Paolo Terranova, MD
1,2, Paolo Valli, MD
2, Peppino
Terranova, MD
1, Simonetta Dell’Orto, MD
2, Enrico
Maria Greco, MD
2
1Divisione di Cardiologia, Azienda Ospedaliera “Luigi
Sacco” – Polo Universitario, Istituto di Scienze Biomediche LITA;
University of Milan, Italy
2Unità Operativa di Cardiologia, Presidio
Ospedaliero “Causa Pia Ospedaliera Uboldo”, Cernusco sul Naviglio,
Azienda Ospedaliera di Melegnano, Milano
Funding
and conflict of interest statement by the authors: For
the present study no fund has been received by any of the authors of
the paper from Vitatron and/or its Associated and all the authors state
that they have no conflict of interest in this manuscript.
Address for
correspondence: Paolo Terranova, MD, Via Sangro, 13, 20132 –
Milan. E–mail: terranovapaolo@hotmail.com, Paolo.Terranova@unimi.it
Abstract
Introduction. Atrial
fibrillation (AF), the most common and rising disorder of cardiac
rhythm, is quite difficult to control and/or to treat. Non
pharmacological therapies for AF may involve the use of dedicated
pacing algorithms to detect and prevent atrial arrhythmia that could be
a trigger for AF onset. Selection 900E/AF2.0 Vitatron DDDRP pacemaker
(1) keeps an atrial arrhythmia diary thus providing detailed onset
reports of arrhythmias of interest, (2) provides us data about the
number of premature atrial contractions (PACs) and (3) plots heart rate
in the 5 minutes preceding the detection of an atrial arrhythmia.
Moreover, this device applies four dedicated pacing therapies to reduce
the incidence of atrial arrhythmia and AF events.
Aim of the Study. To analyze the reliability to record
atrial arrhythmias and evaluate effectiveness of its AF preventive
pacing therapies.
Material and Methods. We enrolled 15 patients (9 males
and 6 females, mean age of 71±5 years, NYHA class I–II), with a
DDDRP pacemaker implanted for a “bradycardia–tachycardia” syndrome,
with advanced atrioventricular conduction disturbances. We compared the
number and duration of AF episodes’ stored in the device with a
contemporaneous 24h Holter monitoring. After that, we switched on the
atrial arrhythmias detecting algorithms, starting from an atrial rate
over 180 beats per minute for at least 6 ventricular cycles, and ending
with at least 10 ventricular cycles in sinus rhythm. Thereafter, in
order to evaluate the possible reduction in PACs number and in number
and duration of AF episodes, we tailored all the four pacing preventive
algorithms. Patients were followed for 24±8 months (from 20 to
32 months).
Results. All 59
atrial arrhythmia episodes occurred in the first part of this trial,
were correctly recorded by both systems, with a correlation coefficient
(r) of 0.96. During the follow–up, we observed a significant reduction
not only in PACs number (from 83±12/day to 2.3±0.8/day)
but also in AF episodes (from 46±7/day to 0.12±0.03/day)
and AF burden (from 93%±6% to 0.3%±0.06%). An increase in
atrial pacing percentages (from 3%±0.5% to 97%±3%) was
also contemporaneously observed.
Conclusion. In
this pacemaker, detection of atrial arrhythmia episodes is highly
reliable, thus making available an appropriate monitoring of heart
rhythm, mainly suitable in AF asymptomatic patients. Moreover, the
significant reduction of atrial arrhythmia episodes indicates that this
might represent a suitable therapeutic option for an effective
preventive therapy of AF in paced brady–tachy patients.
Key Words: Sick Sinus
Syndrome, Atrial Fibrillation, Atrial Pacing, Pacing Algorithms,
Non-Pharmacological Therapy
Introduction
Atrial fibrillation (AF) represents one of the major clinical, social
and economical medical challenge
1,2. Progressive ageing is associated
with an inevitable rising in incidence and prevalence of this rhythm
disorder
3,4,
which causes not only impairments in functional
capability being associated to a greater incidence of cerebro-vascular
events, but also a rising request for emergency room visits and
hospital admission, mainly in patients affected by left ventricular
dysfunction or by other significant cardiovascular diseases.
