An Australian risk prediction model for 30-day mortality after isolated coronary artery bypass: the AusSCORE.

OBJECTIVE: Our objective was to identify risk factors associated with 30-day mortality after isolated coronary artery bypass grafting in the Australian context and to develop a preoperative model for 30-day mortality risk prediction. SUMMARY BACKGROUND DATA: Preoperative risk associated with cardiac surgery can be ascertained through a variety of risk prediction models, none of which is specific to the Australian population. Recently, it was shown that the widely used EuroSCORE model validated poorly for an Australian cohort. Hence, a valid model is required to appropriately guide surgeons and patients in assessing preoperative risk. METHODS: Data from the Australasian Society of Cardiac and Thoracic Surgeons database project was used. All patients undergoing isolated coronary artery bypass grafting between July 2001 and June 2005 were included for analysis. The data were divided into creation and validation sets. The data in the creation set was used to develop the model and then the model was validated in the validation set. Preoperative variables with a P value of less than .25 in chi(2) analysis were entered into multiple logistic regression analysis to develop a preoperative predictive model. Bootstrap and backward elimination methods were used to identify variables that are truly independent predictors of mortality, and 6 candidate models were identified. The Akaike Information Criteria (AIC) and prediction mean square error were used to select the final model (AusSCORE) from this group of candidate models. The AusSCORE model was then validated by average receiver operating characteristic, the P value for the Hosmer-Lemeshow goodness-of-fit test, and prediction mean square error obtained from n-fold validation. RESULTS: Over the 4-year period, 11,823 patients underwent cardiac surgery, of whom 65.9% (7709) had isolated coronary bypass procedures. The 30-day mortality rate for this group was 1.74% (134/7709). Factors selected as independent predictors in the preoperative isolated coronary bypass AusSCORE model were as follows: age, New York Heart Association class, ejection fraction estimate, urgency of procedure, previous cardiac surgery, hypercholesterolemia (lipid-lowering treatment), peripheral vascular disease, and cardiogenic shock. The average area under the receiver operating characteristic was 0.834, the P value for the Hosmer-Lemeshow chi(2) test statistic was 0.2415, and the prediction mean square error was 0.01869. CONCLUSION: We have developed a preoperative 30-day mortality risk prediction model for isolated coronary artery bypass grafting for the Australian cohort.

Does prior percutaneous coronary intervention adversely affect early and mid-term survival after coronary artery surgery?

OBJECTIVES: To determine the association between previous percutaneous coronary intervention (PCI) and results after coronary artery bypass graft surgery (CABG). BACKGROUND: Increasing numbers of patients undergoing CABG have previously undergone PCI. METHODS: We analyzed consecutive first-time isolated CABG procedures within the Australasian Society of Cardiac and Thoracic Surgeons Database from June 2001 to May 2008. Logistic regression and propensity score analyses were used to assess the risk-adjusted impact of prior PCI on in-hospital mortality and major adverse cardiac events. Cox regression model was used to assess the effect of prior PCI on mid-term survival. RESULTS: Of 13,184 patients who underwent CABG, 11,727 had no prior PCI and 1,457 had prior PCI. Mean follow-up was 3.3 +/- 2.1 years. Patients without prior PCI had a higher EuroSCORE value (4.4 +/- 3.3 vs. 3.6 +/- 3.0, p < 0.001), were older, and more likely to have left main stem stenosis and recent myocardial infarction. There was no difference in unadjusted in-hospital mortality (1.65% vs. 1.55%, p = 0.78) or major adverse cardiac events (3.0% vs. 3.0%, p = 0.99) between patients with or without prior PCI. After adjustment, prior PCI was not a predictor of in-hospital (odds ratio: 1.22, 95% confidence interval [CI]: 0.76 to 2.0, p = 0.41) or mid-term mortality at 6-year follow-up (hazard ratio: 0.94, 95% CI: 0.75 to 1.18, p = 0.62). CONCLUSIONS: In this large registry study, prior PCI was not associated with increased short- or mid-term mortality after CABG. Good outcomes can be obtained in the group of patients undergoing CABG who have had previous PCI.

