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Ann Thorac Surg 2007;84:808-816
© 2007 The Society of Thoracic Surgeons

Original Articles: Cardiovascular

Results and Predictors of Early and Late Outcome of Coronary Artery Bypass Grafting in Patients With Severely Depressed Left Ventricular Function

Farzan Filsoufi, MDa,*, Parwis B. Rahmanian, MDa, Javier G. Castillo, MDa, Joanna Chikwe, FRCS (CTh)a, Annapoorna S. Kini, MD, MRCPb, David H. Adams, MDa

a Department of Cardiothoracic Surgery, Mount Sinai School of Medicine, New York, New York
b Cardiovascular Institute, Mount Sinai School of Medicine, New York, New York

Accepted for publication April 27, 2007.

* Address correspondence to Dr Filsoufi, Mount Sinai School of Medicine, 1190 Fifth Ave, New York, NY 10029-1028 (Email: farzan.filsoufi{at}mountsinai.org).


   Abstract
Top
 Abstract
Introduction
 Patients and Methods
 Results
 Comment
 References
 
Background: Coronary artery bypass grafting (CABG) is a well-accepted therapeutic approach in patients with symptomatic multivessel coronary artery disease and severely depressed left ventricular function. However, the potential impact of off-pump CABG in this group of patients remains unknown. In addition, there are only scarce data regarding long-term survival and its predictors in this patient population.

Methods: We retrospectively analyzed prospectively collected data of 2,725 consecutive patients (mean age, 65 ± 11 years; 843 (31%) female) undergoing CABG between January 1998 and December 2005 (ejection fraction [EF] ≤ 0.30; n = 495, 18%). Outcome measures included hospital mortality, major complications, and long-term survival. Multivariate analysis was performed to identify predictors of hospital mortality and late survival. Subgroup analysis for patients with EF less than or equal to 0.30 undergoing conventional CABG (n = 424, 86%) versus off-pump CABG (n = 71, 14%) was performed.

Results: Hospital mortality was 1.8% (EF ≤ 0.30, 3.6%; EF > 0.30, 1.4%; p = 0.002). Off-pump CABG did not have an impact on operative mortality (on-pump, 4%; off-pump, 3%; p = 0.509). Ejection fraction of 0.30 or less was not an independent risk factor of hospital mortality but predicted respiratory failure (odds ratio [OR] = 2.3) and sepsis (OR, 1.4). Long-term survival was significantly decreased in patients with EF of 0.30 or less: 1-year and 5-year survival 88% ± 1.5% and 75% ± 2.2% versus 96% ± 0.4% and 81% ± 1.2%, respectively (p = 0.001). Reoperation (OR, 6.9), peripheral vascular disease (OR, 3.2), chronic obstructive pulmonary disease (OR, 3.0), congestive heart failure (OR, 2.7), and female sex (OR, 2.1) were independent predictors of long-term survival.

Conclusions: Excellent results after CABG can be expected in patients with EF of 0.30 or less, with minimal increase in mortality and acceptable postoperative morbidity. Long-term survival remains limited, but recent results are substantially better than historical reports. Careful preoperative patient selection and perioperative management are essential in these patients undergoing CABG.


   Introduction
Top
 Abstract
 Introduction
Patients and Methods
 Results
 Comment
 References
 
In patients with symptomatic multivessel coronary artery disease and severely depressed left ventricular (LV) function (ejection fraction [EF] ≤ 0.30), coronary artery bypass grafting (CABG) is the optimal therapeutic approach and remains superior to medical therapy [1–3]. Recent clinical series reporting on the outcome of CABG suggest that up to 15% of patients present with severely depressed LV function [4]. The postoperative outcome of these patients has traditionally been worse compared with patients with moderate to good LV function [5]. An analysis from the New York State cardiac surgery database including patients who underwent CABG from 1997 to 1999 showed that in-hospital mortality and morbidities were significantly higher in patients with depressed LV function compared with patients with normal LV function [6]. In this study, the mortality rate of the group with an EF less than or equal to 0.30 was 4.8% compared with 1.4% in patients with normal LV function. More recently it has been suggested that off-pump CABG may be beneficial in patients with severely depressed LV function by avoiding prolonged ischemic times [7].

