The autonomic nervous system may play an important

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1 Preoperative Heart Rate Variability Predicts Atrial Fibrillation After Coronary Bypass Grafting Takeshi Kinoshita, MD, Tohru Asai, MD, PhD, Takako Ishigaki, Tomoaki Suzuki, MD, PhD, Atsushi Kambara, MD, PhD, and Keiji Matsubayashi, MD, PhD Division of Cardiovascular Surgery and Clinical Laboratory, Shiga University of Medical Science, Otsu, Japan Background. The purpose of the present study was to investigate the association between preoperative heart rate variability and atrial fibrillation after off-pump coronary artery bypass graft surgery. Methods. Of 524 consecutive patients undergoing isolated coronary artery bypass surgery, 390 were retrospectively analyzed after excluding the following 134 cases: on-pump surgery (n 6), emergency (n 106), chronic atrial fibrillation (n 17), and pacemaker rhythm (n 5). The following time-domain factors of heart rate variability were calculated: standard deviation of all normal-tonormal QRS (SDNN) and square root of mean of sum of squares of differences between adjacent normal-to-normal QRS (RMSSD). Results. Atrial fibrillation occurred in 98 patients (25%) after surgery. Patients not having atrial fibrillation had significantly lower heart rate variability than did patients having atrial fibrillation, with median values of 91 versus 121 for SDNN and 19 versus 25 for RMSSD. Reduced heart rate variability was significantly associated with a lower risk of postoperative atrial fibrillation: the adjusted hazard ratio (95% confidence interval) was 0.29 (0.17 to 0.49) for SDNN 99 ms or less and 0.47 (0.30 to 0.74) for RMSSD 20 ms or less. The area under the receiver operating characteristic curves for SDNN and RMSSD as a predictor of postoperative atrial fibrillation was and 0.696, respectively. Conclusions. Reduced time-domain factors in preoperative 24-hour heart rate variability are independently associated with a lower risk of atrial fibrillation after off-pump coronary artery bypass surgery. (Ann Thorac Surg 2011;91: ) 2011 by The Society of Thoracic Surgeons The autonomic nervous system may play an important role as a trigger and risk marker for developing atrial fibrillation (AF) after coronary artery bypass graft surgery. Analysis of heart-rate variability (HRV) has been widely used to assess cardiovascular autonomic activity. The relationship between preoperative HRV and AF after coronary artery bypass surgery has been investigated with divergent results [1-4]. The purpose of the present study was to investigate the association between preoperatively measured HRV and the occurrence of AF after off-pump coronary artery bypass graft surgery. Patients and Methods Between January 2003 and December 2008, 524 consecutive patients underwent isolated coronary artery bypass surgery by a single surgeon at our institution. Except for 1 reoperative case and 5 salvage cases, all patients underwent myocardial revascularization using the offpump technique without conversion to cardiopulmonary bypass during the operation. A total of 390 patients was retrospectively analyzed, after excluding 6 patients who were revascularized using cardiopulmonary bypass, 106 Accepted for publication Dec 23, Address correspondence to Dr Kinoshita, Division of Cardiovascular Surgery, Shiga University of Medical Science, Tsukinowa-cho, Seta, Otsu, Shiga , Japan; kinotake@belle.shiga-med.ac.jp. patients who underwent emergent surgery, 17 patients who had chronic atrial fibrillation or flutter, and 5 patients who had pacemaker rhythm. All patients had previously granted permission for use of their medical records for research purposes. The study was approved by the Institutional Review Board. The endpoint was new-onset AF after operation, which was diagnosed when there was an irregular cardiac rhythm without P waves lasting more than 60 minutes. After operation, all patients underwent continuous electrocardiographic monitoring using a bedside monitor in the intensive care unit and telemetry on the hospital ward until postoperative day 7. When episodes of arrhythmia were captured by an automatic alarm function, 