© 2003 by European Society of Cardiology
Contributions of permanent cardiac pacing in the treatment of atrial fibrillation
Medical Clinic III, Heart Centre, University-Hospital Hamburg-Eppendorf Martinistr. 52, D-20246 Hamburg, Germany
Manuscript submitted 25 May 2004. Accepted after revision 28 June 2004.
*Tel.: +49 40 428035304; fax: +49 40 428035766. E-mail address: schuchert{at}uke.uni-hamburg.de
| Abstract |
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Newer indications for permanent cardiac stimulation include the prevention of paroxysmal atrial fibrillation (AF) and cardiac resynchronisation in patients suffering from advanced heart failure. Direct comparisons between VVI and DDD or AAI pacing showed an advantage conferred by physiological pacing on the risk of developing AF during long-term follow-up in patients with sinus node dysfunction, AV block, or both. Furthermore, in patients with conventional pacing indications and paroxysmal atrial tachyarrhythmias, a high percentage of atrial pacing was associated with a lighter AF burden. This article reviews several important issues involved in the optimisation of cardiac pacing with a view to prevent paroxysmal AF by new, dedicated pacing algorithms. The AF SuppressionTM algorithm significantly reduced the rates of symptomatic paroxysmal AF. This algorithm, which confers its benefit by maintaining the atrial pacing rate slightly above the spontaneous sinus rate, should be activated in patients with a history of atrial tachyarrhythmia. Implanting the lead in the low atrial septum seems to reduce further the frequency of tachyarrhythmic events. Future indications for this mode of pacing may be extended to patients at high risk of new-onset or recurrent AF, such as candidates for cardiac resynchronisation therapy or implantable cardioverter/defibrillator recipients.
Key Words: atrial fibrillation, atrial pacing, overdrive pacing, atrial pacing algorithm
| Introduction |
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Present-day permanent cardiac pacing is no longer limited to the prevention of bradycardia or asystole in patients with advanced atrioventricular (AV) block or sinus node dysfunction. Newer indications include (a) prevention of paroxysmal atrial fibrillation (AF), and (b) cardiac resynchronisation in patients suffering from advanced heart failure. This article reviews several important issues involved in the optimisation of cardiac pacing with a view to preventing paroxysmal AF (Fig. 1, Table 1).
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| Pacing system |
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The first issue addressed is the choice of "appropriate pacing devices". Available options are either a VVI or a physiological (DDD or AAI) pacing system. Direct comparisons between the two systems revealed no advantage conferred by physiological pacing on overall survival, though it lowered the risk of developing AF during long-term follow-up [1
| Atrial pacing rate |
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A second important factor is the optimisation of the atrial pacing rate with respect to the spontaneous sinus rate. In patients with conventional pacing indications and paroxysmal atrial tachyarrhythmias, a high percentage of atrial pacing was associated with a lighter AF burden [5
Most state-of-the-art dual-chamber pacemakers offer new functions, which continuously compare the lower atrial pacing rate with the actual sinus rate and allow the delivery of an atrial paced rate just above the spontaneous sinus rate. In St. Jude Medical pacing devices, the AF SuppressionTM algorithm "controls" the sinus rate by increasing the paced atrial rate when two intrinsic beats are detected within any of 16 consecutive cardiac cycles (Fig. 1). The rate of overdrive pacing and the duration of overdrive pacing are programmable. The lower rate overdrive (LRO) controls the degree of overdrive pacing between 45 and 59 bpm, and is set to pace at a rate 10 bpm faster than the spontaneous rate. The upper rate overdrive (URO) is effective between 150 and 180 bpm, and is set at 5 bpm above the intrinsic rate. The increase in overdrive rate between LRO and URO is based on linear regression. The maximum overdrive pacing rate is limited by the maximum sensor rate regardless of sensor activation. The rate dictated by the AF SuppressionTM algorithm is consistently the same as or higher than the sensor-indicated rate. Once stable pacing is achieved, the system continues to pace at that rate for a number of overdrive pacing cycles programmable between 15 (nominal) and 40, before it decreases in search of the underlying rate. The dynamic rate recovery, which determines the decrease from overdrive pacing to base rate, is set at 8 ms per cycle for rates >100 bpm, and at 12 ms for rates between 45 and 100 bpm.
