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Europace 2003 5(4):403-409; doi:10.1016/S1099-5129(03)00082-5
© 2003 by European Society of Cardiology
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Incremental programming of atrial anti-tachycardia pacing therapies in bradycardia-indicated patients: effects on therapy efficacy and atrial tachyarrhythmia burden

B. Hügl1, C. W. Israel2, C. Unterberg3, T. Lawo4, J. C. Geller5, I. M. Kennis6, D. E. Euler6, J. L. Koehler6, D. A. Hettrick6 on behalf of the AT500 Verification Study Investigators

1Heart Center, Leipzig/Central Clinic Bad Berka, Germany; 2J.W. Goethe University, Department of Cardiology Frankfurt, Germany; 3Georg-August Universitätskliniken Gottingen, Germany; 4Bergmannsheil, Department of Cardiology, Ruhr-Universität Bochum, Germany; 5University Hospitals Magdeburg, Department of Medicine Germany; 6Medtronic Inc. Minneapolis, MN, USA

Manuscript submitted 5 November 2002. Accepted after revision 15 June 2003.

Correspondence: Burkhard Hügl, MD, Central Clinic Bad Berka, Robert-Koch-Allee 9, 99437 Bad Berka, Germany. Tel.: +49-36458-50; Fax: +49-36458-42180. E-mail: bvehuegl{at}aol.com


   Abstract
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 Abstract
Introduction
 Methods
 Results
 Conclusions
 References
 
AIMS: Efficacy of pace-termination of atrial arrhythmias (ATP) may depend on atrial cycle length and regularity. Whether device programming of ATP therapies can improve ATP efficacy and alter atrial tachyarrhythmia burden is unknown.

METHODS AND RESULTS: ATP efficacy was evaluated in 61 patients (39 males; 66±10 years) with a standard indication for pacing, 95% with a history of AT/AF. Each patient was implanted with a novel DDDRP pacemaker capable of delivering ATP therapy. ATP efficacy and AT/AF frequency and burden were compared within each patient during a period of nominal ATP programming (NP) followed by a period of aggressive incremental programming (IP). Adjusted ATP-termination efficacy was higher during IP than during NP (54.8% vs 37.9%, P<0.05). No differences in AT/AF frequency (3.3±5.9 vs 3.2±6.9 day–1) or burden (18±28% vs 18±29%) were observed comparing NP with IP. The majority of episodes during both the NP (81%) and IP (77%) periods terminated within 10 min. Episodes lasting 24 h or more accounted for only 0.4% of the episodes in both groups, but accounted for 38% of the average burden during NP and 51% during IP.

CONCLUSIONS: Device programming of ATP therapies can influence the number of treated episodes and the efficacy of ATP therapies although arrhythmic frequency and burden may not change. Total atrial arrhythmia burden is disproportionately influenced by long (>24 h) episodes.

Key Words: Atrial arrhythmias, atrial fibrillation, atrial flutter, anti-tachycardia pacing, implantable devices


   Introduction
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 Abstract
 Introduction
Methods
 Results
 Conclusions
 References
 
Atrial arrhythmias are commonly observed in patients eligible for dual chamber pacemaker implantation. These rhythm disturbances are often associated with symptoms such as palpitations and dizziness as well as increased thromboembolic risk and decreased quality of life[1]Go. Novel dual chamber devices include preventive pacing overdrive algorithms in addition to therapeutic stimulation. These anti-tachyarrhythmic pacing (ATP) therapies enable the device to pace-terminate atrial arrhythmias with relatively high device-classified raw success rates, about 50% or more[2–Go5]Go. The efficacy of ATP-termination may depend on the rate and regularity of the arrhythmia[6]Go. However, some faster or more irregular rhythms might still be susceptible to ATP. Similarly, irregular fibrillatory rhythms may express regularity early in the episode, and hence vulnerability to ATP. Indeed, multiple transitions in both cycle length and cycle length regularity may occur over the course of a long arrhythmic episode[4]Go. Whether more aggressive programming of ATP therapies in combination with pacing prevention algorithms can further improve ATP efficacy compared with less aggressive programming is unknown. The present multi-centre trial investigated the impact of aggressive incremental ATP programming in combination with preventive atrial pacing algorithms on ATP efficacy in a dual chamber pacemaker population with a history of atrial fibrillation (AF).


