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© 2013 Wiley Periodicals, Inc.
ORIGINAL ARTICLE _____________________________________________________________
The Impact of Postoperative Atrial Fibrillation and Race on Long-Term Survival after Coronary Artery Bypass Grafting Wesley T. O’Neal, M.D.,* Jimmy T. Efird, Ph.D., M.Sc.,y,z Stephen W. Davies, M.D.,§ Jason B. O’Neal, M.D.,{ Curtis A. Anderson, M.D.,y T. Bruce Ferguson, M.D.,y W. Randolph Chitwood, M.D.,y and Alan P. Kypson, M.D.y *Department of Internal Medicine, Wake Forest University School of Medicine, Winston-Salem, North Carolina; yDepartment of Cardiovascular Sciences, East Carolina Heart Institute, Brody School of Medicine, East Carolina University, Greenville, North Carolina; zCenter for Health Disparities, Brody School of Medicine, East Carolina University, Greenville, North Carolina; §Department of General Surgery, University of Virginia School of Medicine, Charlottesville, Virginia; and {Department of Anesthesia, Critical Care, and Pain Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts ABSTRACT Background and Aim: Postoperative atrial fibrillation (POAF) is a known predictor of in-hospital morbidity and short-term survival after coronary artery bypass grafting (CABG). The impact of race and longterm survival has not been examined in this population. We aimed to examine the influence of these factors on long-term survival in patients undergoing CABG. Methods: Patients undergoing first-time, isolated CABG between 1992 and 2011 were included in this study. Long-term survival was compared in patients with and without POAF and stratified by race. Hazard ratios (HR) and 95% confidence intervals (CI) were computed using a Cox regression model. Results: A total of 2,907 (22%) patients developed POAF (black n = 370; white n = 2,537) following CABG (N = 13,165). Median follow-up for study participants was 8.2 years. Long-term survival after CABG differed by POAF status and race (no POAF: HR = 1.0; white POAF: adjusted HR = 1.1, 95% CI = 1.06–1.2; black POAF: adjusted HR = 1.4, 95% CI = 1.2–1.6; pTrend = 0.0002). Black POAF patients also died sooner after surgery than their white counterparts (adjusted HR = 1.2, 95% CI = 1.02–1.4). Conclusion: Black race was a statistically significant predictor of decreased survival among POAF patients after CABG. This finding provides useful outcome information for surgeons and their patients. doi: 10.1111/jocs.12178
(J Card Surg 2013;28:484–491)
Postoperative atrial fibrillation (POAF) has been reported in 16–33% of patients after isolated coronary artery bypass grafting (CABG) and is associated with increased postoperative complications, longer hospital stays, and increased costs.1–5 POAF has been shown to be an independent predictor of decreased long-term
Conflict of interest: The authors acknowledge no conflict of interest in the submission. Address for correspondence: Wesley T. O’Neal, M.D., Wake Forest University School of Medicine, Department of Internal Medicine, Medical Center Boulevard, Winston-Salem, NC 27517. Fax: þ1-336716-2273; e-mail: [email protected]
survival after CABG in studies with relatively homogenous populations.4–9 To the best of our knowledge, the impact of race has not been examined among POAF patients after CABG. Survival paradoxes are well-documented in the literature.10 For example, conventional cardiovascular risk factors such as black race, hypercholesterolemia, hypertension, and obesity are associated with increased survival among some patient populations.11,12 In a recent study of CABG patients with chronic obstructive pulmonary disease, long-term survival was observed to be similar for black and white race.13 The rationale for the current study was to determine if a similar survival paradox was present
J CARD SURG 2013;28:484–491
among black POAF patients undergoing isolated CABG in our rural, racially dichotomous population. Consistent with the expected force of mortality among blacks, we hypothesized that white POAF patients would have better long-term survival than black POAF patients.14 MATERIALS AND METHODS Details of the study database and methodology have been previously described and are summarized below.13,15,16
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Management of POAF The management of POAF at our institution involves restoring sinus rhythm in patients within 24 hours with the use of antiarrhythmic drugs or by electrical cardioversion. Telemetry is used to continuously monitor patients after surgery. Patients discharged in AF are anticoagulated with warfarin and referred for cardioversion in 4 to 6 weeks. Patients discharged home on antiarrhythmic agents are followed by cardiology. Additionally, the decision to stop warfarin and other post-discharge medication changes is determined by the patient’s cardiologist.
