Europace Advance Access originally published online on January 11, 2008
Europace 2008 10(2):138-146; doi:10.1093/europace/eum277
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PACING
Atrial lead location at the Bachmann's bundle region results in a low incidence of far field R-wave sensing
browska-Kugacka1
ski2
Zago
don3
1 Department of Cardiology and Electrotherapy, Medical University of Gdask, ul. D
binki 7, 80-211 Gdask, Poland;
2 Department of Cardiology, Medical University of Lublin, Poland;
3 Department of Hygiene and Epidemiology, Medical University of Gdask, Poland
Manuscript submitted 14 August 2007. Accepted after revision 22 November 2007.
* Corresponding author. Tel: +48 58 349 39 10; fax: +48 58 349 39 20. E-mail address: elew{at}amg.gda.pl
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Abstract |
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Aims: The aim of the study was to investigate far field R-wave sensing (FFRS) rate and characteristics at different right atrial (RA) positions in patients treated with multisite atrial pacing, with the RA lead implanted at the Bachmann's bundle (BB) area in 69 patients, in comparison to RA appendage (RAA) in 70 patients.
Methods and results: All measurements were done during sinus rhythm in supine patients, with unipolar (UP) and bipolar (BP) sensing configuration. The presence, amplitude threshold (FFRS trsh) and FFRS timing were determined. Sensing safety margin was defined as the ratio of sensed P-wave vs. FFRS trsh, for both the minimal (Pmin) and the mean (Pmean) P-wave amplitude. At both atrial locations BP sensing was superior to UP in FFRS rejection (P < 0.0001). At 0.5 mV sensitivity level (BP) FFRS occurred in 1% of patients at the BB site vs. 11% at the RAA (P = 0.01). FFRS trsh (BP) was 0.2 ± 0.1 mV at the BB vs. 0.4 ± 0.3 mV in the RAA position (P < 0.0001). Sensing safety margin, when determined for the Pmin amplitude was 
5 in 99% of patients from the BB group, in comparison to 66% of RAA patients (P < 0.0001), in whom it was <2 in 13%. Even with the use of BP leads equipped with a 10 mm tip-to-ring spacing FFRS incidence was lower at the BB site (P < 0.01), FFRS trsh was lower (P < 0.001), and sensing safety margin was higher vs. RAA (P = 0.002).
Conclusion: Bachmann's bundle area features optimal conditions for signal sensing, and such atrial lead positioning may offer advantages to prevent oversensing of R-wave, thus improving functioning of standard dual chamber pacemakers, ICDs and CRT-Ds.
Key Words: Oversensing, Far field R-wave sensing, Bachmann's bundle, Atrial fibrillation, Atrial blanking time, Atrial lead
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Introduction |
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With modern dual chamber (DDD) pacemakers and dual chamber implantable cardioverter defibrillator (ICD) adequate atrial sensing is a prerequisite for reliable functioning of these devices. It is especially important in patients with paroxysmal atrial tachyarrhythmias, in whom automatic mode switch algorithms are involved or prevention and termination therapies for atrial fibrillation (AF) are provided. Bipolar (BP) atrial electrogram amplitudes were shown to be lower in AF and atrial flutter,1
that requires higher atrial sensitivity and thereby increases the risk of sensing of ventricular depolarization in the atrial channel of the device, that is called far field R-wave sensing (FFRS).
Far field R-wave sensing may have various consequences if interferes with algorithms for whom atrial sensing is a key function.2–4 It is particularly unfavourable in patients with AF, as it can induce false positive mode switching, that both results in unfavourable atrio-ventricular dissociation, and may lead to over-estimation of the AF burden5–7 with important impact on further treatment in patients with AF.
