From the Department of Cardiology, Skejby Sygehus, Aarhus University
Hospital, Aarhus, Denmark.
Correspondence to Henning Rud Andersen, MD, DMSc, Department of Cardiology, Skejby Sygehus, Aarhus University Hospital, 8200 Aarhus N, Denmark.
Methods—Two hundred twenty-five consecutive patients with sick
sinus syndrome and intact AV conduction were randomized to undergo
single-chamber atrial pacing (110 patients) or single-chamber
ventricular pacing (115 patients). Follow-up after 3 months
and then yearly included measurement of the PQ interval and, in
patients with atrial pacemakers, determination of the atrial
stimulus–Q intervals at pacing rates of 100 and 120 bpm. The
occurrence of AV block in the atrial group was recorded. During
follow-up (mean, 5.5±2.4 years), there was no change in PQ interval in
either group and no change in atrial stimulus–Q intervals or
Wenckebach block point in the atrial group. Four of 110 patients in the
atrial group developed grade 2 to 3 AV block that required upgrading of
the pacemaker (0.6% per year). Two of these 4 patients had right
bundle-branch block at pacemaker implantation.
Conclusions—AV conduction, estimated as PQ interval and atrial
stimulus–Q interval at atrial pacing rates of 100 and 120 bpm and the
Wenckebach block point, remains stable during long-term follow-up.
Thus, treatment with single-chamber atrial pacing is safe and can be
recommended to patients with sick sinus syndrome without bundle-branch
block.
Follow-up visits occurred after 3 and 12 months and subsequently once a
year. At each follow-up visit, PQ interval at sinus rhythm, Stim-Q100,
and Stim-Q120 were measured as parameters of AV conduction
in patients with atrial pacemakers (and without atrial fibrillation).
In patients with ventricular pacemakers, PQ interval was
measured during sinus rhythm. Furthermore, the follow-up visits
included physical examination, 12-lead ECG, and pacemaker check-up.
Follow-up evaluation was not blinded.
Termination of Study
Ethics
Analysis
Ninety-four patients (85%) randomized to undergo atrial pacing were
treated as randomized during follow-up. Of the remaining 16 patients
randomized to undergo atrial pacing, ventricular leads were
initially implanted in 6 patients; the reasons were Wenckebach block at
<100 bpm on the atrial pacing test (1 patient), atrial fibrillation
during implantation (2 patients), intra-atrial electrogram of <2.5 mV
(2 patients), and high stimulation threshold (1 patient). After
implantation, 1 patient developed a high stimulation threshold on the
first postoperative day and instead had the lead implanted in the right
ventricle. During follow-up, 4 patients had ventricular
leads implanted because of infection after 3 months (1 patient), lead
fracture after 1 year (1 patient), isolation defect of a bipolar lead
after 3 years (1 patient), and loss of atrial sensing after 6 years (1
patient). The physicians in charge of the repeat operations chose to
implant ventricular leads instead of new atrial leads in
these 4 patients, although no AV block was documented. In 1 patient
with bradytachy syndrome, it was necessary to replace a
defective pacemaker after 6 years. During pacemaker replacement, the
patient had paroxysmal atrial fibrillation, and although the atrial
lead was intact, the physician in charge of the operation chose to
implant an additional ventricular lead and a new
dual-chamber pacemaker. The pacemaker system was upgraded to a
dual-chamber system in 4 patients because of AV block.
