Europace Advance Access originally published online on January 9, 2006
Europace 2006 8(2):96-101; doi:10.1093/europace/euj024
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NOT PACING THE RIGHT VENTRICLE
Use of a new cardiac pacing mode designed to eliminate unnecessary ventricular pacing
Medizinische Universitatsklinik IIIUniversitätskliniken des Saarlandes Innere Medizin III, 66421 Homburg Germany ; Nouvelles Cliniques Nantaises Nantes France ; CHU d'Angers France ; CHU de Rennes France ; CHG d'Albi France ; CHU de Rouen France ; Clinique BIZET Paris France ; CHU de Grenoble France ; ELA Medical Le Plessis-Robinson France
Manuscript submitted 11 July 2005. Accepted after revision 1 October 2005.
Corresponding author. Tel: +49 6841 1623300; fax: +49 6841 1623269. E-mail address: ingfro{at}uniklinikum-saarland.de
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Abstract |
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Aims To examine the performance of AAIsafeR2, a new pacing mode to minimize the cumulative proportion of ventricular pacing in patients who do not need regular ventricular support.
Methods and results The safety of AAIsafeR2 was examined in 123 recipients (73±12 years old, 51% men) of dual chamber pacemakers implanted for sinus node dysfunction, paroxysmal AV block or the bradycardia-tachycardia syndrome. Data were collected from pacemaker diagnostics, and the first 43 patients underwent 24-h Holter recordings before being discharged from the hospital with AAIsafeR2 activated. No adverse event related to AAIsafeR2 was observed. All ventricular pauses detected on Holter tapes triggered immediate back-up ventricular pacing. Appropriate switches to DDD occurred in 97 of 123 patients. In 69 of 123 devices (56%) switches to DDD were non-sustained, and the average % ventricular pacing in this group was 0.2±0.5%.
Conclusion AAIsafeR2 mode seems to be safe and reliable in patients with infrequent slowing or pauses in ventricular activity, while maintaining ventricular pacing below 1%.
Key Words: Sinus node dysfunction, Dual chamber pacing, Atrioventricular conduction, Atrial pacing, Ventricular pacing
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Introduction |
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In patients with sinus node dysfunction (SND), use of AAI is uncommon (with the exception of some Scandinavian countries). In paroxysmal high-degree or complete atrioventricular (AV) block and in vagally mediated bradycardia, single chamber atrial pacemakers are contraindicated although ventricular support is only rarely needed.1
As a result, these patients are usually exposed to an unnecessary proportion of ventricular pacing due to DDD operation for safety reasons. This drains the pulse generator battery and, more importantly, has long-term adverse effects on ventricular function in a subset of vulnerable patients.2–4 The AAIsafeR pacing mode is designed to combine the advantages of AAI with the safety of DDD pacing. The clinical applications of a first version of this pacing mode have recently been described.5 It was associated with a marked decrease in the percentage of ventricular paced events in selected patients. However, it was limited by a high incidence of permanent switches to DDD in patients who had clusters of AV block episodes. The Symphony DR 2450/2550 cardiac pacemaker (ELA Medical, Montrouge, France) contains an upgraded version of the AAIsafeR mode (AAIsafeR2), which switches automatically from AAI(R) to DDD(R) or DDIR in the event of marked AV conduction abnormalities or sustained atrial arrhythmia, and it spontaneously returns to AAI(R) mode as soon as stable AV conduction is re-established. Beside substantial improvements in its specification, AAIsafeR2 was updated with new Holter functions. This report describes the observations made within 1 month after pacemaker implantation in a population of patients who received devices loaded with AAIsafeR2, the second generation of this pacing mode. |
Methods |
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The AAIsafeR and AAIsafeR2 pacing modes
AAIsafeR behaves like the AAI mode in the absence of AV block. An atrial escape interval is started by atrial events falling outside the Window of Atrial Rate Acceleration Detection (WARAD). This is calculated from the preceding normal atrial intervals (sensed or paced) and is 62.5% of a cycle length longer than 750 ms or 75% of the cycle length if it measures no more than 750 ms. Ventricular far field signals which are detected on the atrial channel are treated as atrial events.