This easily implemented and programmable algorithm was prospectively studied in the single-blind randomised multicentre ADOPT trial, which included 288 patients with conventional pacing indications and a documented history of AF within the month prior to implantation of a DDDR pacing system [9]
. The patients were randomly assigned to programming of the algorithm ON (treatment group, n = 130) or OFF (control group, n = 158). Over the following 6 months of follow-up, the patients were instructed to record all symptoms consistent with an episode of atrial tachyarrhythmia with a cardiac event monitor. The percentage of atrial pacing in the treatment group was significantly higher (93%) than in the control group (68%, P < 0.0001). Furthermore, the overall symptomatic AF burden, defined as the total number of AF days divided by the cumulative follow-up days, was 2.50% in the control group vs. 1.87% in the treatment group, a relative difference of 25% (P = 0.005, Fig. 2). Limitations of this study were the evaluation of only symptomatic episodes verified by an external loop recorder, because extended diagnostic counters were not available in the implanted pacemakers. The total number of AF episodes as determined by the device memory revealed no significant reduction, but the mode switch algorithm in these devices was relatively insensitive compared with today's pacemakers.
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Nearly all pacemaker manufacturers have developed similar pacing functions. Ricci and co-workers reported the results of a randomised cross-over study of the consistent atrial pacing algorithm (Medtronic), designed to maintain a high percentage of atrial pacing [10]
Extended pacing functions, which initiate overdrive atrial pacing in response to specific events, for example after sensing premature atrial complexes or after spontaneous termination of an atrial tachyarrhythmia have also been tested. In ASPECT, a multicentre trial of three programmable pacing algorithms in 277 patients randomised between atrial septal vs. non-septal pacing, no objective benefit was conferred by the combined algorithms on the frequency of daily episodes of atrial tachyarrhythmias or on the overall atrial arrhythmic burden [11]
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| Atrial antitachycardia pacing |
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Atrial antitachycardia pacing (ATP) can terminate atrial flutter or AF of recent onset in up to 50% of attempts. The ATTEST study tested the hypothesis that pace-termination of organised atrial tachyarrhythmias would prevent the development of AF [12]
| Alternate atrial pacing sites |
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The antiarrhythmic efficacy of pacing from one or two non-conventional atrial pacing sites has recently been evaluated (Fig. 3). In studies from single institutions, the simultaneous implantation of two atrial leads was found effective in the prevention of recurrent AF [13,
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The most frequently used approach, currently, consists of implanting one lead in the upper or lower part of the atrial septum. Bailin and co-workers studied the implantation in the upper part of the atrial septum and demonstrated that patients with septal atrial leads had lower rates of permanent AF compared with patients with conventionally placed leads [15]
| Candidates for preventive atrial pacing |
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Most studies discussed earlier included patients who had conventional pacing indications and a history of AF. In these patients the described approaches were successful. In the few studies performed in patients without symptomatic bradycardia atrial pacing had neutral effects on AF [20
| Conclusions |
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In patients with conventional pacing indications and a history of AF, DDD and AAI pacemakers reduce the risk of further AF during follow-up. In several randomised controlled trials, the AF SuppressionTM algorithm significantly reduced the rates of paroxysmal AF. This algorithm, which confers its benefit by maintaining the atrial pacing rate slightly above the spontaneous sinus rate, should be activated in patients with a history of atrial tachyarrhythmia. Implanting the lead in the lower atrial septum seems to reduce further the frequency of tachyarrhythmic events measured by automatic mode switches. Future indications for this mode of pacing may be extended to patients at high risk of new-onset or recurrent AF, and candidates for cardiac resynchronisation therapy or implantable cardioverter/defibrillator patients.
| References |
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