Atrial fibrillation (AF) commonly complicates the postoperative course after coronary artery bypass grafting (CABG). Among the general population, African Americans have been shown to have a lower prevalence of AF than European Americans. Although many factors have been identified to predict risk for postoperative AF, race has not been examined. All patients aged ≥18 years who underwent CABG at Henry Ford Hospital during a 5-year period from January 1, 2004, to December 31, 2008, were included. Patients were excluded for any previous diagnosis of AF or if they had concomitant valve surgery at the time of CABG. The incidence of AF was determined by International Classification of Diseases, Ninth Revision, coding from postoperative hospitalization records. Overall, 1,001 patients were eligible for analysis. Of these, 731 (73%) were European American and 270 (27%) were African American. The African American group had a higher prevalence of hypertension (75.6% vs 58.8%, p <0.001) and heart failure (22.6% vs 15.7%, p = 0.01) and a trend toward a higher prevalence of diabetes mellitus (38.1% vs 33.4%, p = 0.159). Postoperative AF was diagnosed in 214 European Americans (29.3%) and 50 African Americans (18.5%) (p = 0.001). In multivariate analysis adjusting for age strata, gender, hypertension, diabetes, and heart failure, African Americans had less postoperative AF than European Americans, with an adjusted odds ratio of 0.539 (95% confidence interval 0.374 to 0.777, p = 0.001). In conclusion, African Americans have a significantly reduced incidence of AF compared to European Americans after CABG.
To date, there have been no published studies searching for differences in the risk for postoperative atrial fibrillation (AF) between African Americans and European Americans. Mounting evidence consistently shows that African Americans have a significantly lower prevalence of AF compared to European Americans, a finding that is particularly remarkable considering that African Americans paradoxically have a higher rate of many commonly identified risk factors for AF, including hypertension, diabetes mellitus, and heart failure. Recent published data investigating this racial discrepancy in AF prevalence have shown this pattern in several clinical settings, including patients with heart failure and advanced age, as well as in subjects within the broader general population. We sought to determine whether the reduced risk for AF in African Americans compared to European Americans is similarly observed in patients during the postoperative hospitalization after coronary artery bypass grafting (CABG).
We performed a retrospective analysis to investigate the incidence of AF during the postoperative hospitalization of all patients who underwent CABG at Henry Ford Hospital from January 1, 2004, to December 31, 2008. Patients who underwent CABG were included if they were aged ≥18 years and self-reported their race as either European American or African American. Patients were excluded if they had any history of AF or if they had any previous cardiac surgery. Given the previously established increased risk for postoperative AF associated with valvular heart surgery, all patients who underwent valvular repair or replacement concomitant with their CABG were excluded. Demographic and diagnostic information was pulled from the Henry Ford Health System corporate database. Data management was performed with Microsoft Access (Microsoft Corporation, Redmond, Washington), and all statistical calculations were performed using SPSS (SPSS, Inc., Chicago, Illinois). Diagnoses of AF were extracted from the database by pulling the associated diagnosis code (code 427.31 from the International Classification of Diseases, Ninth Revision, Clinical Modification) from the postoperative hospitalization discharge summary in all patients. Co-morbid diagnoses (including hypertension, heart failure, and diabetes mellitus) were identified from the International Classification of Diseases, Ninth Revision, coding from all clinical encounters (inpatient, outpatient, and emergency room visits) for each patient during a 2-year lead-in period before their individual dates of surgery. Multivariate analysis was performed using the aforementioned demographic data (gender and age, stratified by decade of life: 18 to 40, 41 to 50, 51 to 60, 61 to 70, and ≥70 years) and co-morbid conditions to determine the adjusted odds ratio for the risk for AF during the postoperative hospitalization.
A total of 1,409 patients underwent CABG at Henry Ford Hospital during the study period. Of these, 215 were excluded because of concomitant valve surgery at the time of CABG, and another 138 were excluded because of a self-reported racial classification other than European American or African American. Of the remaining 1,056 patients, 55 were excluded because of histories of AF, leaving a total of 1,001 patients eligible for analysis.
The demographics of the patient population are listed in Table 1 . Among the study population, women constituted a higher proportion of the African American population than European American. Overall, African Americans had a higher burden of measured co-morbidities, including hypertension and heart failure, as well as a trend toward a higher prevalence of diabetes mellitus ( Figure 1 ).
|Variable||African American||European American||p Value|
|(n = 230)||(n = 731)|
|Men||147 (54.4%)||550 (75.2%)||<0.001|
|Mean age (years)|
|18–40||6 (2.2%)||13 (1.8%)|
|41–50||27 (10.0%)||49 (6.7%)|
|51–60||67 (24.8%)||177 (24.2%)|
|61–70||81 (30.0%)||233 (31.9%)|
|≥70||89 (33.0%)||259 (35.4%)|
|Hypertension||204 (75.6%)||430 (58.8%)||<0.001|
|Diabetes mellitus||103 (38.1%)||244 (33.4%)||0.159|
|Heart failure||61 (22.6%)||115 (15.7%)||0.011|
Postoperative AF was diagnosed in 264 of the 1,001 subjects (26.4%). The incidence of postoperative AF was markedly increased in European Americans compared to that in African Americans (214 in European Americans [29.3%] vs 50 in African Americans [18.5%], p = 0.001). This relation held for older and younger patient groups, with a significantly lower frequency of post-CABG AF in African Americans compared to European Americans in patients aged <60 years as well as those aged ≥60 years ( Figure 2 ).
In multivariate analysis, after adjusting for age strata, gender, hypertension, diabetes, and congestive heart failure, African Americans had less postoperative AF than European Americans, with an adjusted odds ratio of 0.539 (95% confidence interval 0.374 to 0.777, p = 0.001). In multivariate analysis, the only other factor that had a significant effect on AF incidence was increasing age stratum, with an adjusted odds ratio of 1.749 (95% confidence interval 1.48 to 2.07, p <0.001) for developing AF with each progressive advancement in 10-year age stratum ( Figure 3 ).