Unlike that in standard AAI architecture, the blanking interval is split into post-atrial and post-ventricular components of 105 ms+ noise sampling periods in order to improve atrial sensing capabilities while minimizing the susceptibility to ventricular far field signals. In addition, the escape interval is reset by premature ventricular complexes (PVC; ventricular event without preceding atrial event) to prevent the next atrial pacing stimulus from initiating a conducted (but again premature) ventricular complex. Protection against atrioventricular cross-talk is operative in the same way as in DDD mode. This also applies to the handling of PVCs which closely follow an atrial event (safety window pacing).
No AV delay is initiated after sensed or paced atrial events. First-, second- and third-degree AV block are allowed up to a predetermined level before conversion to DDD mode occurs. The PR and AR intervals are permanently monitored, and values >350 ms for PR and >450 ms for AR are classified abnormal (default values, intervals programmable). The device automatically switches to DDD(R), and uses the programmed AV delay(s) in response to (1) >6 consecutive abnormal AR/PR intervals (a situation similar to ‘first degree AVB’; Fig. 1), (2) >3 blocked atrial events in the last 12 cycles (‘second degree AVB’; Fig. 2), (3) >2 consecutive blocked atrial events (‘high degree AVB’), or (4) a ventricular pause of programmable duration (between 2 and 4 s).
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Once in DDD mode, regular attempts are made to return to AAI and to allow for recovery of spontaneous AV conduction. The device switches to AAI mode if 12 consecutive R waves have been sensed, or if it has been working for 100 cycles in DDD(R) mode. Switch to AAI(R) is disabled until the next device reprogramming (1) if >5 switches to DDD per day have occurred over 3 consecutive days, or (2) if
15 switches have been counted within 1 day. AAIsafeR2 introduced the following modifications: (1) Instead of counting the number of switches to DDD, the device measures the duration of dual chamber operation, and uses >50% of the time in DDD mode as the criterion of ‘persistent’ AV conduction abnormality. (2) At rest, the switch to DDD mode upon sensing of first degree AV block can be disabled. (3) If AV block is detected during exercise (at heart rates >100 bpm), the event is not counted for ‘persistent’ DDD operation. (4) While functioning in DDD(R) after an episode of persistent AV block, the device systematically launches a conversion attempt to return to AAI(R). This occurs every morning during awakening when neuro-endocrine adaptation may favour AV conduction (Fig. 3).
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The record of mode switches includes logs of all switching criteria, 7 AV marker chains with synchronous AV electrograms, and histograms of the AR and PR intervals measured during AAI(R) operation. With AAIsafeR2, statistics are split additionally into diurnal vs. nocturnal and into resting vs. exercise events.
Patient recruitment and data collection
The study protocol was reviewed and approved by one Ethics Committee in each participating country and for individual centres if required. Patients were eligible for the study if they had a Class I indication for permanent pacing (except for permanent complete AV block), had a resting PR interval 
250 ms and had given informed consent. The AAIsafeR2 mode was downloaded in the RAM of Symphony DR and D dual-chamber pacemakers (models 2550 and 2450) and was activated after implantation. Post-implantation tests before hospital discharge included the assessment of sensing and pacing functions, retrieval of diagnostics from pacemaker memory and a 24 h ambulatory electrocardiogram (ECG) recording in a subset of the first 43 study patients. Stored data were collected again at 1 month of follow-up.
The safety of AAIsafeR2 pacing was judged from the concordance between Holter events and those logged in the device memory. Synchronization of both recordings was attempted by starting the Holter monitor and resetting the data log at the same time. Holter data were only accepted if the recording time was 12 h minimum and the quality of recordings permitted analysis. Special attention was paid to the occurrence of paroxysmal AV block which was not detected by the device (false negative events). The 1-month statistics were used to confirm the effective prevention of ventricular pacing by the AAIsafeR2 mode in relation to different pacing indications. Data were separately analyzed for patients who experienced no switch at all, for those who had only transient commutations, and those who had persistent switches to DDD mode during the 1-month period.
