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(Circulation. 2000;102:761.)
© 2000 American Heart Association, Inc.
Clinical Investigation and Reports |
From the Divisions of Cardiology, University of Michigan Medical Center, Ann Arbor, and Oakwood Hospital, Dearborn, Mich (E.G.D., M.A., F.M., S.A.S.), and the Division of Cardiothoracic Surgery, Oakwood Hospital, Dearborn, Mich (R.D.).
Correspondence to Emile Daoud, MD, 3545 Olentangy River Rd, Room 325, Columbus, OH 43214. E-mail egd{at}mocc.cc
| Abstract |
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Methods and ResultsIn a double-blind, randomized fashion, 118
patients who underwent open heart surgery were assigned to right atrial
pacing at 45 bpm (RA-AAI; n=39), right atrial triggered pacing at a
rate of
85 bpm (RA-AAT; n=38), or simultaneous right and
left atrial triggered pacing at a rate of
85 bpm (Bi-AAT; n=41).
Holter monitoring was performed for 4.8±1.4 days after surgery to
assess for episodes of atrial fibrillation lasting >5 minutes. The
prevalence of postoperative atrial fibrillation was significantly less
in the patients randomized to biatrial AAT pacing when compared with
the other 2 pacing regimens (P=0.02). An episode of
atrial fibrillation occurred in 4 (10%) of 41 patients in the Bi-AAT
group compared with 11 (28%) of 39 patients in the RA-AAI group
(P=0.03 versus Bi-AAT) and 12 (32%) of 38 patients in
the RA-AAT group (P=0.01 versus Bi-AAT). There was no
difference in the occurrence of atrial fibrillation between the right
atrial AAI and AAT groups (P=0.8). There was no
significant difference among the 3 groups with regard to the number of
postoperative hospital days (7.3±4.2 days), morbidity (5.1%), or
mortality rate (2.5%).
ConclusionsSimultaneous right and left atrial triggered pacing is well tolerated and significantly reduces the prevalence of postopen heart surgery atrial fibrillation.
Key Words: valves bypass surgery arrhythmia
| Introduction |
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| Methods |
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Study Protocol
The study design was approved by the Oakwood Hospital Human
Research Committee and was a double-blind protocol in which the
surgical staff and principal investigators and the patient were unaware
of the assigned pacing modality. Clinical data, lead
parameters, and Holter data were collected and recorded
into the database by independent blinded investigators.
Patients were randomly assigned in a double-blind fashion immediately
after surgery to 1 of 3 pacing modes: (1) right atrial pacing with an
inhibited mode at a rate of 45 bpm (RA-AAI; n=39); (2) right atrial
pacing with a triggered mode at a rate
10 beats greater than the
patients intrinsic sinus rate but not <85 bpm (RA-AAT; n=38); or (3)
simultaneous right and left atrial pacing (biatrial pacing)
with a triggered mode
10 beats greater than the patients sinus rate
but not <85 bpm (Bi-AAT; n=41). Triggered pacing with relatively rapid
rates was selected to suppress atrial ectopy and dispersion of
refractoriness. Atrial ectopy or an increase in dispersion of
refractoriness is frequently associated with induction of atrial
fibrillation.16 17 18 19 20 After completion of the surgical
procedure, 2 temporary unipolar epicardial leads (model 6500,
Medtronic, Inc) were attached to the anterior-superior aspect of the
right atrium, and a second pair of epicardial leads was attached to the
posterior-inferior aspect of the left atrium between the
coronary sinus and the right inferior
pulmonary vein (Figure 1
). The
lead was a multifilament, braided, stainless steel, insulated conductor
that terminated in an uninsulated 3-mm (surface area 7.5
mm2) stainless steel electrode. This electrode
was attached to a curved needle with polypropylene suture, and the
proximal end of the suture was coiled to reduce dislodgment. In
patients assigned to either RA-AAI or RA-AAT pacing, the right atrial
pair of unipolar leads was connected to an external pacemaker generator
(Pacesetter, Inc), and the proximal ends of the left atrial epicardial
pacing electrodes were taped to the chest wall. Biatrial pacing was
achieved by simultaneous bipolar pacing of the right and
left atria (Figure 1
). Pacing was performed at 3 times the
capture threshold, and the sensitivity was set at 0.25 mV. Pacing was
initiated within 12 hours after surgery and continued until 24 hours
before discharge, at which time the pacing leads were removed. There
were no complications related to removal of the leads.