   Methods
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 Abstract
 Introduction
 Methods
Results
 Conclusions
 References
 
A prospective multi-centre clinical study was designed to demonstrate the safety and efficacy of a new implantable pulse generator (AT500TM, Medtronic Inc., Minneapolis, MN) for preventing, diagnosing and treating atrial tachyarrhythmias in patients with a standard indication for a permanently implanted pacemaker. Results of this study have recently been published[2]Go. Patients were recruited from 33 centres and they underwent pre-implant assessment to ensure fulfilment of eligibility criteria. Each centre obtained Ethics Committee approval and all patients provided written informed consent.

Eligibility
Patients were required to meet the class I or class II implantation criteria for dual chamber pacing[7]Go and have a life expectancy of at least 1 year. Patients were considered ineligible if they had a mechanical right heart valve, an existing unipolar pacing lead that would not be replaced for this study, suspected accessory conduction pathways, or an implantable cardioverter-defibrillator.

Device operation
The present investigation employed a novel dual chamber implantable pulse generator (Medtronic AT500TM) that automatically classifies atrial rhythms based on the pattern of rate and regularity of both atrial and ventricular sensed events (Fig. 1). Atrial arrhythmias with shorter cycle lengths are considered AF, whereas atrial arrhythmias with longer cycle lengths are classified as atrial tachycardia (AT), depending on device programming. AT and AF detection zones may overlap to permit the delivery of therapies for fast regular arrhythmias. If the atrial cycle length is within this overlap zone, the atrial rhythm is classified as AT if the cycle length is regular and AF if it is not[8]Go. Atrial arrhythmia episodes terminate via detection of five consecutive beats of sinus or atrial paced rhythm or 3 min of unclassified atrial rhythm.

The device may deliver various combinations of ATP therapies including both ‘burst+’ and ‘ramp’ pacing therapies[2]Go. Only atrial arrhythmias classified by the device as AT by cycle length criteria in the AT zone or by the cycle length regularity criterion in the overlap zone are treated. ATP therapies are classified as ‘successful’ if the arrhythmia is terminated before AT/AF is redetected within 3 min after the last ATP sequence. In addition to ATP therapies, the device software includes three distinct programmable pacing algorithms designed to prevent atrial tachyarrhythmia occurrence. These include an atrial overdrive algorithm, a temporary atrial overdrive mode designed to avoid short–long intervals following a premature atrial contraction and a post-mode-switch overdrive pacing mode designed to inhibit the early recurrence of atrial tachyarrhythmias following termination of AT.



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  		Figure 1 AT/AF detection zone programming for NP (top) and typical IP (bottom). Only episodes classified by the device as AT as opposed to AF were treatable with ATP. Arrhythmic episodes with cycle lengths in the overlap zone were classified as AT if regular, AF if not.

 
Device counter data were used to determine raw frequency and burden as well as raw ATP efficacy and distributions of episode durations. The device also stores an atrial (or ventricular) electrogram as well as device markers prior to arrhythmia onset and again just prior to time of detection or termination for up to 35 AT/AF episodes between programmer interrogations. This subset of data from treated episodes was manually reviewed to determine the appropriateness of AT detection and termination.

Protocol
Each patient was implanted with a DDDRP pacing system. After a 1-month stabilization period, prevention features and ATP detection and therapies were activated and programmed to nominal settings for the next 2 months, as per the study protocol (Table 1 and Table 2). After 3 months, ATP therapies were allowed to be reprogrammed more aggressively by the investigator. Patients with more aggressive programming were selected for the present analysis. ATP efficacy and AT/AF frequency and burden were compared within each patient during the initial period of nominal device programming (NP) with a second period of more aggressive incremental programming (IP). NP included up to 18 sequences of ATP treatment for regular AT episodes longer than 1 min, atrial cycle length of 220–360 ms (Table 1). IP included any programming that widened the AT detection zone (e.g. 150–360 ms) and/or increased the maximum number of sequences above 18 or decreased the minimum time from detection to treatment (Table 1 and Table 2).