There are several factors that may influence the occurrence of FFRS, among whom atrial sensing polarity and atrial sensitivity being programmed are of main importance.4,8 With modern devices programming of longer post-ventricular atrial blanking (PVAB) time can be helpful, as it would eliminate most FFRS. Despite the atrial filter characteristics of the pacing device and the programmability of the pacemaker, lead design and location may also affect the FFRS.9 It was reported that FFRS signals of lower amplitude were recorded when the atrial lead was placed at the lateral wall compared with the right atrial appendage (RAA) position.10,11 However, data on FFRS with respect to the atrial lead implantation site are limited, and there are no published reports we are aware of to have evaluated effects of the lead positioning at the Bachmann's bundle (BB) region.
The aim of the present study was to investigate the rate and characteristics of FFRS in patients with multisite atrial pacing with the right atrial (RA) lead implanted at the BB area in comparison to the RAA position. Moreover, the effects of the use of BP leads with a 10 or 15 mm tip-to-ring spacing were evaluated.
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Patients
The study involved 139 patients treated with multisite atrial pacing for sinus node dysfunction with symptomatic recurrent AF. They were implanted with two BP atrial leads and a standard DDD pacemaker. Only patients with sustained spontaneous sinus rhythm >40 bpm, and at least 3 months after implantation when one may expect stable pacing and sensing conditions, entered the study. Multisite atrial pacing incorporated the RA lead implanted at the BB region (BB group) or in the RAA (RAA group), and the other lead at coronary sinus (CS) ostium or in the mid- or distal CS. The technique of lead implantation in the BB area, and ECG characteristics during pacing in this region has been reported.12
The RA lead was connected to the atrial port, and the CS lead to the ventricular port of DDD pacemaker. The study has been approved by local ethical committee and all patients gave their written informed consent. The FFRS measurements were performed 3–9 months after implantation, during a routine control of the pacing system. The BB group consisted of 69 patients (33 men) in the mean age of 70 ± 9 years. The RAA group comprised 70 patients (34 men) aged 70 ± 10 years.
Implanted devices
In both groups patients received DDD pacemakers: Axios DR or Philos DR (Biotronik GmbH, Berlin, Germany). The atrial sensitivity level in these devices is programmable from 0.1 to 1.0 mV at 0.1 mV intervals and between 1.0 and 7.5 mV at 0.5 mV intervals. The PVAB time was fixed at 50 ms. At the BB region only screw-in leads with interelectrode spacing of 10 mm were positioned (Biotronik Elox P 53BP in 46 and Selox SR 53BP in 23 patients). At the RAA predominantly J-shaped tined leads were implanted with a tip-to-ring distance of 15 mm (Biotronik Synox SX 53JBP in 44, Polyrox PX 53JBP in 11 patients), and in 15 patients screw-in leads with a tip-to-ring distance of 10 mm were implanted (Elox P 53BP in 10, Selox SR 53BP in 5 patients). Characteristics of the leads is shown in Table 1.
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Methodology
All measurements were performed with patients in the supine position. With the use of the automatic P-wave amplitude test available in both of the pacemaker models, the minimal (Pmin) and the mean (Pmean) sensed P-wave amplitude were established. During the test such sensitivity setting was chosen that allowed precise determination of every sensed P-wave amplitude within the test duration (12 s). Special attention was focused if ventricular signal detection interfered with P-wave amplitude measurements, and if this happened the test was repeated. To determine the intra-individual variability in the sensed P-wave amplitude the difference between the Pmean and Pmin amplitude was calculated in each patient, both in unipolar (
P-UP), and BP sensing configuration (P-BP). Using the same test the FFRS after sensed R-waves was evaluated at the highest available testing atrial sensitivity of 0.1 mV, with simultaneous recording of the RA intracardiac electrogram (IEGM), marker channels and surface ECG by means of pacemaker programmer (Biotronik ICS 3000). During the test the presence of the atrial sense marker coincident with the R-wave was monitored, and if FFRS occurred the IEGM was frozen and displayed at the programmer screen at a sweep speed of 100 mm/s. Then, using an electronic calliper system (with an accuracy of 3 ms) the interval between the beginning of the QRS complex on the surface ECG and the first atrial FFRS marker was measured to determine FFRS timing (Figure 1). Next, the automatic P-wave amplitude test was repeated with the atrial sensitivity gradually decreased step by step, until no FFRS was seen (as indicated by the absence of an atrial sense marker coincident with the R-wave). The FFRS threshold (FFRS trsh) was defined as the highest atrial sensitivity at which no FFRS occurred (Figure 2). If FFRS was not present at the most sensitive setting of 0.1 mV FFRS trsh was assumed to be equal to 0.1 mV. To establish the sensing safety margin the ratio of the Pmin amplitude and the Pmean amplitude vs. FFRS trsh was estimated for each patient. Sensing safety margin was determined as a continuous variable and as a categorical variable with three levels: <2, 3, and 5.
