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Valley-Columbia Heart Center, Ridgewood, New Jersey
Accepted for publication July 30, 2009.
* Address correspondence to Dr Brizzio, Valley–Columbia Heart Center, 223 N Van Dien, Ridgewood, NJ 07450 (Email: brizma{at}valleyhealth.com).
Presented at the Poster Session of the Forty-fifth Annual Meeting of The Society of Thoracic Surgeons, San Francisco, CA, Jan 26–28, 2009.
| ADULT CARDIAC SURGERY:
The Annals of Thoracic Surgery CME Program is located online at http://cme.ctsnetjournals.org. To take the CME activity related to this article, you must have either an STS member or an individual non-member subscription to the journal.
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Abstract |
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Methods: We analyzed 4,869 consecutive isolated CABG performed in our institution. Of these, 3,490 (71.7%) were off-pump and 1,379 (28.3%) were on-pump. Propensity matched samples of 1,379 off-pump and 1,379 on-pump were compared on clinical presentation and The Society of Thoracic Surgeons (STS) predicted scores for risk of postoperative mortality and stroke. Univariate analyses were used to compare the relationship of off-pump and on-pump groups to postoperative mortality and stroke. Multivariate logistic regression was used to determine the unique association between all variables and occurrence of mortality after stroke.
Results: No differences were found for sex, diabetes mellitus, history of renal failure, prior stroke, or timing of surgery. Postoperative mortality occurred in 75 patients (2.7%) and stroke in 47 (1.7%). The off-pump patients had a lower rate of stroke (1.0% versus 2.4%; p < 0.01) compared with on-pump patients. Mortality after stroke occurred in 14 patients, with a lower rate occurring in the off-pump group (14.3% versus 36.4%; p = 0.07). Multivariate analyses controlling for the effect of preoperative risk factors and STS mortality risk demonstrated that off-pump status was independently associated with an 84% decrease in the risk of death after stroke (adjusted odds ratio 0.157, 95% confidence interval: 0.035 to 0.711, p = 0.016).
Conclusions: Off-pump CABG is associated with lower stroke rates and stroke-related mortality. It may be useful to consider off-pump CABG for patients who are at higher risk for postoperative stroke.
Stroke continues to be a devastating complication after coronary artery bypass graft surgery (CABG) [1]. Previous studies have shown postoperative stroke rates between 1.3% and 3.6%. This rate varies depending on the type of operation and preoperative comorbidities [1, 2]. There is some evidence to suggest that off-pump CABG is associated with better outcomes compared with on-pump CABG, specifically with a lower incidence of stroke and mortality [3, 4]. This study was designed to determine the frequency, severity, and death-related incidence of stroke comparing off-pump and on-pump CABG at a single institution.
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Material and Methods |
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A total of 4,869 consecutive patients with isolated CABG were available for inclusion into the current study. Of these, 3,490 operations (71.7%) were performed without cardiopulmonary bypass (off pump) and 1,379 (28.3%) with cardiopulmonary bypass (on pump; Fig 1). Initial comparisons of the demographics and preoperative morbidities of the overall patient sample are presented in Table 1. Although the risk of stroke using the STS stroke risk model was similar (1.76% versus 1.70% off pump versus on pump), the STS risk of mortality showed that off-pump patients had a significantly lower risk of mortality compared with on-pump patients (2.14% versus 2.64%; p < 0.0001). To provide a more balanced comparison between the two groups, propensity matching was employed [5, 6]. After propensity matching, off-pump and on-pump patients were similar in most baseline factors, although the rates of prior CVA and peripheral vascular disease were significantly higher in the off-pump group (Table 2).
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Surgical Technique
Each patient underwent either an off-pump or on-pump procedure performed at the discretion of the surgeon, who decided which procedure was more appropriate at the time of the operation. The factors evaluated included level of difficulty, characteristics of the aorta, targets sizes, hemodynamic stability, and tolerance to cardiac mobilization. Off-pump cases were performed with one of several commercially available stabilizing devices. There were some minor variations in the surgical technique because there were four different surgeons involved in the procedures. There were nonuniform criteria for grafting sequences. Intracoronary shunts were used occasionally, and proximal anastomosis was performed using partial occlusion clamp. However, in cases with a partially calcified aorta, the Enclosed Device (Novare Surgical Systems, Cupertino, CA) was utilized. For extremely calcified aortas, the "no touch technique" was applied.
Traditionally, cardiopulmonary bypass cases were performed with standard technique: central cannulation, roller pumps, membrane oxygenators, appropriate filters, antegrade and retrograde cardioplegia, and mild hypothermia at 30° to 34° C. Cerebral mixed O2 saturation (INVOS; Somanetics, Troy, MI) has been monitored in both groups since 2002.
Patients who were converted to an on-pump procedure during an off-pump procedure were excluded from the cohort (17 patients), although in this small group (0.3% of the total population studied), there were no strokes or 30-day postoperative mortality.