Study design This was a retrospective cohort study of patients undergoing first-time, isolated CABG at the East Carolina Heart Institute between 1992 and 2011. Demographic data, comorbid conditions, coronary artery disease (CAD) severity, and surgical data were collected at the time of surgery. Patients with and without POAF were compared. Only black and white patients were included to minimize the potential for residual confounding (1% other races). Racial identity was self-reported. Emergent cases were considered a clinically different population with a different etiology following surgery and were not included in our analysis (n ¼ 417). The study and a waiver of participant consent was approved by the Institutional Review Board at the Brody School of Medicine, East Carolina University. Operative procedure In most cases, the left internal mammary artery was used for left anterior descending revascularization. Cardiopulmonary bypass or off-pump coronary artery bypass was selected depending upon patient presentation and surgeon preference. Cold-blood cardioplegia was used to achieve cardiac arrest. Distal anastomoses were performed first followed by proximal anastomoses. If off-pump coronary artery bypass was performed, left internal mammary artery to left anterior descending artery anastomosis was performed first, followed by the remaining distal anastomoses. Proximal anastomoses of the saphenous vein conduits were sewn directly to the ascending aorta.
Data collection and follow-up The East Carolina Heart Institute is a populationbased tertiary referral center and is the largest standalone hospital devoted to cardiovascular care in the state of North Carolina. Nearly all patients treated at the East Carolina Heart Institute live and remain within a 150-mile radius of the medical center, facilitating reliable data capture. The primary sources of data extraction were the STS Adult Cardiac Surgery Database and the electronic medical record at the Brody School of Medicine. Cardiovascular surgery information at our facility has been reported to the STS since 1989. Data quality and cross-field validation are routinely performed by the Epidemiology and Outcomes Research Unit at the East Carolina Heart Institute. An electronic medical record was first introduced at the Brody School of Medicine in 1997. Records from 1989 to 1997 were retrospectively scanned into the electronic medical record. Local and regional clinics were consolidated under a single electronic medical record in 2005 which allowed for efficient patient follow-up. The electronic medical record system applies multiple logic comparisons to reliably reduce mismatching of patient data across clinics and follow-up visits. The STS database is linked to the electronic medical record through a unique patient medical record number. The National Death Index was used to obtain death dates for patients lost to follow-up and also used to validate death information captured in our electronic medical record.17 Linkage with the National Death Index was based on a multiple criteria, deterministic matching algorithm.18
Definitions
Statistical analysis
Atrial fibrillation (AF) was characterized by a chaotic/ irregular atrial rhythm and accompanied by a variable rate and irregular ventricular rhythm. POAF was defined as having a first-time episode of AF lasting longer than 1 hour after surgery requiring treatment according to established Society of Thoracic Surgeons (STS) criteria. Patients were excluded if a history of preoperative paroxysmal, persistent, or permanent AF/atrial flutter was documented. Mortality was defined as any cause of death postoperatively regardless of time from surgery. CAD was defined as at least 50% stenosis and confirmed by angiography before surgery.
Categorical variables were reported as frequency and percentage while continuous variables were reported as mean standard deviation. Follow-up time was measured from the date of surgery to the date of death or censoring. Survival probabilities were computed using the Kaplan–Meier product-limit method and stratified by POAF and race. The log-rank test was used to compare survival between patients with and without POAF and among POAF patients by race. Cox proportional hazard regression models were used to compute hazard ratios (HR) and 95% confidence intervals (CI) for long-term mortality. The initial
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multivariable models included variables that have been previously reported to be associated with cardiovascular-related mortality, regardless of their statistical significance in our dataset.15 These included age (continuous), sex, race, hypertension, CAD severity, heart failure, and prior stroke. The post-hoc addition of other variables into the model was performed in a pairwise fashion. The test statistic of Grambsch and Therneau19 was used to check the proportional hazards assumption. Statistical significance for categorical variables was tested using the chi-square (x2) method and the Kruskal–Wallis procedure for continuous variables. PTrend was computed using a likelihood ratio test. In the case of race, order of categories for the trend test was based on the a priori assumption of a greater force of mortality among black patients. Few values were missing in our analysis (
© 2013 Wiley Periodicals, Inc.