Different
therapeutic strategies, both pharmacological and non pharmacological,
are available to restore sinus rhythm, prevent arrhythmia recurrences
and cardio–embolic events and control the mean ventricular rate
1,2,5.
What is still a challenge is how to tailor appropriate strategy and
therapy for each patient.
It is an
affirming concept that AF should not be considered as a simple cardiac
rhythm disturbance, but rather as a syndrome with a variety of clinical
presentations and two frequently negative hemodynamic feature: (1) the
lack of atrial contribution to ventricular filling and (2) the
irregularity and/or the fast shortening of cardiac cycle
lenght
1,2,5,6. The abnormal automaticity of pulmonary
veins’ foci
7
represents a critical determinant for AF onset. It’s well known,
nowadays, that a (1) critical atrial mass is necessary to maintain the
re-entry atrial circuits
8
and that (2) the adrenergic activation
determines a pro-arrhythmic effect on bursts originating from the
pulmonary veins[9] or on arrhythmia recurrence after a
cardioversion
10.
Notwithstanding, it’s almost impossible to figure
out a temporal prevision of the evolution of this “AF syndrome” in each
patient.
In 1995,
Wijffels and coll.
11
showed, for the first time, that AF causes
several changes in atrial electrophysiological properties that could be
responsible for the clinical progression and maintenance of this
tachyarrhythmia. The persistence of electrical disorders was found to
be proportional to the duration of atrial high–rate pacing
8,11.
There are
three main electrophysiological assumptions
12–14 for pacing
prevention of AF widely accepted:
1. to reduce the arrhythmogenetic
effects of bradycardia and, in particular, the atrial refractory
periods dispersion;
2. to override atrial premature contractions (PACs), as a possible
cause of AF onset;
3. to reduce the compensatory pauses after an atrial or a ventricular
premature contraction, thus reducing the dispersion of atrial
refractoriness induced by the “short cycle – long
cycle” mechanism.
A prospective
randomised study from Andersen and coll.
15
on 225 patients with sick
sinus syndrome, showed that atrial pacing (AAI) not only significantly
reduced the incidence and burden of AF and thromboembolisms when
compared with ventricular one, but also that there was a significant
reduction in total and cardiovascular mortality.
To improve the
capability to prevent the onset of AF, other several approaches have
been tested. In patients with marked intraatrial conduction period
delays, Saksena
16 and
Daubert
17 suggested to
resynchronize both
atria with dual–site atrial pacing, in different stimulation sites, in
order to reduce the consequent atrial electrical abnormalities.
Nowadays, this approach has been less considered, because of a low
efficacy on AF incidence and burden, with frequent episodes of
cross–talk and interference due to the dipole wide range, and because
of the higher threshold needed for left atrial pacing. As alternative
solutions, Padeletti and coll.
18
suggested the use of a single
atrial lead on atrial septum. Several studies are still ongoing, with
contrasting preliminary results.
It’s also well
known that variability in the origin of PACs should increase the
probability of a re-entry mechanism, mainly in presence of an anomalous
substrate. On this account, it has been proposed to reduce atrial rate
variability using an overdrive atrial steady stimulation alone,
although this approach did not obtain significant results.
Alternatively, other pacing techniques such as bursts and drives
algorithms have been proposed. Several trials
19–24 have been done to
evaluate the safety and efficacy of these devices in terminating
spontaneous atrial tachyarrhythmias, but the results were quite
disomogeneous and so this approach is far from being definitively
accepted.
In particular,
the Atrial Dynamic Overdrive Pacing Trial (ADOPT)
25 evaluated the
effects of atrial overdrive pacing algorithms in 319 patients (mean age
71±10 years) with paroxysmal atrial fibrillation (3-3.5
documented atrial fibrillation episodes in the 12 weeks prior to
implant). Atrial pacing reduced symptomatic atrial fibrillation burden
(On: 1.9% vs. Off: 2.5%). Symptomatic atrial fibrillation burden
decreased over time for both groups. No significant difference was
noted in the number of atrial fibrillation episodes (On: 3.2 ±
8.6 vs. Off: 4.3 ± 11.5) or total hospitalizations (On: 9% vs.
