Asian Cardiovascular
and Thoracic Annals
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Clinical and echocardiographic predicators of postoperative atrial fibrillation
Mohamed Ahmed Elawady and Mohamed Bashandy
Asian Cardiovascular and Thoracic Annals published online 5 November 2013
DOI: 10.1177/0218492313503572
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Original Article
Asian Cardiovascular & Thoracic Annals
0(0) 1-5
ß The Author(s) 2013
Clinical and echocardiographic
predicators of postoperative
atrial fibrillation
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DOI: 10.1177/0218492313503572
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Mohamed Ahmed Elawady1,2 and Mohamed Bashandy1,3
Abstract
Background: Postoperative atrial fibrillation is the most common arrhythmia after coronary artery bypass grafting, with a
reported incidence of 10% to 60%. Preoperative clinical and echocardiographic data, especially the atrial electromech- anical
interval, predict postoperative atrial fibrillation in elective coronary artery bypass patients.
Methods: A prospective study evaluated preoperative clinical and echocardiographic data in 192 patients who under- went
elective coronary artery bypass from 2010 to 2012.
Results: 18 (9.37%) patients developed postoperative atrial fibrillation. Compared to patients without postoperative atrial
fibrillation, these 18 had significantly longer intensive care unit and hospital stays, they were significantly older (58.62 Æ
10.02 vs. 53.22 Æ 8.23 years; p ¼ 0.02), with a larger left atrial volume (83.39 Æ 8.31 vs. 55.47 Æ 8.37 cm3, p ¼ 0.001),
longer atrial electromechanical interval (133.67 Æ 8.15 vs. 98.05 Æ 6.71 ms p < 0.0001), and lower tissue Doppler imaging
systolic velocity wave amplitude (6.6 Æ 1 vs. 9.4 Æ 2.2 cmÁsÀ1; p ¼ 0.001); they also had a higher preva- lence of hypertension
(61.11% vs. 38.5%; p ¼ 0.04). Using 115 ms as the cutoff value of atrial electromechanical interval enabled us to detect patients
who developed postoperative atrial fibrillation with 100% sensitivity, 77% specificity, 78% positive predictive value, and 100%
negative predictive value.
Conclusion: Older hypertensive patients are at higher risk of developing postoperative atrial fibrillation. Preoperative
measurement of atrial electromechanical interval by tissue Doppler echocardiography is a useful predictor of
postoperative atrial fibrillation in coronary artery bypass patients.
Keywords
Atrial fibrillation, atrial function, left, blood flow velocity, coronary artery bypass, echocardiography, doppler
Introduction
Postoperative atrial fibrillation (POAF) is the most
common arrhythmia after coronary artery bypass graft- ing
(CABG), with a reported incidence of 10% to 60%.1-4
POAF is self-limiting in most cases, but even when
uncomplicated, its treatment requires additional medical and
nursing time. In a minority of cases, POAF
is associated with thromboembolic complications and
postoperative stroke, leading to longer intensive care
unit and hospital stays and significantly increased
costs.4,5 The onset of POAF in 70% of cases occurs during
the first 4 postoperative days, and only 6% develop atrial
fibrillation after the 6th day; 22% of these patients have 2
episodes of POAF.6 The exact pathophysiological
mechanisms responsible for the
onset and persistence of postoperative atrial arrhyth- mias
are incompletely understood. Factors facilitating POAF can
be classified as: acute factors directly related to surgery, such
as adrenergic stimulation; and factors that reflect a chronic
and progressive process of remodeling or ageing of the
heart, such as left atrial enlargement.7 Risk factors for POAF
include advanced
Saud Al-Babtain Cardiac Center, Dammam, Saudi Arabia
Cardiothoracic Surgery Department, Banha Faculty of Medicine, Banha
University, Egypt
3
Cardiology Department, Faculty of Medicine, Alazhar University, Egypt
1
2
Corresponding author:
Mohamed Ahmed Elawady, MD, Cardiothoracic Surgery Department,
Banha Faculty of Medicine, Banha University, Banha 2344, Egypt.
