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orIginal papers
Adv Clin Exp Med 2013, 22, 4, 519–527
ISSN 1899–5276
© Copyright by Wroclaw Medical University
Marta Obremska1, A–D, F, Dorota Zyśko2, A–D, F, Rafał Nowicki1, A–D, F,
Anna Goździk1, A–D, F, Maciej Rachwalik1, A–D, F, Tomasz Grzebieniak3, A–C, E, F,
Wojciech Kustrzycki1, A–C, E, F
Temporary Resolution of Chronic Atrial Fibrillation
After Cardiac Surgery and the Prolongation
of Ventricular Repolarization
Przemijające ustąpienie utrwalonego migotania przedsionków
po zabiegu kardiochirurgicznym
związane z wydłużeniem okresu repolaryzacji komór
Department of Cardiac Surgery, Wroclaw Medical University, Wrocław, Poland
Teaching Department for Emergency Medical Services, Wroclaw Medical University, Wrocław, Poland
3
Department of Cardiology Wroclaw Medical University, Wrocław, Poland
1
2
A – research concept and design; B – collection and/or assembly of data; C – data analysis and interpretation;
D – writing the article; E – critical revision of the article; F – final approval of article; G – other
Abstract
Background. Chronic atrial fibrillation may temporarily resolve after cardiac surgery. Prolongation of the ventricular repolarization period may be the electrophysiological background for this phenomenon.
Objectives. The aim of the study was to assess the association between resolution of atrial fibrillation and changes
in the duration of the ventricular repolarization period in patients with pre-operative chronic atrial fibrillation who
underwent cardiac surgery.
Material and Methods. A retrospective analysis of the medical recordings of patients with chronic atrial fibrillation who underwent cardiac surgery was performed. After exclusions the study group comprised 51 patients
with chronic atrial fibrillation who underwent surgery in the Cardiac Surgery Department of Wrocław Medical
University in 2008 and 2009. The12-lead EKGs performed before and after the surgery were assessed and the QT
and R-R intervals were measured. The patients were divided into Group 1, in whom atrial fibrillation persisted after
the cardiac surgery, and Group 2, whose atrial fibrillation resolved after the surgery.
Results. In 31 patients (60.8%) atrial fibrillation disappeared during the first 24 hours after cardiac surgery. A significant prolongation of the QT interval after the surgery was found in Group 2 that was not observed in Group 1.
Multiple regression analysis revealed that QT interval duration after surgery is related to the resolution of atrial
fibrillation independently from the duration of the R-R interval duration and the need for cardiac pacing.
Conclusions. Spontaneous temporary resolution of atrial fibrillation is a common finding after cardiac surgery in
patients with chronic atrial fibrillation. This phenomenon is related to a prolonged QT interval, therefore it may
have an electrophysiological basis rather than a hemodynamic background. Further studies are required to assess
the clinical importance of the prolongation of the QT interval after cardiac surgery (Adv Clin Exp Med 2013, 22,
4, 519–527).
Key words: atrial fibrillation, QT interval, cardiac surgery.
Streszczenie
Wprowadzenie. U niektórych pacjentów z utrwalonym migotaniem przedsionków po zabiegu kardiochirurgicznym
obserwuje się zjawisko krótkotrwałego ustąpienia migotania przedsionków. Do tej pory nie prowadzono badań nad
powiązaniami tego zjawiska ze zmianami czasu trwania okresu repolaryzacji komór w okresie pooperacyjnym.
Cel pracy. Ocena zależności między wystąpieniem zjawiska ustąpienia migotania przedsionków a czasem trwania
okresu repolaryzacji mięśnia komór u pacjentów po operacji kardiochirurgicznej na otwartym sercu.
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M. Obremska et al.
