Download Prevention of Atrial Fibrillation After Cardiac Surgery

Prevention of Atrial Fibrillation After
Cardiac Surgery*
The Significance of Postoperative Oral Amiodarone
Sotiris C. Stamou, MD, PhD; Peter C. Hill, MD, FCCP; George A. Sample, MD;
Elizabeth Snider, MS; Albert J. Pfister, MD; Robert C. Lowery, MD; and
Paul J. Corso, MD
Study objectives: Atrial fibrillation (AF) is a common occurrence after cardiac surgery (10 to 53%)
that contributes to increased length of stay and hospital cost. Recent evidence suggests that
treatment with amiodarone may provide safe and effective prophylaxis against AF in many
patients undergoing cardiac operations. This study sought to investigate whether oral amiodarone administered postoperatively would reduce the incidence of postoperative AF.
Design: Prospective nonrandomized cohort study.
Patients and participants: In this prospective study, 1,196 consecutive patients who underwent
various open-heart procedures with cardiopulmonary bypass between July 1999 and February
2000 received oral amiodarone, 400 mg bid, from the transfer to the cardiovascular recovery
room until the day of hospital discharge, or up to 7 days postoperatively. The incidence of AF in
this group of patients was compared with a group of 1,246 patients who underwent cardiac
surgery with cardiopulmonary bypass in the preceding 8-month period (November 1998 to June
1999) at the same institution without receiving amiodarone postoperatively.
Setting: Tertiary health-care center.
Measurement and results: AF developed in 294 patients (25%) in amiodarone-treated group and
in 385 patients (31%) in the control group (p ⴝ 0.001). In multivariate logistic regression analysis,
oral amiodarone treatment emerged as an independent predictor of lower risk of AF (odds ratio,
0.7; 95%; 95% confidence interval, 0.6 to 0.9; p ⴝ 0.002) and shorter hospital length of stay (odds
ratio, 0.8; 95% confidence interval, 0.5 to 0.9; p ⴝ 0.006).
Conclusions: Postoperative oral amiodarone treatment is a safe and effective regimen associated
with a reduced incidence of new-onset AF and decreased length of hospital stay. Prospective
randomized trials are needed to evaluate the benefits of amiodarone treatment relative to its side
effect profiles.
(CHEST 2001; 120:1936 –1941)
Key words: administration, oral; atrial fibrillation, prevention and control; comparative study
Abbreviations: AF ⫽ atrial fibrillation; CABG ⫽ coronary artery bypass grafting
fibrillation (AF) is a frequent adverse event
A trial
after cardiac surgery, occurring in 10 to 53% of
patients.1–7 Postoperative AF has been associated
with increased morbidity and prolonged hospitalization after cardiac surgery.8 Prophylactic strategies to
prevent AF after cardiac surgical procedures, most
commonly involving verapamil, digoxin,9,10 or ␤-adrenergic antagonists, have been evaluated.11 Digoxin
*From the Section of Cardiac Surgery, Department of Surgery,
Washington Hospital Center and MedStar Research Institute,
Washington, DC.
Manuscript received November 8, 2000; revision accepted May
4, 2001.
Correspondence to: Paul J. Corso, MD, Director of Cardiac
Surgery, Washington Hospital Center, 106 Irving Street NW,
Suite 316, South Tower, Washington, DC 20010; e-mail:
[email protected]
and verapamil were not found to be as effective as
prophylactic amiodarone in preventing postoperative
AF.12 In previous studies,11,13–15 prophylactic therapy with ␤-adrenergic antagonists has been reported
to reduce AF rate, but other studies16 –18 have failed
to confirm this beneficial effect.
In contrast to the ␤-adrenergic antagonists, amiodarone, as a class III antiarrhythmic agent, has a
direct antifibrillatory effect on the atrium that may
reduce postoperative AF.12,19,20 Other investigators
have shown7,21 that administration of amiodarone
appeared to prevent new-onset AF and decrease
hospital length of stay in a group of patients after
cardiopulmonary bypass. In this study, we sought to
investigate the role of oral amiodarone administered
in the early postoperative period in preventing AF
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Clinical Investigations
and reducing postoperative length of stay in a large
patient population after cardiac surgery.