Email: mohamedawady@yahoo.com
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2
Asian Cardiovascular & Thoracic Annals 0(0)
age, male sex, low ejection fraction, hypertension, smoking,
and diabetes mellitus. 8 As atrial contractile dysfunction may
predict the development of POAF in patients undergoing
CABG, measurement of preopera- tive atrial function may be
useful to identify patients at increased risk of POAF.9
Doppler echocardiographic measurements of left atrial
function, such as transmitral filling velocities and atrial
filling fraction or atrial area changes by planimetry, failed to
predict POAF because transmitral flow velocities are more
dependent on the atrioventricular pressure gradient rather
than atrial contractility only, and it is highly sensitive to
changes in loading conditions.10 Tissue Doppler imaging, a
rela- tively new technology, allows direct noninvasive measurements of myocardial velocities.11 Direct assessment of the
mitral annular velocity during atrial systole by tissue
Doppler imaging analysis has proved to be sen- sitive and
reproducible for quantifying left atrial con- tractile function,
and it reflects atrial contractile function better than
transmitral atrial filling velocity, regardless of the severity
of diastolic dysfunction. 12 Assessment of possible left atrial
dysfunction in patients with coronary artery disease, by
tissue Doppler echocardiographic imaging of the mitral
annu- lus, especially measurement of the atrial electromechanical interval (AEMI) as a marker of atrial impairment,
could be helpful in predicting those at
risk of developing post-CABG atrial fibrillation.11,13
Patients and methods
A prospective study was undertaken from May 2010 to
May 2012 to assess preoperative clinical and echocardiographic data, especially AEMI, as predictors of POAF in
elective CABG patients at Saud Babtain Cardiac Center.
Inclusion criteria were elective CABG on conventional
cardiopulmonary bypass, left ventricu- lar ejection fraction
535%, preoperative sinus rhythm and no history of atrial
fibrillation. Exclusion criteria were age >70 years, history
of atrial fibrillation, chronic obstructive pulmonary disease,
poor left ven- tricular function, associated valvular heart
disease, renal failure on regular dialysis, recent preoperative
myocardial infarction (<1 month), emergency or urgent
CABG, redo CABG, current use of antiarrhyth- mic drugs,
of-pump CABG, and postoperative low cardiac output
syndrome. There were 192 eligible patients enrolled in this
study.
From the day of admission until the day of discharge, all
patients had a daily standard 12-lead electrocardio- gram
(ECG). In the cardiovascular intensive care unit, POAF was
detected using a Siemens SC 9000XL bedside arrhythmia
monitor (Siemens Medical Systems, Danvers, MA, USA).
Postoperatively, all patients were
monitored in the ward by continuous ECG telemetry
monitoring (Siemens). A 12-lead ECG was carried out if a
patient had atrial fibrillation, and a second 12-lead ECG was
obtained when they returned to sinus rhythm.
All patients underwent preoperative transthoracic
echocardiography with tissue Doppler imaging analysis
(Vivid 7; GE Medical Systems, Vingmed, Norway). The left
ventricular end-systolic and end-diastolic dimen- sions were
obtained according to the recommendations of the American
Society of Echocardiography, in para- sternal long-axis view
with the M-mode cursor pos- itioned just beyond the
mitral leaflet tips perpendicular to anteroseptal and
posterior left ven- tricular walls. Left atrial volume was
determined by the biplane area-length method, tracing the
endocar- dium and measuring the vertical axis of the left
atrium in apical 4- and 2-chamber views at the maximal atrial
dimension. The left ventricular ejection fraction was
assessed in 2-dimensional echocardiography by the modified
biplane Simpson method in apical 4- and 2-chamber views.
The A wave (late atrial filling vel- ocity) was measured
using pulsed-wave Doppler across the mitral valve in apical
4-chamber view with the line parallel to the flow and the
sample volume at the tip of the mitral valve leaflets; an
average of 3 con- secutive cardiac cycles was obtained. The
tissue Doppler property was activated to obtain myocardial
velocities, Am wave (peak velocity during atrial systole)
and AEMI (time interval from the onset of the P wave
in the surface ECG to the beginning of atrial systole) were
measured as the average of 3 cardiac cycles with the 3-mm
sample volume placed at the lateral mitral annulus in apical
4-chamber view.