Materiał i metody. Analiza retrospektywna dokumentacji pacjentów z utrwalonym migotaniem przedsionków,
którzy przebyli zabieg kardiochirurgiczny. Grupę badaną stanowiło 55 pacjentów operowanych w latach 2008–
–2009, u których przed operacją stwierdzono utrwalone migotanie przedsionków. Z badania wyłączono 2 pacjentów, u których po zabiegu kardiochirurgicznym była konieczna reoperacja w pierwszej dobie lub były stosowane
aminy katecholowe ze względu na stan oraz 2 pacjentów, u których była stosowana stała stymulacja serca w okresie przedoperacyjnym. Od 2009 r. w Klinice Chirurgii Serca jako rutynowe postępowanie stosuje się ablację lewego przedsionka i dlatego do badania nie włączono kolejnych pacjentów. Ostatecznie do badania zakwalifikowano
51 pacjentów w wieku 65,8 ± 9,2 lat, w tym 29 kobiet i 22 mężczyzn. Przeprowadzono analizę zapisu EKG przed operacją i w pierwszym dniu po operacji. Pacjentów podzielono na 2 grupy: grupa 1 – osoby, u których po zabiegu nadal
utrzymywało się migotanie przedsionków, oraz grupa 2 – osoby, u których migotanie przedsionków ustąpiło.
Wyniki. Ustąpienie migotania przedsionków w pierwszej dobie po zabiegu stwierdzono u 31 pacjentów, w tym
u 25 pacjentów rytm zatokowy oraz u 6 pacjentów rytm węzłowy. Nie stwierdzono istotnych różnic między wiekiem, rozkładem płci, rozkładem wykonywanych zabiegów kardiochirurgicznych, stężeniem potasu oraz częstością
stosowania czasowej stymulacji serca w pierwszej dobie po zabiegu między badanymi grupami. W pierwszej dobie
po zabiegu 8 pacjentów wymagało stosowania czasowej stymulacji serca, w tym 4 pacjentów z grupy 1 i 4 pacjentów
z grupy 2. Stwierdzono w grupie 2 istotne wydłużenie odstępu QT po zabiegu w porównaniu z jego czasem trwania
przed zabiegiem, czego nie obserwowano w grupie 1. (422 ± 67 ms vs 386 ± 41 p < 0.02; w grupie 1 (408 ± 70 ms vs
381 ± 42 ms, p = n.s.).W obu grupach nie stwierdzono istotnych różnic między czasem trwania odstępu R-R przed
i po zabiegu. Również czas trwania odstępu QTf i QTc po zabiegu jest istotnie dłuższy niż przed zabiegiem w grupie 2, a nie różni się istotnie w grupie 1. W przeprowadzonej analizie regresji wielokrotnej wykazano, że dłuższy
czas trwania odstępu QT po zabiegu jest związany z ustąpieniem migotania przedsionków (wystąpieniem rytmu
zatokowego lub węzłowego) niezależnie od czasu trwania odstępu R-R oraz stosowania stymulacji serca.
Wnioski. Przemijające ustąpienie migotania przedsionków jest częstym zjawiskiem po zabiegu kardiochirurgicznym u pacjentów z utrwalonym migotaniem przedsionków. Ustąpienie migotania przedsionków jest związane
z wydłużeniem odstępu QT. Obserwacja ta wskazuje na elektrofizjologiczne, a nie hemodynamiczne podłoże tego
zjawiska. Dalsze badania są potrzebne do oceny klinicznego znaczenia wydłużenia odstępu QT po zabiegu kardiochirurgicznym (Adv Clin Exp Med 2013, 22, 4, 519–527).
Słowa kluczowe: migotanie przedsionków, odstęp QT, operacja kardiochirurgiczna.
Metabolic disturbances during cardiac surgery
involving extracorporeal circulation are caused by
hypothermia, ischemia or reperfusion and may influence the electrophysiological properties of the
myocardium [1, 2]. The prolongation of the QTc
interval in such circumstances is a well-documented phenomenon that lasts up to 60 hours after surgery [3]. Prolonging the repolarization period of the atrial myocardium can lead to resolution
of atrial fibrillation in patients with pre-operative
chronic atrial fibrillation. However, atrial fibrillation usually returns if an additional ablation is
not performed [4–7]. To date no research has been
published concerning the relation between this
phenomenon and changes in the duration of repolarization during the early post-operative period.
The aim of this study was to assess the relationship between the incidence of resolution of
atrial fibrillation and the duration of the ventricular repolarization period in patients who underwent open heart surgery.
The study was approved by the local Bioethical Committee.