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All measurements were performed with UP and BP atrial sensing configuration, and results were compared between both atrial sites. Moreover, results were compared according to the type of atrial leads used, for 10 and 15 mm tip-to-ring spacing leads at the RAA position, and for 10 mm interelectrode distance leads at the BB and RAA site. For practical reasons these comparisons were performed only for BP sensing configuration.
Statistical methods
Data are presented as means with standard deviations or medians with ranges where appropriate. A 
2-test was used to analyse differences between categorical variables. For normally distributed continuous variables the Student's t-test was applied. If variables did not follow normal distribution Mann–Whitney U-test was performed for comparisons of independent variables. Wilcoxon signed rank test was used for comparisons of related variables. STATISTICA software (version 7.1, StatSoft, Inc.) was used to calculate statistics. P < 0.05 was considered statistically significant.
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Results |
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Basic pacing and sensing characteristics at the time of the FFRS measurements were performed are shown in Table 2. There were no differences between both atrial sites in the Pmin and Pmean values of sensed P-wave amplitudes. The differences between Pmean and Pmin (
P) were not different between both sites, as well as between UP and BP sensing configurations. The mean P-UP was 0.47 ± 0.38 mV in the RAA group and 0.49 ± 0.54 mV in the BB group (P = ns). The mean P-BP was 0.55 ± 0.54 mV, and 0.53 ± 0.65 mV, respectively (P = ns).
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Results with respect to the atrial lead implantation site
The FFRS trsh was twice lower at the BB region in comparison to the RAA: 0.2 ± 0.1 mV vs. 0.4 ± 0.3 mV (P < 0.0001). There were no differences between both atrial sites in the mean FFRS trsh with UP configuration. The mean BP FFRS trsh was significantly lower than with UP sensing in both atrial locations (P < 0.0001). The FFRS trsh histograms obtained with BP sensitivity at both atrial sites are presented in Figure 3. At the BB region predominantly FFRS trsh of 0.1 mV were measured, in comparison to mainly 0.5 mV in the RAA. Results of the FFRS trsh and timing measurements are presented in Table 3.
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There were no differences of FFRS rate between both atrial sites at the BP sensitivity of 0.1 mV, but at a setting of 0.5 mV 99% of BB patients had no FFRS, in comparison to 89% of patients from the RAA group (P = 0.01) (Table 4). At the highest sensitivity of 0.1 mV with UP configuration FFRS occurred in all patients from the BB group and in 84% of RAA patients (P < 0.001) (Table 4). The results were similar at a UP sensitivity of 0.5 mV. At both atrial sites FFRS rejection was significantly better with BP sensing, with more patients free from FFRS at both 0.1 and 0.5 mV sensitivity setting (P < 0.0001 vs. UP).
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There were no differences between atrial locations in FFRS timing characteristics (Table 3). At both sites FFRS started earlier with the UP than with BP sensing (P < 0.0001). With the UP configuration in three patients sensing of the R-wave through the RAA lead occurred earlier than the QRS complex on the surface ECG. It was not present at the BB site.