Data Analysis
Data were prospectively collected and stored in a database certified by the STS. Continuous data are displayed as means with standard deviation. Categorical data are expressed as proportions. Univariate statistical tests for continuous data included tests of mean differences using Student's t test. Categorical variables were analyzed using the 
2 test. Multivariate analysis of the dichotomous outcome (death after stroke versus no death after stroke) was analyzed with logistic regression analysis. A value of p less than 0.05 was used to determine the statistical significance of all tests used. Analyses were performed using the SPSS statistical software package, version 17.0 (SPSS, Chicago, IL). Propensity balancing was performed using age, sex, history of diabetes mellitus, smoking, renal failure, prior myocardial infarction, prior stroke, left main disease or triple-vessel disease present, low left ventricular ejection fraction (less than 35%), acuity of the surgery (elective, urgent, emergent), and STS mortality risk score as the predictor variables and on-pump and off-pump status as the dependent variable in a logistic regression model [7] to generate a propensity score for each patient. Propensity scores from the off-pump group were matched with the on-pump group using the Caliper method with 5-to-1 digit matching to randomly select comparable off-pump patients with the 1,379 on-pump patients [8].
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Results |
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The logistic regression analysis controlling for the effect of preoperative risk factors and STS mortality risk demonstrated that pump status was significantly and independently associated with mortality outcome after stroke, with off-pump patients experiencing an 84% reduction in risk of death after stroke (adjusted odds ratio = 0.157, 95% confidence interval: 0.035 to 0.711, p = 0.016; Table 5). Because there were more reoperations in the on-pump group in the propensity-matched sample, the logistic regression analysis was repeated using only those patients having their first operation (off pump = 1,327, and on pump = 1,288). The results of this analysis were identical, with off-pump patients having an 80% reduction in risk of death after stroke (Table 6).
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Comment |
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In this cohort, the overall incidence of stroke in both groups was 1.7% (n = 47), which was similar that in previous reported studies [2, 3]. Other studies reported significant higher incidence of this complication, at 2.2% to 3.2% [1–9]. However, none of these studies compares off-pump versus on-pump patient outcomes.
Sedrakyan and colleagues [3] in a meta-analysis of systematically reviewed trials found a 50% relative risk reduction of stroke when coronary surgery is performed off pump. In a recent report from Filsoufi and colleagues [10], the mortality rate in patients with stroke was more than 10-fold increased compared with patients not having this complication, but differences between off-pump and on-pump CABG regarding this complication were not analyzed.
After propensity matching, the off-pump group had a significantly higher risk for postoperative stroke compared with the on-pump group, and the results still showed a statistically significant decrease in stroke in the off-pump patients. The mortality after the stroke occurred was 14% for the off-pump group versus 36% for the on-pump group. However, the most important finding was that if a patient had a stroke after CABG, the chances of dying were reduced by more than 80% if the operation was done off pump. Given the other improved outcomes after surgery in the off-pump group, this would suggest that the off-pump patients have experienced fewer traumas. The multivariate analysis of first-time operations indicates that this finding is robust and independent of other risk factors, a finding we are the first to demonstrate.
The exact reason for higher mortality rates in early strokes after CABG using cardiopulmonary bypass remains unclear. We strongly believe that the aortic calcifications play a crucial role in the occurrence of stroke after CABG. Previous studies have investigated the influence of aortic calcification and stroke [11, 12]. In a retrospective analysis, van der Linden and colleagues [13] demonstrated that the sole presence of calcification in the ascending aorta significantly increased the risk of stroke: 6.4% for patients with compromised aorta compared with 1.5% for those without. Unfortunately, the STS database does not record the level of aortic calcification, so in this analysis, that factor was not evaluated. Many studies have demonstrated that the systematic use of epiaortic ultrasonography before the aorta manipulation may reduce the incidence of stroke [13, 14]. In this group of patients, the aorta was not scanned. However, in all the cases, the aorta was managed cautiously and probably influenced in part the decision to perform the operation off or on pump. As we mentioned before, alternative strategies were used for significantly compromised aortas to perform the proximal anastomosis. Hence, that may have had an impact in our results.
Considering the devastating effect of postoperative stroke on surgical outcomes including quality of life and significant increase in health care costs, these findings should have a major clinical implication. We suggest the importance of preoperative identification of this high risk population and the implementation of all available preventive strategies, including the decision to perform coronary surgery without the utilization of the cardiopulmonary bypass.
Study Limitations
This is retrospective analysis of prospectively collected data, and the conclusions may be limited. This is a single-institution study in which the operations were performed by four different surgeons with slightly different techniques. We have evaluated only the first 30 days of postoperative outcomes, as defined in the STS database. Our study did not collect data about the severity of calcification of the aorta, and that might have influenced the results.
Conclusions
Stroke is still a devastating complication after CABG. The mortality associated with this complication is high. The utilization of off-pump CABG is associated with a significant decrease in the risk of early postoperative stroke and an 84% decrease in the risk of death after the neurologic event occurs. The off-pump approach should be considered an alternative to reduce the mortality and stroke rates for coronary artery surgery.
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