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CHADS2 score predicts atrial fibrillation followingcardiac surgery
Sohail Sareh, MS,a William Toppen, BA,a Laith Mukdad, BA,a
Nancy Satou, RN,a Richard Shemin, MD,a Eric Buch, MD,b
and Peyman Benharash, MDa,*aDivision of Cardiothoracic Surgery, David Geffen School of Medicine, University of California at Los Angeles, Los
Angeles, CaliforniabDivision of Cardiology, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles,
California
a r t i c l e i n f o
Article history:
Received 4 January 2014
Received in revised form
2 February 2014
Accepted 11 February 2014
Available online xxx
Keywords:
CHADS2 score
Cardiac surgery
Atrial fibrillation
Risk assessment
Postoperative complications
* Corresponding author. UCLA Division of Ca90095. Tel.: þ1 310 206 6717; fax: þ1 310 206
E-mail address: Pbenharash@mednet.ucl0022-4804/$ e see front matter ª 2014 Elsevhttp://dx.doi.org/10.1016/j.jss.2014.02.007
a b s t r a c t
Background: Atrial fibrillation (AF) following cardiac surgery portends higher morbidity and
increased health expenditure. Although many anatomic and patient risk factors have been
identified, a simple clinical scoring system to identify high-risk patients is lacking. The
CHADS2 score is widely used to predict the risk of stroke in patients with AF. We assessed
the utility of this scoring algorithm in predicting the development of de novo postoperative
atrial fibrillation (POAF) in cardiac surgery patients.
Material and methods: A total of 2120 patients from 2008 to 2013 were identified for inclusion
in our analysis. CHADS2 scores were calculated, and patients grouped into low- (0), inter-
mediate- (1) and high-risk (�2) categories. A multivariate regression model was developed
to account for known risk factors of AF.
Results: Of the2120patients, 344 (16.2%)patients developeddenovoPOAFduring theirprimary
hospitalization. Mean CHADS2 scores for POAF patients and no POAF patients were 2.1 � 1.2
and 1.7 � 1.3 (P < 0.0001), respectively. CHADS2 score was a significant predictor of AF on
multivariate regressionanalysis (adjustedodds ratio, 1.26; 95%confidence interval, 1.14e1.40).
As CHADS2 score increased from 0 to 6, the probability of POAF increased from 11.1% to 32.7%
(P<0.0001).Comparedwiththe low-riskgroup, the intermediate-riskandhigh-riskgroupshad
a 1.73- and 2.58-fold increase inoddsof developing POAF, respectively (P< 0.02 and P< 0.0001).
Conclusions: CHADS2 score is a powerful and convenient predictor of developing POAF. We
recommend its utilization in identifying high-risk patients that may benefit from phar-
macologic prophylaxis.
ª 2014 Elsevier Inc. All rights reserved.
1. Introduction
factors for the development of AF include advanced age, dia-With over 350,000 annual hospitalizations attributed to atrial
fibrillation (AF), it is estimated to account for $6e$26 billion of
health care spending in the United States annually [1,2]. Risk
rdiac Surgery, 10833 Le C5901.a.edu (P. Benharash).ier Inc. All rights reserved
betes, hypertension, valvular heart disease, heart failure,
obesity, smoking, and chronic renal disease among others [3e5].
AF is also a common complication after cardiac operations, with
its incidence ranging between 10% and 60% [6e9]. Although the
onte Avenue, 62-249 Center for Health Sciences, Los Angeles, CA
.
Table 1 e Baseline clinical and operative characteristics.
Characteristic Total (n ¼ 2120) No AF (n ¼ 1776) AF (n ¼ 344) P value
CHADS2 characteristics
Heart failure or EF �40, % 43.4 41.8 51.5 0.001
Hypertension, % 66.2 64.4 76.7 <0.0001
Age, y (mean � SD) 62.1 � 14.7 60.7 � 12.8 69.4 � 11.6 <0.0001
Diabetes mellitus, % 26.7 27.0 24.4 0.32
Cerebrovascular disease, % 10.1 9.9 11.6 0.32
Risk factors
Female, % 33.8 33.6 34.9 0.65
Vascular disease, % 54.9 53.5 61.9 0.004
Smoker, % 21.2 21.4 20.3 0.66
Body mass index, kg/m2 (mean � SD) 27.2 � 0.13 27.2 � 0.14 27.4 � 0.33 0.58
Dyslipidemia, % 55.9 54.2 64.5 0.0004
Anemia, % 49.6 46.5 50.2 0.21
Elevated creatinine, % 14.5 14.9 12.5 0.25
Dialysis, % 6.0 6.3 4.7 0.25
Mitral insufficiency, % 13.8 13.6 15.1 0.45
Aortic insufficiency, % 12.4 11.4 17.4 0.002
Peripheral vascular disease, % 8.1 7.9 9.0 0.48
Preoperative meds
Beta-blocker, % 60.2 59.3 64.8 0.06
Statin, % 58.6 57.0 67.2 0.0005
Aspirin, % 51.2 50.3 56.1 0.05
Anticoagulant, % 13.5 13.7 12.5 0.56
Coumadin, % 4.6 4.7 4.1 0.59
Operative characteristics
Valve surgery, % 44.3 41.6 58.7 <0.0001
Procedure time, min (mean � SD) 330 � 154 323 � 154 364 � 145 <0.0001
Cardiopulmonary bypass time, min (mean � SD) 121 � 89 118 � 90 142 � 75 <0.0001
Perioperative RBC transfusions, n (mean � SD) 1.5 � 2.5 1.5 � 2.5 1.8 � 2.5 0.03
EF ¼ ejection fraction.