In addition, most clinical series have primarily focused on early operative mortality and morbidities, and limited data are available with respect to the predictors of outcome in this high-risk group mainly because of the small number of patients included in these previous studies. Finally, little is known with respect to long-term survival and its predictors in this patient population. Herein we report our clinical experience in a large and contemporary single-center series of patients with severely depressed LV function who underwent CABG between 1998 and 2005. In this study we sought to determine the early outcome, predictors of early mortality as well as midterm survival, and predictors of late mortality in this patient population. Furthermore, we performed a subgroup analysis comparing conventional CABG with off-pump CABG.


   Patients and Methods
Top
 Abstract
 Introduction
 Patients and Methods
Results
 Comment
 References
 
Study Population
We analyzed a series of 2,725 patients undergoing isolated CABG procedures at the Mount Sinai Medical Center between January 1998 and December 2005. Data were prospectively collected and analyzed retrospectively.

The study group was determined by the preoperative EF. Patients with an EF less than or equal to 0.30 formed the study group, whereas patients with an EF greater than 0.30 served as the control group. Patients undergoing reoperations or emergent procedures were included in this analysis. Patients who were admitted in cardiogenic shock or undergoing cardiopulmonary resuscitation before admission to the operating room were excluded (n = 25). The preoperative EF was assessed by echocardiography (n = 2,088, 77%), LV angiogram (n = 614, 22%), and radionuclide studies (n = 23, 1%).

The protocol was approved by our local institutional review board and compliant to the Health Insurance Portability and Accountability Act regulations and the ethical guidelines of the 1975 declaration of Helsinki, as revised in 2000. The approval included a waiver of informed consent.

Data Collection and Outcome Analysis
Clinical variables were prospectively entered into the New York State Department of Health (NYSDH, State Cardiac Advisory Committee) data registry. The NYSDH data registry represents a mandatory verified peer-reviewed data collection system including all adult cardiac surgery procedures in the state of New York and records and analyzes data in a strictly supervised and widely reported fashion.

Patient demographics and risk factors, operative information, and postoperative outcome data were retrospectively analyzed. Additional information was obtained from patient charts when necessary. In addition, the logistic EuroSCORE was used for risk stratification [8]. The EuroSCORE is a risk stratification system using multiple preoperative risk factors to predict operative mortality. Patients with a predicted mortality by EuroSCORE were stratified as follows: EuroSCORE less than or equal to 3%, low risk; EuroSCORE 3% to 9%, moderate risk; EuroSCORE 9% to 25%, high risk; and EuroSCORE greater than 25%, very high risk.

Outcome measures for this study included hospital mortality, major postoperative complications (perioperative myocardial infarction, respiratory failure, renal failure, deep sternal wound infection, bleeding requiring reoperation, unplanned reoperation, stroke, gastrointestinal complications), length of hospital stay, and late survival. Hospital mortality was defined as death after the procedure before patient’s discharge regardless of the duration of hospitalization. Patients who died after discharge from hospital but within 30 days after the procedure were also considered as hospital deaths. Respiratory failure was defined as prolonged ventilator therapy (>72 hours) or need for reintubation or tracheostomy. Renal failure was defined as creatinine greater than 2.5 mg/dL for more than 7 postoperative days or the need for dialysis. Stroke was defined as a new permanent neurologic event occurring perioperatively or postoperatively. Follow-up survival information was obtained by cross-matching the patient’s social security number with the web-based social security death index (www.ssa.gov).

Surgical Management
All patients underwent a median sternotomy. Eighty-five percent (n = 2,316) of procedures were performed using cardiopulmonary bypass (CPB). The remaining 15% (n = 409) of procedures were performed without the use of CPB (off-pump CABG). Since 2003, epiaortic ultrasonography was performed systematically in all patients to detect any atherosclerotic lesions of the ascending aorta before cannulation and clamping. The surgical strategy was defined according to the presence or absence of calcification in the ascending aorta and its extent [9].