All patients continued on their usual drugs including
aspirin until the morning of surgery, but clopidogrel was
stopped at least 5 days before surgery. All patients had a
midline sternotomy. The left internal mammary artery was
harvested and skeletonized. All operations were performed
using a conventional cardiopulmonary bypass machine with
crossclamping of the aorta, and antegrade cold blood
cardioplegic solution was given every 20 minutes.
Cardiopulmonary bypass was con- ducted using a membrane
oxygenator and mild hypo- thermia (351C).
All demographic data, preoperative, operative and
postoperative data were collected, and statistical ana- lysis
was conducted using SPSS version 18.0 software (SPSS,
Inc., Chicago, IL, USA). Values of continuous variables are
expressed as mean Æ standard deviation, and categorical
variables are expressed as numbers and percentages. The
studied variables were assessed by uni- variate analysis.
Continuous variables were compared using the unpaired t
test, and the chi-square test was used to compare categorical
variables. The best cutof point for the AEMI to predict the
possibility of POAF
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Elawady and Bashandy
3
Discussion
was defined by receiver-operating characteristic curve
analysis. A p value less than 0.05 was considered statistically significant.
Results
Eighteen (9.37%) patients developed POAF during
hospital stay (group 1) and 174 (90.63%) did not develop
POAF (group 2). All patients in group 1 suc- cessfully
reverted to sinus rhythm. Patients in group 1 were
significantly older than those in group 2, and the prevalence
of hypertension was significantly higher in group 1 (Table 1).
Table 2 shows the preoperative echo- cardiographic
parameters of both groups. Patients in group 1 had a
significantly larger mean left atrial
volume, lower tissue Doppler imaging mean A m wave
amplitude, and longer AEMI, but there were no statistically significant diferences between the 2 groups in terms
of left ventricular ejection fraction, left ventricu- lar endsystolic and end-diastolic dimensions, or trans- mitral A
wave amplitude. This study demonstrated that the use of
preoperative AEMI derived by Doppler tissue imaging as a
reflection of intraatrial conduction was useful in predicting
the development of POAF in CABG patients, with a cutof
value of 115 ms which carries a specificity of 77%, a
sensitivity of 100%, a positive predictive value of 78%, and
a negative pre- dictive value of 100%. There were no
significant difer- ences in operative data between groups, but
the mean intensive care unit and hospital stays were
significantly longer in group 1 (Table 3).
Table 1. Preoperative demographic data and clinical status of
patients undergoing coronary artery bypass, according to the
development of postoperative atrial fibrillation.
Variable
Group 1
(n ¼ 18)
Group 2
(n ¼ 174)
p value
Mean age (years)
Male
58.62 Æ 10.02
15 (83.33%)
53.22 Æ 8.23
153 (87.93%)
0.02
0.37
3 (16.67%)
21 (12.07%)
0.48
11 (61.11%)
67 (38.5%)
0.04
7 (38.89%)
70 (40.23%)
14 (77.78%)
6 (33.33%)
Female
Hypertension
Diabetes mellitus
Dyslipidemia
Smoker
Group 1
(n ¼ 18)
Group 2
(n ¼ 174)
p value
0.68
LV ejection fraction
Atrial volume (cm3)
43.83% Æ 6.55%
83.39 Æ 8.31
47.09%Æ8.9%
55.47 Æ 8.37
0.13
<0.001
142 (81.61%)
0.69
A wave (cmÁsÀ1)
49 (28.16%)
0.84
12 (66.67%)
98 (56.32%)
0.26
Beta blocker
15 (83.33%)
154 (88.51%)
0.46
ACE inhibitor
9 (50%)
84 (48.28%)
0.7
Calcium channel blocker
5 (27.78%)
51 (29.31%)
0.8
16 (88.89%)
148 (85.06%)
0.9
ACE: angiotensin-converting enzyme.
Table 2. Preoperative echocardiographic parameters according to
the development of postoperative atrial fibrillation.
