Giovanni Luca Botto*, R. Ricci*, W. Bonini, T. Broffoni, M. Santini*, A. Puglisi**, P. Azzolini**, C. Pignalberi**, A. Capucci***, G. Boriani****, A.Spampinato°, F. Bellocci°, A. Proclemer°°, A. Grammatico°°°, F. De Seta°°° and the ISSAF/CAP Group.
Sant’Anna Hospital, Como; *San Filippo Neri Hospital, Roma; ***Fatebenefratelli Hospital, Roma; ***Civile Hospital, Piacenza; ****Sant’Orsola Hospital, University of Bologna; °Villa Tiberia Hospital, Roma; °°S. Maria della Misericordia Hospital, Udine; °°° Medtronic Italia, Italy
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Despite the remarkable advances in the management of AF
in the last decade, prevention of recurrences remains a difficult clinical problem. Many important, but
non-randomized, retrospective studies, have suggested that pacing in the atrium in patients with sick
sinus syndrome lead to reduction in the occurrence of AF and mortality1. However, retrospective
studies are appropriately criticized for bias in mode selection and the inability to account for the
effect of associated co-morbidities. The study by Andersen et al was the first one that prospectively
demonstrated a statistically reduction in the incidence of AF in patients paced AAI vs VVI2. There are
a variety of approaches to prevent AF with pacing involving pacing
modality3 and site4-6, pacing
basic rate and extent of atrial overdrive and, more recently, the use of dedicated pacing algorithms7.
Consistent atrial pacing (CAP) is a new pacing algorithm that has been designed to achieve a high
percentage of atrial pacing as a means to suppress AF recurrences7. Aim of the present study was
to validate CAP algorithm in patient with AF related to brady-tachy syndrome and to evaluate the
relation between atrial pacing percentage and arrhythmia recurrences.
CAP algorithm monitors beat by beat spontaneous atrial activity and continuously updates the atrial
escape interval (AEI) to overdrive suppress it. After every sensed atrial event outside post ventricular
atrial refractory period, AEI is shortened by a programmable value, nominally 50 msec. After a
programmable number of paced atrial events, nominally 10, AEI is lengthened by a programmable
value, nominally chosen as long as 20 msec. AEI shortening is limited by the programmed upper rate
value while AEI lengthening is limited by the programmable lower rate value. The software can be
loaded into the RAM memory of the pacemaker via telemetry, using a custom research telemetry
device which is linked to a standard IBM class personal computer. The software includes a diagnostic
which can be interpreted by a special Microsoft Excel spreadsheet.
In order to evaluate the impact of intermittent or continuous overdrive atrial pacing on paroxysmal
AF recurrences, we enrolled 35 pts, 16 males and 19 females, mean age 75±9 year, with
symptomatic brady-tachy form of sick sinus syndrome with at least 3 episodes of PAF during the
last month.
Sick sinus syndrome criteria were sinus bradycardia<50 bpm, sinus arrest in excess of 3 sec on two occasion, or brady-tachy syndrome (bradycardia-dependent atrial tachyarrhythmias). Patients with left atrial dimension>45 mm or congestive heart failure were excluded.
The pre-implant follow-up evaluation included clinical data, 12 leads ECG, echocardiogram, 24-hour
Holter monitoring, symptom-limited exercise test, and two self-administred questionnaire to assess
the psyco-physical capacity of the patients.
All patients were implanted with a dual chamber PM (Thera DR 7940-7960, Medtronic Inc.,
Minneapolis, USA) with automatic mode switching which automatically changes, during atrial
tachycardia, from an atrial tracking to a non-atrial tracking mode, based upon atrial tachycardia
criteria. The reliability of this algorithm was evaluated in a previous study8. The technology of Thera
DR with the software loaded, providing diagnostic data regarding the number of the arrhythmic
episode, the tachy-rate, the duration and the day-time of the mode switch that have occurred
between follow-up visits, was utilized to detect the post-implant arrhythmic events. All atrial leads
implanted were on bipolar. Intermittent atrial pacing was obtained by programming the device in
DDDR mode, continuous atrial pacing through CAP algorithm.
At the implant, all patients were randomly assigned to DDDR+CAP (Gr. CAP) or DDDR (Gr. DDDR) pacing
mode and followed for two months. After the first month the two groups cross-overed and changed
their mode of pacing respectively from DDDR+CAP to DDDR and from DDDR to DDDR+CAP. The
automatic switch-mode was activated in both groups. After one and two-month of follow-up all
patients underwent a new evaluation including: clinical data, diagnostic data from the PM and
questionnaire for the psyco-physical capacity. Forty-five % of patients were on antiarrhythmic
treatment which did not change during the study period.