Material and Methods
The study group comprised 55 consecutive patients with pre-operative chronic atrial fibrillation
who were operated on in 2008 and 2009 at Wroclaw Medical University’s Department of Cardiac Surgery (Wrocław, Poland). Two patients were
excluded from the study because it was necessary
to perform a reoperation during the first 24 hours
after the cardiac surgery or to use catecholamine.
A further two patients were excluded because of
permanent pre-operative cardiac pacing. Since
2009, ablation of the left atrium has been routinely
performed, which is why no further patients were
included in the study.
All in all, a total of 51 patients (average age
65.8 ± 9.2 years) were studied, of which 29 were
women and 22 were men. Among the patients
studied, six underwent coronary artery surgery;
11 underwent both coronary artery and valvular
surgery; and 34 patients underwent valvular surgery, including three patients who had additional
Bentall surgery.
A 12-lead electrocardiogram was performed
on each patient both before the surgery and the
morning after the operation. The QT interval was
assessed by averaging three consecutive QT intervals, and the R-R interval was calculated by averaging the R-R intervals in a three-second strip of the
electrocardiogram.
Typically, the QT interval was calculated in
lead II, but in five cases where the T wave was
indistinct in that lead, lead V6 was used. In each
Chronic Atrial Fibrillation After Cardiac Surgery and the Prolongation of Ventricular Repolarization
patient, the same lead was assessed before and after the cardiac surgery.
An adjusted QT interval was calculated as
well, using the Framingham formula QTf = QT +
0.154(1 – R-R), where R-R and QT are expressed
in seconds, and using Bazett’s formula QTc=QT/
/(R-R)1/2.
The following clinical data were noted: co-existing conditions and their pharmacological treatment, potassium concentration after the cardiac surgery, and the use of temporary cardiac pacing after
surgery. For each patient, cardiopulmonary bypass,
aortic cross-clamp and reperfusion times as well as
echocardiographic parameters such as the left atrium diameter, the end diastolic diameter of the left
ventricle and the ejection fraction were noted.
The patients were divided into two groups:
Group 1 consisted of patients in whom atrial fibrillation persisted after the surgery, and Group 2
comprised subjects with atrial fibrillation that resolved after the surgery. Post-operative resolution
of atrial fibrillation lasting up to the morning of
the first post-operative day was observed in 31 patients (60.8%). At that time, sinus rhythm occurred
in 25 patients and junctional rhythm was found in
six patients. While the second ECG was being performed, eight patients (four from each group) required temporary cardiac pacing.
Statistical Analysis
Continuous variables were presented as mean
and standard deviation. Discrete variables were
presented as number and percentage. The significance of differences between the means of independent variables was assessed by the Student’s
t test and the Mann-Whitney U test; in cases of dependent variables it was assessed by the Student’s
t test for dependent variables and the Wilcoxon
test. The significance of the differences between
discrete variables was assessed by the chi2 test.
A ROC curve analysis was performed to find
the cut-off point for corrected QT intervals after the operation to distinguish patients with and
without chronic atrial fibrillation resolution with
the highest sensitivity and specificity.
A multiple regression analysis was performed
to examine relations between the duration of the
QT interval after surgery and the duration of R-R
interval, the use of cardiac pacing after surgery, the
resolution of atrial fibrillation, the patient’s gender, the patient’s age, reperfusion time and the
type of operation.
A second multiple regression analysis was performed to find associations between reperfusion
time and cross clamp time and atrial fibrillation
resolution.
521
A logistic regression analysis was performed
to assess relations between atrial fibrillation resolution on the first post-operative day and the type
of operation and the corrected QT interval above
the cut-off point.
The threshold of statistical significance was set
at p < 0.05.
Results
Demographics and Clinical Data
The patients’ demographics, clinical and echocardiographic data, concomitant treatment, the
type of surgery performed, aortic cross clamp
times and the necessity for cardiac pacing on the
first post-operative day are presented in Tables 1
and 2.
There were no statistically significant differences between the groups regarding age, gender
distribution, the type of surgery (with the exception of tricuspid valve repair), the plasma potassium level and the necessity for cardiac pacing
while the EKG on the first post-operative day was
performed.
The reperfusion time was significantly longer
in Group 1 than in Group 2.