One hundred nine patients (95%) randomized to undergo
ventricular pacing were treated as randomized during
follow-up. All patients randomized to undergo ventricular
pacing were discharged from the hospital with ventricular
pacing. During follow-up, 1 patient had the pacing system changed to
atrial pacing; in an additional 3 patients, an upgrade to a
dual-chamber system was necessary, and 2 patients had the pacemaker
system explanted.1
PQ Interval During Follow-Up
Atrial Stimulus–Q Intervals and Wenckebach Block Point During
Follow-Up
The 4 patients with right bundle-branch block at implantation who did
not develop AV block and 5 of 6 patients with fascicular block at
implantation all had a Wenckebach block point of
Development of AV Block in the Atrial Group
Influence of Medication During Follow-Up
Among the 34 patients in the atrial group in whom the Wenckebach
block point changed between consecutive follow-up visits (Figure 3
The 0.6% annual incidence rate of AV block requiring upgrade of
the pacemaker system found in the present prospective study
confirms observational findings; most studies have reported an annual
incidence rate of significant AV block of
<1%.12 13 14 15 16 17 18 19 In a literature survey of 28 studies
of atrial pacing, Rosenqvist and Obel20 reported
an annual incidence rate of second- and third-degree AV block of 0.6%
per year. Similarly, in an observational study performed by Bernstein
et al12 of 187 patients, an 0.9% annual
incidence rate of second- and third-degree AV block was reported, and
Witte et al13 reported first- to third-degree AV
block or fascicular block in 11 of 261 patients (0.8% per year).
However, a higher incidence of high-degree AV block (1.8% per year)
was reported by Brandt et al,21 probably because
more patients with bundle-branch block and bifascicular block were
included in their study.
As indicated by the results of the present study and several
observational studies,15 21 22 23 24 the presence of
bundle-branch block at the time of implantation is associated with an
increased risk of the development of AV block, whereas isolated
fascicular block is not associated with such a
risk.21 22 Thus, the present study confirms
that single-chamber atrial pacing should be avoided in patients with
right bundle-branch block, as is the case in patients with left
bundle-branch block, whereas it can still be used in patients with
isolated fascicular block. Patients with right or left bundle-branch
block should be treated with a dual-chamber pacemaker.
The present trial is the first prospective study to document
that PQ interval and atrial stimulus–Q interval at atrial pacing rates
of 100 and 120 bpm remain stable during long-term follow-up in patients
with sick sinus syndrome. Criteria used for the selection of patients
for inclusion in the present study were PQ interval of
In several patients in the present study, the Wenckebach
block point changed 2, 3, or even 4 times during follow-up, with or
without changes in medication. That demonstrates that the atrial
stimulus–Q interval and Wenckebach block point undergo large
spontaneous variations over time, probably influenced by
physiological variables such as autonomous
tone.26 27 This further illustrates that the
Wenckebach block point measured at the time of implantation is a poor
predictor for late deterioration of AV conduction.
In the present study, PQ interval increased slightly in the
ventricular group but not in the atrial group during
follow-up. The cause of prolongation of the PQ interval in the
ventricularly paced patients is not known, but it might be
associated with the increased left atrial dilatation seen in this
group.2 The enlarged atrium might result in a
prolonged intra-atrial conduction time,28 which
is reflected in the 12-lead ECG as a prolonged PQ interval.
In the atrial group, more patients were treated with
antiarrhythmic agents by the last follow-up than at the time of
pacemaker implantation. This probably reflects that many antiarrythmic
drugs which caused bradycardia were withdrawn prior to pacemaker
implantation and introduced again after pacemaker implantation.
However, despite the increase in the use of antiarrhythmic medication,
AV conduction remained stable during follow-up.
Why should single-chamber atrial pacing be used instead of
dual-chamber pacing? Dual-chamber pacing protects the patients in case
of AV block or atrial fibrillation with bradycardia, whereas patients
with atrial pacemakers require repeat operation with upgrade of the
pacemaker if 1 of these situations occurs. However, very few patients
with sick sinus syndrome and atrial pacemakers develop
ventricular bradycardia and must be exposed to the risk of
repeat operation. Some observational studies indicate that dual-chamber
pacing is superior to single-chamber ventricular pacing in
patients with sick sinus syndrome.29 30 31 On the
contrary, the largest observational study that compared the use of
dual-chamber pacing with ventricular pacing failed to
demonstrate any differences in the rates of congestive heart
failure32 or death33
between the 2 groups, which may indicate that ventricular
stimulation caused by dual-chamber pacing has the same harmful effect
on the heart as ventricular stimulation caused by
single-lead ventricular pacing.34 35
In the prospective randomized PASE trial that compared dual-chamber
pacing with single-chamber ventricular pacing, the 1-year
incidence rates of death and stroke were less in the group treated with
dual-chamber pacing, but the differences between groups were not
significant.36 Thus, the beneficial effect of
dual-chamber pacing versus ventricular pacing has not yet
been documented in prospective trials, whereas it has been demonstrated
that single-chamber atrial pacing is superior to single-chamber
ventricular pacing.1 2 Therefore,
based on prospective data, single-chamber atrial pacing should be
considered the treatment of choice in patients with sick sinus syndrome
and normal AV conduction.