Statistical analysis
Data are presented as mean±standard deviation (SD). The Kruskal-Wallis test was used for comparisons of non-continuous variables. A P-value <0.05 was considered statistically significant.
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Results |
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AAIsafeR2 was tested in 123 patients (51% men) with an age of 73±12 years. The indication for permanent pacing was paroxysmal AV block in 46%, SND in 32%, and the bradycardia-tachycardia syndrome in 22% of patients.
Safety analysis
No AAIsafeR2-related symptom or major adverse clinical event was observed during the study period. In the 43 patients who had in-hospital Holter recordings, no inappropriate commutation from AAI to DDD was documented. All episodes of paroxysmal AV block caused immediate switching from AAI to DDD. In any instance of persistent switch to DDD mode pacing, a daily attempt to return to AAI was documented, and no false switch back from DDD to AAI occurred.
Effectiveness of AAIsafeR2
At the end of the 1-month follow-up, 28 units (23%) had switched to persistent DDD pacing, 69 (56%) had transient switches, and 26 (21%) had no switch at all (Table 1). In patients with no or only transient switches to DDD (more than two thirds of the overall population), the mean proportion of ventricular pacing was nearly 0% (0.13±0.47%). In contrast, a significantly higher percentage of ventricular pacing (P<0.0001) was observed in those patients (23%) who experienced persistent switches, most of whom (73%) were paced for AV block. The mean percentage of atrial pacing was similar among the three groups of patients (Table 1).
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At 1-month, the cause of switching to DDD was first degree AVB (1%), second degree AVB (8%), third degree AVB (8%), mixed AVB types (55%), mixed AVB and ventricular pause criterion (26%) and an isolated ventricular pause in 2%. In patients without sustained commutation to DDD, the mean percentage of ventricular pacing was 0.2±0.5% (median=0%, range 0–3). Switches to DDD occurred mainly during daytime (82% of switches) and at rest (81% of switches).
AV block was the predominant pacing indication among patients who experienced persistent switches (P<0.001, Fig. 4).
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Discussion |
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Detrimental effects of ventricular pacing
Large double-blinded, prospective studies have demonstrated the superiority of ‘physiological’ (AAI or DDD mode) over single chamber ventricular (VVI) pacing in terms of atrial arrhythmia prevention, incidence of the pacemaker syndrome and quality of life.6
–10 They failed to show any benefit in survival8–11 with the only exception being the Danish trial6 which yielded a significantly better prognosis with ‘physiological’ vs. single-chamber ventricular pacing. The ‘physiological’ mode in this study, however, was AAI rather than DDD.6 Evidence of some deleterious effects of ventricular pacing came from the DAVID trial which showed a close relationship between the cumulative percentage of ventricular pacing and the composite study endpoint of mortality and heart failure in recipients of implantable cardioverter-defibrillators (ICDs).3 A sub-study of the MOST trial4 suggested that the risk of hospitalization for heart failure increases with the proportion of ventricular pacing (VVI and DDD). But this relation was non-linear and—in DDD(R) mode—showed the maximum slope between 0 and 40% of ventricular stimulation. A comparison between AAI and DDD pacing in patients with sinus node disease demonstrated a lower incidence of atrial fibrillation, if pacing of the ventricles was avoided.2 A strategy which prevents unnecessary stimulation and the induction of asynchrony within the ventricles is, therefore, likely to confer a clinical benefit. This obviously does not apply to patients with AVB who need frequent or permanent ventricular pacing support.