Off: 13%) between the two groups. Quality-of- life improved in both
groups.
Moreover, in
the ATTEST study
26 was
evaluated the effectiveness of an atrial
therapy device utilizing preventative and antitacycardia pacing in
patients with symptomatic atrial fibrillation. The implanted device was
an AT500 (Medtronic Inc, Minneapolis, MN) DDDR pacemaker, with a mode
switching algorithm (DDIR) during atrial tachyarrhythmias. Atrial
antitachycardia pacing was available in rate adaptive burst or ramp
modes, and the device also could employ 3 preventative atrial pacing
algorithms to attempt to prevent AF/AT recurrences. After a one-month
run in period, patients were randomized to either atrial prevention or
termination on or off, and followed for three months. At the end of the
trial, there was observed no significant difference between the two
groups in the run in period or in follow up in either frequency, burden
or symptomatic frequency of AT/AF. The efficacy of device ATP was 54%
in converting atrial arrhythmias to sinus rhythm as evaluated by the
device and the accuracy of the detection algorithm was 99.9%.
Based on the
hypothesis of the effectiveness of a non–pharmacological antiarrhythmic
electrical therapy, our study was aimed at evaluate the reliability of
the four specific pacing algorithms of the DDDRP pacemaker, the
Selection® 900E/AF2.0 Vitatron™, and to reduce the trigger
mechanisms, possibly responsible for AF onset.
Materials and Methods
We initially evaluated the atrial arrhythmia
recording reliability in 15 patients, implanted with a Selection™
900E/AF2.0 Vitatron® device, for a “brady–tachy” syndrome, with
advanced atrioventricular conduction disturbances. Patients were
enrolled in a period of 10 months, starting from January 2000 and
ending in October 2000. Patients were 9 males and 6 females, with a
mean age of 71±5 years, without any previous history of
myocardial infarction, angina, diabetes and other known risk factors
and in I NYHA functional Class. All patients were initially under oral
anticoagulant therapy (INR 2.0–3.0) and IC antiarrhythmic drug therapy
(Acetate Flecainide 200 mg per day) for at least 6 months prior to
implant. Therapies were not discontinued during the follow–up.
In order to
evaluate the Selection™ 900E/AF2.0 Vitatron® atrial arrhythmia
recording reliability, we compared the number of atrial arrhythmic
episodes and their onset and duration,properly stored in the pacemaker,
with a contemporaneous 24h standard Holter cassette recording (Ela
Medical™ Synetec® System, version 1.20). A statistical correlation
analysis was performed. The pacemaker parameters were settled in order
to record atrial arrhythmic episodes lasting at least 6 ventricular
cycles for their onset and 10 ventricular cycle for their ending. The
atrial cut–off detection rate was of 180 atrial waves per minute.
Clinical and follow–up features of our population are summarized in
Table 1. Data are expressed
as mean ± SEM. Paired t–Student test
was performed.
Table
1 – Patients baseline caracteristics and follow-up
The second aim
was a middle–term efficacy evaluation (mean follow up 24±8
months, i.e. from 20 to 32 months) of all the four Selection™
900E/AF2.0 Vitatron® available pacing algorithms, in order to
prevent the trigger mechanisms, possibly responsible for AF onset. Each
pacing algorithm was tailored according to the clinical and
electrophysiological features of each patient, according to the
previously recorded atrial arrhythmic events.
The four used
atrial pacing algorithms were the following four:
1. Pace Conditioning™:
this algorithm consist on a permanent overdrive
atrial pacing with an atrial pacing rate of about 15 b.p.m. higher than
the beneath intrinsic effective atrial rate.
2. PAC
Suppression™: this algorithm is designed to reduce the incidence
of atrial tachyarrhythmia by a temporary stable atrial overdrive pacing
following a PAC. This algorithm provides a temporary atrial overdrive
pacing lasting for 600 ventricular cycles after a sensed PAC. At the
end of this 600 ventricular cycles, the pacing rate progressively
reduces till the lower rate limit or till the emergence of a stable
sinus rhythm.