|
After surgery, each patient was admitted to an intensive care unit and
was subsequently transferred to a monitored unit. An investigator
evaluated patients daily. Two-lead telemetric monitoring was performed
continuously until the day of hospital discharge or for
7 days after
surgery. Electrocardiographic data were stored for 24 hours and
reviewed on a daily basis. Arrhythmia detection and assessment
of pacemaker function were also screened through daily 3-lead Holter
monitors obtained for up to 5 days after surgery. Right and left atrial
capture threshold, sensitivity, and lead impedance were measured with a
portable pacing analyzer (Ventritex, Inc). An episode of atrial
fibrillation was counted if it persisted for >5 minutes. After an
episode of atrial fibrillation, atrial pacing was discontinued, and the
patient was withdrawn from further analysis. The cardiac
surgery team directed management of atrial fibrillation. Patients were
reevaluated in the cardiac surgery outpatient clinic
6 weeks after
surgery.
Statistical Analysis
Data were analyzed on an intention-to-treat basis.
Continuous variables are expressed as mean±1 SD. Continuous
variables were compared by means of a paired or unpaired
t test as appropriate. Multiple continuous variables
were compared by means of ANOVA. Categoric variables were compared
by means of
2 analysis.
Analysis of repeated measures was used to compare daily
measurement of the right and left atrial capture threshold,
sensitivity, and lead impedance. The time to first occurrence of atrial
fibrillation and the survival of pacing electrode function were
assessed by Kaplan-Meier analysis. A value of P
< 0.05 was considered significant.
| Results |
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ß-Receptor antagonists were prescribed in 101 (86%) of 118 patients. ß-Blocker therapy did not have a statistically significant impact on the prevalence of atrial fibrillation in any group (P=0.4).
Sinus rhythm was present in each patient when evaluated in the
cardiac surgery outpatient clinic
6 weeks after hospital
discharge.
Hospital Length of Stay and Morbidity and Mortality Rates
The length of hospitalization was not significantly different
among patients assigned to Bi-AAT (7.0±5.3 days), RA-AAI (6.6±2.6
days), and RA-AAT (7.7±3.8 days) pacing (P=0.6). The
frequency of major postoperative complications and deaths were similar
between treatment groups (P=1.00 and P=0.3,
respectively; Table 3
).
|
Lead Analysis
The duration of successful pacing was significantly less for
biatrial pacing (3.1±1.2 days) compared with right atrial pacing in an
inhibited mode (4.1±1.4 days, P=0.003) and with right
atrial pacing in a triggered mode (3.8±1.2 days, P=0.04).
There was no significant difference in the duration of successful
pacing when comparing RA-AAI with RA-AAT pacing (P=0.3). The
mean atrial rate was 92.4±8.2 bpm for the Bi-AAT group, 95.4±8.2 bpm
for the RA-AAT group (P=0.10 versus Bi-AAT), and 69.8±14.2
bpm in the RA-AAI group (P<0.0001 versus RA-AAT and
Bi-AAT). The mean amplitude of the measured P wave was 1.5±0.8 mV and
was not statistically different between groups (P=0.4).
Survival of right atrial leads was substantially greater than left
atrial leads (P<0.001; Figure 3
).
|
| Discussion |
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60%, is well-tolerated, and is not
associated with increased postoperative complications. Additionally,
right atrial pacing by itself has no significant antiarrhythmic
effect. Although biatrial pacing reduced episodes of postoperative AF, there was no reduction in the length of hospitalization. Since the safety of placing and removing left atrial active fixation leads was uncertain, patients were observed for complications for 1 day after lead removal. Therefore, patients without AF remained hospitalized an additional day but, for patients with AF, the leads were often removed while management of AF was ongoing. The absence of complications after removing the 4 leads implies that in future studies, patients can be discharged on the day that pacing wires are removed.
Possible Mechanisms
Two mechanisms may explain how simultaneous
right and left atrial triggered pacing at a rate faster than the
patients sinus rate prevented atrial fibrillation. The first is that
dispersion of atrial refractoriness is reduced with biatrial pacing.
Clinical studies have demonstrated that premature atrial contractions
result in dispersion of atrial refractoriness and establish nonuniform
anisotropic conduction, particularly near the coronary sinus
and posterior triangle of Koch.16 17 18 21 22 These regional
differences in atrial electrophysiology are essential for reentry,
which facilitates initiation of atrial fibrillation. In this study, a
triggered pacing mode was chosen to assure early activation of the
atrial myocardium near the coronary sinus in
response to premature atrial contractions sensed in either the right or
left atria and hence reduce atrial dispersion.