Materials and Methods
Patients
All patients (n ⫽ 3,694) who underwent cardiac surgery at the
Washington Hospital Center between November 1998 and February 2000 were identified using the computerized database
system of the Section of Cardiac Surgery at the Washington
Hospital Center. Patients with preoperative bradycardia (heart
rate ⬍ 60 beats/min; n ⫽ 240) who were dependent on a pacemaker (n ⫽ 34), who underwent cardiac transplantation (n ⫽ 6),
who underwent coronary artery bypass grafting (CABG) without
cardiopulmonary bypass (n ⫽ 860), or had preoperative AF
(n ⫽ 112) were excluded from the study. Of the remaining
patients (n ⫽ 2,442), 1,196 patients had been prospectively entered in a clinical protocol between July 1, 1999, and February 1,
2000, which included postoperative oral administration of amiodarone, 400 mg bid. Baseline characteristics and early in-hospital
outcomes were recorded and compared with those of patients
who underwent cardiac surgery during the preceding 8-month
period from November 1, 1998, to June 30, 1999 (n ⫽ 1,246).
failed to convert AF to sinus rhythm within 24 h. Patients who did
not convert to sinus rhythm within 48 h, despite the aforementioned protocol, received anticoagulation with IV heparin and
were discharged receiving oral warfarin.
Statistical Analysis
Primary comparisons were made between patients with vs
without postoperative oral intake of amiodarone. All statistical
analyses were two tailed. Categorical variables were compared
using Fisher’s Exact ␹2 test for proportions with appropriate
degrees of freedom. In the analysis of continuous variables, the
Student’s unpaired t test was used for variables with normal
distributions and the Mann-Whitney U test was used for variables
with nonnormal distributions. A stepwise logistic regression
analysis was conducted to determine the independent predictors
of postoperative AF (dependent variable), including all variables
with p ⬍ 0.20 in the univariate analysis as independent variables.
Following the same methodology, we also investigated the independent predictors of prolonged hospital stay (⬎ 7 days; 75th
percentile of postoperative stay). All p values ⬍ 0.05 were
considered statistically significant. Statistical analysis was performed using statistical software (Statistical Package for the
Social Sciences for Windows 95, Version 9.0; SPSS; Chicago, IL).
Results
Definitions
Preoperative Variables: Diabetes was defined as a history of
diabetes mellitus, regardless of duration of the disease or need for
oral agents or insulin. COPD was defined as FEV1 ⬍ 75% of
predicted and/or long-term use of bronchodilators. Chronic renal
insufficiency was defined as a serum creatinine value ⱖ 2.0
mg/dL.
Postoperative Variables: Low-output syndrome was defined as
the postoperative use of inotropic support for ⬎ 48 h for the
purpose of generating an adequate cardiac output. Prolonged
ventilatory support was defined as pulmonary insufficiency requiring ventilatory support for ⬎ 48 h. Stroke was defined as any
new major (type II) neurologic deficit presenting in the hospital
and persisting ⬎ 72 h.22 Transient ischemic attacks were not
included in this analysis. Postoperative AF was defined as newonset AF detected by telemetry analysis and requiring treatment.
Patients with AF that did not resolve during their hospital stay
were considered to have persistent AF.
Baseline clinical and demographic characteristics
are summarized in Table 1. The incidence of congestive heart failure was lower in patients who
received postoperative amiodarone (3% in the amiodarone-treated group vs 5% in the control group;
p ⫽ 0.006). Congestive heart failure was added to
the logistic regression model in order to adjust for
this obvious imbalance between the patients of the
two groups. Preoperative administration of ␤-blockers was similar between patients of the two groups.
Treatment with ␤-blockers was continued in all
patients during the postoperative period.
Table 1—Baseline and Demographic Patient
Characteristics (Univariate Analysis)*
Treatment of AF
Treatment of AF was based on duration of new-onset AF for
ⱖ 20 min or ⬎ 60 min in a 24-h period and included heart rate
control, chemical cardioversion, and/or electrical cardioversion.