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  		Table 1 AT detection programming

 


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  		Table 2 ATP therapy programming settings

 
Statistical methods
The software packages SAS 6.12 (SAS, Cary, NC) and S-plus 2000 (MathSoft, Seattle, WA) were used for data analyses. ATP efficacy calculations were corrected using the generalized estimating equations (GEE) statistical method[9,Go10]Go with an exchangeable correlation structure. This technique controls for multiple responses within a patient by assuming a common correlation between any two responses. The resulting corrected observed performance measures are estimates of the average patient therapy efficacy. Continuous variables were reported as the mean±SD or as the median along with the range. Statistical significance was assumed when P<0.05.


   Results
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 Abstract
 Introduction
 Methods
 Results
Conclusions
 References
 
Patients
ATP efficacy was evaluated in 61 patients, 39 males; age 66±10 years, participating in a larger prospective, multi-centre study of 325 patients with a class I/II (American Heart Association/American College of Cardiology) indication for pacing (Table 3). Most patients (95%) also had a history of AT/AF. Mean left ventricular ejection fraction was 55±16%. Six patients were New York Heart Association (NYHA) class III. Fifty-one percent of patients maintained stable antiarrhythmic drug medications throughout the trial.

Of the 325 patients enroled until August 16, 2000, 61 patients completed the 6 months follow-up period and were reprogrammed after 3 months from NP to IP (Table 1). Forty-nine of the 61 patients experienced at least one AT/AF episode during either period. Of these, six patients experienced only untreated episodes due to high rate or irregularity (i.e. AF). Thirty-six patients experienced 3407 treated of the 14,011 total detected episodes over a follow-up period of 67±37 days during the NP period. Forty-three patients experienced 10,162 treated of the 20,678 detected episodes over a follow-up of 117±66 days during the IP period. The fraction of treated episodes was higher during IP than during NP (0.49 vs 0.24).


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  		Table 3 Patient demographics

 
ATP efficacy
The GEE adjusted ATP-termination efficacy for all treated episodes was significantly higher during IP than during NP (Table 4). No differences in AT frequency (3.3±5.9 vs 3.2±6.9 day–1) or burden (18±28 vs 18±29%) were observed comparing NP with IP (Wilcoxon signed rank test). A total of 2195 treated AT/AF episodes from 43 of the 49 patients with treated episodes were logged into the diagnostic memory storage of the device. Each of these episodes had a stored EGM and was manually reviewed to determine the appropriateness of AT detection and termination. Thus, 1786 of the treated and stored episodes (81%) in 43 patients were appropriately detected and terminated by the device. The efficacy of ATP on this subset of appropriate episodes was higher during IP than during NP (Table 4). The device classified 611 (34%) of the 1786 stored and reviewed episodes as AF. More episodes showed transitions from AF to AT or vice versa within a single AT/AF episode in the NP vs IP group (68% [56–79%] vs 27% [21–34%]; P<0.001, GEE [95% C.I.]).


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  		Table 4 ATP efficacy

 
The cumulative ATP efficacy based on ATP sequence number was higher during IP than during NP (Fig. 2). Figure 2 also shows that ATP efficacy increased up to about 10 sequences and then tended to plateau in both groups. In addition, ATP efficacy was higher for IP than NP based on cycle length at episode detection (Fig. 3A). There was a tendency for ATP efficacy to increase at longer cycle lengths in both groups. Furthermore, there were more treated episodes at shorter cycle lengths when the programming zone was expanded during the IP period (Fig. 3B). An additional analysis was performed to determine if ATP efficacy was influenced by the time to the last therapy (Fig. 4). Figure 4 shows that the greatest efficacy was achieved when the time to the last pacing therapy was 5 min or less in both groups.