12-lead electrocardiography was performed and assessed by the physicians. All patients enrolled in the study were admitted to our hospital at least 5 days before surgery and underwent 24-hour ambulatory electrocardiography before surgery using a Marquette SEER-MC (GE Medical Systems, Milwaukee, WI). Analysis of the electrocardiogram was performed using a Marquette MARS 8000 (GE Medical Systems). When a recording was of too poor quality for evaluation, it was repeated. The following two timedomain measurements of HRV were calculated as recommended by the Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology [5]: standard deviation of all nor by The Society of Thoracic Surgeons /$36.00 Published by Elsevier Inc doi: /j.athoracsur

2 Ann Thorac Surg KINOSHITA ET AL 2011;91: HEART RATE VARIABILITY AND AF AFTER CABG 1177 Fig 1. Distribution of (A) standard deviation of all normal-to-normal QRS complexes (SDNN), and (B) square root of mean of sum of squares of differences between adjacent normal-to-normal QRS complexes (RMSSD). mal-to-normal QRS complexes (SDNN) and square root of mean of sum of squares of differences between adjacent normal-to-normal QRS complexes (RMSSD). The standard deviation of averages of normal-to-normal QRS complexes in all 5-minute segments of entire recording (SDANN) was not included in the present study because SDANN strongly correlated to SDNN (correlation coefficient 0.97, p 0.01). Anesthetic and Surgical Technique The induction of anesthesia was achieved with intravenous administration of fentanyl citrate, midazolam, and vecuronium bromide. Anesthesia was maintained with intravenous administration of fentanyl and propofol and inhalation administration of low concentrations of sevoflurane as necessary. Anticoagulation was achieved with heparin after the conduits were harvested. The activated clotting time was maintained at more than 250 s. The off-pump technique was used for all patients. The details of the surgical technique were described previously [6]. Perioperative Management In principle, we did not alter the medication prescribed by the cardiologist who referred the patient. No patients took amiodarone preoperatively. Most of patients were extubated on the day of surgery, and oral medication was initiated on postoperative day 1. Blood potassium levels were measured in arterial blood gas samples every 2 to 4 hours in the intensive care unit and adjusted to obtain a target blood potassium level of 4.0 to 5.0 meq/l using intravenous administration of potassium chloride. Once patients were transferred to the floor, blood potassium levels were checked every morning and adjusted with oral potassium chloride. Statistical Analysis Normal distribution was checked using a Kolmogorov- Smirnov test. Correlations between two continuous variables were checked using Spearman rank correlation. Comparisons in clinical characteristics between two groups were performed using Pearson s 2 test for categorical variables, unpaired t test for normally distributed variables, and Mann-Whitney s U test for skewed variables. Unadjusted and adjusted hazard ratios (HR) and 95% confidence intervals (CI) for the association between each HRV measurement and postoperative AF were estimated using the Cox proportional hazard models. Variables statistically significant in univariate comparisons were entered into the multivariate Cox model. The estimated AF-free survival rates were calculated separately for each HRV measurement using the Kaplan- Meier method and compared using the log rank test. For Kaplan-Meier estimates and Cox models, each HRV measurement was dichotomized at the median value, and hazard ratio was computed for the upper versus lower 50th percentiles of the measurement. To evaluate the impact of each HRV measurement in explaining postoperative AF, receiver operating characteristic curves were constructed and the areas under the curves determined. The area under the curve of the two curves was compared using the method described by Hanley [7]. All statistical testing was two-sided. Results were considered statistically significant at a level of p less than Fig 2. Distribution of atrial fibrillation onset (n 98).