On-Pump Coronary Revascularization
After systemic heparinization with an activated clotting time level of at least 400 seconds, CPB was instituted between the ascending aorta and the right atrium using a two-stage cannula. After aortic cross-clamp, high potassium blood cardioplegia was administered in an antegrade or retrograde fashion for myocardial protection. In addition, we have routinely administered a solution of antegrade warm blood cardioplegia before removal of the aortic cross-clamp ("hot-shot" cardioplegia) in these patients since 2003 [10]. Distal anastomoses were completed first, followed by proximal anastomoses using the single aortic cross-clamp technique [11]. The left internal mammary artery was routinely anastomosed to the left anterior descending artery. Aortic cross-clamp was released hereafter, and the patients were weaned from CPB after a short reperfusion. After the completion of CPB, protamine was given depending on the heparin level.

Off-Pump Coronary Revascularization
The procedure was performed based on surgeon’s preference. This technique, however, was favored particularly in elderly patients with atherosclerotic disease of the ascending aorta. In patients undergoing off-pump CABG, heparin was administered to achieve an activated clotting time of 300 seconds. Coronary stabilizer and cardiac positioning devices were used to access the coronary arteries under beating heart conditions. Intracoronary shunts were systematically used in all patients to prevent prolonged myocardial ischemia while distal anastomoses were created. After the completion of the procedure, protamine was administered depending on the heparin level.

Statistical Analyses
Normally distributed continuous variables are presented as mean ± standard deviation and otherwise as median and interquartile range. Categorical variables are shown as the percentage of the sample. A probability value less than 0.05 was considered as significant for all statistical methods. The {chi}2 test was used to evaluate potential confounders of the relationship between EF and hospital mortality and morbidities. Stepwise multivariate logistic regression was then performed to assess the influence of EF as an independent risk factor for hospital mortality and postoperative morbidities. In the group of patients with low EF, univariate and multivariate analysis was performed in the same manner to identify predictors of in-hospital mortality and late mortality.

The potential confounders introduced into multivariate analysis included age, sex, diabetes mellitus, congestive heart failure, previous cardiac procedure, body mass index, hypertension, myocardial infarction, chronic obstructive pulmonary disease, peripheral vascular disease, renal failure, hepatic failure, urgency of procedure, and use of internal mammary artery.

Long-term survival of discharged patients was analyzed using Kaplan–Meier survival curves. These analyses included the impact of low EF on survival after CABG in the overall population and the effect of preoperative risk factors and EuroSCORE on survival in the low EF group. Differences in patient characteristics were controlled by Cox proportional hazard analysis. The statistical analyses were performed with the use of SPSS 15 (SPSS Inc, Chicago, IL).


   Results
Top
 Abstract
 Introduction
 Patients and Methods
 Results
Comment
 References
 
Demographic Data and Preoperative Risk Factors
The median age in the overall patient population was 66 years (interquartile range, 58–73 years), and 69% (n = 1,882) of patients were male. Severely depressed LV function (EF ≤ 0.30) was present in 495 (18%) patients.

There were significant differences in preoperative comorbidity between patients with EF of 0.30 or less and those with EF greater than 0.30 (Table 1). Patients with EF of 0.30 or less were more likely to present with congestive heart failure (p < 0.001), a history of myocardial infarction (p < 0.001), or as an emergency (p < 0.001), and were more likely to have additional risk factors including peripheral vascular disease (p < 0.001), diabetes mellitus (p = 0.014), chronic obstructive airways disease (p < 0.001), and renal failure (p < 0.001). The proportion of patients with a high or very high EuroSCORE (logistic EuroSCORE >9%) was significantly greater in the EF of 0.30 or less group (48%) compared with the EF greater than 0.30 group (15%; p = 0.001).


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  		Table 1 Patient Characteristics According to the Ejection Fraction Strata
 
The mean predicted mortality by EuroSCORE increased significantly during the study period from 12% ± 10% (1998–2002) to 15% ± 11% (2003–2005; p < 0.001).

Patient Demographics Comparing On-Pump Versus Off-Pump Revascularization
Among the 495 patients with depressed LV function, 424 underwent conventional CABG with CPB whereas 71 underwent off-pump coronary revascularization. Patients who underwent off-pump CABG were significantly older and presented with a higher EuroSCORE predicted mortality compared with patients who underwent conventional CABG (Table 2). In addition, as expected, these patients had significantly more atherosclerotic lesions (calcification) of the ascending aorta.


