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 Table of Contents  
ORIGINAL ARTICLE
Year : 2016  |  Volume : 1  |  Issue : 1  |  Page : 15-19

Long-term outcome of isolated coronary artery bypass surgery in blacks


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 Publication25-Jul-2016

Correspondence Address:
Jonathan Nwiloh
Department of Surgery, Atlanta Medical Center, Atlanta, GA
USA
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Source of Support: None, Conflict of Interest: None


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  Abstract 

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

How to cite this URL:
Nwiloh J, Onwuanyi A, Oduwole A. Long-term outcome of isolated coronary artery bypass surgery in blacks. Niger J Cardiovasc Thorac Surg [serial online] 2016 [cited 2020 Dec 1];1:15-9. Available from: http://www.nigjourcvtsurg.org/text.asp?2016/1/1/15/186849


  Introduction Top


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. [1],[2] Moreover, for patients undergoing CABG, the coronary artery surgery study registry showed a higher long-term mortality rate in blacks compared to whites, [3] and similarly short-term analysis equally shows blacks having higher operative mortality (OM) in large society of thoracic surgeons (STS) database reviews. [4],[5]


  Materials and Methods Top


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].
Table 1: Preoperative baseline characteristics

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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.
Table 2: Operative variables

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  Results Top


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].
Figure 1: Overall survival after CABG.

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Figure 2: Male versus female Kaplan-Meier survival after CABG.

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Table 3: Multivariate logistic regression of risk factors

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Table 4: Observed coronary artery bypass graft surgery mortality

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Table 5: Early postoperative outcome

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  Discussion Top


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. [6] 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. [4] 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. [5] specifically directly compared whites and blacks in the STS database undergoing isolated CABG from 1994 to 1997 (a period overlapping with Hartz et al.) [4] 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. [7] 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. [8] Review of smaller single institutional studies such as reported by Zacharias et al. [9] 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. [10] 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. [11] 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. [12] 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 [4],[5],[8] and gender [4] 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, [9],[10],[11],[12] except one study with a gender difference in OM in favor of men. [12] A major advantage of this smaller institutional reviews however is the ability to report long-term outcome showing worse 5 years survival in blacks [10] and in Medicaid patients. [9] 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. [4],[5],[6],[7],[8],[9],[10] 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, [4],[5],[8],[9] and the higher number of urgent cases 85.2% compared to 27.9% in the National STS database review by Bridges et al. [5] 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. [13] 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 [14] 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 [4],[5] 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 Top


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. [15]

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Gillum RF, Gillum BS, Francis CK. Coronary revascularization and cardiac catheterization in the United States: Trends in racial differences. J Am Coll Cardiol 1997;29:1557-62.  Back to cited text no. 1
    
2.
Maynard C, Ritchie JL. Racial differences in outcomes of veterans undergoing coronary artery bypass grafting. Am J Cardiol 2001;88:893-5, A8.  Back to cited text no. 2
    
3.
Taylor HA Jr., Mickel MC, Chaitman BR, Sopko G, Cutter GR, Rogers WJ. Long-term survival of African Americans in the coronary artery surgery study (CASS). J Am Coll Cardiol 1997;29:358-64.  Back to cited text no. 3
    
4.
Hartz RS, Rao AV, Plomondon ME, Grover FL, Shroyer AL. Effects of race, with or without gender, on operative mortality after coronary artery bypass grafting: A study using The Society of Thoracic Surgeons National Database. Ann Thorac Surg 2001;71:512-20.  Back to cited text no. 4
    
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Bridges CR, Edwards FH, Peterson ED, Coombs LP. The effect of race on coronary bypass operative mortality. J Am Coll Cardiol 2000;36:1870-6.  Back to cited text no. 5
    
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Head SJ, Davierwala PM, Serruys PW, Redwood SR, Colombo A, Mack MJ, et al. Coronary artery bypass grafting vs. percutaneous coronary intervention for patients with three-vessel disease: Final five-year follow-up of the SYNTAX trial. Eur Heart J 2014;35:2821-30.  Back to cited text no. 6
    
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Rumsfeld JS, Plomondon ME, Peterson ED, Shlipak MG, Maynard C, Grunwald GK, et al. The impact of ethnicity on outcomes following coronary artery bypass graft surgery in the Veterans Health Administration. J Am Coll Cardiol 2002;40:1786-93.  Back to cited text no. 7
    
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Konety SH, Vaughan Sarrazin MS, Rosenthal GE. Patient and hospital differences underlying racial variation in outcomes after coronary artery bypass graft surgery. Circulation 2005;111:1210-6.  Back to cited text no. 8
    
9.
Zacharias A, Schwann TA, Riordan CJ, Durham SJ, Shah A, Habib RH. Operative and late coronary artery bypass grafting outcomes in matched African-American versus Caucasian patients: Evidence of a late survival-medicaid association. J Am Coll Cardiol 2005;46:1526-35.  Back to cited text no. 9
    
10.
Gray RJ, Nessim S, Khan SS, Denton T, Matloff JM. Adverse 5-year outcome after coronary artery bypass surgery in blacks. Arch Intern Med 1996;156:769-73.  Back to cited text no. 10
    
11.
Higgins RS, Paone G, Borzak S, Jacobsen G, Peterson E, Silverman NA. Effect of payer status on outcomes of coronary artery bypass surgery in blacks. Circulation 1998;98(19 Suppl):II46-9.  Back to cited text no. 11
    
12.
Pollock B, Hamman BL, Sass DM, da Graca B, Grayburn PA, Filardo G. Effect of gender and race on operative mortality after isolated coronary artery bypass grafting. Am J Cardiol 2015;115:614-8.  Back to cited text no. 12
    
13.
Cooper WA, O′Brien SM, Thourani VH, Guyton RA, Bridges CR, Szczech LA, et al. Impact of renal dysfunction on outcomes of coronary artery bypass surgery: Results from the Society of Thoracic Surgeons National Adult Cardiac Database. Circulation 2006;113:1063-70.  Back to cited text no. 13
    
14.
Biancari F, Vasques F, Mikkola R, Martin M, Lahtinen J, Heikkinen J. Validation of EuroSCORE II in patients undergoing coronary artery bypass surgery. Ann Thorac Surg 2012;93:1930-5.  Back to cited text no. 14
    
15.
Jacobs JP, Shahian DM, He X, O′Brien SM, Badhwar V, Cleveland JC Jr., et al. Penetration, completeness, and representativeness of the society of thoracic surgeons adult cardiac surgery database. Ann Thorac Surg 2016;101:33-41.  Back to cited text no. 15
    


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