Options to avoid ventricular pacing and their limitations
While AAI is currently considered the optimal pacing mode for patients with SND (including the bradycardia-tachycardia syndrome),12 it has its own limitations. These include
- the risk of subsequent AVB13–17 at any time after implantation;
- a suboptimal AV sequence due to long AV delays especially if rate modulation is active during exercise (‘AAIR pacemaker syndrome’ 18);
- slow ventricular response or pauses during atrial fibrillation which cannot be corrected by atrial pacing 13.
Dual chamber pacing is required on demand
- in patients with intermittent AV block who can only otherwise be served by a VVI system with low intervention rate if malconduction is really rare;19
- in patients with neurocardiogenic syncope.12
To avoid ventricular pacing outside the bradyarrhythmic event and to provide for optimum haemodynamic support20–22 if syncope is imminent, differential AV timing is critical for both conditions.
AAIsafeR2 vs. other pacing modes
AAI pacing with ventricular backup may be achieved by different options:
- DDD(R) pacing with a fixed long AV delay has been shown to be ‘inefficient in reducing ventricular pacing in one third of patients with SND’, it was associated with a high risk of arrhythmias caused by repetitive retrograde AV conduction and was ‘not recommended for general use in SND patients’.23 In addition, long AV delays may impair the detection of atrial tachycardia due to lengthened refractory periods and may increase the risk of R-on-T-stimulation which can result in malignant arrhythmia.
- AV hysteresis has been introduced to overcome the problem of intermittent prolongation or block of AV conduction.24 The basic principle is to use two different AV delays: a short one which is tailored to haemodynamics while pacing the ventricle, and a long one (short AV delay plus hysteresis interval) which essentially prevents ventricular pacing in case of intact AV conduction (Fig. 5). Both AV delays are started by an atrial event and, upon time-out, trigger the ventricular stimulus. Modifications include a set of short and long AV delays (after atrial paced or sensed events, rate modulated AV delay etc.) and different mechanisms of active search for intrinsic ventricular activity. The potential to reduce ventricular pacing depends on the length of the hysteresis interval24 and/or the maximum AV interval allowed. An algorithm which continuously adapts the technical AV delay to the actual intrinsic AV interval (DDD/AMC25,26) has recently shown a significant reduction of ventricular pacing from 95% (DDD) to 37% (DDD/AMC),26 but this is obviously not enough to prevent deleterious effects of (right) ventricular stimulation. Moreover, an unpublished sub-analysis of the PIPAF study indicates that DDD/AMC is ineffective in preventing ventricular pacing if special functions of AF prevention are activated.27
- The essential difference from AV hysteresis is that AAIsafeR does not trigger an AV delay while pacing in AAI mode. This allows for lengthening of the intrinsic AV interval and even for a loss of ventricular activity without immediate intervention in the ventricle (Fig. 5). Instead of using the AV time-out as the only criterion of the need for ventricular support, the algorithm makes several logical decisions:
- Some degree of advanced AV block (and the necessity of ventricular pacing) is judged from a definite number of missing R waves (see Methods). A similar backup mechanism is provided by managed ventricular pacing (MVP)28,29 (Medtronic, Minneapolis, USA) which differs slightly in the criteria used for switching from AAI to DDD but has been demonstrated to reduce the cumulative proportion of ventricular pacing to less than 5% in recipients of dual chamber ICDs with and without a history of AV block.28,29
- Unlike the first version of the algorithm, AAIsafeR2 can be programmed to discriminate between rest and exercise before using a ‘first degree AV block’ criterion for switching. This intends to prevent ventricular pacing if vagal tone slows down the AV conduction (for example at night) and the haemodynamic consequences are marginal as long as heart rate is maintained. When diastole shortens during exercise, however, programme settings define the maximum AV delay allowed to avoid P-on-T on the surface ECG, cannon waves as the mechanical consequence and the ‘AAIR pacemaker syndrome’ as the well-known complication of AAIR pacing.17
- The maximum pause criterion serves as a safety feature to prevent prolonged asystole.