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  		Table 2 Characteristics of Patients With Severly Depressed Left Ventricular Function According to the Operative Procedure (On-Pump Versus Off-Pump)
 
Operative Characteristics
The number of grafts in the low EF group and control group was 3.4 ± 1 and 3.3 ± 1, respectively (p = 0.492). Patients with depressed LV function received significantly fewer internal mammary artery bypass grafts (n = 403, 81% versus n = 1,947, 87%; p = 0.001) and had a longer CPB time (125 ± 40 minutes) compared with the control group (119 ± 37 minutes; p = 0.005). The cross-clamp time was not significantly different. The difference in CPB time is probably related to a prolonged reperfusion period after the release of the aortic cross-clamp in patients with severely depressed LV function.

In the cohort of patients with low EF, the mean number of grafts was significantly lower in the off-pump group (2.6 ± 1) compared with the on-pump group (3.4 ± 1; p < 0.001; Table 3).


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  		Table 3 Operative Data
 
Hospital Mortality
The overall hospital mortality among our study population was 1.8% (n = 50). The mortality among low EF patients was 3.6% (n = 18) compared with 1.4% (n = 32) in patients with EF greater than 0.30 (p = 0.002; Table 4). When patients with EF of 0.30 or less were stratified by EuroSCORE, there was no mortality in the subgroup of patients with EF of 0.30 or less and a low EuroSCORE. In the remaining risk groups, the mortality was 3.4% (8 of 237) for patients with a moderate EuroSCORE, 3.4% (6 of 179) for patients with a high EuroSCORE, and 6.8% (4 of 59) for patients with very high EuroSCORE (p = 0.425). Operative mortality decreased during the study period from 4% (1998–2002) to 2.6% (2003–2005), but this did not reach statistical significance. There was no difference in mortality when patients with low EF were compared in regard to the use of CPB (on-pump, n = 16, 4% versus off-pump, n = 2, 3%; p = 0.509; Table 5).


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  		Table 4 Postoperative Outcome According to the Left Ventricular Function
 

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  		Table 5 Postoperative Outcome of Patients With Severely Depressed Left Ventricular Function According to the Operative Procedure (On-Pump Versus Off-Pump)
 
Predictors of Hospital Mortality
The independent predictors of hospital mortality for the overall cohort were renal failure (odds ratio [OR], 5.7; 95% confidence interval [CI], 2.8 to 11.7; p < 0.001), peripheral vascular disease (OR, 2.9; CI, 1.6 to 5.4; p = 0.001), hypertension (OR, 2.3; CI, 1.1 to 4.7; p = 0.022), cardiac reoperation (OR, 3.3; CI, 1.2 to 8.9; p = 0.017), and intraaortic balloon pump support (OR, 4.8; CI, 2.0 to 11.6; p < 0.001). The presence of EF of 0.30 or less was not found to be an independent predictor of in-hospital mortality in multivariate regression analysis (OR, 1.43; CI, 0.72 to 2.86; p = 0.311).

Table 6 shows risk factors for hospital mortality in the group of patients with severely depressed LV function. Multivariate regression analysis revealed that congestive heart failure (OR, 2.9), hemodynamic instability (OR, 4.4), and preoperative intraaortic balloon pump (OR, 5.1) were independent predictors of hospital mortality. However, the results of the multivariate analysis should be interpreted with caution because of the relatively small number of events in this subgroup as reflected by large confidence intervals.


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  		Table 6 Predictors of Hospital Mortality in Patients With Low Ejection Fraction (≤0.30)
 
Morbidity
Patients with EF of 0.30 or less had a significantly higher rate of postoperative respiratory failure (p < 0.001) and sepsis (p = 0.003) compared with the control group (EF > 0.30; Table 4), and in multivariate logistic regression analysis EF of 0.30 or less remained an independent predictor of these two complications (respiratory failure, OR, 2.3; CI, 1.8 to 2.9; p < 0.001; sepsis, OR, 1.4; CI, 1.1 to 1.9; p < 0.01). Among patients with low EF postoperative morbidities were similar in on-pump and off-pump CABG groups (Table 5).