ORIGINAL ARTICLE _____________________________________________________________
The Impact of Postoperative Atrial Fibrillation and Race on Long-Term Survival after Coronary Artery Bypass Grafting Wesley T. O’Neal, M.D.,* Jimmy T. Efird, Ph.D., M.Sc.,y,z Stephen W. Davies, M.D.,§ Jason B. O’Neal, M.D.,{ Curtis A. Anderson, M.D.,y T. Bruce Ferguson, M.D.,y W. Randolph Chitwood, M.D.,y and Alan P. Kypson, M.D.y *Department of Internal Medicine, Wake Forest University School of Medicine, Winston-Salem, North Carolina; yDepartment of Cardiovascular Sciences, East Carolina Heart Institute, Brody School of Medicine, East Carolina University, Greenville, North Carolina; zCenter for Health Disparities, Brody School of Medicine, East Carolina University, Greenville, North Carolina; §Department of General Surgery, University of Virginia School of Medicine, Charlottesville, Virginia; and {Department of Anesthesia, Critical Care, and Pain Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts ABSTRACT Background and Aim: Postoperative atrial fibrillation (POAF) is a known predictor of in-hospital morbidity and short-term survival after coronary artery bypass grafting (CABG). The impact of race and longterm survival has not been examined in this population. We aimed to examine the influence of these factors on long-term survival in patients undergoing CABG. Methods: Patients undergoing first-time, isolated CABG between 1992 and 2011 were included in this study. Long-term survival was compared in patients with and without POAF and stratified by race. Hazard ratios (HR) and 95% confidence intervals (CI) were computed using a Cox regression model. Results: A total of 2,907 (22%) patients developed POAF (black n = 370; white n = 2,537) following CABG (N = 13,165). Median follow-up for study participants was 8.2 years. Long-term survival after CABG differed by POAF status and race (no POAF: HR = 1.0; white POAF: adjusted HR = 1.1, 95% CI = 1.06–1.2; black POAF: adjusted HR = 1.4, 95% CI = 1.2–1.6; pTrend = 0.0002). Black POAF patients also died sooner after surgery than their white counterparts (adjusted HR = 1.2, 95% CI = 1.02–1.4). Conclusion: Black race was a statistically significant predictor of decreased survival among POAF patients after CABG. This finding provides useful outcome information for surgeons and their patients. doi: 10.1111/jocs.12178
(J Card Surg 2013;28:484–491)
Postoperative atrial fibrillation (POAF) has been reported in 16–33% of patients after isolated coronary artery bypass grafting (CABG) and is associated with increased postoperative complications, longer hospital stays, and increased costs.1–5 POAF has been shown to be an independent predictor of decreased long-term
Conflict of interest: The authors acknowledge no conflict of interest in the submission. Address for correspondence: Wesley T. O’Neal, M.D., Wake Forest University School of Medicine, Department of Internal Medicine, Medical Center Boulevard, Winston-Salem, NC 27517. Fax: þ1-336716-2273; e-mail: [email protected]
survival after CABG in studies with relatively homogenous populations.4–9 To the best of our knowledge, the impact of race has not been examined among POAF patients after CABG. Survival paradoxes are well-documented in the literature.10 For example, conventional cardiovascular risk factors such as black race, hypercholesterolemia, hypertension, and obesity are associated with increased survival among some patient populations.11,12 In a recent study of CABG patients with chronic obstructive pulmonary disease, long-term survival was observed to be similar for black and white race.13 The rationale for the current study was to determine if a similar survival paradox was present
J CARD SURG 2013;28:484–491
among black POAF patients undergoing isolated CABG in our rural, racially dichotomous population. Consistent with the expected force of mortality among blacks, we hypothesized that white POAF patients would have better long-term survival than black POAF patients.14 MATERIALS AND METHODS Details of the study database and methodology have been previously described and are summarized below.13,15,16
O’NEAL, ET AL. ATRIAL FIBRILLATION AND SURVIVAL
485
Management of POAF The management of POAF at our institution involves restoring sinus rhythm in patients within 24 hours with the use of antiarrhythmic drugs or by electrical cardioversion. Telemetry is used to continuously monitor patients after surgery. Patients discharged in AF are anticoagulated with warfarin and referred for cardioversion in 4 to 6 weeks. Patients discharged home on antiarrhythmic agents are followed by cardiology. Additionally, the decision to stop warfarin and other post-discharge medication changes is determined by the patient’s cardiologist.