For rate heart control, 5 mg of IV metoprolol was infused over a
1-min period every 5 min until the patient’s heart rate was ⬍ 110
beats/min or until a maximum dose of 15 mg was administered.
After heart rate control was accomplished, oral metoprolol, 25 to
100 mg bid, was administered. In patients contraindicated to
receive ␤-adrenergic antagonists, IV diltiazem (15 to 25 mg over
2 min until the heart rate was controlled and then 30 to 60 mg
tid) or oral digoxin (loading dose of 1 mg and then 0.125 to 0.25
mg qd) were administered. When heart rate control was
achieved, chemical conversion of AF was accomplished with oral
procainamide (loading dose of 1 g followed by 750 mg qid,
adjusted for body weight) or increase in oral amiodarone to 600
mg bid. Electrical cardioversion (transthoracic synchronous discharge of 50 to 200 J) was administered when drug cardioversion
Amiodarone
Control
Group
Group
(n ⫽ 1,196) (n ⫽ 1,246) p Value
Characteristics
Age, yr
Age ⬎ 75 yr
Male patients
Diabetes
Ejection fraction ⬍ 35%
Hypertension
Previous cerebrovascular accident
Congestive heart failure
History of myocardial infarction
Chronic renal insufficiency
Preoperative ventilator
Redo sternotomy
Preoperative ␤-blockers
64 ⫾ 12
229 (19)
836 (70)
300 (25)
330 (28)
770 (64)
136 (11)
36 (3)
457 (38)
22 (2)
7 (1)
103 (9)
502 (42)
64 ⫾ 12
245 (20)
849 (68)
302 (24)
340 (27)
784 (63)
127 (10)
56 (5)
483 (39)
19 (1)
15 (1)
96 (8)
489 (39)
0.78
0.76
0.36
0.63
0.89
0.47
0.36
0.006
0.13
0.76
0.13
0.42
0.41
*Data are expressed as mean ⫾ SD or No. (%).
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Table 2—Operative and Postoperative Patient Characteristics (Univariate Analysis)*
Characteristics
Amiodarone
Group
(n ⫽ 1,196)
Control
Group
(n ⫽ 1,246)
p Value
Procedures
CABG
CABG and valve replacement
Valve surgery
Other
Aortic cross-clamp time, min
Aortic cross-clamp time ⬎ 120 min
Cardiac- or bleeding-related reoperation
Myocardial infarction
Stroke
Pulmonary edema/ARDS
Pleural effusion/thoracentesis
Prolonged ventilation
Hemodialysis
Low-output syndrome
Postoperative IABP
Small-bowel infarction
GI bleeding
Postoperative LOS
In-hospital mortality
813 (68)
123 (10)
133 (11)
127 (11)
53 ⫾ 36
35 (3)
54 (4)
16 (1)
31 (3)
12 (1)
37 (3)
68 (6)
8 (1)
116 (10)
17 (1)
1 (0.1)
21 (2)
6⫾3
34 (3)
934 (75)
122 (10)
112 (9)
78 (6)
53 ⫾ 27
30 (2)
53 (4)
12 (1)
37 (3)
6 (0.5)
33 (3)
64 (5)
12 (1)
123 (10)
10 (1)
5 (0.4)
34 (3)
8⫾4
39 (3)
0.40
0.69
0.1
0.05
0.88
0.45
1.00
0.45
0.62
0.16
0.54
0.60
0.80
0.89
0.09
0.21
0.13
0.01
0.72
*Data are expressed as mean ⫾ SD or No. (%); IABP ⫽ intra-aortic balloon pump; LOS ⫽ length of stay.
The patients of the two groups were similar with
respect to the types of operative procedures and
complications (Table 2). Only postoperative length
of stay was significantly different (lower) in patients
who received amiodarone than in patients in the
control group (p ⫽ 0.01). During the study period,
AF developed in 25% of patients in the amiodaronetreated group vs 31% in the control group
(p ⬍ 0.001; Table 3). Other arrhythmic complications were similar between patients of the two
groups (Table 3).