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  		Figure 2 Cumulative ATP efficacy for NP (grey circles) and IP (black squares) for stored treated and reviewed episodes. NP programming allowed a maximum of 18 ATP sequences per episode. IP programming typically allowed a maximum of 30 ATP sequences. In general early sequences were more likely to terminate an episode than later sequences. Overall ATP efficacy was higher for IP programming. NP: 631 episodes in 35 patients; IP: 1155 episodes in 41 patients.

 



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  		Figure 3 (A) Adjusted estimate of ATP efficacy based on median cycle length (12 beats) at episode detection for NP and IP for stored treated reviewed episodes. In general, IP had higher efficacy than NP at all cycle lengths. (B) Number of episodes within cycle length range. Since treatment can occur much later than detection, CL at detection does not necessarily indicate CL at time of therapy. NP: 631 episodes in 35 patients; IP: 1155 episodes in 41 patients.

 



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  		Figure 4 Adjusted ATP efficacy based on time to last ATP therapy for stored treated and verified episodes. Time to last ATP therapy is similar to episode duration for successfully treated episodes. Few episodes were treated beyond 30 min with IP programming. Longer duration episodes were less likely to have successful ATP therapy. NP: 631 episodes in 35 patients; IP: 1155 episodes in 41 patients.

 
Episode duration
The duration of the treated episodes that were stored by the device was analysed in order to determine the effect of the atrial pacing therapies on AT/AF duration. A paired analysis was made during each period to compare the duration of episodes that were successfully terminated by ATP with those episodes that were not successfully terminated (Table 5). Successful pacing shortened the median episode duration from about 1 h to <4 min in both groups (P<0.001).


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  		Table 5 Paired treated episode median duration{dagger}

 
The distribution of duration for all episodes (treated and untreated combined) is shown in Fig. 5. The distribution tended to be skewed towards short episodes in both groups. There was no significant difference in the proportion of episodes that fell within each interval of the histogram comparing NP with IP. Eighty-one percent of episodes lasted ≤10 min during NP vs 78% during IP. During both periods, 0.4% of the episodes in 19 patients lasted 24 h or more. It was possible to estimate the burden due to episodes ≥24 h duration in each patient from the daily burden diagnostic. These long episodes were responsible for 38% of the average NP burden and 51% of the average IP burden of the entire population.



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  		Figure 5 The T distribution of episode duration for all episodes during NP and IP was similar. Most episodes had duration 0–10 min.

 
Discussion
This is the first study to examine the influence of ATP programmable variables on device-classified therapy efficacy. The main finding of the present investigation was that IP of ATP therapies increased the fraction of treated arrhythmia episodes, the number of individual therapy sequences and device-classified ATP efficacy in the same patients. However, such programming did not result in further reduction in AT frequency or burden.

The high number of AT/AF transitions observed in both study periods indicates that atrial rhythms may vary in both rate and regularity throughout the time course of the episode as previously observed[4]Go. In contrast with other devices available to treat atrial tachyarrhythmias[3]Go, the present device delivers ATP therapy only when the rhythm is classified by the device as AT. Thus, AT/AF transitions are relevant since they will have an impact on therapy delivery. The greater number of AT/AF transitions during the NP period (78%) compared with the IP period (30%) was due to the greater zone of overlap during the NP period (Fig. 1). Patients thought to experience exclusively fast and/or irregular rhythms may in fact experience discrete periods of increased regularity and longer cycle lengths that provide an opportunity to apply ATP. Furthermore, aggressive IP of ATP therapies to treat faster and less regular rhythms, and early application of that therapy during periods when the rhythm may be more susceptible, increased overall device-classified therapy efficacy.