3. Post–PAC
Response™: this algorithm is designed to reduce the
post–extrasystolic pauses by controlling the atrial rate in the 2 beats
after a PAC. The first atrial paced beat’s rate is determined by an
averaging between the previous physiologic RR interval and the PAC
pairing rate. From the second beat onwards, the atrial fleeing rate
returns to the atrial physiologic rate.
4.
Post–Exercise Rate Control™: the post–exercise rate control has
been
specifically designed to prevent a too fast lowering of heart rate
after a physical activity. The post–exercise rate increases
proportionally to the difference between the physiological heart rate
and the target heart rate, i.e. 90% of the physiological heart rate.
Results
During the first part of this trial, i.e. that comparing Holter
recordings and pacemaker storage data, we observed 59 episodes of
paroxysmal AF, lasting from some seconds to some minutes, with a highly
significant correlation coefficient between Holter and pacemaker
recordings (r=0.96) (
Fig. 1).
The AF mean duration was of 70,9±46,8 s. in the Holter group and
of 69,6±47,4 in pacemaker recordings (p = 0.881; 95% confidence
interval: –18.48 to 15.88). Differences between timing and duration of
the two recordings is likely to be due to the cassette tracking speed
features.
Fig.
1 - Concordance Between Holter and Pacemaker Recordings
As shown in
Fig. 2, during the second half of
our trial, the antiarrhythmic algorithms produced a significant and
progressive reduction in AF episodes (from 46±7 episodes/day to
0,12±0,03 episodes/day; p<0.001; 95% confidence interval:
41.69 to 50.07) and in AF burden (from 93%±6% to
0,3%±0,06%; p<0.001; 95% confidence interval: 89.53 to
95.87), with a concomitant increase in atrial pacing percentage (from
3%±0.5% to 97%±3%; p<0.001; 95% confidence interval:
–95.61 to –92.39). AF burden was evaluated and measured during the
follow up period using the pacemaker storage data, and no comparison
were made with AF burden prior to implant, because of the lack of a
real value of this data in our patients, that were sometimes
asymptomatic ones. We observed also a decrease in premature atrial
contractions from 83±12 PACs/day to 2,3±0,8 (p<0.001;
95% confidence interval: –87.06 to –74.34) (
Fig. 2). The same method
was used
to record APCs in the pre- and post- implant period, i.e. the Holter
monitoring, and also during all the follow up period, i.e. a
retrospective analysis of pacemaker data storage.
Fig. 2 -
Supraventricular Tachyarrhythmia Reduction After Switching on the 4
Pacing Preventive Therapies
However, it
was unfeasible to perform a reliable multivariate analysis because of
the reduced number of patients, because of the lack of multiple risk
factors, because of the contemporaneous usage in the same patients of
acetate flecainide and of pacing prevention algorithms.
Discussion and Conclusion
Presently,
very few clinical randomised trials
29–32 have compared the
overlapping between pacemaker stored data and Holter monitoring ones,
so that there is not a significant evidence of data about the
reliability of these devices in properly recognising and monitoring
supraventricular tachyarrhythmias. It’s also well known that bipolar
leads often are not enough able to discriminate ventricular far field
from normal P-wave amplitude or from wavelets of AF. An Atrial Blanking
feature, long enough, may completely mask this phenomenon, but it also
represents a blind interval for the atrial channel, sometimes
subsequently resulting in a possible negative effect for an optimal
arrhythmia detection. Recently, Nicotra
33
carried out a method for
atria l sensing and blanking programming in order of guarantee reliable
diagnostics in patients with paroxysmal AF. They proposed a decisional
flow-chart based on the scanning of ventricular far field timing and
amplitude that could focus and quantify this phenomenon for every kind
of implanted device (
Fig. 3).
This approach was also used in the present study during the follow–up.
Fig.