Short- and midterm outcomes of coronary artery bypass surgery performed by surgeons in training.

OBJECTIVE: The effect of training on outcomes in cardiac surgery is poorly studied. We aimed to study the results of coronary artery bypass grafting procedures performed by surgeons in training across our state with respect to short- and midterm postoperative outcomes. METHODS: All coronary artery bypass grafting surgeries performed by trainee surgeons between July 2001 and December 2006 were compared with those performed by consultant surgeons using mandatory prospectively collected statewide data. Early mortality; prolonged ventilation or intensive care unit stay; return to operating theater for bleeding, stroke, myocardial infarction, or renal failure; and 5-year survival were compared using propensity score analysis. RESULTS: A total of 7745 surgeries were included in this study. Trainees performed 983 (13%) surgeries. Trainee surgeries had longer perfusion and crossclamp times. Crude early postoperative outcomes were similar between trainee and consultant surgeries. After propensity score adjustment, early outcomes remained similar, with the exception of myocardial infarction (0.8% in trainee surgeries vs 0.4% in consultant surgeries, P = .046). Adjusted 1-, 3-, and 5-year survivals were similar between trainee and consultant surgeries: 95.3% versus 95.5%, 90.8% versus 92.0%, and 86.3% versus 87.1%, respectively. CONCLUSION: Coronary artery bypass grafting performed by trainee surgeons within a supervised program is safe with acceptable short- and midterm outcomes.

Contemporary results show repeat coronary artery bypass grafting remains a risk factor for operative mortality.

BACKGROUND: Reoperative coronary artery bypass grafting (redo CABG) shows improving outcomes, but with varying degrees of improvement. We assessed contemporary outcomes after redo CABG to determine if redo status is still a risk factor for early postoperative complications and midterm survival. METHODS: Isolated CABG procedures (June 1, 2001 to May 31, 2008) within the Australasian Society of Cardiac and Thoracic Surgeons Cardiac Surgery Database were included. Redo status as a predictor for early outcomes was assessed with logistic regression analysis. Midterm survival was determined from the National Death Index. Effect of redo status on midterm survival was assessed using a Cox proportional hazards model. RESULTS: Inclusion criteria were met by 13,436 patients, and 458 (3.4%) underwent redo CABG. Operative mortality was 4.8% for redo CABG and 1.8% for first-time CABG (p < 0.001). After adjustment, redo status remained a predictor for operative mortality (odds ratio [OR], 2.1; 95% confidence interval [CI], 1.3 to 3.6), myocardial infarction (OR, 2.8; 95% CI, 1.6 to 6.0), and prolonged ventilation (OR, 1.5; 95% CI, 1.1 to 2.0). Unadjusted survival was lower for the redo CABG group vs the first-time CABG group at up to 6 years (p = 0.01, log-rank test. After adjusting for differences in patient variables, redo status was not a predictor of midterm survival (OR, 1.03; 95% CI, 0.78 to 1.35; p = 0.85). CONCLUSIONS: Early postoperative outcomes of redo CABG are encouraging. Midterm survival is excellent; however, redo remains a significant risk factor for operative mortality in contemporary practice.

Prosthesis-patient mismatch is associated with higher operative mortality following aortic valve replacement.

BACKGROUND: Prosthesis-patient mismatch (PPM) occurs when the valve prosthesis implanted at surgery is too small in relation to patient's body size, causing high transvalvular gradients. We investigated if severe PPM is related to early morbidity and mortality after aortic valve replacement (AVR). METHODS: We analysed prospectively collected data of 701 consecutive patients undergoing AVR between June 2001 and February 2006 at two Australian public hospitals. The indexed valve effective orifice area (IEOA) was estimated for each valve prosthesis implanted. PPM was defined as

Obesity and early complications after cardiac surgery.