Dual chamber pacing reduces the number of symptomatic PAF episodes: figure 1 shows the behaviour
of symptomatic PAF episodes as evaluated by anamnestic and ECG data. There is a statistically
significant decrease of symptomatic PAF episodes in both compared with pre-implant evaluation,
while there is no difference between DDDR+CAP and DDDR pacing modes.
Fig. 1
Twenty-seven out of 35 (77%) patients in Gr. CAP and 30/35 (85%) patients in Gr. DDDR were
free from paroxysmal AF recurrences during each month period (p=NS). Twenty-four patients,
10 (29%) from Gr. CAP and 14 (40%) from Gr. DDDR, did not have any mode switching episode
stored in the PM memory during the follow-up period (p=NS).
Atrial pacing rate was significantly higher in Gr. CAP patients compared to Gr. DDDR patients (96±7
vs 78±27%; p<0.01) (Fig. 2). In Gr. CAP patients the number of premature atrial complexes/day was lower compared to Gr. DDDR patients (537±716 vs 2342±4123 beats/day; p<0.03) (Fig. 3). Despite the present observation, the number of mode-switching/day and the duration of the mode-switching activation were not different between the two groups (respectively Gr. CAP 1.5±2.7 vs Gr. DDDR 1.5±2.9; p="NS," and Gr. CAP 1.1±2.2 vs Gr. DDDR 1.1±2.7 min; p="NS)."
Fig. 2
The patients showed good tolerance for the algorithm with no proarrhythmic effect.
In recent years, pacing for prevention of AF has been a subject of intense interest. Several
prospective studies are now available to demontrate that atrial-based pacing reduces the
incidence of atrial fibrillation and the developing of permanent atrial fibrillation. Andersen et al
demontrated a statistically reduction in the incidence of AF in patients paced AAI vs VVI2. The
Canadian Trial of Physiologic Pacing (CTOPP) demonstrated physiologic pacing (DDD/AAI) to be
associated with a reduced rate in the development of chronic AF from 3.78% per year to 2.87 per
year at the 3-year analysis9. In a smaller study by Schrepf et al, paroxysmal AF occurred more
frequently in patients when paced VVI than when they were paced DDD10.
Atrial overdrive pacing may act to reduce the occurrence of AF by preventing bradycardia-dependent
onset of the arrhythmia, by suppressing ectopic atrial foci, that could precipitate AF, and by altering
the atrial activation sequence.
In DDDR operation atrial overdrive occurs when sensor rate is higher than sinus rate. In DDDR±CAP
pacing mode, atrial overdrive occurs practically at all the times. The present study showed that the
CAP algorithm was able to significantly increase the percentage of atrial pacing from 78% in DDDR
mode up to 96% in DDDR±CAP mode, with good patient tolerance and no proarrhythmic effect.
Moreover CAP algorithm significantly decreased the number of premature atrial contraction per
day, compared to DDDR mode alone, thus reducing a potential trigger for arrhythmia induction.
Fig. 3
Our preliminary results confirm that atrial-based pacing has a marked antiarrhythmic effect in pts
with brady-tachy form of sick sinus syndrome but, despite the present observation, the number
of mode-switching per day and the duration of the mode-switching activation were not different
between the CAP-on period compared to the CAP-off period. For this reason the impact of CAP
algorithm is currently under evaluation in different clinical settings. The factors potentially involved
in conditioning patients’ response to the algorithm include baseline burden of AF episodes,
baseline electrophysiologic substrate in term of conduction and refractoriness, atrial pacing
technique (standard right auricolar pacing3, interatrial septum
pacing1 or dual site atrial pacing4,5),
number of premature atrial contraction and relationship between premature atrial contractions
and mode-switching.
At present time, preliminary data on clinical use of the CAP algorithm are only to be considered
as promising, while other evaluations are in progress.
Appendix
ISSAF/CAP participation centers
F. Bellocci, A. Spampinato, C. Pignalberi, Clinica Villa Tiberia, Roma; R. Ricci, M. Santini, Ospedale San Filippo Neri, Roma; A. Puglisi, P. Azzolini, Ospedale Fatebenefratelli, Roma; G. L. Botto, W. Bonini, T. Broffoni, Ospedale Sant’Anna, Como; G. Boriani, L. Frabetti, M. Biffi, A. Branzi, Policlinico Sant’Orsola, Bologna; F. Groppi, G.Q. Villani, A. Capucci, Ospedale Civile, Piacenza; A. Proclemer, S. Maria della Misericordia Hospital, Udine; A. Grammatico, S. Cavaglia, F. De Seta, Medtronic Italia, Roma.
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