j o u r n a l o f s u r g i c a l r e s e a r c h x x x ( 2 0 1 4 ) 1e62
underlyingmechanismof postoperative atrial fibrillation (POAF)
is not fully understood, inflammation and oxidative stress from
the cardiac procedure are thought to play a significant role [10].
Adverse outcomes associated with POAF include neurologic,
renal, and infectious complications, as well as death [7,11,12].
Prophylactic regimens such as amiodarone are effective in
reducing the incidence of POAF but limited data are available on
the appropriate identification of high-risk patients who would
benefit most from prophylactic therapy [5,12,13].
The CHADS2 method is a commonly used clinical scoring
system that allows identification of AF patients at high risk of
developing a thromboembolism. This methodology is then
used by practitioners to decide anticoagulation regimens for
noncardiac surgical patients with AF [14e16]. Because the
CHADS2 score consists of risk factors also associated with the
development of AF, its utility in predicting the development of
POAF has been considered. Earlier studies have validated its
efficacy in predicting POAF over the course of multiple years
[17,18]. However, the highest incidence of POAF occurs within
3 d of the procedure [19]. The focus of this study was to assess
the utility of the CHADS2 scoring algorithm in identifying
patients at an increased risk of developing de novo AF
following a cardiac operation.
2. Methods
Between January 2008 and March 2013, 3454 patients who
underwent cardiac surgery at the Ronald Reagan Medical
Center at UCLA were identified. Exclusion criteria for our
analysis included documented history of AF; preoperative
antiarrhythmic drug use; and undergoing an operation
for arrhythmia, ventricular assist device insertion, extracor-
poreal membrane oxygenation, or transplant. All patient
datadincluding demographics, cardiovascular risk factors,
preoperative cardiac status, perioperative data, and post-
operative eventsdwere retrieved electronically from the
institutional database and supplemented with the hospital’s
electronic health records.
A CHADS2 score (0e6) was assigned to each patient based
on medical history, with scoring criteria set on definitions
specified by the STS Adult Cardiac Database Specifications
Version 2.73 [20]. Congestive heart failure (NYHA class II or
greater or left ventricular ejection fraction <40%), hyperten-
sion, age�75 y, and diabetesmellitus were assigned one point
each, whereas stroke and transient ischemic attack received
two points. Patients were then risk-stratified into low-risk (0),
intermediate-risk (1), and high-risk (�2) categories based on
their CHADS2 score according to guidelines published in
CHEST by Lip et al. [21].
The primary end point in this study was the development
of de novo POAF for over 30 s. Hospital discharge and in-
hospital mortality were considered secondary outcomes.
Patient demographics and risk factors are presented as
means with standard deviations, and differences between
POAF and no postoperative atrial fibrillation groups have
been demonstrated via Student t-test. A multivariate logistic
regression model was developed to account for the following
Table 2 e Patient outcomes.