- Some degree of advanced AV block (and the necessity of ventricular pacing) is judged from a definite number of missing R waves (see Methods). A similar backup mechanism is provided by managed ventricular pacing (MVP)28
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Safety and efficacy of AAIsafeR2 |
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Considering the number of patients studied and the limited time frame of follow-up, this report must be considered preliminary. Although robust data are only available in 43 patients with simultaneous recordings of Holter ECG and pacemaker diagnostics, the absence of any adverse event or symptom in 123 patients supports the safety of the algorithm. This is underlined by the finding that 56% of patients had transient mode commutations and 23% developed AV conduction abnormalities which resulted in long-lasting switches to DDD. Although most of these events might have remained without clinical consequences, AAIsafeR2 offered the safety of ventricular back-up pacing in all instances.
In first applications, AAIsafeR has been shown to be effective in limiting the cumulative ventricular pacing rate to 0.2±0.4% in those patients who had no permanent switch to DDD.5 This finding is reproduced by the present study in patients without persistent commutation. By enabling daily conversion attempts from DDD to AAI, the upgraded version of the algorithm reduced the incidence of long-lasting DDD operation from 35% (AAIsafeR) to 23% (AAIsafeR2). The reduction may also reflect different inclusion criteria which restricted spontaneous AV intervals to 250 ms for SND in the present but not in the earlier study. This limit was used in a first attempt to expose only patients to single chamber atrial pacing whose intrinsic AV conduction was likely to preserve physiological atrioventricular mechanics. In future studies and clinical practice, however, it may be preferable to apply this requirement controlled by echocardiography to exclude premature closure of the mitral valve.
In conclusion, the AAIsafeR2 mode seems to be safe and to preserve ventricular pacing reliably in case of paroxysmal AV block. At the same time, it provides for a low percentage of ventricular paced cycles. Its memory appears to be an efficient tool to document paroxysmal AV block. The efficacy of this new pacing mode in the prevention of AF with atrial overdrive pacing remains to be confirmed in ongoing studies (Prevention Of Atrial Arrhythmia In Patients Without AV Conduction Disease, PREFACE).
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Appendix |
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The following investigators and institutions participated in the evaluation of the AAIsafeR2 mode:
F Anselme, MD, CHRU C. Nicolle, Rouen, France; JM Davy, MD, CHRU Montpellier, Montpellier, France; P Defaye, MD, CHRU Grenoble, Grenoble, France; D Galley, MD, CHG d'Albi, Albi, France; Daniel Gras, MD, Nouvelles Cliniques Nantaises, Nantes, France; G Jauvert, MD, Clinique Bizet, Paris, France; D Lamaison, MD, CHRU Clermont-Ferrand, Clermont-Ferrand, France; P Mabo, MD, CHRU Pontchaillou, Rennes, France; JL Marcon, MD, CHG Annonay, Annonay, France; N Sadoul, MD, CHRU Brabois, Nancy, France; J Victor, MD, CHRU Angers, Angers, France; Gert Fröhlig, Medizinische Universitatsklinik III, Homburg, Germany; E Himmrich, MD, Univ. Mainz, Mainz, Germany; K Schwabe, MD, Segeberg Klinikum GmbH, Bad Segeberg, Germany; U Wiegand, MD, Univ. Lübeck, Lübeck, Germany; E Aime, MD, Ist. Pol. San Donato, S Donato (MI), Italy; R Cazzin, MD and G Pastore, MD, Portogruaro (VE), Italy; L Frabetti, MD, S Orsola, Bologna, Italy; C Orvieni, MD, Vigevano (PV), Italy; M Ridarelli, MD, Terni, Italy; A Vicentini, MD, Peschiera del Garda (VR), Italy.
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Acknowledgements |
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We wish to thank Gaelle David for her assistance in data monitoring, Rémi Nitzsché and Rodolphe Ruffy for reviewing the manuscript. This study was sponsored by ELA Medical, a SORIN Group company.
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References |
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