The mean values of the ratios of the Pmin and Pmean amplitude vs. FFRS trsh are shown in Table 3. In the BP configuration the mean ratio at the BB region was more than twice the estimated one at the RAA position for the Pmean amplitude, and nearly three times higher considering the Pmin amplitude. There were no differences between both atrial locations with the UP sensing. At both atrial sites the mean ratios were higher in BP than in UP sensing mode (P < 0.0001). In 99% of BB patients sensing safety margin was 5 when determined for the Pmin amplitude, in comparison to the 66% of patients from the RAA group (P < 0.0001), in whom it was <2 in 13% of patients (Table 5). Theoretical percentages of patients that could be safe-programmed to a permanent sensitivity setting of 0.3 and 0.5 mV with a double margin for P-wave sensing and double margin for rejection of FFRS were presented in Table 6.
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Results with respect to the type of atrial lead implanted in the right atrial appendage
Two types of atrial leads were used in the RAA: 55 patients received a passive fixation lead with a tip-to-ring spacing of 15 mm, and 15 patients received a screw-in lead with a tip-to-ring distance of 10 mm. We found no differences of FFRS trsh, as well as P-wave amplitudes, timing parameters and sensing safety margins between both types of atrial leads (Table 7). We did not find differences of the prevalence of sensing safety margin of
3 and 5 did between both types of atrial leads (Table 8), however those comparisons may lack statistical power. At the BP sensitivity of 0.1 mV FFRS occurred more frequently in patients with 10 mm, than in those with 15 mm interelectrode spacing lead: 71% vs. 24% of patients, respectively (P < 0.01). However, no differences in FFRS rates were confirmed at the BP sensitivity of 0.5 mV: 5% vs. 21% of patients, respectively (P = ns).
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Results with respect to the use of atrial leads with a 10 mm tip-to-ring spacing at the right atrial appendage and Bachmann's bundle site
Atrial leads with short tip-to-ring distance were implanted in 15 patients in the RAA, and in 69 patients at the BB region. At the BB position the mean FFRS trsh was lower (P < 0.001) and the sensing safety margin was higher when determined for both the Pmin and Pmean amplitudes, in comparison to the RAA (P = 0.002). There were no differences between both atrial sites in terms of P-wave amplitudes and FFRS timing parameters (Table 9). In 99% of BB patients the safety margin was
5 when determined for the Pmin amplitude, in comparison to 79% of patients from the RAA group (P = 0.001), where it was <2 in 14% of patients (Tables 5 and 8). With the use of these leads FFRS occurred less frequently at the BB site. At the BP sensitivity of 0.1 mV FFRS was recorded in 71% of patients in the RAA, and in 30% of BB patients (P < 0.01). At the sensitivity of 0.5 mV the FFRS rate was 21% in the RAA, as compared with 1% at the BB site (P < 0.001).
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Discussion |
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The occurrence of FFRS is well known and at 0.1 mV BP atrial sensitivity 90–100% of patients with conventional DDD pacemakers showed far field sensing after paced R-waves, and 71–92% after sensed R-waves.4
,8 FFRS can interfere with several diagnostic and therapeutic functions of modern dual chamber devices, including ICD.4 It can lead to inadequate activation of automatic mode switch,5–7 and in devices with prevention and termination therapies for AF may even induce AF if inappropriate atrial pacing is delivered.13 It was also reported that FFRS caused inadequate behaviour of dual chamber ICD.14,15
With the programmability of PVAB time in modern devices FFRS-related consequences can be easily solved. However, it should be emphasized that long atrial blanking periods may decrease the sensitivity of arrhythmia detection, especially atrial flutter if every other flutter wave will not be sensed.4,16 That is why different algorithms of 2:1 lock-in protection have been provided. In patients with dual chamber ICD or combined biventricular pacing and ICD therapy (CRT-D) a long PVAB time, as it decreases the sensitivity of AF detection, may result in false positive ventricular tachycardia recognition and inappropriate therapy delivery in the presence of AF being fast conducted to ventricles. Thus, for reliable AF detection programming of short PVAB time is recommended,17 as well as higher atrial sensitivity setting is necessary to detect low amplitude AF.1 However, both such settings promote FFRS occurrence. So, it is of interest if the location of the lead within the atrium offers any additional advantages to those obtained with discerning programming of different atrial sensing features.