The median length of hospital stay was longer in patients with low EF when compared with the control group (EF ≤ 0.30, 8 days; EF > 0.30, 6 days; p = 0.001).

Long-Term Survival
The mean follow-up time was 4.2 ± 2.5 years. Long-term survival of discharged patients was significantly decreased in patients with low EF compared with patients with EF greater than 0.30 (Fig 1). One- and five-year survival rates were 88% ± 1.5% and 75% ± 2.2%, respectively, for low EF patients versus 96% ± 0.4% and 81% ± 1.2%, respectively, for patients with EF greater than 0.30 (p = 0.001). Within the group of patients with EF of 0.30 or less there was a significant difference in long-term survival when patients were divided into low to moderate and high risk by logistic EuroSCORE (Fig 2).


Figure 1
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  		Fig 1. Late survival after coronary artery bypass grafting stratified by left ventricular function. (A) Stratified by ejection fraction (EF) less than or equal to 0.30 and greater than 0.30. (B) Stratified by ejection fraction less than or equal to 0.20, 0.21 to 0.30, 0.31 to 0.50, and greater than 0.50.

 

Figure 2
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  		Fig 2. Late survival of patients with ejection fraction less than or equal to 0.30 stratified by EuroSCORE.

 
Predictors of Long-Term Survival in Patients With Ejection Fraction Less Than or Equal to 0.30
Univariate analysis revealed age older than 70 years, female sex, previous cardiac operation, peripheral vascular disease, aortic calcification, chronic obstructive pulmonary disease, and congestive heart failure as predictors of mortality during follow-up in patients with EF less than or equal to 0.30 (Table 7). Further multivariate logistic regression analysis showed that previous cardiac operation (OR, 6.9), peripheral vascular disease (OR, 3.2), chronic obstructive pulmonary disease (OR, 3.0), congestive heart failure (OR, 2.7), and female sex (OR, 2.1) were independent predictors of mortality during follow-up. The type of surgical procedure (on-pump versus off-pump CABG) was not a predictor of long-term survival.


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  		Table 7 Multivariate Predictors of Long-Term Unadjusted Mortality in Patients With Severely Depressed Left Ventricular Function (Ejection Fraction ≤0.30)
 

   Comment
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
References
 
In this observational study, we report our experience in a large and contemporary series of patients with severely depressed LV function undergoing CABG. The main findings of this study include very low operative mortality, which declined across the study period despite a statistically significant increase in the percentage of patients with high predicted mortality risk by logistic EuroSCORE. We show that severely depressed LV function does not appear to be an independent predictor of early mortality in patients undergoing CABG in our practice. However, low EF is an independent predictor of postoperative respiratory failure and sepsis. We also demonstrate that long-term survival remains significantly reduced in patients with low EF, particularly in the subgroup with a high preoperative predicted mortality by EuroSCORE. Five independent predictors of long-term survival were identified, including previous cardiac operation (OR, 6.9), peripheral vascular disease (OR, 3.2), chronic obstructive pulmonary disease (OR, 3.0), congestive heart failure (OR, 2.7), and female sex (OR, 2.1). Finally we confirm previous studies showing similar results in patients with depressed LV function undergoing conventional versus off-pump revascularization.

Prevalence of Low Ejection Fraction in Patients Undergoing Coronary Artery Bypass Grafting
The reported prevalence of severe LV dysfunction in patients undergoing CABG in large series and registries has ranged from 3.4% to 15% [6, 12]. A single institution series of 4,100 patients undergoing isolated CABG between 1990 and 1999 reported a prevalence of 3.4% with EF less than 0.30 [12]. The prevalence of EF less than 0.30 in a registry of more than 100,000 patients undergoing CABG in the United Kingdom during a period of 6 years has remained steady at approximately 6% to 7% [13]. At the other end of the scale is the prevalence of patients with EF of 0.30 or less of 14.8% reported by a recent analysis of 55,515 patients from the New York State cardiac surgery database who underwent surgery between 1997 and 1999 [6]. The differences may be partly explained by different definitions of severely depressed LV; however, most studies choose an EF of less than or equal to 0.30 [6, 12, 14, 15]. In our study we report a prevalence of 18% of patients with EF less than or equal to 0.30, confirming the apparent trend in increasing numbers of patients with severely depressed LV function referred for myocardial revascularization. As a result of the steady increase in the incidence of congestive heart failure in developed countries, it is expected that a growing number of patients with ischemic cardiomyopathy and LV dysfunction will require myocardial revascularization [16].