3 - Decisional Flow-Chart
Our data
confirm the significant reliability of Selection™ 900E/AF2.0
Vitatron® algorithms for detecting and monitoring AF. Moreover, we
recorded a significant number of supraventricular tachyarrhythmia’s
episodes, thus making stronger the statistical reliability of these
data. Subsequently, we detected a progressive and significant reduction
in AF burden and episodes. This decreasing in AF episodes and burden
may be mainly related to the increase of atrial pacing, obtained by
using a newly designed pacing overdrive algorithm responsible of atrial
ectopic beats’ suppression in keeping with several trials
11–28.
Most of the
discussed trials showed a lower reduction in AF episodes and burden if
compared with our study (AF burden decreasing from 85% to 35% vs. a
reduction from 93% to 0.3%; p<0.001; 95% confidence interval: –9.253
to –6.747). As showed in our recordings, the exceeding share of AF
episodes and AF burden reduction is more likely to be entrusted to the
newly designed four preventive pacing algorithms stored in the tested
device (Selection® 900E/AF2.0® Vitatron™ pacemaker).
Alternatively, as the data shown in fig. 2 seems to underline, i.e.
that the efficacy of pacing for reducing AF episodes/day was evident
after only six months of treatment, may suggest that also atrial
remodelling could play a role. Electrical, mechanical and anatomical
remodelling indicate structural alterations that, once established, may
vanish any attempt to restore sinus rhythm. Atrial fibrosis is probably
the most critical factor of the remodelling process and appears to be
largely media ted by several mechanisms. Our clinical data indicate
that these non pharmacological interventions may reduce, in a
roundabout way, AF burden and episodes, probably interfering also with
someone of those electrical and structural remodelling processes. It is
possible, however, that having a very few patients, although followed
for a median time of 24 months, we have overestimated the general
possible reduction in AF episodes and burden because of a strong
selection of our patients. In particular, we selected our patients on
the basis of their atrial tachyarrhythmias’ onset mechanisms, and we
tailored the available preventive pacing algorithms in each patient on
the basis of each onset. This tailoring of pacing preventive algorithms
on the basis of the different onsets in each patient, associated with
the well known anti–remodelling effect of atrial overdrive pacing on
atrial refractoriness dispersion, was the more important goal of our
study and the likely reason of the observed marked reduction in AF
episodes and burden. Therefore, these examined pacing algorithms may
represent an effective therapeutical options to contrast the nearly
inevitable progression of this arrhythmia towards its permanent form.
The AF
antiarrhythmic drugs therapy represents the first and more effective
therapy, although it is well known that it is not always effective and
free from side effects. In our patients, implanted for a sick sinus
syndrome and at least partially resistant to AF pharmacological
treatment, new interventional non–pharmacological solutions, such as
tailored antiarrhythmic pacing algorithms, may represent a further
effective therapeutical option. Recent analysis of AFFIRM
33 and RACE
trial
34 showed that, in
patients older than 65 years, with well
defined risk factors, a therapeutical strategy based on ventricular
rate control is not inferior to a strategy of maintaining sinus rhythm
(rhythm control). However, this issue is still debated. Indeed, other
clinical trials and sub–analysis
35–40
showed that sinus rhythm
restoration has to be preferred compared to rhythm control.
In conclusion,
our experience suggests the reliability of well tailored pacing
algorithms on AF control in selected patients with brady-tachy
syndrome, refractory to pharmacological rhythm control. However, we
should say that this study is partially limited by the small and highly
selected sample used, that reduces the possibility of translating
theses results to general population. Moreover, this was not a truly
randomized, controlled study, and so interpretation of the clinical
significance of the reduction of AF episodes, as also shown however by
several other trials in International Literature, is uncertain, thus
not allowing us for making really definitive conclusions. The main
information, however, we can derive from this trial is that we should
better evaluate, before every pacemaker implantation, the different AF
onsets of each patient eligible for such a procedure, because only a
really profound knowledge of the different onset mechanisms of atrial
tachyarrhythmias in each subject may give us the possibility of
choosing a really effective implantable device for these sometimes very
different patients, thus obtaining the maximum effective clinical
results from these pacing algorithms in terms of reduction of AF
episodes and burden.
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