Programming techniques to provide incremental ATP therapy include increasing the maximum number of possible ATP sequences per episode, increasing the range of cycle lengths over which ATP may be applied, decreasing the range of cycle lengths that must satisfy regularity criteria for treatment (Fig. 1) and decreasing the minimum episode duration before initiating treatment. Increasing the number of sequences did not seem to have a great impact, since cumulative efficacy did not improve greatly between 18 and 30 sequences for IP (Fig. 2). Increasing the cycle length range and reducing the overlap zone where the regularity criterion is applied (Fig. 1) resulted in greater efficacy based on cycle length at detection (Fig. 3). This programming also resulted in many more applications of ATP therapy to shorter cycle lengths (Fig. 3). Most successfully treated episodes in the IP group had all therapies delivered within 5 min (Fig. 4). Very few episodes in the IP group were treated after 30 min. The distribution of all episodes based on episode duration was similar between groups (Fig. 5). In those stored episodes that were reviewed, successful treatment with ATP shortened episode duration from about 1 h to <4 min in both groups (Table 5).

The observation that increased device-classified ATP efficacy did not result in concomitant reductions in AT/AF burden warrants discussion. Since the fraction of treated episodes was higher during the IP period, ATP efficacy was higher and successful therapy reduced episode duration, it seems reasonable that AT burden (i.e. the percentage of time spent in AT/AF) should have decreased. Possible explanations for these discordant observations include the following:

  1. ATP shortens episode duration, but more episodes occur.
  2. Multiple ATP therapies may be pro-arrhythmic and hence increase the duration of non-successfully treated episodes.
  3. ATP terminates many short duration rhythms that would have terminated spontaneously without therapy, thus having little impact on burden.
  4. ATP decreases the duration of many treated episodes, but overall burden calculation is biased by a few extremely long duration episodes.

The first hypothesis implies an increase in frequency in the IP group that was not observed. The second hypothesis implies that IP should result in decreased duration of successfully treated episodes and an increased duration of non-successfully treated episodes. However, the data in Fig. 5 and Table 5 show that device programming did not alter episode duration. The third hypothesis is supported by the observation that the majority of episodes in both groups lasted 10 min or less and thus, there could have been a high incidence of spontaneous episode termination. The fourth hypothesis is supported by the observation that long episodes (≥24 h) comprised only 0.4% of the total episodes but were responsible for 38% of the average burden during NP and 51% during IP. Thus, the impact on burden of decreasing the duration of episodes destined to last minutes or hours by ATP may be diluted by a few episodes of long duration.

Limitations
The results of the present investigation should be interpreted within the constraints of several potential limitations. The present device limits the maximum number of ATP therapies during each episode. Thus, all therapies can be exhausted within the first few minutes (Fig. 4) of a long episode and no further ATP can be applied even if the rhythm becomes vulnerable to ATP. Also, ATP therapy may terminate an AT episode by accelerating a stable AT into an unstable AF rhythm[11]Go. The device would likely classify such therapies as ‘non-successful’ since redetection of AT/AF would likely occur before episode termination. Similarly, spontaneously terminating episodes may be classified as ‘successfully treated’ by the device, since the software classifies an episode as successfully treated if episode termination criteria are met before redetection criteria are met. Also, the study periods were not randomized and the follow-up times during NP and IP were not equal. The decision to programme ATP more aggressively was made by the investigator based on stored diagnostic data on ATP efficacy during the study period. Only about half of the patients (51%) maintained a stable antiarrhythmic drug regimen throughout the entire study period. Despite adjustments in drug type or dosage, burden and frequency were not different between study periods.

The efficacy data in Table 4 are based on all episodes recorded in all patients during the entire follow-up period. These episodes cannot be manually screened to validate accuracy of episode detection and termination. Therefore, a subset of episodes, consisting of all episodes stored with EGM representing 16% of the total episodes, was manually reviewed. ATP efficacy was calculated on the reviewed episodes where detection and termination were determined to be appropriate. The adjusted efficacy based on this subset was very similar to the adjusted efficacy for all treated episodes (Table 4). In addition, both the raw and adjusted efficacy values are similar to those recently reported[2Go–5]Go.