A second possible mechanism by which simultaneous biatrial triggered pacing may prevent atrial fibrillation is through the suppression of atrial ectopy. Atrial fibrillation is often initiated by a premature atrial beat, especially during periods of sinus bradycardia. Biatrial pacing at a relatively rapid rate may result in overdrive suppression of atrial ectopy that may have otherwise initiated atrial fibrillation.23 24 This latter mechanism seems less likely because overdrive suppression of atrial ectopy would also be expected with RA-AAT pacing. However, in the present study, AAT pacing from the right atrium had no effect on the prevalence of atrial fibrillation.
Previous Studies
Short- and long-term clinical trials have investigated the effect
of dual-site atrial pacing.13 14 15 18 21 22 The results of
these trials suggest that dual-site pacing, in combination with
antiarrhythmic therapy, increases the arrhythmia-free interval
and the percentage of patients who remain free of an atrial
fibrillation recurrence. The current study confirms these
findings and demonstrates that triggered biatrial pacing reduces the
prevalence of postoperative atrial fibrillation in patients not
receiving class I or III antiarrhythmic medications.
Two studies have assessed the effect of temporary epicardial atrial pacing for the prevention of postopen heart surgery atrial fibrillation.25 26 Neither study found biatrial pacing to be beneficial. However, both of these studies differ from the present study in several important ways. Neither of the earlier studies performed biatrial triggered pacing at a rate that was always faster than the patients intrinsic rate. Triggered pacing provides the theoretical advantage of reduced atrial dispersion and overdrive suppression of atrial ectopy. Next, in one of the earlier studies, adequate atrial sensing was difficult to achieve, and atrial undersensing may have initiated atrial fibrillation.25 In the current study, atrial sensing was set at 0.25 mV, thus reducing the likelihood of sensing failure. Finally, the present study enrolled 118 patients, whereas the previous studies only included 21 and 61 patients.25 26
Preliminary studies from other centers have demonstrated that biatrial pacing reduces postoperative atrial fibrillation.27 28 29 30 Three of these studies, however, did not control for the effect of placement of epicardial left atrial leads and/or the effect of continuous high-rate pacing.27 28 29 The fourth study30 had a design comparable to the current study and reported a similar degree of reduction (69%) in atrial fibrillation with biatrial pacing versus no pacing
Pacing Electrode Performance
Previous studies have reported that temporary atrial epicardial
electrodes are prone to failing.31 32 Although the lead
used in this study is reported to perform reasonably
well,33 34 >60% of right and 80% of left atrial
electrodes failed by the fifth postoperative day. In the present
study, the incidence of atrial fibrillation was greatest in the first 3
days after open heart surgery. Hence, later lead failure may not have
had a substantial impact on prevention of atrial fibrillation.
Surgical Technique
To optimize pacing parameters and to achieve
consistent positioning of the epicardial leads in a secure
fashion, only 1 surgeon participated in this study. Right atrial lead
placement was in a conventional position; however, the position of the
left atrial leads was chosen to preexcite the
posterior-inferior region of the left atrium near the
coronary sinus. Achieving a stable position in this area did
not result in excessive bypass pump times or complications.
ß-Blocker Therapy
The results of this study may reflect an additive effect of
biatrial pacing and ß-blockade, since 86% of patients were
administered ß-blockers. However, this seems unlikely because the
prevalence of atrial fibrillation among the 3 groups was unaffected by
ß-blocker therapy.
Clinical Implications
An ideal prophylactic approach is one that is
effective in a diverse patient population and that is associated with
minimal expense and risk. Biatrial pacing for prevention of atrial
fibrillation after open heart surgery may be such a technique. Unlike
class I or class III antiarrhythmic agents, biatrial pacing is not
associated with a risk of ventricular
proarrhythmia, bradycardia, or hypotension, nor does biatrial
pacing need to be initiated before surgery.10 Whether
future advances in electrode technology and pacing
algorithms35 or hybrid therapies, such as biatrial pacing
in conjunction with antiarrhythmic therapy, may further reduce the
prevalence of postoperative atrial fibrillation remains to be
determined.
| Acknowledgments |
|---|
Received December 20, 1999; revision received March 2, 2000; accepted March 10, 2000.
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