The present study aimed to assess the effect of atrial lead implantation site on the incidence of FFRS during sinus rhythm and its characteristics. In comparison to previous studies, that defined the FFRS trsh as the lowest atrial sensitivity where such sensing occurred4,18 we used more rigorous criterion. We determined the FFRS trsh as the highest sensitivity at which no FFRS constantly occurred, similar to Cools et al.8 and Nash et al.9 Moreover, when calculating the sensing safety margin as the ratio between the sensed P-wave amplitude and the estimated FFRS trsh, we established it for both: the Pmin and the Pmean amplitude. Taking into account the Pmin amplitude reveals the real safety of the programmed atrial sensitivity at a given FFRS trsh. It was performed for the first time, as in previous studies only the Pmean amplitude was considered.8,9
Our data confirm the findings of other studies, that BP atrial sensing is clearly superior in rejecting FFRS compared with the UP configuration,8,19–21 and it was observed at both: the BB and RAA sites. FFRS started earlier with UP sensing compared with BP, that was also documented by Cools et al.8 The FFRS timing was measured at the highest sensitivity setting of 0.1 mV, and the possible explanation is that UP configuration allowed recording of the initial portion of the ventricular signal, which was rejected with BP sensing. However, it remains to be proven by a study assessing the ‘width’ of the refractory sense markers, also with different sensitivity settings. Moreover, and only with the UP configuration, in 4% of RAA patients FFRS occurred before the QRS complex on the surface ECG. It was also reported in studies performed in patients with conventional DDD pacemakers, that during sinus rhythm atrial sensing of the far field R-wave occurred often before the R-wave was sensed in the ventricular channel.4,6,19 Cools et al.8 found it mainly with UP sensing (56% of patients), but it was also noted with BP configuration (12%). It is so because in these cases the ventricular activation begins in the area closer to the base of the heart than to the apex. With such far field sensing an algorithm of ‘negative blanking’ is necessary, which rejects an atrial sensed event if it is closely followed by ventricular sensing. However, our data indicate that this was no more present with atrial lead implanted at the BB region.
In previous studies, that investigated the occurrence of FFRS and their characteristics, the atrial lead was mainly located in the RAA, that is a conventional atrial pacing site in patients referred for dual chamber pacing or ICD.4,8,9 There are only a few studies that evaluated effects of different atrial lead locations,18,19,22 some of them presented only in abstract form.10,23 Okrglicki et al.10 and Kantharia et al.11 reported that with the RA lead in the lateral position far field R-wave signals with lower amplitudes were seen. In a study by Timmis et al.22 BP recordings were performed and intracardiac amplitudes of the P-wave and far field R-wave signals were measured at three different locations: RAA, high right atrium (HRA), and low lateral atrium. The ratios between the P-wave and FFRS amplitude were the greatest in the HRA, however the differences were not significant compared with the RAA and low right atrium. Brouwer et al.19 also found no differences regarding FFRS between the HRA and RAA, and the worst characteristics was shown in the low right atrium, where the amplitude and slew-rate of endocardial far field R-wave signals were significantly higher. Our study is the first that reports on the FFRS at the BB region. Moreover, our group of 139 patients outnumbers other studies. Only Brouwer et al.19 investigated larger population, however they used different methods based on endocardial recordings, and performed their measurements during pacemaker implantation.
In our study, using BP sensing configuration, that is known to be superior to UP in rejecting of FFRS, the results on the FFRS prevalence and characteristics favour the BB site. This can be explained by Kirchoff's law, which states that the electrical potential at any location is inversely related to its distance from the current source.24 Moreover, lead position at the BB area and the location of its dipoles may be more successful in FFRS rejection with BP sensing.