3 1178 KINOSHITA ET AL Ann Thorac Surg HEART RATE VARIABILITY AND AF AFTER CABG 2011;91: All analyses were performed with the SPSS statistical package, version 11.0 (SPSS, Chicago, IL). Results Figure 1 presents the distribution of SDNN and RMSSD. The SDNN had normal distribution, but distribution of the RMSSD was skewed. Spearman rank correlation tests identified positive correlation between SDNN and RMSSD (correlation coefficient 0.57, p 0.01). Atrial fibrillation occurred in 98 patients (25.1%, 98 of 390) after surgery, most often on postoperative day 2 (29%), with 76% occurrence on postoperative days 1, 2, 3, or 4 (Fig 2). Baseline characteristics according to each HRV measurement dichotomized at median are shown in Table 1. The two groups had closely similar characteristics. Patients with measurements at median or lower had lower hematocrit and estimated glomerular filtration rate and were more likely to have diabetes mellitus with poorly controlled glycemia. They also had worse left ventricular function, larger left atrium, and a greater number of ventricular premature beats. Conversely, supraventricular premature beats and nonsustained supraventricular tachycardia occurred more frequently in patients with measurements greater than the median. Diabetic patients (n 212) had significantly shorter SDNN and RMSSD than nondiabetic patients (n 178); the median values (interquartile range) were as follows: SDNN 89 (72 to 115) versus 114 (901 to 27; p 0.01); RMSSD 18 (13 to 27) versus 22 (18 to 29; p 0.01). The results of univariate comparisons between patients with and without postoperative AF are summarized in Table 2. Univariate predictors of postoperative AF were age, male sex, hematocrit, estimated glomerular filtration rate, diabetes mellitus, hemoglobin A1c 7.0% or greater, nonsustained supraventricular tachycardia of 1 or more in 24 hours, preoperative use of statin, and operative duration. Patients having AF had significantly longer SDNN and RMSSD than did patients not having AF: the median values (interquartile range) were as follows: SDNN 121 (106 to 145) versus 91 (74 to 115; p 0.01); RMSSD 25 (20 to 35) versus 19 (14 to 25; p 0.01). Kaplan-Meier estimates of AF-free survival were significantly lower for patients with measurements greater than median than for patients with measurements at median or less (Fig 3). Unadjusted and adjusted HRs (95% CIs) for the association between each measurement and postoperative AF are summarized in Table 3. The Table 1. Baseline Characteristics According to Variables Dichotomized at Median SDNN RMSSD 99 ms 99 ms 20 ms 20 ms n 195 n 195 p Value n 186 n 204 p Value Age, years Male sex 164 (84) 158 (81) (83) 167 (82) 0.68 Body mass index, kg/m Hematocrit, % Estimated GFR, ml min m Diabetes mellitus 130 (67) 80 (41) (69) 82 (40) 0.01 Hemoglobin A1c, % Smoking 105 (54) 103 (53) (54) 105 (51) 0.65 Hypertension 126 (65) 120 (62) (66) 126 (62) 0.59 Chronic pulmonary disease 41 (21) 29 (15) (17) 39 (19) 0.34 Peripheral arterial disease 30 (15) 24 (12) (15) 26 (13) 0.30 Prior myocardial infarction 81 (42) 81 (42) (47) 89 (44) 0.32 NYHA class III or IV 50 (26) 45 (23) (26) 46 (23) 0.61 Ejection fraction, % Left atrial dimension, mm Triple-vessel disease 136 (70) 138 (71) (70) 144 (71) 0.55 Supraventricular premature beats 30 in 24 hours 85 (44) 104 (53) (44) 107 (52) 0.01 Nonsustained supraventricular tachycardia 1 in 85 (44) 111 (57) (42) 118 (58) hours Ventricular premature beats 10 in 24 hours 100 (51) 78 (40) (54) 77 (38) 0.01 Preoperative drugs Renin angiotensin system inhibitors 110 (56) 110 (56) (58) 110 (54) 0.57 Beta blockers 102 (52) 104 (53) (52) 110 (54) 0.71 Statin 124 (64) 141 (72) (65) 145 (71) 0.18 Data are number (%), mean SD. GFR glomerular filtration rate; NYHA New York Heart Association; RMSSD square root of mean of sum of squares of differences between adjacent normal-to-normal QRS complexes; SDNN standard deviation of all normal-to-normal QRS complexes.