Conclusions
Received January 16, 1998;
revision received May 21, 1998;
accepted June 3, 1998.
© 1998 American Heart Association, Inc.
Clinical Investigation and Reports
Atrioventricular Conduction During Long-Term Follow-Up of Patients With Sick Sinus Syndrome
Abstract
Top
Abstract
Introduction
Methods
Results
Discussion
References
Background—It has been claimed
that patients with sick sinus syndrome have an increased risk of
developing AV block, but this has never been assessed prospectively.
The aim of the present study was to evaluate in a prospective trial
AV conduction during the long-term follow-up of patients with sick
sinus syndrome.
Key Words: sick sinus syndrome • pacing • atrioventricular block • follow-up studies
Introduction
Top
Abstract
Introduction
Methods
Results
Discussion
References
In prospective randomized evaluation, single-chamber
atrial pacing is superior to single-chamber ventricular
pacing in patients with sick sinus syndrome due to lower overall and
cardiovascular mortality rates, less atrial
fibrillation, less arterial thromboembolism, and less heart
failure.1 Therefore, it has been recommended that
such patients be treated with single-chamber atrial
pacing.1 2 3 In retrospective analyses, it
has been claimed that patients with sick sinus syndrome have an
increased risk of developing AV block after the implantation of an
atrial pacemaker,4 5 6 but until now this risk has
never been assessed prospectively. Based on the claimed risk reported
in retrospective analyses, it is frequently recommended in the
literature that a ventricular pacemaker lead also be
implanted into these patients.4 5 7 Therefore,
when a physiological pacemaker system is selected
for patients with sick sinus syndrome, a dual-chamber pacing system is
most often implanted instead of a single-chamber atrial pacing
system.8 This strategy is chosen despite the lack
of prospective data to document the risk of AV block and despite the
lack of prospective trials to document the superiority of dual-chamber
pacing over single-chamber atrial or ventricular
pacing.9 The aim of the present prospective
study was to evaluate the AV conduction and the risk of developing AV
block during long-term follow-up of patients with sick sinus
syndrome.
Methods
Top
Abstract
Introduction
Methods
Results
Discussion
References
The study design has been described in detail
previously.1 10 The trial was conducted as a
single-center study at Skejby University Hospital. All patients who
were referred to receive treatment with their first pacemaker during
the recruitment period of May 15, 1988, through December 31, 1991, were
evaluated for randomization. The patients were asked to participate in
the trial if the inclusion criteria (symptomatic
bradycardia of <50 bpm or symptomatic QRS pauses of >2
seconds) and none of the exclusion criteria were
met.10 After giving informed consent, patients
were randomized before implantation to receive treatment with
single-chamber atrial or ventricular pacing stratified in
blocks of 10-year age groups. Medical history, physical examination,
12-lead standard ECG, and echocardiography were
done before implantation. Patients were excluded from randomization who
had grade 1 AV block defined as a PQ interval of >0.22 second in
patients 
70 years old and >0.26 second in patients >70 years
old,11 grade 2 or 3 AV block, or bifascicular or
complete left bundle-branch block. Right bundle-branch block or
fascicular block was not considered a contraindication for inclusion in
the study. Patients underwent an atrial pacing test during pacemaker
implantation at 100 and 120 bpm; 1:1 atrioventricular
conduction at 100 bpm was required for an atrial pacemaker to be
implanted. If second-degree AV block occurred at a pacing rate of <100
bpm, the lead was implanted in the right ventricle. PQ interval during
sinus rhythm and atrial stimulus–Q interval at atrial pacing rates of
100 bpm (Stim-Q100) and 120 bpm (Stim-Q120) were determined at
pacemaker implantation in all patients. Medical treatment was not
discontinued before implantation.