Outcome Total (n ¼ 2120) No AF (n ¼ 1776) AF (n ¼ 344) P value
CHADS2 score (mean � SD) 1.8 � 1.3 1.7 � 1.3 2.1 � 1.2 <0.0001
Low risk (0), % 17.1% 18.8% 8.4% <0.0001
Intermediate risk (1), % 27.4% 28.2% 23.6% 0.08
High risk (�2), % 55.5% 53.1% 68.0% <0.0001
Total intensive care unit, h (mean � SD) 97.7 � 184.2 88.2 � 147.2 147.1 � 307.3 <0.0001
Length of stay, d (mean � SD) 9.4 � 10.8 8.8 � 10.4 12.7 � 12.2 <0.0001
In-hospital mortality, % 2.6% 2.5% 2.9% 0.64
j o u rn a l o f s u r g i c a l r e s e a r c h x x x ( 2 0 1 4 ) 1e6 3
known risk factors and potential confounders: female gender,
obesity, dyslipidemia, history of smoking, anemia (hematocrit
< 36% in females and <39% in males), elevated creatinine
(>1.4 mg/dL in females and >1.5 mg/dL in males), aortic
insufficiency, mitral insufficiency, preoperative beta-blocker
use, preoperative angiotensin-converting enzyme inhibitor
use, preoperative statin use, preoperative aspirin use, preop-
erative warfarin use, preoperative anticoagulation use, valve-
related procedure, procedure time, and perioperative blood
transfusion. To avoid duplication and interdependence, vari-
ables containedwithin the CHADS2 score were not included in
the model. Adjusted odds ratio with 95% confidence intervals,
as well as a predicted probability of developing AF was
calculated for each CHADS2 score. To determine specificity
and sensitivity, an optimal cutoff was set based on the pre-
dicted probability of POAF in the high-risk category. All sta-
tistical analyses were performed using STATA 12.1 software
(StataCorp 2011, College Station, TX), and all tests were
considered significant if P values were <0.005.
Table 3 e Adjusted odds ratio for developing atrialfibrillation.
Variable Odds ratio (95% CI) P value
CHADS2 score 1.26 (1.14e1.40) <0.0001
Low risk (0) 1.00 (Reference)
Intermediate risk (1) 1.73 (1.09e2.73) 0.02
High risk (�2) 2.58 (1.67e4.00) <0.0001
Body mass index, kg/m2 0.99 (0.97e1.01) 0.49
Dyslipidemia 1.09 (0.81e1.46) 0.58
Smoking 0.92 (0.68e1.23) 0.57
Female 1.07 (0.82e1.38) 0.63
Anemia 0.79 (0.61e1.01) 0.06
Elevated creatinine 0.84 (0.56e1.26) 0.40
Dialysis 0.78 (0.42e1.45) 0.44
Peripheral vascular disease 1.01 (0.66e1.55) 0.04
Mitral insufficiency 0.77 (0.54e1.10) 0.15
Aortic insufficiency 1.10 (0.78e1.55) 0.60
Pre-Op anticoagulant 0.89 (0.62e1.28) 0.53
Pre-Op coumadin 0.90 (0.49e1.63) 0.72
Pre-Op beta blocker 1.11 (0.86e1.45) 0.43
Pre-Op statin 1.34 (1.00e1.81) 0.05
Valve surgery 1.94 (1.47e2.56) <0.001
Procedure time 1.00 (1.00e1.00) 0.007
RBC transfusion 1.00 (0.95e1.06) 0.89
Pre-Op ¼ preoperative.
3. Results
Of the 2120 patients (66.2% male) included in the study, 344
(16.2%) patients developed POAF during their primary hospital-
ization period. Baseline characteristics such as demographics,
risk factors, and preoperativemedications are shown in Table 1.
Themean CHADS2 score for the PAOF and NPAOF patients were
2.1� 1.2 and 1.7� 1.3, respectively (P< 0.0001). Figure 1 displays
the distribution of CHADS2 scores between the POAF andNPOAF
patients. Significant differences in secondary outcomes such as
total intensive care unit hours and hospitalization period were
also found (Table 2). When adjusted for risk factors as displayed
in Table 3, a larger preoperative CHADS2 score was associated
with significantly higher odds of developing POAF (adjusted
odds ratio, 1.26; 95%confidence interval, 1.14e1.40; P< 0.0001). A
patient’s probability of developing POAF increased from11.1% to
32.7% as CHADS2 score increased from 0 to 6 (P < 0.0001), as
illustrated in Figure 2. Anemia, preoperative statin use, valve-
related procedures, and procedure time were also significantly
associated with POAF.
In the stratified model, 8.0%, 13.9%, and 19.9% of patients
developed POAF in the low-, intermediate-, and high-risk
groups, respectively. Compared with the low-risk group, pa-
tients in the intermediate-risk and high-risk groups had a 1.73-
and 2.58-fold increase in adjusted odds of developing POAF,
respectively (P< 0.02 and P< 0.0001). This CHADS2 stratification
scheme correctly classified 67.5% of patients, with a specificity
of 70.7% and sensitivity of 50.9% for the development of POAF.
4. Discussion
Postoperative AF is a complex issue that has garnered
particular attention asmore convincing evidence regarding its
negative impact on morbidity and survival is found. Although
this arrhythmia is short-lived and most cases resolve within
6e8 wk, POAF leads to a definite increment in long-term
mortality and cost of health care. Increased adrenergic drive,
atrial stretch, and inflammation in the period following sur-
gery have been cited as possible causes of POAF [10]. Perhaps,
a relevant question to ask is whether AF is simply a marker of
worse cardiovascular risks.