4 Ann Thorac Surg KINOSHITA ET AL 2011;91: HEART RATE VARIABILITY AND AF AFTER CABG 1179 Table 2. Univariate Comparisons Between Patients With ( ) and Without ( ) Postoperative Atrial Fibrillation AF( ) n 292 AF( ) n 98 Hazard Ratio (95% CI) p Value Age, years ( ) 0.01 Male sex 234 (80) 88 (90) 1.65 ( ) 0.03 Body mass index, kg/m ( ) 0.69 Hematocrit, % ( ) 0.04 Estimated GFR, ml min m ( ) 0.04 Diabetes mellitus 178 (61) 34 (34) 0.60 ( ) 0.01 Hemoglobin A1c 7.0% 106 (36) 12 (12) 0.72 ( ) 0.01 Smoking 158 (54) 52 (53) 0.79 ( ) 0.76 Hypertension 188 (64) 62 (63) 0.92 ( ) 0.66 Chronic pulmonary disease 52 (18) 18 (18) 1.35 ( ) 0.79 Peripheral arterial disease 40 (14) 16 (16) 1.41 ( ) 0.52 Prior myocardial infarction 152 (52) 44 (45) 0.89 ( ) 0.22 NYHA class III or IV 73 (27) 22 (22) 0.92 ( ) 0.43 Ejection fraction, % ( ) 0.53 Left atrial dimension, mm ( ) 0.47 Triple-vessel disease 210 (72) 64 (65) 1.06 ( ) 0.42 Supraventricular premature beats 30 in 24 hours 134 (46) 54 (55) 1.17 ( ) 0.20 Nonsustained supraventricular tachycardia 1 in 128 (44) 70 (71) 1.94 ( ) hours Ventricular premature beats 10 in 24 hours 134 (46) 44 (45) 0.95 ( ) 0.65 Preoperative drugs Renin angiotensin system inhibitors 159 (55) 51 (52) 0.90 ( ) 0.54 Beta blockers 153 (52) 53 (54) 0.79 ( ) 0.61 Statin 200 (68) 49 (50) 0.56 ( ) 0.01 Operative data Operative duration, hours ( ) 0.03 Inotropic support 24 hours 24 (19.8) 80 (18.6) 1.05 ( ) 0.80 Intubation time, hour 9 (7 13) 9 (6 12) 1.01 ( ) 0.17 Drugs initiated at postoperative day 1 Renin angiotensin system inhibitors 199 (68) 65 (66) 0.90 ( ) 0.67 Beta blockers 237 (81) 79 (81) 0.96 ( ) 0.89 Statin 234 (80) 77 (79) 0.94 ( ) 0.69 Data are number (%), mean SD. AF atrial fibrillation; CI confidence interval; GFR glomerular filtration rate; NYHA New York Heart Association. following variables that were statistically significant in univariate comparisons were entered into a multivariate Cox model as adjusters: age, male sex, hematocrit, estimated glomerular filtration rate, diabetes mellitus, preoperative statin, nonsustained supraventricular tachycardia of 1 or more in 24 hours, and operative duration. Each measurement at median or less was significantly associated with a lower risk of postoperative AF after adjustment for potential confounders. Other variables statistically significant in the multivariate model were age (HR 1.35 per 10-year increase; 95% CI 1.12 to 1.59; p 0.01), diabetes mellitus (HR 0.56; 95% CI 0.36 to 0.87; p 0.01), event of supraventricular nonsustained tachycardia more than 1 per 24 hours (HR 1.81; 95% CI 1.21 to 2.95; p 0.01), preoperative statin (HR 0.67; 95% CI 0.52 to 0.89; p 0.01), and operative duration (HR 1.29 per 1-hour increase; 95% CI 1.10 to 1.57; p 0.02). When hemoglobin A1c of 7.0% or greater was included in the multivariate Cox model instead of diabetes, the adjusted HR and 95% CI of hemoglobin A1c 7.0% or greater were 0.70 and 0.61 to 0.79, respectively. The strong association of hemoglobin A1c with postoperative AF was reflected by the area under the receiver operating characteristic curves (Fig 4). No significant difference in area under the curve was found between the measurements (difference in area 0.068, standard error of difference 0.044, p 0.13). Comment The major finding of our study, which enrolled 390 patients undergoing off-pump coronary artery bypass surgery, was that reduction in the time-domain measurements of 24-hour HRV was independently associated with a lower risk of postoperative AF. A number of investigators have reported on the relationship between preoperative HRV and AF after coronary artery bypass surgery [1-3]. Chamchad and col-

5 1180 KINOSHITA ET AL Ann Thorac Surg HEART RATE VARIABILITY AND AF AFTER CABG 2011;91: Fig 3. Kaplan-Meier estimates of survival free from atrial fibrillation (AF). (A) Standard deviation of all normal-to-normal QRS complexes (SDNN). (B) Square root of mean of sum of squares of differences between adjacent normal-to-normal QRS complexes (RMSSD). Fig 4. Receiver operator characteristic curves for predicting postoperative atrial fibrillation: standard deviation of all normal-to-normal QRS complexes (SDNN [solid line]); and square root of mean of sum of squares of differences between adjacent normal-to-normal QRS complexes (RMSSD [broken line]). (AUC area under curve; CI confidence interval.) leagues [1] evaluated preoperative 24-hour HRV in 88 patients undergoing on-pump coronary artery bypass surgery and demonstrated that advanced age and peak point correlation dimension were independently associated