Mortality and Morbidity
Patients with EF of 0.30 or less undergoing CABG have been consistently shown in the literature to have higher operative mortality and reduced long-term survival compared with patients with EF greater than 0.30. The in-hospital mortality reported in this patient group during the late 1980s was as high as 20% [17, 18]. This has decreased significantly: the majority of series of low EF patients undergoing CABG in the 1990s reported early mortalities between 5% and 15% [19, 20], whereas the majority of series describing results in patients operated on after 2000 were reporting mortalities of less than 5% [15, 21]. In the Canadian registry database, 431 patients with EF less than 0.30 were operated on between 1996 and 2001 with an overall mortality of 4.6% [14]. This is comparable to the mortality reported on patients operated on between 1997 and 1999 by the New York State cardiac surgery database study, which reported 6.5% and 4.1% in-hospital mortality in patients with EF less than 0.20 and between 0.21 and 0.30, respectively [6]. Our results reflect the steady improvement in mortality seen in the literature, particularly during the second period of our study, in which we observed a mortality of 2.6% in this population. This improvement occurred despite a significant increase in the percentage of patients with high or very high predicted operative mortality by logistic EuroSCORE. This enhancement in operative outcome is certainly multifactorial and probably related to improvements in myocardial protection strategies and perioperative management of related comorbidity, as well as improved case selection involving myocardial viability studies. Despite the fact that our study was not designed to give information with respect to incremental changes in operative and perioperative management (such as epiaortic scanning, improved myocardial protection, and intensive insulin therapy), we believe that these have made a significant contribution to the reduction in operative mortality.

Historically severely depressed LV function has been identified as an independent risk factor for early mortality [22–24]. However, EF of 0.30 or less was not shown by multivariate logistic regression analysis to be an independent risk factor for early mortality (OR, 1.43; CI, 0.72 to 2.86; p = 0.311) in our study. Recent studies have suggested that the significance of severely depressed LV function as a predictor of mortality may be decreasing: odds ratios for severely depressed LV function did not reach statistical significance in multivariate analysis of two contemporary patient series [24, 25]. The study by Davierwala and associates [24], who analyzed the impact of EF on patients undergoing CABG during three time periods from 1990 to 2001, showed that the impact of this factor on early mortality declined across the study so that low EF was no longer an independent predictor in the last period of their study. This decline in the predictive value of low EF lends further support to the hypothesis that evolution in case selection and operative and perioperative management has significantly improved outcomes in these high-risk patients.

In this study we were able to identify independent predictors of mortality in patients with low EF undergoing CABG. Most previous series have been limited by small sample size and therefore unable to reach statistical significance in multivariate analysis. We show that congestive cardiac failure (OR, 4.47; CI, 1.16 to 14.14) and preoperative presence of an intraaortic balloon pump (OR, 4.78; CI, 1.16 to 19.77) are independent predictors of hospital mortality in patients with low EF undergoing CABG. These results are in accordance with findings from the Patch trial database [20] and an analysis from the New York State cardiac surgery database [6], which identified congestive heart failure as an independent predictor of mortality in CABG patients with low EF. Furthermore, the study from the New York State Department of Health identified additional risk factors such as increased age, female sex, hepatic failure, renal failure, emergent procedure, myocardial infarction less than 6 hours before the operation, and previous cardiotomy to be significant predictors of in-hospital mortality in this group [6].

In our analysis, we were not able to confirm the relevance of the above risk factors. Although our study includes one of the largest series of patients with low EF undergoing CABG, the sample size may not have been large enough to identify some of these factors.