Electrocardiographic Parameters
In Table 3, the duration of the QT, R-R, QTc
and QTf intervals before and after the surgery in
the studied groups is presented.
A significant prolongation of the QT interval
after the surgery was found in Group 2 (422 ± 67 ms
vs 386 ± 41 p < 0.02) but not in Group 1 (408 ± 70 ms
vs 381 ± 42 ms, p = ns.). The same was true of the
QTc and QTf parameters. The QTc on the first
post-operative day in Group 2 was also longer than
the QTc in Group 1, which was not the case when
QT and QTf duration were analyzed.
The ROC curve analysis revealed that a QTc
higher than 396 ms with high specificity and low
sensitivity correlated with atrial fibrillation resolution resolution (Fig. 1).
The multiple regression analysis revealed that
QT interval duration after surgery is related to the
resolution of atrial fibrillation independently from
the R-R interval duration and the necessity for cardiac pacing (Table 4).
The logistic regression analysis revealed that
a QTc on the first post-operative day higher than
396 was independently related to atrial fibrillation
resolution (OR 17.4 95% CI; 1.62–186.7), whereas
tricuspid valve repair was related to atrial fibrillation maintenance (OR: 5.2; CI: 1.29–21.1).
522
M. Obremska et al.
Table 1. Treated valvular diseases, CABG and Bentall procedures performed, cardiopulmonary bypass time, aortic cross
clamp time, reperfusion time
Tabela 1. Operowane wady zastawkowe, wykonywanie zabiegu CABG i Bentalla, czasy krążenia pozaustrojowego,
zakleszczenia aorty i reperfuzji
Group 1
(Grupa 1)
Group 2
(Grupa 2)
p
Mitral regurgitation n (%)
(Niedomykalność mitralna n (%))
13 (65)
21 (67)
ns.
Mitral stenosis n (%)
(Stenoza mitralna n (%))
7 (35)
8 (26)
ns.
Aortal regurgitation n (%)
(Niedomykalność aortalna n (%))
4 (20)
6 (19)
ns.
Aortal stenosis n (%)
(Stenoza aortalna n (%))
2 (10)
5 (16)
ns.
Tricuspid regurgitation n (%)
(Niedomykalność trójdzielna n (%))
14 (70)
10 (32)
< 0.01
Valvular surgery n (%)
(Zabieg na zastawkach n (%))
13 (65)
18 (58.1)
ns.
CABG n (%)
(Pomosty wieńcowe n (%))
3 (15)
3 (9.7)
ns.
CABG and valvular surgery n (%)
(Pomosty wieńcowe i zabieg na zastawkach n (%))
4 (20)
7 (22.6)
ns.
Bentall and valvular surgery n (%)
(Operacja Bentalla i zabieg na zastawkach n (%))
0 (0)
3 (9.7)
ns.
Cardiopulmonary bypass time (min)
(Czas krążenia pozaustrojowego (min))
126.6 ± 35.9
111.8 ± 42.3
ns.
Aortic cross-clamp (min)
(Czas zakleszczenia aorty (min))
59.8 ± 24.4
64.1 ± 30.8
ns.
Reperfusion time (min)
(Czas reperfuzji (min))
66.8 ± 24.2
47.7 ± 18.42
< 0.01
Serious ventricular arrhythmic events occurred in two patients (3.9%), both of whom were
in Group 2.
The phenomenon of chronic atrial fibrillation
resolution had a transitory nature, and on the third
post-operative day only two patients maintained
a rhythm different to atrial fibrillation (one patient
had sinus rhythm, the other atrial tachycardia).
It was found that reperfusion time was related to the cross clamp time and AF resolution
(Table 5).
Discussion
Spontaneous conversion to sinus rhythm in patients with chronic atrial fibrillation has been described in the case of severe hyperkalemia [8] and
after electrocardioversion [9]. Those observations
point out the sustaining action of the sinoatrial
mode over a period of long-term atrial fibrillation
and the possibility of regaining its pacing function
after fibrillatory atrial wave suppression. Moreover, in cases of sinoatriale node inefficiency, nodal escape rhythm may occur.