with postoperative AF. In their study, preoperative SDNN and RMSSD were not significant predictors of postoperative AF, but in agreement with our findings, patients having postoperative AF (n 13) tended to have longer RMSSD ( versus , p ) and lower prevalence of diabetes mellitus (18% versus 37%, p ) than patients not having AF (n 75). This difference may be partly explained by the relatively small number of enrolled patients. Hakala and coworkers [2] investigated whether preoperative short-term measurement of HRV could identify patients at high risk of AF after on-pump coronary artery bypass surgery and reported that postoperative AF could not be predicted from short-term HRV [2]. Frost and colleagues [3] analyzed HRV and supraventricular ectopic activity using Table 3. Unadjusted and Adjusted Hazard Ratios for Association Between Variables and Postoperative Atrial Fibrillation Unadjusted HR (95% CI) p Value Adjusted HR (95% CI) p Value SDNN 99 ms 0.22 ( ) ( ) 0.01 RMSSD 0.36 ( ) ( ) ms CI confidence interval; HR hazard ratio; RMSSD square root of mean of sum of squares of differences between adjacent normalto-normal QRS complexes; SDNN standard deviation of all normalto-normal QRS complexes. preoperative 24-hour Holter monitoring in 102 nondiabetic patients undergoing on-pump coronary artery bypass surgery. They concluded that reduced vagal tone was significantly associated with a higher risk of postoperative AF. Vagal tone was calculated as the percentage of successive normal-to-normal interval differences greater than 6%, and correlated positively with RMSSD [5]. The reason for this controversial result, which does not concur with our finding that reduction in timedomain measurements is predictive of postoperative AF, is unclear, but may be related to the exclusion by Frost and coworkers of diabetic patients, who accounted for 55% of our study sample. Frost and colleagues [3] also demonstrated that supraventricular ectopic beats and nonsustained supraventricular tachycardia occurred more often in patients with postoperative AF, a finding in agreement with those of the present study. There have been a number of studies demonstrating lower incidence of postoperative AF in diabetic patients undergoing coronary surgery [8, 9]. In a prospective study of 2,417 patients undergoing on-pump coronary artery bypass surgery [8], diabetic patients had a lower incidence of postoperative AF than nondiabetic patients (24% versus 28% [relative risk 0.84, 95% CI: 0.72 to 0.99; p 0.04]). Halkos and coworkers [9] examined 3,089 patients undergoing elective primary coronary surgery and demonstrated that higher hemoglobin A1c was predictive of postoperative AF: the incidence of AF was 20.9% among patients with hemoglobin A1c less than 7.0% and 15.1% among patients with hemoglobin A1c 7.0% or greater (p 0.007), and the adjusted odds ratio (95% CI) of hemoglobin A1c being associated with postoperative AF was 0.89 per 1% increase (0.80 to 0.98). In

6 Ann Thorac Surg KINOSHITA ET AL 2011;91: HEART RATE VARIABILITY AND AF AFTER CABG 1181 keeping with these studies, the incidence of AF in the present study was significantly lower among diabetic patients than nondiabetic patients (16% versus 36% [adjusted HR 0.56; p 0.01]). Diabetic patients have been reported to have lower HRV than nondiabetic patients. In diabetic neuropathy, characterized by alteration of small nerve fibers, a reduction in HRV precedes the clinical expression of autonomic neuropathy [10-13]. In the present study, diabetic patients had significantly reduced time-domain measurements. The exact mechanisms that explain the protective effect of reduced preoperative HRV on postoperative AF are not clear. Several investigators have reported the association between postoperative HRV and AF after coronary artery bypass surgery. Dimmer and associates [14] performed analysis of HRV in four sequential 15-minute intervals preceding the onset of AF after coronary artery bypass surgery in 64 patients undergoing elective surgery and showed that the patients having AF had higher postoperative SDNN than patients without postoperative AF in the first 45 minutes, although the difference was not statistically significant probably because of small sample size; SDNN showed an increase in the AF group in the last 15 minutes (significant versus patients without AF and within the AF group). The investigators concluded that a shift in the autonomic balance with a loss of vagal tone and a moderate increase in sympathetic tone were observed in patients before the onset of AF compared with patients