|Year : 2016 | Volume
| Issue : 1 | Page : 15-19
Long-term outcome of isolated coronary artery bypass surgery in blacks
Jonathan Nwiloh1, Anekwe Onwuanyi2, Adefisayo Oduwole2
1 Department of Surgery, Atlanta Medical Center, Atlanta, GA, USA
2 Department of Medicine, Section of Cardiology, Morehouse School of Medicine, Atlanta, GA, USA
|Date of Web Publication||25-Jul-2016|
Department of Surgery, Atlanta Medical Center, Atlanta, GA
Source of Support: None, Conflict of Interest: None
Objective: There are conflicting data on the influence of race and gender on the outcome of patients undergoing coronary artery bypass graft surgery (CABG), with blacks and females showing higher operative mortality (OM) in some series and not others. Materials and Methods: The medical records of 176 black patients undergoing isolated CABG by a single surgeon from 2000 to 2014 were retrospectively reviewed. The mean age was 61.9 ± 11.2 years and majority 93 (52.8%) were males. Identified risk profiles were peripheral vascular disease 53 (30.1%) patients, insulin-dependent diabetes mellitus 49 (27.8%), end-stage renal disease (ESRD) 27 (15.3%), chronic obstructive pulmonary disease 27 (15.3%), cerebrovascular disease 24 (13.6%), and HIV/AIDS 5 (2.8%). One hundred and forty (79.5%) had severe triple vessel disease, 30 (17.0%) left main disease, and ejection fraction mean 43.0 ± 14.3. Results: One hundred and twenty-eight patients (72.7%) underwent on-pump and 48 patients (27.3%) off-pump coronary artery bypass graft (OPCAB), with 150 (85.2%) urgent surgeries. EuroSCORE-II (ES-II) score was 3.86 ± 3.18 while observed OM was 6.81% (12/176). There was no difference in OM between males and females 6.45% versus 7.22% (P = 0.924) and on-pump and OPCAB 7.81% versus 4.16% (P = 0.604). Univariate analysis identified ESRD and ES as predictors but on multivariate analysis only ESRD with odds ratio 4.630 (95% CI: 1.321-16.229, P = 0.017). The society of thoracic surgeons (STS) quality measurement task force major complications were acute kidney injury 6.81%, prolonged ventilation 6.81%, stroke 3.40%, deep sternal wound infection 2.27%, and reoperation 1.70%. Overall 1 and 5 years survival was 90.0% and 73.9%, respectively, with no significant difference between males and females 92.4% and 75.0% versus 86.4% and 70.9%, respectively, when P = 0.764. Conclusion: The observed/expected 1.76 ratio may partly be due to higher number of urgent and ESRD patients of 85.2% and 15.3% compared to 27.9% and 2.36-7.90%, respectively, in the STS database. Our ESRD patients had 4 times odds of death than non-ESRD. Despite males having slightly higher risk profiles, long-term survival was similar with females and overall 1 and 5 years survival comparable to blacks in other series.
Keywords: Blacks, coronary artery bypass graft surgery, survival
|How to cite this article:|
Nwiloh J, Onwuanyi A, Oduwole A. Long-term outcome of isolated coronary artery bypass surgery in blacks. Niger J Cardiovasc Thorac Surg 2016;1:15-9
| Introduction|| |
Coronary artery bypass graft surgery (CABG) one of the most commonly performed major surgical procedure has been demonstrated to be effective in the treatment of ischemic heart disease since first introduced over 50 years ago. However, several studies in the past have observed large racial disparities in the application of CABG and percutaneous coronary intervention (PCI) with blacks less likely to be offered these technologically advanced services compared to whites having comparable disease severity. , Moreover, for patients undergoing CABG, the coronary artery surgery study registry showed a higher long-term mortality rate in blacks compared to whites,  and similarly short-term analysis equally shows blacks having higher operative mortality (OM) in large society of thoracic surgeons (STS) database reviews. ,
| Materials and Methods|| |
Between January 2000 and December 2014, 176 patients with ischemic heart disease underwent isolated CABG by a single surgeon. They comprised 93 (52.8%) males and 83 (47.2%) females, with mean age 61.9 ± 11.3 and range 31-90 years. One hundred and fifty (85.2%) had urgent, 22 (12.5%) elective, and 4 (2.3%) emergency surgeries. One hundred and forty (79.5%) had severe triple vessel disease, thirty (17.0%) left main (LM) with an overall mean ejection fraction 43.0 ± 14.3. Majority 98 (55.7%) patients were diabetics and 27 (15.3%) had end-stage renal disease (ESRD). Other baseline demographics are summarized in [Table 1].