Finally, it has to be emphasized that these results relate only to patients with a standard indication for pacing.


   Conclusions
Top
 Abstract
 Introduction
 Methods
 Results
 Conclusions
References
 
In summary, device programming of ATP therapies can influence the number of treated episodes as well as the efficacy of ATP therapies. The influence of this improved efficacy on overall control of atrial arrhythmias is uncertain, but arrhythmic frequency and burden were not changed. The measurement of overall burden may not reflect the ability of successful ATP therapy to shorten episode duration since burden may be too greatly influenced by long episodes. It is possible that optimal programming may reduce the frequency of symptomatic episodes without altering the overall arrhythmic burden. Additional studies will be required to demonstrate the clinical value of these ATP therapies in patients with bradycardia indication for a pacemaker implant and a history of AT/AF.


   Footnotes
 
This study was sponsored by Medtronic Inc., Minneapolis, MN.


   References
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 Abstract
 Introduction
 Methods
 Results
 Conclusions
 References
 
[1] Benjamin EJ, Wolf PA, D'Agostino RB, Silbershatz H, Kannel WB, Levy D. Impact of atrial fibrillation on the risk of death: the Framingham Heart Study. Circulation 1998; 98: 946–952.[Abstract/Free Full Text]

[2] Israel CW, Hügl B, Unterberg C, et al. Pace-termination and pacing for prevention of atrial tachyarrhythmias: Results from a multicenter study with an implantable device for atrial therapy. J Cardiovasc Electrophysiol 2001; 12: 1121–1128.[CrossRef][Web of Science][Medline]

[3] Schoels W, Swerdlow CD, Jung W, Stein KM, Seidl K, Haffajee CJ. Worldwide clinical experience with a new dual-chamber implantable cardioverter defibrillator system. J Cardiovasc Electrophysiol 2001; 12: 521–528.[CrossRef][Web of Science][Medline]

[4] Israel CW, Ehrlich JR, Gromefeld G, et al. Prevelance, characteristics and clinical implications of regular atrial tachyarrhythmias in patients with atrial fibrillation: insights from a study using a new implantable device. J Am Coll Cardiol 2001; 38: 355–363.[Abstract/Free Full Text]

[5] Swerdlow CD, Schoels W, Dijkman B, et al. Detection of atrial fibrillation and flutter by a dual-chamber implantable cardioverter-defibrillator. Circulation 2000; 101: 878–885.[Abstract/Free Full Text]

[6] Adler SW 2nd, Wolpert C, Warman EN, Musley SK, Koehler JL, Euler DE. Efficacy of pacing therapies for treating atrial tachyarrhythmias in patients with ventricular arrhythmias receiving a dual-chamber implantable cardioverter defibrillator. Circulation 2001; 104: 887–892.[Abstract/Free Full Text]

[7] Gregoratos G, Abrams J, Epstein AE, et al. ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices — summary article: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (ACC/AHA/NASPE Committee to Update the 1998 Pacemaker Guidelines). J Am Coll Cardiol 2002; 40: 1703–1719.[Free Full Text]

[8] Dijkman B and Wellens HJ. Diagnosis and therapy of atrial tachyarrhythmias in the dual chamber implantable cardioverter defibrillator. J Cardiovasc Electrophysiol 2000; 11: 1196–1205.[CrossRef][Web of Science][Medline]

[9] Liang KY and Zeger SL. Longitudinal data analysis using generalized linear models. Biometrika 1986; 73: 13–22.[Abstract/Free Full Text]

[10] Zeger S, Liang KY, Albert PS. Models for longitudinal data: a generalized estimating equation approach. Biometrics 1988; 44: 1049–1060.[CrossRef][Web of Science][Medline]

[11] Hii JT, Mitchell LB, Duff HJ, et al. Comparison of atrial overdrive pacing with and without extra stimuli for termination of atrial flutter. Am J Cardiol 1992; 70: 463–467.[CrossRef][Web of Science][Medline]


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