Variable
Old myocardial infarction
Lipid lowering drugs
Post-CABG atrial fibrillation is associated with higher
morbidity and mortality rates.1-4 Perioperative administration of antiarrhythmic drugs, especially amiodar- one
intravenously and orally, was found to be efective in reducing
the incidence of POAF in patients undergo- ing CABG, but it
has many side efects, so it is wise to give it as a prophylactic
measure to certain groups of patients with higher risk of
POAF.14 Many studies have attempted to recognize risk
factors for POAF, concen- trating mainly on preoperative
echocardiographic par- ameters. Older age and poor left
ventricular function are considered the most important risk
factors for POAF;6,7,11,15-19 but other risk factors including
dia- betes, hypertension, dyslipidemia, and smoking have
given conflicting results.18 Some studies have focused on
preoperative AEMI derived by Doppler tissue
imaging as a predictor of POAF. 15-19
In our study, although the incidence of POAF was greater
in men, there was no significant sex diference between
groups, which has been a matter of debate in some
studies.16,18 Our POAF patients were older and had a greater
prevalence of hypertension than non- POAF patients, which
is similar to the findings of other studies which concluded
that POAF is more common in hypertensive patients, 4-8 and
those who developed POAF were significantly
older.15,16,18,19 This can be explained by more atrial fibrosis,
conduct- ive tissue abnormality, and muscle atrophy, which
occur with advanced age.17 In our study, diabetes, smoking,
and dyslipidemia were not considered dependant risk
factors for POAF, which is similar to many studies on
diabetes as a risk factor for POAF.6,7,15-19 We found no
diference between the 2 groups regarding the use of
preoperative drugs such as beta blockers, angiotensinconverting enzyme inhibi- tors, calcium antagonists, or lipid
lowering agents, in
agreement with previous findings.11,18,20
AEMI (ms)
Am wave (cmÁsÀ1)
39.6 Æ 1.8
133.67 Æ 8.15
41.2 Æ 4.4
0.12
98.05 Æ 6.71
<0.0001
6.6Æ1
9.4Æ 2.2
0.001
LVEDD (cm)
5.24 Æ 0.7
5.02 Æ 0.89
0.64
LVESD (cm)
3.74 Æ 0.67
3.63 Æ 0.87
0.78
AEMI: atrial electromechanical interval; Am wave: peak velocity during
atrial systole; LV: left ventricular; LVEDD: left ventricular end-diastolic
dimension; LVESD: left ventricular end-systolic dimension.
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4
Asian Cardiovascular & Thoracic Annals 0(0)
Group 1
(n ¼ 18)
Group 2
(n ¼ 174)
p value
CABG patients. The use of 115 ms as a cutof value
of AEMI can detect POAF in CABG patients with
77% specificity, 100% sensitivity, 78% positive predictive value, and 100% negative predictive value.
71.28 Æ 20.31
69.68 Æ 18.97
0.15
Funding
47.66 Æ 13.0
45.96 Æ 14.3
0.59
This research received no specific grant from any funding
agency in the public, commerical, or not-for-profit sectors.
3.1 Æ 0.6
2.9 Æ 0.6
0.41
48.7 Æ 11.3
26.9 Æ 3.9
0.001
9.46 Æ 1.1
7.76 Æ 0.8
0.007
Table 3. Perioperative data according to the development of
postoperative atrial fibrillation.
Variable
Cardiopulmonary
bypass (min)
Crossclamping (min)
No. of grafts
Intensive care unit
stay (h)
Hospital stay (days)
Conflict of interest statement
None declared
References
Although only patients with good left ventricular
function were included in our study, the preoperative left
ventricular ejection fraction in patients who devel- oped
POAF was lower but not significantly diferent between the 2
groups, as reported by Ac¸il and col- leagues20 but some
other studies noted significantly lower preoperative left
ventricular ejection fraction in patients who developed
POAF.11-17 Patients who devel- oped POAF had significantly
larger left atrial volumes than those without POAF, as found
by Ac¸il and col- leagues,20 which can be explained by
increased atrial muscle, shortening of the refractory period,
and pro- longation of atrial conduction time. Our study
demon- strated that preoperative AEMI was longer in
patients who developed POAF than those who maintained
sinus
rhythm
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vs.
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are similar to the findings of Roshanali and colleagues11 who
used tissue Doppler imaging-derived AEMI as a predictor of
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AEMI 115 ms was selected with 100% sensitivity so it
detected all patients who developed POAF; similarly,
Roshanali and colleagues11 used 120 ms as a cutof value of
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AEMI may be secondary to increased left atrial volume, and
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is secondary to increased left atrial volume. Further studies
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