All the surgeries were performed via a full median sternotomy, with on-pump CABG using standard cardiopulmonary bypass techniques, mild to moderate systemic hypothermia, and cold blood cardioplegia administered antegrade plus or minus retrograde during ischemic cross-clamping for distal graft anastomoses. Off-pump coronary artery bypass graft surgery (OPCAB) was performed using one of the standard stabilizing devices. Operative variables are summarized in [Table 2]. OM was regarded as death within 30 days of surgery or during the same hospitalization. Only patients who continued follow-up after their standard 3 months office visits and were subsequently seen in the hospital or could be reached by telephone were included. Follow-up was obtained in 88.4% of patients who survived the surgery. All data were entered into an Excel spreadsheet and then imported into Sigma Plot (Systat Software, Inc., San Jose, CA, USA) for statistical analysis. Categorical variables were reported as frequencies and percentages, while continuous variables were expressed as a mean ± standard deviations. Univariate analysis by unpaired Student's t-test with two-tailed distribution was used for continuous variables, and Chi-square exact test or Fisher's exact test was used for categorical variables. Multivariate analysis was performed by logistic regression analysis. Survival was estimated using the Kaplan-Meier method, and the log-rank test was used to determine the significance of survival distributions among groups. A probability value of <0.05 was considered statistically significant.
| Results|| |
One hundred and twenty-eight (72.7%) patients underwent on-pump CABG, consisting of 68 (53.1%) males and 60 (46.9%) females, while 48 (27.3%) patients underwent OPCAB consisting of 25 (52.1%) males and 23 (47.9%) females. Three (1.7%) patients were redo CABG and left internal mammary artery (LIMA) was used in 168 (95.4%) patients. Observed OM was 6.81% versus expected 3.86 with an observed/expected ratio of 1.76. The unadjusted OM for OPCAB was 4.16% (2/48) versus on-pump CABG 7.81% (10/128) P = 0.604 and 6.45% (6/93) in males versus 7.22% (6/83) in females P = 0.924. Univariate analysis identified ESRD and EuroSCORE (ES) as significant variables, but on multivariate model, only ESRD had a significant predictive value with odds ratio (OR) 4.630 (95% confidence interval [CI]: 1.321-16.229) P = 0.017 [Table 3]. Mortality analysis by low-risk ES <6.0, 5.0% versus 3.27%, P = 0.923 or high-risk ES, 6.0 or greater 18.10% versus 9.09%, P = 1.0, respectively, between men and women was similar [Table 4]. The causes of deaths were recurrent ventricular fibrillation three (1.70%) patients, sepsis three (1.70%), cerebrovascular accident two (1.13%), cardiogenic shock one (0.56%), ischemic bowel one (0.56%), respiratory arrest one (0.56%), and complete heart block one (0.56%). The most frequently observed STS quality measurement task force (QMTF) major morbidities were respiratory failure and acute kidney injury (AKI) in 6.81% of patients each, respectively. However, only 1 of 12 (8.33%) patients with AKI required temporary hemodialysis [Table 5]. The overall stroke rate was 3.40% (6/176) but was 3.90% (5/128) in on-pump versus 2.08% (1/48) in OPCAB group. Three (1.70%) patients all on-pump were returned to surgery for postoperative bleeding. Deep sternal wound infection (DSI) occurred in only four (2.27%) diabetics, all on-pump patients, three of whom were insulin dependent, and one also had ESRD. LIMA was used in all DSI patients except one undergoing redo CABG. Among the survivors, follow-up was possible in 88.4% (145/164) patients, with a mean follow-up duration of 49.9 ± 35.2 months. Kaplan-Meier estimated overall survival for 1 and 5 years was 90.0% and 73.9% [Figure 1]. Survivals was similar for males compared to females with 92.4% and 75.0% versus 86.4% and 70.9%, respectively P = 0.764 [Figure 2].