In 1995, it was decided that the last patient included should be
followed up for 5 years before final data analysis, which was
determined to be performed on December 31, 1996.
The study was approved by the National Danish Ethical Committee
and was conducted in accordance with the rules of the Helsinki
Declaration.
Power calculations were done before start of the study and have
been reported previously.10 All statistical
analyses were done according on an intention-to-treat basis.
Continuous variables are expressed as mean (SD) values. Treatment
groups were compared with the use of 
2 test
(2-tailed) for discrete variables and of 2-tailed Student's
t test or paired t test for continuous
variables. Changes in parameters of AV conduction
within treatment groups were analyzed by comparing mean values
before pacemaker implantation with mean values at last follow-up (last
ambulatory visit before end of study or death of patient) with the use
of a paired t test. Changes between groups were evaluated by
comparing mean values at the time of implantation, mean values at the
time of last follow-up, and mean change from pacemaker implantation to
last follow-up with the use of a Student's t test. To
reduce the number of statistical tests, intergroup comparisons were not
done repeatedly at several time points after implantation—only at the
last follow-up or on change from implantation to last follow-up. A
P value of <0.05 was deemed significant. SPSS for Windows
was used for statistical analysis.
Results
Top
Abstract
Introduction
Methods
Results
Discussion
References
A total of 225 patients (142 women and 83 men; mean age, 76 years;
age range, 50 to 92 years) were randomized to undergo atrial
pacing (110 patients) or ventricular pacing (115 patients),
respectively. Baseline parameters in the 2 groups have been
reported previously10 and were equal between
groups. Baseline parameters of AV conduction are shown in
Table 1
. A total of 1294 ambulatory
visits were performed during the study period, and no patients were
lost to follow-up. One patient, who emigrated after the 1-year
follow-up visit, underwent subsequent follow-up by telephone interview,
but no ECG recordings were accessible for this patient. Mean
follow-up until death or end of study was 5.5 (2.4) years for the total
study population and equal in the atrial (5.7 [2.3] years) and
ventricular (5.3 [2.5] years) groups.
View this table:
[in a new window]
Table 1. Baseline ECG
Variables
A total of 1515 investigational 12-lead ECGs were evaluated during
the study (767 in the atrial group and 748 in the
ventricular group). PQ intervals in the atrial and
ventricular groups are shown in Figure 1. At inclusion in the study, there was
no difference in PQ interval between the 2 groups (Table 1
). Mean
follow-up time of PQ interval was significantly longer in the atrial
group (4.7 [2.3] years) than in the ventricular group
(3.9 [2.2] years) (P=0.006, t test) because
more patients in the ventricular group developed atrial
fibrillation. In the ventricular group, PQ interval
increased during follow-up from 185 (32) ms at implantation to 199 (37)
ms at last follow-up in patients with sinus rhythm (109 patients)
(P<0.001, paired t test). In the atrial group,
PQ interval changed from 190 (30) to 191(33) ms (105 patients)
(P=0.65, paired t test). The increase in PQ
interval from implantation to last follow-up was significantly higher
in the ventricular group (17 [36] ms) than in the atrial
group (2 [34] ms) (P=0.002, t test). There was
no significant difference between treatment groups in PQ interval at
last follow-up (P=0.09, t test).
View larger version (18K):
[in a new window]
Figure 1. PQ interval (mean [SD]) during follow-up in
patients with single-chamber atrial and ventricular
pacemakers. Numbers below abscissa indicate numbers of patients in whom
PQ interval was measured.