Study design This was a retrospective cohort study of patients undergoing first-time, isolated CABG at the East Carolina Heart Institute between 1992 and 2011. Demographic data, comorbid conditions, coronary artery disease (CAD) severity, and surgical data were collected at the time of surgery. Patients with and without POAF were compared. Only black and white patients were included to minimize the potential for residual confounding (1% other races). Racial identity was self-reported. Emergent cases were considered a clinically different population with a different etiology following surgery and were not included in our analysis (n ¼ 417). The study and a waiver of participant consent was approved by the Institutional Review Board at the Brody School of Medicine, East Carolina University. Operative procedure In most cases, the left internal mammary artery was used for left anterior descending revascularization. Cardiopulmonary bypass or off-pump coronary artery bypass was selected depending upon patient presentation and surgeon preference. Cold-blood cardioplegia was used to achieve cardiac arrest. Distal anastomoses were performed first followed by proximal anastomoses. If off-pump coronary artery bypass was performed, left internal mammary artery to left anterior descending artery anastomosis was performed first, followed by the remaining distal anastomoses. Proximal anastomoses of the saphenous vein conduits were sewn directly to the ascending aorta.
Data collection and follow-up The East Carolina Heart Institute is a populationbased tertiary referral center and is the largest standalone hospital devoted to cardiovascular care in the state of North Carolina. Nearly all patients treated at the East Carolina Heart Institute live and remain within a 150-mile radius of the medical center, facilitating reliable data capture. The primary sources of data extraction were the STS Adult Cardiac Surgery Database and the electronic medical record at the Brody School of Medicine. Cardiovascular surgery information at our facility has been reported to the STS since 1989. Data quality and cross-field validation are routinely performed by the Epidemiology and Outcomes Research Unit at the East Carolina Heart Institute. An electronic medical record was first introduced at the Brody School of Medicine in 1997. Records from 1989 to 1997 were retrospectively scanned into the electronic medical record. Local and regional clinics were consolidated under a single electronic medical record in 2005 which allowed for efficient patient follow-up. The electronic medical record system applies multiple logic comparisons to reliably reduce mismatching of patient data across clinics and follow-up visits. The STS database is linked to the electronic medical record through a unique patient medical record number. The National Death Index was used to obtain death dates for patients lost to follow-up and also used to validate death information captured in our electronic medical record.17 Linkage with the National Death Index was based on a multiple criteria, deterministic matching algorithm.18
Definitions
Statistical analysis
Atrial fibrillation (AF) was characterized by a chaotic/ irregular atrial rhythm and accompanied by a variable rate and irregular ventricular rhythm. POAF was defined as having a first-time episode of AF lasting longer than 1 hour after surgery requiring treatment according to established Society of Thoracic Surgeons (STS) criteria. Patients were excluded if a history of preoperative paroxysmal, persistent, or permanent AF/atrial flutter was documented. Mortality was defined as any cause of death postoperatively regardless of time from surgery. CAD was defined as at least 50% stenosis and confirmed by angiography before surgery.
Categorical variables were reported as frequency and percentage while continuous variables were reported as mean standard deviation. Follow-up time was measured from the date of surgery to the date of death or censoring. Survival probabilities were computed using the Kaplan–Meier product-limit method and stratified by POAF and race. The log-rank test was used to compare survival between patients with and without POAF and among POAF patients by race. Cox proportional hazard regression models were used to compute hazard ratios (HR) and 95% confidence intervals (CI) for long-term mortality. The initial
486
O’NEAL, ET AL. ATRIAL FIBRILLATION AND SURVIVAL
multivariable models included variables that have been previously reported to be associated with cardiovascular-related mortality, regardless of their statistical significance in our dataset.15 These included age (continuous), sex, race, hypertension, CAD severity, heart failure, and prior stroke. The post-hoc addition of other variables into the model was performed in a pairwise fashion. The test statistic of Grambsch and Therneau19 was used to check the proportional hazards assumption. Statistical significance for categorical variables was tested using the chi-square (x2) method and the Kruskal–Wallis procedure for continuous variables. PTrend was computed using a likelihood ratio test. In the case of race, order of categories for the trend test was based on the a priori assumption of a greater force of mortality among black patients. Few values were missing in our analysis (