The main finding of the current study was
that temporary resolution of chronic atrial fibrillation after cardiac surgery is related to the prolongation of the QT interval. Although the QT interval represents the repolarization process of the
ventricles and not the atria, in most cases atrial
and ventricular repolarization prolong and shorten together [10–14]. Atrial but not ventricular repolarization is prolonged after potassium channel blockers specific for the atria, such as IKur, are
used. However, in that case the QT interval is not
changed. Given these relationships, it can be assumed that the mechanism leading to the resolution of atrial fibrillation in this case is prolonged
atrial repolarization.
The restoration of sinus rhythm in patients
with chronic atrial fibrillation after cardiac surgery
Chronic Atrial Fibrillation After Cardiac Surgery and the Prolongation of Ventricular Repolarization
523
Table 2. Demographics, clinical, echocardiographic data and operative variables
Tabela 2. Dane demograficzne, klinicznej i dotyczące zabiegu chirurgicznego
Group 1
(Grupa 1)
n = 20
Group 2
(Grupa 2)
n = 31
p
Male sex (%)
(Płeć męska (%))
30
52
ns.
Age (mean±SD)
(Wiek (średnia ±SD))
66.7 ± 10.0
65.2 ± 8.7
ns.
Arterial hypertension n (%)
(Nadciśnienie tętnicze n (%))
10 (50)
21 (68)
ns.
Diabetes (%)
(Cukrzyca (%))
2 (10)
8 (26)
ns.
Hypothyreosis n (%)
(Niedoczynność tarczycy n (%))
4 (20)
2 (6.5)
ns.
COPD n (%)
(POCHP n (%))
3 (15)
1 (3)
ns.
Previous myocardial infarction (%)
(Uprzedni zawał serca (%))
4 (20)
4 (13)
ns.
Beta-blocker (%)
(Leki blokujące kanał beta (%))
13 (65)
25 (81)
ns.
Digoxin (%)
(Digoksyna (%))
6 (30)
10 (32)
ns.
ACEI n (%)
(IEK n (%))
11 (55)
14 (45)
ns.
Amiodarone n (%)
(Amiodaron n (%))
0 (0)
0 (0)
ns.
Thiazyde n (%)
(Tiazydy n (%))
1 (5)
5 (16)
ns.
Spironolacton n (%)
(Spironolokton n (%))
9 (45)
12 (39)
ns.
Furosemide n (%)
(Furosemid n (%))
8 (40)
17 (55)
ns.
COPD – chronic obstructive pulmonary disease.
CABG – coronary artery bypass graft.
EF – ejection fraction.
LA – left atrium diameter.
LVEDd – left ventricular diastolic diameter.
ACEI – angiotensin converting enzyme inhibitor.
POCHP – przewlekła obracyjna choroba płuc.
CABG – przęsłowanie tętnic wieńcowych.
EF – frakcja wyrzutowa.
LA – wymiar lewego przedsionka.
LVEDd – wymiar rozkurczowy lewej komory.
IEK – inhibitor enzymu konwertującego angiotensynę.
is a well-known phenomenon [4]. However, this
phenomenon usually lasts a very short time unless ablation of the left atrium is performed as
well [6, 15, 16].
The possibility of proarrhythmia after orthotropic heart transplantation has been systematically
examined, but the results of those studies cannot be
applied to the study population. A transplanted heart
is vegetatively denervated, and among other factors
that may account for the problem of prolonged QT
intervals and ventricular arrhythmias is the use of
amiodaron to treat arrhythmia of the native heart
and the post-surgical use of immunosuppressive
drugs, which prolong the QT interval [17, 18].
It has been reported that the sinus node myocardial fibers are more resistant to cardioplegia
than other myocardial fibers [19], which may be
related to the temporary conversion of atrial fibrillation to sinus rhythm.
The results obtained in the current study indicate that there is a connection between the resolution of atrial fibrillation and the prolongation
of the repolarization period shortly after cardiac
surgery. Measurement of the atrial repolarization
524
M. Obremska et al.
Table 3. Duration of QT, R-R and QTf intervals before cardiac surgery and on the first post-operative day
Tabela 3. Czas trwania odstępu QT, R-R I QTf przed i w czasie pierwszego dnia po zabiegu kardiochirurgicznym
Group 1
(Grupa 1)
n = 20
Group 2
(Grupa 2)
n = 31
p
QT (ms) before
(QT (ms) przed)
381 ± 42
386 ± 41
ns.
