Patients were stratified into three risk groups and followed-up in outpatient consultations at 30 and 60 days, in order to check for complications and deaths.

Sample

In order to detect a correlation with r greater than 0.3, with statistical power of 90% and a 5% significance level, we calculated that the minimum sample size would be 113 patients. We enrolled 202 patients on this study, who were part of the sample for a study published by Nery and Barbisan⁵.

Statistical analysis

The data collected were analyzed using the program Statistical Package for the Social Sciences (SPSS version 15.0). Categorical variables are given as absolute frequencies and percentages. Continuous variables with normal distribution are given as means and standard deviations and variables without normal distribution are shown as median and interquartile amplitude (IQ). The level of agreement between scores was assessed using the Intraclass Correlation Coefficient. Predicted mortality (in percentage terms) was defined as the sum of the mortality scores according to each model, divided by the number of patients assessed. The observed mortality was the actual number of deaths divided by the corresponding number of patients. The outcome of interest in this study was death. For any given pair, the predictions of the logistic model are defined as agreeing with the outcome when the patient who died had a greater predicted probability of death than the survivor. The c-statistic is the proportion of predictions agreeing with the outcome. Possible values are in the range of 0.5 to 1. 6 The greater the value of the c-statistic, the greater the model's accuracy or discriminatory power. The c-statistic is also known as the area under the curve of the receiver operating characteristic (ROC AUC).

RESULTS

Thirteen of the 215 patients interviewed at three public hospitals in Rio Grande do Sul were excluded because they were not eligible for surgery. Table 1 lists demographic, anthropometric and clinical variables for the patients. There was a greater proportion of men and a high number of smokers. Preoperative physical activity was defined as any type of physical activity lasting at least 30 minutes, three times a week up to 2 weeks before surgery. The patients who underwent CABGS were classified into one of three risk bands by the Cleveland Clinic and EuroSCORE scales. It was observed that there was moderate agreement between the two scores in terms of classifying patients into different risk bands, with agreement being most evident among high risk patients. Kappa correlation = 0.432; P<0.001. Cleveland score: low risk 142 patients (70.3%), intermediate risk 56 patients (27.7%) high risk 4 patients (2%). EuroSCORE: low risk 155 patients (76.7%), intermediate risk 43 patients (21.3%) and high risk 4 patients (2%). Both scales differentiated significantly between the scores attributed to patients who died and those who survived. Analyzing the medians and interquartile amplitudes, according to the Cleveland score patients who died scored up to two points in the 25% quartile and up to five points in the 75% quintile, with a median of three points (P=0.004). The same occurred with the EuroSCORE, by which the patients who died scored up to one point in the 25% quintile and four points in the 75% quintile with a median of two points (P=0.039). Table 2 relates the number of patients classified into each category according to the Cleveland score and the EuroSCORE to actual surgical mortality. According to the Cleveland score, 142 patients were low risk, 56 were intermediate risk and 4 were high risk. According to the EuroSCORE, there were 155 low risk, 43 intermediate risk and 4 high risk patients. A correlation was observed between increase in the incidence of death and increase in the category of risk for both scores. Figure 1 illustrates the sensitivity and specificity of the Cleveland score and the EuroSCORE for predicting mortality, plotted on a ROC curve. The comparison between the two scores is slightly favorable to the Cleveland Clinic score. We observed 72.5% and 66.5% sensitivity for predicting surgical mortality for the Cleveland score and EuroSCORE, respectively.

DISCUSSION

NOur study shows the applicability of both scores for predicting mortality in patients undergoing elective CABGS in Rio Grande do Sul. Similarity between the two was moderate and the Cleveland score proved a little more sensitive with respect to the outcome death. In contrast, a study conducted by Moraes et al. with a group of 752 patients who underwent CABGS at the Instituto do Coração de Pernambuco in 2003 and 2004, the EuroSCORE proved to be a simple and objective scale and was a satisfactory predictor of surgical mortality⁷. Andrade et al. assessed the applicability of the EuroSCORE with 840 patients undergoing valve surgery and observed that the score proved to be a satisfactory predictor of surgical mortality and helpful for identifying risk during valve surgery in Pernambuco⁸. There are many differences between countries in terms of the indications for surgery, technical capacity and the characteristics of the patients given CABGS. These differing characteristics can affect the risk stratification performance of different scores. Several different risk stratification models have been validated with the objective of preventing mortality and major cardiac adverse events during and after coronary artery bypass graft surgery (CABGS)^9-16. The scientific evidence suggests that the Cleveland Clinic score and the EuroSCORE are the most useful for predicting the prognosis of patients given CABGS. In both cases the variable emergency surgery had the greatest power to predict mortality¹⁷. Validation of these instruments at different institutions therefore appears to be recommendable. Limitations: the small number of patients enrolled on this study is a result of the fact that this was a secondary objective of a larger project designed to evaluate the influence of physical activity in free time on the prognosis of patients given CABGS, and the sample size was calculated for that study⁵. The sample size would have had to be greater in order to assess the outcome mortality. Another factor that impacts on this outcome is developments in surgical techniques and preoperative and postoperative care, reducing the number of complications and, consequently, of deaths.

CONCLUSION

The Cleveland Clinic and EuroSCORE surgical risk prediction instruments are effective for predicting mortality among elective CABGS patients.

Conflicts of interest: none

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Correspondência: Av. Princesa Isabel, 370 - Santana Porto Alegre - RS CEP: 90620-000

Publication Dates

• Publication in this collection
  30 Nov 2010
• Date of issue
  2010

History

• Accepted
  08 July 2010
• Received
  20 Nov 2009