| Discussion|| |
PCI with drug-eluting stents is now the preferred and most commonly deployed method for revascularization; however, CABG is still considered the standard revascularization strategy for critical LM stenosis and severe triple vessel disease, especially in diabetics and decreased left ventricular systolic function. This was demonstrated by Syntax trial showing a 5 years CABG superiority over PCI with respect to major adverse cardiac and cerebrovascular events, of death, myocardial infarction and repeat revascularization.  Since PCI is now used for majority of less complex cases, there has been an increased acuity of illness with multiple comorbidities and higher risk profiles in patients now been referred for surgical revascularization over the last decade or so. This paradigm shift in the surgical referral of sicker patients perhaps maybe more so in blacks who are usually more socioeconomically disadvantaged compared to whites, more likely to be uninsured or underinsured and therefore less likely to seek timely medical care and often present to the emergency room for their primary and specialist health-care needs. These and other confounders might perhaps partially explain the higher surgical risk and lower long-term survival in blacks compared to whites observed in some series. For decades, there has been an unresolved debate on whether any racial or gender differences exists in patients undergoing CABG after adjusting and matching risk profiles. Hartz et al.  in a review of an earlier STS dataset from 1994 to 1996 of 441,542 patients found that race and gender were independent predictors of mortality after CABG, holding all other risk factors the same. Their review however was not just limited to whites and blacks but Caucasians and non-Caucasians, with the following patient distribution; Caucasians 88.1%, blacks 3.9%, Hispanics 2.2%, Asian/Pacific Islander 1.0%, American Indian/Alaskan 0.3%, and unknown and missing 4.6%. However, Bridges et al.  specifically directly compared whites and blacks in the STS database undergoing isolated CABG from 1994 to 1997 (a period overlapping with Hartz et al.)  and identified 555, 939 whites and 25.850 blacks with an OM of 3.14% versus 3.83%, respectively. Unadjusted OR 1.23 (CI: 1.15-1.31). The unadjusted OM for black men was 3.30% versus 2.64% for white men, P = 0.05, while for women, it was 4.49% versus 4.41%, respectively. They concluded from this data that black race is an independent predictor of OM after CABG except for very high-risk patients. In a more limited study covering 43 Veterans Health Administration (VHA) hospitals, Rumsfeld et al.  identified 29,333 Caucasians, 2570 blacks, and 1525 Hispanics who underwent CABG between 1995 and 2000. Adjusted 30 days mortality was 3.6% versus 3.9% P = 0.48 and 6 months mortality 5.8% versus 6.3% P = 0.27 for whites and blacks, respectively. However, similar observations for whites and Hispanics were 3.6% versus 2.8% P = 0.09 and 5.8% versus 4.5% P = 0.04 for 30 days and 6 months, respectively. They concluded that ethnicity did not appear to be a strong risk factor for adverse outcome in the VHA. In contrast, however, another large review outside of the STS database from Centers for Medicare and Medicaid Services (CMS) registry of Medicare patients undergoing CABG from 1997 to 2000 came to a different conclusion. Among the 566,785 whites and 24,354 blacks studied, blacks had a higher unadjusted post-OM at 30 (6.4% vs. 5.2%), 90 (8.3% vs. 6.6%), and 365 days (13.5% vs. 9.8%) P = 0.001. After adjustments for patient characteristics, mortality was 8%, 11%, and 25% higher in blacks at 30, 90, and 365 days.  Review of smaller single institutional studies such as reported by Zacharias et al.  of 6073 Caucasians and 304 blacks undergoing isolated CABG from 1991 to 2003 found similar OM 2.5% versus 3.0%, P = 0.81, respectively. Unadjusted Kaplan-Meier survival at 1, 5, and 10 years (93.4%, 80.3%, and 66.1% vs. 94.8%, 86.5%, and 71.7%) was worse in blacks but similar for matched groups. They concluded that after risk adjustment race did not predict OM and that African-American race was not per se associated with a worse operative or long-term outcome. Their review however interestingly identified that Medicaid (an insurance coverage for the poor and indigents) a reflection of socioeconomic status which was more prevalent in the black cohort, 29.0% versus 6.3% in whites was associated with worse late survival, especially in younger non-Medicare patients. Hazard ratio = 1.96, P = 0.003, nearly doubling mortality. In another single institutional report, Gray et al.  in reviewing 3113 whites and 115 blacks all insured found similar 30 days mortality 4.1% versus 5.2%, respectively, P = 0.48. 2.0% from each cohort had Medicaid. Blacks had worse long-term outcome at 1 and 5 years 84.0% versus 92.0% and 64.0% versus 82.0%, respectively, P = 0.001. In contrast, another review by Higgins et al.  on the effect of payer status on the outcome of CABG of 2282 whites and 494 blacks from 1990 to 1996 observed 30 days mortality of 2.5% versus 5.5%, respectively, P = 0.001. 