The goal of this studywas to assess the clinical utility of the
CHADS2 score in identifying patients at a higher risk of
developing de novo POAF. Our analysis has indicated that
patients with an elevated CHADS2 score (�2) have a signifi-
cantly higher risk of developing POAF comparedwith a patient
with a low CHADS2 score (0). Because the CHADS2 score is an
aggregate of risk factors associated with the long-term
development of AF, our findings are not surprising. A recent
nationwide cohort study from Taiwan found the CHADS2score to be useful in risk stratification over the course of a
Fig. 1 e Distribution of CHADS2 Score.
j o u r n a l o f s u r g i c a l r e s e a r c h x x x ( 2 0 1 4 ) 1e64
9.0-y mean follow-up period [18]. However, our analysis has
indicated that the CHADS2 score also serves as a reliable
predictor of developing AF in the immediate postoperative
period. The majority of patients in our analysis were correctly
classified between POAF and no postoperative atrial fibrilla-
tion groups using our risk stratification scheme, further con-
firming its utility as a predictor of de novo AF.
Moreover, our logistic regressionmodel found that patients
undergoing a valve-related procedurewere at a significant risk
of developing AF. Prior studies have attributed this increased
risk to longer bypass and cross-clamp times associated with
valve procedures, as well as surgical cannulation and dissec-
tion techniques [7,22]. In addition, preoperative statin use was
also associated with the development of AF. Current literature
is inconsistent regarding the protective effects of statin use on
the development of POAF [23,24]. However, a recent study
suggests that statins may be beneficial only in patients with a
high CHADS2 score [25]. In our analysis, we accounted for a
substantial number of factors such as the aforementioned in
an attempt to validate our findings of the predictive value of
the CHADS2 score.
Although recommended guidelines for antiarrhythmic
prophylaxis have been established by multiple organizations
Fig. 2 e Probability of POAF with 95% confidence intervals.
[26,27], few institutions have standardized their prophylactic
approach and the practice is widely underused [28]. This is in
part due to the side effects and costs of antiarrhythmic agents.
Amiodarone, for instance, is associated with heart block, as
well as pulmonary, hepatic, and thyroid toxicity. In this
retrospective study of cardiac surgical patients, the CHADS2score functioned as a practical and effective risk stratification
tool for the development of POAF. Therefore, institutions may
use this scoring system to formulate a targeted prophylaxis
strategy. Additional investigation is warranted via a prospec-
tive study that includes the CHADS2 risk schema in deter-
mining prophylactic management of patients.
This study has several limitations. The retrospective and
single-center nature of this study limits generalization of our
findings. However, the large number of patients, the rigorous
reporting of POAF at our institution, and the vast set of vari-
ables in the database serve to offset this shortcoming. The low
incidence of AF in this cohort may be explained by the fact
that we excluded patients with preoperative AF. Patients with
AF before surgery are thought to have substrate changes in the
structure of the atria that predisposes them to further epi-
sodes [19]. Moreover, although large left atrial volume has
been independently associated with the development of
POAF, consistent data on this preoperative factor were not
available for our patient population [29]. Thus, wewere unable
to adjust for this factor in our multivariate analysis.
5. Conclusion
In this retrospective study of adult cardiac surgical patients,
we evaluated the utility of the CHADS2 scoring system in
predicting de novo POAF. Patients with a CHADS2 score of �2
have a higher probability of developing AF compared with
those with a score of <2. This scoring system could be used to
develop a targeted prophylaxis strategy to reduce AF after
cardiac surgery.
Acknowledgment
The authors thank Peter Hsiue and the UCLA Statistical
Consulting Group for their invaluable contributions to this
project.
Author Contributions: S.S.: Study design, data collection,
data analysis, data interpretation, article drafting; W.T.: Data
analysis, data interpretation, article drafting, critical re-
visions; L.M.: Data collection, article drafting, critical re-
visions; N.S.: Data collection, data analysis, critical revisions;
R.S.: Study concept, study design, data interpretation, critical
revisions; E.B.: Study design, data interpretation, critical
revisions; P.B.: Study concept, study design, data collection,
data analysis, data interpretation, article drafting, critical
revisions.
Disclosure
The authors reported no proprietary or commercial interest in
any product mentioned or concept discussed in this article.
j o u rn a l o f s u r g i c a l r e s e a r c h x x x ( 2 0 1 4 ) 1e6 5
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