without AF. Although lack of available data on postoperative SDNN did not enable us to examine the association between preoperative and postoperative SDNN, we can suggest a hypothesis that patients with higher preoperative SDNN have higher postoperative SDNN and are at a higher risk of postoperative AF. In clinical practice, HRV can be determined easily by computer. Although the present study was not designed to identify patients who would benefit from prophylactic use of antiarrhythmic drugs such as beta blocker, amiodarone, sotalol, and statin, preoperative measurement of HRV might be useful for noninvasive risk stratification of patients at high risk for postoperative AF. The present study has a number of potential limitations. Firstly, only patients undergoing off-pump surgery were enrolled; secondly, there were no available data on HRV after surgery. In conclusion, reduced time-domain measurement in preoperative 24-hour HRV is an independent predictor of AF after isolated off-pump coronary artery bypass surgery. Further studies are necessary to investigate the mechanism underlying the association between depressed HRV and postoperative AF and to work out a strategy to improve outcomes for high-risk patients identified by HRV analysis. References 1. Chamchad D, Djaiani G, Jung HJ, Nakhamchik L, Carroll J, Horrow JC. Nonlinear heart rate variability analysis may predict atrial fibrillation after coronary artery bypass grafting. Anesth Analg 2006;103: Hakala T, Vanninen E, Hedman A, Hippeläinen M. Analysis of heart rate variability does not identify the patients at risk of atrial fibrillation after coronary artery bypass grafting. Scand Cardiovasc J 2002;36: Frost L, Mølgaard H, Christiansen EH, Jacobsen CJ, Allermand H, Thomsen PE. Low vagal tone and supraventricular ectopic activity predict atrial fibrillation and flutter after coronary artery bypass grafting. Eur Heart J 1995;16: Jideus L, Ericson M, Stridsberg M, Nilsson L, Blomstrom P, Blomstrom-Lundqvist C. Diminished circadian variation in heart rate variability before surgery in patients developing postoperative atrial fibrillation. Scand Cardiovasc J 2001;35: Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Heart rate variability: standards of measurement, physiological interpretation and clinical use. Circulation 1996;93: Kinoshita T, Asai T, Nishimura O, Suzuki T, Kambara A, Matsubayashi K. Off-pump bilateral versus single skeletonized internal thoracic artery grafting in patients with diabetes. Ann Thorac Surg 2010;90: Hanley JA, McNeil BJ. The meaning and use of the area under a receiver operating characteristic (ROC) curve. Radiology 1982;143: Mathew JP, Parks R, Savino JS, et al. Atrial fibrillation following coronary artery bypass surgery: predictors, outcomes, and resource utilization. JAMA 1996;276: Halkos ME, Puskas JD, Lattouf OM, et al. Elevated preoperative hemoglobin A1c level is predictive of adverse events after coronary artery bypass surgery. J Thorac Cardiovasc Surg 2008;136: Malpas SC, Maling TJ. Heart-rate variability and cardiac autonomic function in diabetes. Diabetes 1990;10: Ewing DJ, Neilson JMM, Traus P. New method for assessing cardiac parasympathetic activity using 24-hour electrocardiograms. Br Heart J 1984;52: Pagani M, Malfatto G, Pierini S, et al. Spectral analysis of heart rate variability in the assessment of autonomic diabetic neuropathy. J Auton Nerv System 1988;23: Freeman R, Saul JP, Roberts MS, Berger RD, Broadbridge C, Cohen RJ. Spectral analysis of heart rate in diabetic neuropathy. Arch Neurol 1991;48: Dimmer C, Tavernier R, Gjorgov N, Van Nooten G, Clement DL, Jordaens L. Variations of autonomic tone preceding onset of atrial fibrillation after coronary artery bypass grafting. Am J Cardiol 1998;82:22 5. INVITED COMMENTARY The developmentof postoperative atrial fibrillation continues to be one of the leading complications after all types of cardiac and thoracic operations. This leads to prolongation of the hospital length of stay and adds significantly to the final cost of providing health care. Although it is generally accepted as a relatively benign process, numerous lifethreatening complications can occur as a result of atrial fibrillation. This can include embolic strokes and other end-organ damage, bleeding complications from attempted anticoagulation, and loss of a critical augmentation of cardiac output that sinus rhythm provides some patients with marked ventricular impairment. The literature is replete 2011 by The Society of Thoracic Surgeons /$36.00 Published by Elsevier Inc doi: /j.athoracsur