Stim-Q100 and Stim-Q120 during follow-up in the atrial group
are shown in Figure 2. The mean follow-up
time of Stim-Q100 was 4.5 (2.4) years, and the mean follow-up time of
Stim-Q120 was 4.4 (2.4) years. Stim-Q100 increased a mean of 1 (42) ms
(P=0.82, paired t test) to 245 (48) ms (100
patients) from implantation to last follow-up, and Stim-Q120 increased
a mean of 9 (50) ms (P=0.10, paired t test) to
267 (54) ms (93 patients) from implantation to last follow-up. The
Wenckebach block point remained stable and unchanged in 66 patients
(60%) during the follow-up period, but in 34 patients, it changed
(Figure 3). Of the 99 patients with a
Wenckebach block point of 
120 bpm at inclusion in the study, 77
patients had a Wenckebach block point of 120 bpm, 14 patients had a
Wenckebach block point of 100 to 119 bpm, and 1 patient had a
Wenckebach block point of <100 bpm at last follow-up. Of the 9
patients with a Wenckebach block point of 100 to 119 bpm at inclusion
in the study, 3 patients had a Wenckebach block point of 120 bpm, 4
patients had a Wenckebach block point of 100 to 119 bpm, and 1 patient
had a Wenckebach block point of <100 bpm at last follow-up. There was
no significant difference between Wenckebach block point at the time of
implantation and that at the last follow-up (Wenckebach block point of
120, 100 to 119, and <100 bpm, 99, 9, and 1 versus 80, 18, and 2;
2 test=4.97, df=2,
P=0.09). The 2 patients with a Wenckebach block point of
<100 bpm at last follow-up were asymptomatic, and their
pacemakers were not upgraded. One of these patients had a Wenckebach
block point of 90 bpm, and the other had a Wenckebach block point just
below 100 bpm at last follow-up. The Wenckebach block point at last
follow-up is missing for 10 of 110 patients due to treatment with
single-chamber ventricular pacemakers at all follow-up
visits (8 patients), atrial fibrillation at the only follow-up visit (1
patient), and death before first ambulatory follow-up visit (1
patient).
View larger version (20K):
[in a new window]
Figure 2. Atrial stimulus–Q interval (mean [SD]) during
atrial pacing at rates of 100 bpm (Stim-Q100) and 120 bpm (Stim-Q120)
in patients randomized to receive single-chamber atrial pacing. Numbers
below abscissa indicate numbers of patients in whom Stim-Q100 and
Stim-Q120 were measured.
View larger version (27K):
[in a new window]
Figure 3. Alterations in the Wenckebach block point during
the study period in the 34 patients in whom Wenckebach block point
changed during follow-up. At implantation, 28 patients had a Wenckebach
block point of 120 bpm (A), and 6 patients had a Wenckebach block
point of 100 to 119 bpm (B). A total of 84 shifts in the Wenckebach
block point occurred in the 34 patients. Where no number is indicated
on the arrow, each arrow represents 1 patient. The Wenckebach
block point is missing for 1 patient at the 3-year follow-up visit (A);
this patient had a Wenckebach block point of 120 bpm at the 2- and
4-year follow-up visits. AF indicates atrial fibrillation; No, number
of patients; M, months; and Y, years.120 bpm at both
implantation and last follow-up. The last patient with fascicular block
had a Wenckebach block point of 100 to 119 bpm at last follow-up.
The pacemaker system was upgraded to a dual-chamber system
in 4 patients because of AV block (Table 2). One patient developed third-degree AV
block with syncope 7 months after implantation during acute pneumonia
and was upgraded, but there was a normal PQ interval during the
remaining 5 years of follow-up (Stim-Q100 and Stim-Q120 were not
measured during follow-up after upgrading in this case), and the
patient was alive at the end of the study. In 1 patient, the Wenckebach
block point decreased asymptomatically from the interval
100 to 119 bpm to 80 bpm at 1.5 years after implantation because of
treatment with increasing doses of ß-blocker and calcium
antagonist that were necessitated by progression of angina
pectoris, and therefore the pacemaker was upgraded to a dual-chamber
system. This patient died 7 years after primary pacemaker implantation
from noncardiac causes with a well-functioning dual-chamber pacemaker.