With respect to postoperative complications, multivariate logistic regression analysis confirms that EF of 0.30 or less was an independent risk factor for sepsis and respiratory failure in our patient group. These findings are in accordance with the study reported by Topkara and colleagues [6], in which the authors associated severely depressed LV function with respiratory failure, renal failure and dialysis, sepsis, and gastrointestinal complications after CABG.

Long-Term Survival and Predictors
Patients with EF of 0.30 or less had a significantly poorer 1-, 3-, and 5-year survival than patients with EF greater than 0.30. When divided into a high and lower risk group by logistic EuroSCORE, patients with a low to moderate predicted risk (<9%) by EuroSCORE had 1-, 3-, and 5-year survivals of 91.8%, 87.7%, and 83.8%, respectively, compared with 84.0%, 76.6%, and 65.3%, respectively, for patients with EuroSCORE greater than 9% (p < 0.001). These figures are at the upper limit of the long-term survival data recorded in the literature. One-year survivals reported in single-center and registry studies analyzing patients with EF of 0.30 or less undergoing CABG within the last decade range from 81% to 92% [15], 3-year survival ranges from 68% [26] to 87% [15], and 5-year survival when reported ranges from 45% [26] to 78% [14]. It appears from these figures that the increasingly high-risk patient profile may negate any benefit on long-term survival gained by improvements in early outcome. Outcome data from the literature are, however, not risk-adjusted, and comparisons are therefore difficult to make.

Few studies have reported independent predictors of long-term survival in this patient population. In a recent study from the Mayo Clinic, Hillis and coworkers [25] identified age and renal dysfunction as independent predictors of long-term mortality. In multivariate analysis we were able to identify previous cardiac operation (OR, 6.9), peripheral vascular disease (OR, 3.2), chronic obstructive pulmonary disease (OR, 3.0), congestive heart failure (OR, 2.7), and female sex (OR, 2.1) as independent predictors of long-term mortality. The main difference between the study by Hillis and colleagues and our study is that those authors included in their analysis the early hospital mortality whereas our analysis was based only on surviving patients who were discharged from the hospital. Age and renal failure were identified in univariate analysis. However, these factors did not appear as significant in multivariate analysis.

On-Pump Versus Off-Pump Coronary Artery Bypass Grafting
Previous studies have reported the potential benefit of off-pump CABG in elderly patients and patients with atherosclerotic disease of the ascending aorta, and additional comorbidities such as peripheral vascular disease and renal failure [27, 28]. On the basis of these findings, the off-pump CABG procedure was favored in our institution in patients presenting with these comorbidities. We have shown no difference in mortality and morbidity in on-pump versus off-pump CABG in patients with low EF. It is, however, important to emphasize that patients undergoing off-pump surgery in our study were older with significantly higher predicted mortality. Our findings suggest that off-pump CABG can be a valuable alternative in patients with low EF and associated comorbidities. Our results are in accordance with two previous clinical series focusing on the application of off-pump techniques in patients with low EF. These studies adjusted the preoperative risk profile using propensity scores and did not find any difference in outcome between off-pump and conventional myocardial revascularization [7, 15].

Limitations and Strengths
This is a retrospective observational study and conclusions are necessarily limited in their application. Clinical outcomes focused on postoperative morbidity and mortality with no information on late complications, quality of life, cause of death, postoperative EF, or cost-analysis. This is, however, one of the largest single-center analyses of outcomes in patients with EF of 0.30 or less undergoing CABG. The findings of this study are unique in terms of improved outcome in the recent era and identification of independent predictors of early and late outcome. The study also provides useful information with respect to the potential benefit of off-pump surgery in this high-risk group of patients.

Conclusion
Excellent results after CABG can be expected in patients with EF of 0.30 or less, with low operative mortality and acceptable postoperative morbidity. Long-term survival in patients with EF less than or equal to 0.30 remains, however, significantly reduced when compared with patients with EF greater than 0.30. We identify risk factors for poor long-term outcome in this patient group. Future resources should therefore be directed toward improving outcome in these subgroups of patient. Careful preoperative patient selection and perioperative management, including optimal strategies of myocardial preservation, remains essential in patients with EF of 0.30 or less undergoing cardiac surgery.


   References
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 References
 

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