In unfiltered intra-operative recordings the far field R-wave signals in the RAA were found with amplitudes of up to 3 mV.20,25 In the study by Brandt and Worzewski4 the median BP threshold for the sensed R-wave in the RAA was 0.2 mV (0.1–0.4 mV), and it was 0.27 ± 0.18 mV (0.1–0.9 mV) as reported by Cools et al.8 The mean BP FFRS trsh in our RAA patients was higher when compared with these studies, however it was notably lower at the BB region. Moreover, BP sensing safety margin, when determined for the Pmin amplitude was 5 in 99% of BB patients, in comparison to 66% of patients from the RAA group. Thus, our results indicate that programming of high atrial sensitivity (i.e. 0.5 mV), that is mandatory for reliable and fast detection of AF, is much safer with atrial leads implanted at the BB area.
As previously mentioned, also BP leads design may influence the occurrence of FFRS. It was reported that atrial oversensing was more frequent and the amplitude of far field R-waves increased with a longer tip-to-ring spacing.23,26 Reducing the interelectrode distance reduces the incidence of FFRS and improves the ratio between the P-wave and FFRS amplitudes.9,27 However, lead design is always a compromise between the appropriate P-wave amplitudes, rejection of the FFRS, and acceptable mechanical properties. Data on FFRS in relation to the atrial lead design are very limited.8,9,19 Cools et al.8 found that using leads with shorter interelectrode spacing of 10 mm in the RAA is not beneficial in terms of FFRS trsh and timing characteristics, comparing to leads with a tip-to-ring distance of 15 mm, and our results may confirm this finding.
We are not aware of any other clinical studies having demonstrated that the BB region is superior to the RAA in terms of FFRS rate and its characteristics. With BP sensing configuration, that is nowadays widely used in cardiac pacing, the mean FFRS trsh was significantly lower, and the sensing safety margin significantly higher in the BB position, as indicated by the higher ratio between the sensed P-wave amplitude and the estimated FFRS trsh, and at 0.5 mV atrial sensitivity FFRS was seen less frequently at the BB site. Even with the use of leads with a short tip-to-ring spacing of 10 mm, that facilitates rejection of FFRS, the results favour the BB region.
Study limitations
The assignment to the RA lead position was not randomized. Our study groups consisted of patients treated with multisite atrial pacing, and none of them was implanted with a ventricular lead. Thus, the results from our study apply for spontaneous ventricular rhythm, as ventricular pacing was not employed in our patients. It in patients with conventional DDD pacemakers FFRS was reported more frequently after paced than after sensed R-waves,4,8 FFRS trsh were found to be higher and they occurred much later after a ventricular paced than sensed event.8 Thus, although the BB region presents with an excellent sensing characteristics during sinus rhythm that may predict benefits regarding FFRS also during ventricular pacing, further studies are needed. Moreover, due to the ‘lack’ of ventricular lead the FFRS timing was measured in relation to the surface ECG. Thus, it does not allow recommending the PVAB time programming in patients with conventional DDD pacing in whom this is a ventricular sense or pace event that starts the PVAB period. Atrial electrogram recordings during AF were not performed in our study, and it needs to be determined whether the BB region offers an advantage with respect to AF signals compared with the RAA.
An important factor that may influence FFRS occurrence is the sensing performance of the pacemaker depending on the electrical characteristics of sense amplifiers and the input filters. Our study was done with the Biotronik Axios and Philos pacemakers that have identical atrial sensing characteristics. However, the results cannot be extrapolated to other pacemaker models or brands that may have different amplifier and filtering characteristics.
All measurements were performed at rest in the supine position, and if the results hold true in different daily life conditions is not known. However, Cools et al.8 reported that measurements made in the supine position are in general sufficient to predict the presence or absence of FFRS in patients standing or at peak exercise.
Conclusion and clinical implications
The results of our study indicate that with high atrial sensitivity low rate of atrial oversensing can be achieved when the atrial lead is implanted at the BB region. With such atrial lead position additional advantages may be obtained to prevent oversensing of R-wave, thus improving functioning of standard dual chamber pacemakers, ICDs and CRT-D.
Conflict of interest: We declare no conflict of interest.
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The study was supported by Polish Government research grant No. N N402 2383 33.
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References |
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