One patient developed second-degree AV block accompanied by dyspnea
during treatment with a tetracyclic antidepressive drug (maprotiline) 3
years after implantation and died from abdominal cancer 1.5 months
after upgrade of the pacemaker. The last patient developed
second-degree AV block with syncope after 5.8 years. This patient was
still alive at the end of the study. Two of the 4 patients who
developed AV block had right bundle-branch block on their ECG at the
time of randomization. The development of AV block could not have been
predicted by a decrease in the Wenckebach block point or prolongation
of PQ interval or atrial stimulus–Q intervals during follow-up in any
of the 4 patients (Table 2). The incidence of AV block could not be
assessed in the ventricular group.
View this table:
[in a new window]
Table 2. AV Conduction in Patients Developing AV
Block
The number of patients in the atrial group who were treated with
drugs that could influence AV conduction are reported in Table 3. At the time of implantation, 32 of 110
patients were treated with 1 of these drugs, whereas at the last
follow-up, 46 of 109 patients (1 patient in the atrial group died
before the first follow-up visit) were receiving 1 of these drugs
(2 test=4.1, df=1,
P=0.046). Eight of 16 patients in whom the Wenckebach block
point was lower at the last follow-up than at inclusion were treated
with drugs that could influence AV conduction.
View this table:
[in a new window]
Table 3. Antiarrhythmic Drugs During Follow-up in the Atrial
Group ),
the change was associated with an alteration in medication in 16
patients. In 12 of these patients, the change in the Wenckebach block
point from 120 bpm to the interval 110 to 119 bpm was associated with
the patient starting to receive a ß-blocker (4 patients), a calcium
channel blocker (3 patients), digoxin (3 patients), or an
antiarrhythmic drug (2 patients). In 2 patients, the Wenckebach block
point increased from the interval 110 to 119 bpm to 120 bpm at the
same time as the patient stopped receiving digoxin and a ß-blocker
plus an antiarrhythmic drug, respectively. In 2 patients, the
Wenckebach block point increased from the interval 100 to 119 bpm to
120 bpm at the same time as the patient started receiving calcium
channel blocker and digoxin, respectively.
Discussion
Top
Abstract
Introduction
Methods
Results
Discussion
References
The present study documents that in patients with sick sinus
syndrome, AV conduction estimated as PQ interval and atrial stimulus–Q
interval at atrial pacing rates of 100 and 120 bpm remains stable
during long-term follow-up and AV block occurs at a rate of only 0.6%
per year. 0.22
second in patients 70 years old and PQ interval of 0.26 second in
patients >70 years old; in addition, 1:1 AV conduction at an atrial
pacing rate of 100 bpm at implantation was required for the
implantation of an atrial pacemaker. Thus, the present trial also
documents that these criteria could be used safely in the selection of
patients for single-chamber atrial pacing among those with sick sinus
syndrome. Most previous studies have used a Wenckebach point of <120
bpm12 18 21 22 or <130
bpm14 19 25 as a contraindication for
single-chamber atrial pacing. However, as indicated by the present
trial and by other studies,7 21 a Wenckebach
block point of <120 or <130 bpm has a poor predictive value in
identifying patients at risk for the development of high-degree AV
block. Therefore, a Wenckebach block point of 100 bpm, as used in the
present trial, is sufficient to select patients for single-lead
atrial pacing.
AV conduction estimated as PQ interval and atrial stimulus–Q
interval at atrial pacing rates of 100 and 120 bpm remains stable
during long-term follow-up. Thus, treatment with single-chamber atrial
pacing is safe and can be recommended for patients with sick sinus
syndrome without bundle-branch block.
Acknowledgments
This study was supported by grants from the Danish Heart
Foundation and Sygekassernes Helsefond.
References
Top
Abstract
Introduction
Methods
Results
Discussion
References
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