OBJECTIVE: To assess the prevalence of obesity in patients undergoing coronary artery bypass grafting, heart valve surgery, or both procedures, and its association with postoperative outcomes. DESIGN AND SETTING: Retrospective analysis of data, collected by the Australasian Society of Cardiac and Thoracic Surgeons Victorian Cardiac Surgery Database Project, on patients undergoing coronary artery bypass grafting, heart valve surgery, or both procedures, between 1 June 2001 and 31 January 2006. PARTICIPANTS: 11 736 patients divided into four groups: underweight (body mass index [BMI], < 20), normal weight (BMI, 20-30), obese (BMI, > 30 to < 40), and morbidly obese (BMI, >/= 40). MAIN OUTCOME MEASURES: Prevalence of obesity (compared with the age- and sex-matched adult Australian population); associations between obesity and morbid obesity in cardiac patients and adverse postoperative outcomes. RESULTS: 30.4% of patients had a BMI > 30 (28.6% obese, 1.8% morbidly obese) compared with an expected prevalence of 21.2%. Morbid obesity was associated with prolonged ventilation (adjusted odds ratio [OR], 2.4; 95% CI, 1.6-3.7), readmission to intensive care (adjusted OR, 2.2; 95% CI, 1.2-4.1), and length of stay > 14 days (adjusted OR, 2.1; 95% CI, 1.4-3.3). Both obesity and morbid obesity were associated with renal failure (adjusted ORs, 1.4 [95% CI, 1.1-1.7] and 2.9 [95% CI, 1.7-4.9], respectively) and deep sternal wound infection (adjusted ORs, 2.4 [95% CI, 1.5-3.8] and 7.2 [95% CI, 2.8-18.7], respectively). CONCLUSIONS: Obesity is 1.4 times more prevalent in patients having coronary artery bypass grafting or heart valve surgery in Victoria compared with the general adult Australian population. Both obesity and morbid obesity are associated with early morbidity, but not mortality, after operation.

Effect of obesity on early morbidity and mortality following cardiac surgery.

BACKGROUND: The prevalence of obesity in most developed nations, including Australia, continues to rise and represent an increasing public health concern. Obesity has been considered a major risk factor in patients undergoing cardiac and other major surgery. METHODS: We retrospectively analysed prospectively collected data of consecutive patients undergoing cardiac surgery between June 2001 and February 2006 at two Australian public hospitals. Patients were divided into three groups by body mass index (BMI): non-obese (BMI 20-30), obese (BMI>30-40) and morbidly obese (BMI>40). Associations between early mortality and morbidity and obesity were assessed by univariate and multivariate methods. RESULTS: Out of 4053 patients, 85 were excluded for BMI<20. A total of 2743 patients were defined as non-obese, 1136 obese and 89 morbidly obese. There were no significant differences in operative mortality, stroke, pneumonia, new renal failure, atrial fibrillation, prolonged ventilation, reintubation, readmission to intensive care, prolonged length of hospital stay or readmission within 30 days. The morbidly obese group had increased rates of deep sternal infection by univariate (odds ratio [OR] 6.4, 95% confidence interval [CI] 2.1-19.1, p<0.001) and multivariate (OR 13.1, CI 3.4-50.7, p<0.001) analysis. The obese group had a lower rate of re-operation for bleeding by univariate (OR 0.61, CI 0.41-0.91, p=0.01) and multivariate (OR 0.64, CI 0.42-0.99, p=0.04) analysis. CONCLUSION: Apart from an increased rate of deep sternal wound infection, obesity is not associated with early mortality or other post-operative complications. The protective effect of obesity on re-operation for bleeding requires further study.

A retrospective audit of the use of Prothrombinex-HT for refractory bleeding following adult cardiac surgery.

OBJECTIVE: To review the frequency of use, possible efficacy and safety profile of Prothrombinex-HT (CSL Bioplasma, Melbourne, VIC) in treatment of patients with microvascular bleeding refractory to standard measures after cardiothoracic surgery. METHODS: A retrospective chart review was performed of 60 consecutive cardiothoracic surgical patients who received Prothrombinex-HT between February and August 2003. Data collected included baseline demographic information, nature and complexity of surgery, preoperative medications, baseline haematological parameters and evidence of clinically significant prothrombotic complications. Consumption of blood products, haematological parameters and mediastinal bleeding rates before and after administration of Prothrombinex-HT were documented in 22 patients who received Prothrombinex-HT in the ICU. RESULTS: No major prothrombotic complications were noted in the series of 60 patients. Two patients had superficial thrombophlebitis. Blood product consumption and haematological parameters were markedly reduced after administering Prothrombinex-HT. CONCLUSIONS: Use of Prothrombinex-HT was not associated with significant prothrombotic complications. Limited evidence of its efficacy suggests that it should be further evaluated in the setting of cardiothoracic surgery.