52.9% of blacks were on Medicaid, and there was no long-term outcome reported. A current era review by Pollock et al.  of 8154 patients, 78.0% whites, 7.5% blacks, 7.3% Hispanics, and 7.2% other/unknown undergoing CABG from 2004 to 2011 found unadjusted 30 days mortality 2.09% in men and 4.75% in women, about twice as high with an OR 1.96 (CI: 1.44-2.66, P = 0.001), but noted no racial differences. A critical analysis of all the above studies on the influence of gender and race shows a pattern, with the larger database studies analyzing 450,000-570,000 patients and having large number of blacks 17,000-25,000 had the statistical power to definitely show the small but significant racial ,, and gender  differences in OM. These large database studies are however limited by their inability to show outcome after the immediate postsurgical period. In contrast, the smaller single institutional studies with sample sizes 2000-8000 and small number of blacks 115-600 did not appear to have the statistical power to detect the small but significant racial difference, ,,, except one study with a gender difference in OM in favor of men.  A major advantage of this smaller institutional reviews however is the ability to report long-term outcome showing worse 5 years survival in blacks  and in Medicaid patients.  Although our review had no other racial group for comparison, we observed a higher OM of 6.81% compared with other reported reviews showing mortality of 3.90-6.40% in blacks. ,,,,,, This could possibly be due to a number of factors including the higher percentage of ESRD patients of 15.3% in our series compared to 2.36-7.90% range observed in blacks from other series, ,,, and the higher number of urgent cases 85.2% compared to 27.9% in the National STS database review by Bridges et al.  ESRD was the only strong predictor of mortality in our series as in some other reviews. Although on multivariate analysis ESRD had a highly significant P value of 0.017, the wide range of the 95% CI should however cause some caution in interpreting the OR of 4.630. However, Cooper et al.  in an STS database review of 483,914 patients from 2000 to 2003 on the impact of renal failure on outcome of CABG also found a higher OM rate of 9.3% for severe chronic renal disease with glomerular filtration rate <30 ml/min and 9.0% in ESRD patients compared to 1.3-1.8% in patients with normal or mild renal dysfunction. We had previously used the old logistic ES during most of the study period and obtained a higher predicted mortality than our observed mortality. Since the logistic ES is now believed to overestimate operative risk prompting a recent modification to the new ES-II  supposedly a better predictor of OM after isolated CABG, we elected to recalculated risk profiles using the new ES-II for this report. This was preferred to the STS predicted risk of mortality score due to its overall simplicity of use. It is unclear from the original logistic ES model if there were any blacks and what their percentage was in the 14,799 patients cohort used to develop the risk model and if the black race was considered as an increased risk as demonstrated in all the large studies containing over 400,000 white patients and blacks , with the statistical power to show this significant difference. The STS-QMTF performance measure of hospital metrics in addition to the risk-adjusted mortality comprising the five major complications in our series were stroke 3.40%, reoperation 1.70%, DSI 2.27%, prolonged ventilation 6.81%, and AKI 6.81%. The stroke rate was however lower in OPCAB patients 2.08% compared to almost double for on-pump 3.90%. DSI occurred only diabetics and along with reexploration for bleeding were observed only in the on-pump group. Although AKI occurred in 6.81%, only one patient (0.56%) eventually needed temporary hemodialysis. Finally, although many of our patients were either uninsured or had Medicaid, the observed 1 and 5 years survival of 90.0% and 73.7% are comparable to other reported rates for blacks.
| Conclusion|| |
Our study limitations include been retrospective, small sample size, and single surgeon's experience. It however suggests that blacks may have a higher operative risk than predictable by current risk models that might not have taken this into consideration in developing these models and may need further studies in the future to help answer this question and adjust the models if necessary. The worse long-term outcome in blacks may partially be accounted for by higher rates of uninsured or underinsured among blacks resulting in lower utilization rates of secondary risk reduction strategies post-CABG. The recent successful linkage of the STS adult cardiac surgery database to the CMS database will provide more robust and accurate long-term follow-up outcomes and help identify any gender or racial differences that has only been previously provided by smaller sample institutional studies. 
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]