R-R (ms) before
(R-R (ms) przed)
826 ± 169
787 ± 154
ns.
QTc (ms) before
(QTc (ms) przed)
423 ± 44.1
439 ± 41.4
ns.
QTf (ms) before
(QTf (ms) przed)
381 ± 41
381 ± 44
ns.
QT (ms) on the first post-operative day
(QT (ms) pierwszy dzień pooperacyjny)
408 ± 70
422 ± 67*
ns.
R-R (ms) on the first post-operative day
(R-R (ms) pierwszy dzień pooperacyjny)
845 ± 197
739 ± 155
< 0,05
QTf (ms) on the first post-operative day
(QTf (ms) Pierwszy dzień pooperacyjny)
408 ± 70
421 ± 67*
ns.
QTc (ms) on the first post-operative day
(QTc (ms) pierwszy dzień pooperacyjny)
449 ± 68.7
494 ± 67.7**
< 0.05
* – p < 0.02 for: QT before operation vs first post-operative day.
– p < 0.02 for: QTf before operation vs first post-operative day.
** – p < 0.05 for: QTc before operation vs first post-operative day.
#
* – p < 0,02 dla: QT przed operacją vs pierwszy dzień po operacji.
#
– p < 0,02 dla: QTf przed operacją vs pierwszy dzień po operacji.
** – p < 0,05 dla: QTc przed operacją vs pierwszy dzień po operacji.
Table 4. Multiple regression of dependent variable QT interval duration on the first post-operative day.
R2 = 0.36 adjusted R2 = 0.31
Tabela 4. Regresja wielokrotna zmiennej zależnej czas trwania odstępu QT w pierwszym dniu po zabiegu
kardiochirurgicznym. R2 = 0,36 skorygowany R2 = 0,31
BETA
SE
BETA
Bł. St BETA
b
SE b
Bł st b
p
AF resolution (Ustąpienie AF)
0.27
0.12
38
17.0
< 0.05
R-R interval (Odstęp R-R)
0.49
0.12
0.19
0.05
< 0.001
Pacing (Stymulacja)
0.32
0.12
60
21.9
< 0.01
AF – atrial fibrillation.
SE – standard error.
BETA – the standardized regression coefficients.
b – the raw regression coefficients.
R2 – coefficient of determination.
Adjusted R2 – adjusted coefficient of determination.
AF – migotanie przedsionków.
Bł. St. – błąd standardowy.
BETA – standaryzowane współczynniki regresji.
b – niestandaryzowane współczynniki regresji.
R2 – współczynnik determinacji.
Skorygowany R2 – skorygowany współczynnik determinacji.
period is not possible by noninvasive methods. It
could be presumed that prolongation of ventricular repolarization may indicate simultaneous prolongation of atrial repolarization, but that assumption requires further investigation.
Metabolic disorders caused by extracorporeal
circulation might be the reason for the prolongation of the repolarization period of the myocardium caused by the cardiac surgery. The lack of correlation between the size of the left atrium, surgical
525
Chronic Atrial Fibrillation After Cardiac Surgery and the Prolongation of Ventricular Repolarization
Table 5. Multiple regression. Dependent variable: reperfusion time. R2 = 0.36 adjusted R2 = 0.29
Tabela 5. Regresja wielokrotna. Zmienna zależna czas reperfuzji. R2 = 0,36 skorygowany R2 = 0,29
BETA
SE
BETA
Bł. St BETA
b
SE b
Bł st b
p
Cross clamp time
(Czas zakleszczenia aorty)
0.30
0.13
0.23
0.10
< 0.05
AF resolution
(Ustąpienie AF)
–0.40
0.13
–18.2
6.0
< 0.001
AF – atrial fibrillation.
SE – standard error.
BETA – the standardized regression coefficients.
b – the raw regression coefficients.
R2 – coefficient of determination.
Adjusted R2 – adjusted coefficient of determination.