Validation of the EuroSCORE model in Australia.

OBJECTIVE: There is an important role for accurate risk prediction models in current cardiac surgical practice. Such models enable benchmarking and allow surgeons and institutions to compare outcomes in a meaningful way. They can also be useful in the areas of surgical decision-making, preoperative informed consent, quality assurance and healthcare management. The aim of this study was to assess the performance of the European System for Cardiac Operative Risk Evaluation (EuroSCORE) model on the Australasian Society of Cardiac and Thoracic Surgeons (ASCTS) patient database. METHODS: The additive and logistic EuroSCORE models were applied to all patients undergoing cardiac surgery at six institutions in the state of Victoria between 1st July 2001 and 4th July 2005 within the ASCTS database who have complete data. The entire cohort and a subgroup of patients undergoing coronary artery bypass grafting (CABG) only were analysed. Observed and predicted mortalities were compared. Model discrimination was tested by determining the area under the receiver operating characteristic (ROC) curve. Model calibration was tested by the Hosmer-Lemeshow chi-square test. RESULTS: Eight thousand three hundred and thirty-one patients with complete data were analysed. There were significant differences in the prevalence of risk factors between the ASCTS and European cardiac surgical populations. Observed mortality was 3.20% overall and 2.00% for the CABG only group. The EuroSCORE models over estimated mortality (entire cohort: additive predicted 5.31%, logistic predicted 8.76%; CABG only: additive predicted 4.25%, logistic predicted 6.19%). Discriminative power of both models was very good. Area under ROC curve was 0.83 overall and 0.82 for the CABG only group. Calibration of both models was poor as mortality was over predicted at nearly all risk deciles. Hosmer-Lemeshow chi-square test returned P-values less than 0.05. CONCLUSIONS: The additive and logistic EuroSCORE does not accurately predict outcomes in this group of cardiac surgery patients from six Australian institutions. Hence, the use of the EuroSCORE models for risk prediction may not be appropriate in Australia. A model, which accurately predicts outcomes in Australian cardiac surgical patients, is required.

Validation of Euroscore model in an Australian patient population.

BACKGROUND: The purpose of the present paper was to assess the performance of the European system for cardiac operative risk evaluation (EuroSCORE) model in an Australian adult cardiac surgical population. METHODS: The additive and logistic EuroSCORE models were retrospectively applied to predict operative mortality in 2106 consecutive patients undergoing cardiac surgery at St Vincent's Hospital, Melbourne between June 2001 and August 2003, and at Geelong Hospital between June 2001 and April 2004. The entire cohort and a subset of patients undergoing isolated coronary artery bypass graft (CABG) surgery were analysed. Model discrimination and calibration was tested by determining the area under the receiver operating characteristic (ROC) curve and Hosmer-Lemeshow chi2, respectively. RESULTS: There were significant differences in the prevalence of risk factors between the Australian and European cardiac surgical populations. There were 81 deaths (observed mortality 3.85%) in the entire cohort and 39 deaths in the isolated CABG group (observed mortality 2.60%). The EuroSCORE models overestimated mortality (entire cohort: additive predicted 5.75%, logistic predicted 9.93%; isolated CABG: additive predicted 4.87%, logistic predicted 7.71%). Discriminative power was very good for the entire cohort (area under ROC curve, 0.81 (additive) and 0.82 (logistic)). Calibration of both models was poor. CONCLUSION: The additive and logistic EuroSCORE model of risk prediction was not validated in the present population of cardiac surgical patients. The models may not accurately predict outcomes of patients undergoing cardiac surgery in Australia.