Predictors of New-Onset AF
In multivariate logistic regression analysis, the
following variables emerged as independent predic-
tors of AF: age ⬎ 75 years, hypertension, CABG with
valve replacement, ARDS, and prolonged ventilation. Postoperative administration of amiodarone
was associated with a lower incidence of postoperative AF (Table 4), even after adjusting for congestive
heart failure as well as variables with p ⬍ 0.20 in the
univariate analysis comparing the two groups.
Predictors of Prolonged Hospital Stay
Patients in whom AF developed had a prolonged
postoperative length of stay (mean ⫾ SD, 8 ⫾ 4 days
for AF vs 6 ⫾ 3 days for no AF; p ⫽ 0.01). In the
multivariate logistic regression analysis, ejection fraction ⬍ 35%, age ⬎ 75 years, CABG with valve
replacement, prolonged ventilation, postoperative
stroke, ARDS, low cardiac output, and new-onset AF
Table 3—Arrhythmic Complications (Univariate
Analysis)*
Complications
AF
Persistent AF
Ventricular tachycardia
Ventricular fibrillation
Permanent pacemaker
implantation
Atrioventricular
dissociation
Electromechanical
dissociation
Amiodarone
Group
(n ⫽ 1,196)
Control
Group
(n ⫽ 1,246)
p Value
294 (25)
119 (10)
16 (1)
8 (1)
0 (0)
385 (31)
114 (9)
18 (1)
6 (0.5)
1 (0.1)
0.001
0.53
0.86
0.60
1.00
2 (0.2)
1 (0.04)
0.28
1 (0.1)
1 (0.1)
1.00
*Data are expressed as No. (%).
Table 4 —Predictors of New-Onset AF (Multivariate
Analysis)*
Predictors
Preoperative variables
Age ⬎ 75 yr
Hypertension
Operative variables
CABG with valve replacement
Postoperative variables
ARDS
Prolonged ventilation
Amiodarone prophylactic treatment
OR
CI
p Value
2.4
1.3
1.9–3.0
1.0–1.6
⬍ 0.001
0.01
1.4
1.1–1.9
2.9
2.3
0.7
1.1–7.5
1.6–3.4
0.6–0.9
0.01
0.03
⬍ 0.001
0.002
*OR ⫽ odds ratio; CI ⫽ 95% confidence interval.
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Clinical Investigations
were found to prolong postoperative length of stay
(⬎ 7 days), whereas postoperative administration of
amiodarone correlated with an abbreviated postoperative stay (Table 5).
Discussion
AF is one of the most common adverse events
after cardiac surgery, occurring in up to 53% of
patients after cardiac surgery,21 and has been associated with increased morbidity and prolonged hospitalization.8 Several clinical factors have been associated
with AF after cardiac surgical procedures,13,23,24 such as
advanced age, depressed ejection fraction, and preexisting AF. Different mechanisms have been proposed
to explain the high incidence of AF after cardiac
surgery, including withdrawal of ␤-blockers administered preoperatively25; structural changes of the heart,
such as those related to age, effects of cardiopulmonary
bypass, and cardioplegia; as well as the effects of
postoperative hypoxia, hypovolemia, and electrolyte
imbalance.1 Clinical factors that predispose individuals
to AF may act through a common denominator, “the
dispersion of refractoriness,” a term used to describe
the heterogeneity of local atrial refractory periods.5,26
Oral amiodarone has been increasingly used as an
antiarrhythmic agent to prevent the occurrence of
AF after cardiac surgery.21 Amiodarone seems to act
through a prolongation of atrial refractoriness. However, the precise mechanism of action is not well
understood because amiodarone does not predictably lengthen atrial repolarization acutely.27,28 It has
been hypothesized that its effect may stem from its
nonspecific antiadrenergic effect, its class I actions,
or other actions not yet identified.27 Moreover,
amiodarone has coronary vasodilatory effects29 that
may benefit cardiac surgical patients.