Fig. 1. ROC analysis. QTc on the first post-operative day
Ryc. 1. Analiza ROC. QTc pierwszego dnia po operacji
Area under the ROC curve (AUC)
(Pole pod krzywą)
0.681
Standard error
(Błąd standardowy)
0.0748
95% Confidence interval
(95% przedział ufności)
0.535 to 0.804
z statistic
(z statystyka)
2.415
Significance level P (Area = 0.5)
(Poziom istotności)
0.0157
variables and the occurrence of atrial fibrillation
resolution highlights the importance of individual sensitivity to factors extending the QT period in
the occurrence of this phenomenon.
AF – migotanie przedsionków.
Bł. St. – błąd standardowy.
BETA – standaryzowane współczynniki regresji.
b – niestandaryzowane współczynniki regresji.
R2 – współczynnik determinacji.
Skorygowany R2 – skorygowany współczynnik determinacji.
It is well known that in patients with pre-operative sinus rhythm, atrial fibrillation occurs in
15–24% of the cases on the second or third day after the cardiac surgery [20–21]. These data do not
contradict the results of the current study; in fact
they confirm the current results, because the prolongation of the repolarization period was noted shortly after surgery – a timespan in which the
higher risk of atrial fibrillation does not occur.
The current research found complex ventricular arrhythmias occurring in about 4% of the patients. Other authors have reported an increased
incidence of serious ventricular arrhythmias after
cardiac surgery — in large groups of patients there
was a 0.95% probability of atrial fibrillation [22]
and a 2.9% probability of unsustainable ventricular tachycardia occurring [23]. The differences between the results of the current research and those
reported by other authors might be related to the
small size of the current study group. The possibility can’t be excluded that the higher frequency
of serious cardiac dysrhythmias after cardiac surgery in the current study was caused by qualifying patients with pre-operative atrial fibrillation
to the study group; other authors have shown that
this particular group has a higher risk of complications [24, 25]. A case report of a patient from the
study group was presented in a recently published
article [26].
The small size of the study group precluded
the assessment of a correlation between the occurrence of ventricular arrhythmias and the magnitude of QT interval prolongation after cardiac
surgery. Other noninvasive electrocardiographic
parameters which could predict serious arrhythmic events [27] were not assessed.
The prolongation of the QT interval in patients
who experienced temporary resolution of atrial fibrillation seems to be related to electrophysiological
526
M. Obremska et al.
changes rather than the hemodynamic ones. Other
authors have also attributed changes they observed
in the repolarization process in patients who had
undergone aortic valve surgery to electrophysiological changes rather than structural remodeling [28, 29].
An important factor that could affect cardiac
electrophysiological changes in the post-operative
period is the duration of the cardiopulmonary bypass and its components: the aortic cross-clamp
time and the reperfusion time. In the current
study group, these times were about 10–20% longer than those presented in the literature [30]. In
this study, there was no statistically significant difference between the times of the cardiopulmonary
bypass in the two groups of patients, but the reperfusion times differed significantly, being shorter
in the group in which temporary resolution of atrial fibrillation occurred. The multiple linear regression analysis revealed that the time to reperfusion
was positively correlated to the duration of aortic
cross-clamping and negatively correlated to persistence of atrial fibrillation.
While the relationship between reperfusion
time and cross-clamp time is easy to explain (longer cross-clamp time results in longer reperfusion
time), the cause of the observed relationship between the time of reperfusion and the observed
rhythm is difficult to explain. On the one hand,
properties of cell membranes that lead to prolonged repolarization may shorten the reperfusion
time; on the other hand, it is possible that a very
short reperfusion time despite achieving adequate
hemodynamic parameters leads to prolonged repolarization and temporary resolution of atrial
fibrillation.
The authors concluded that spontaneous transient resolution of atrial fibrillation is a common
finding after cardiac surgery in patients with chronic atrial fibrillation. Resolution of atrial fibrillation
is related to QT interval prolongation, which indicates that prolongation of myocardial repolarization is the electrophysiological background of that
phenomenon. Further studies are required to assess the clinical importance QT interval prolongation after cardiac surgery.
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Address for correspondence:
Dorota Zyśko
Teaching Department for Emergency Medical Services
Wroclaw Medical University
Bartla 5
50-618 Wrocław
Poland
Tel.: +48 600 125 283
E-mail: [email protected]
Conflict of interest: None declared
Received: 21.08.2012
Revised: 25.02.2013
Accepted: 12.08.2013