Table 5—Independent Correlates of Prolonged (> 7 d)
Hospital Stay After CABG (Multivariate Analysis)*
Correlates
Preoperative variables
Ejection fraction ⱕ 35
Age ⬎ 75 yr
Operative variables
CABG with valve
replacement
Postoperative variables
Amiodarone
Prolonged ventilation
Stroke
ARDS
Low-output syndrome
Postoperative AF
OR
CI
p Value
1.5
2.3
1.5–1.8
1.8–2.9
0.002
⬍ 0.001
1.8
1.3–2.5
⬍ 0.001
0.8
17.4
6.7
15.1
3.9
3.3
0.5–0.9
10.2–29.8
3.5–12.6
3.9–57.8
2.8–5.4
2.6–4.1
0.006
⬍ 0.001
⬍ 0.001
⬍ 0.001
⬍ 0.001
⬍ 0.001
*See Table 4 for expansion of abbreviations.
In our study, the two groups were comparable
with respect to baseline characteristics, besides a
higher rate of congestive heart failure in patients in
the control group. Postoperative complications were
similar in both groups. Previous authors30 have related amiodarone administration to a high rate of
ARDS, which is estimated to occur in up to 10% of
treated patients. In our series, ARDS incidence was
equally low in both groups and there were no other
pulmonary complications attributable to amiodarone. Similarly, GI complications were not different
between patients of the two groups. Severe complications warranting discontinuation of the medication
(eg, bradycardia) occurred in 1% of patients (n ⫽ 13)
who received amiodarone.
Amiodarone, AF, and Postoperative Stay
Operative techniques and standards of care did
not change significantly during the course of this
study, and all procedures were performed by the
same group of heart surgeons. Preoperative (ejection
fraction ⱕ 35%, advanced age), operative (CABG
with valve replacement) and postoperative variables
(prolonged ventilation, stroke, ARDS, low-output
syndrome, new-onset AF) were found to independently predict prolonged hospital stay. Amiodarone
treatment emerged as an independent predictor of
shorter postoperative stay in patients undergoing
cardiac surgery, confirming the findings of previous
studies.7,21 In the current era of reduced health-care
funds, shortened hospital stay may favorably affect
the relative risk/benefit ratio for cardiac operations,
reduce the use of hospital resources, and therefore
lower the cost of care.
Clinical Implications
Postoperative treatment with oral amiodarone was
well tolerated and resulted in a decreased prevalence
of AF in patients undergoing heart surgery. After
adjusting for age and other correlates, postoperative
treatment with amiodarone was independently associated with a decrease in postoperative length of stay.
Although previous reports have emphasized the requirement of a loading regimen of amiodarone 3 to 7
days before surgery,21 in the present study, initiation
of amiodarone treatment at the early postoperative
period without a preloading phase resulted in a
significant decrease in AF rate. This therapeutic
protocol eliminates the need of preoperative monitoring of potential complications of the treatment
and patient’s compliance (if therapy is started at
home). Moreover, it reduces length of stay since
patients may be admitted to the hospital on the day
of surgery and not before that. Future prospective
studies, despite their limitations, may be needed to
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confirm these results, investigate the long-term contribution of AF to morbidity and mortality in patients
undergoing cardiac surgery, and explore the potential advantage of oral amiodarone therapy with respect to postoperative AF. Moreover, different approaches, such as magnesium infusion, may decrease
the incidence of postoperative AF after CABG.31
Limitations of the Study
Limitations of our study include limitations inherent in any retrospective analysis. However, all data
elements were prospectively entered according to
prespecified definitions.
The main limitation of our study was the nonrandomized single-institution methodology that could
not establish direct causal relationships with certainty. However, retrospective studies with a largeenough sample along with multivariate models, such
as those developed in the study, may be used to more
accurately determine the significance of amiodarone
in preventing postoperative AF after cardiac surgery.
Prospective randomized studies, although of invaluable scientific merit, are limited by the small sample
size (type II statistical error) and significant cost.
Furthermore, it was not possible to determine
from our data exactly when and for how long postoperative AF occurred. This prevented estimation of
the time frame for the increased risk of AF and
subsequent employment of prophylactic measures.
Moreover, the true incidence of AF may be underdiagnosed in our study by limiting the definition of
AF to episodes requiring treatment.
ACKNOWLEDGMENT: We thank Ellen Shair, MA, for her
editorial contribution. We also thank Sherryl A. Orwig, PA-C, and
Carol A. Wegman, PA-C, for their contributions to the completion of the study.
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