Atrial overdriving is beneficial in patients with atrial arrhythmias: first results of the PROVE Study

Health-Related Quality of Life in Pacemaker Patients: A Single and Multidimensional Self-Rated Health Comparison Study

Since implantation of the first permanent pacemaker in 1958, significant advances have been made in pacemaker technology. To date, however, health-related quality of life (HRQoL) in a large pacemaker population has not been investigated. With dwindling clinical resources, it is important to study HRQoL in a pacemaker population in a reliable and straightforward manner. This study aimed to determine and compare single and multidimensional self-rated health (SRH) in a pacemaker population in terms of sociodemographic characteristics, pacemaker mode and symptoms. The findings showed that irrespective of whether the perspective was single or multidimensional, this Swedish pacemaker population (n=697) with a mean age of 76 years had an acceptable HRQoL. Men, aged 65-84 years, persons who were cohabiting, who had their own dwelling, who had a DDD or who had a pacemaker for <or=3 and 4-7 years experienced better HRQoL. Efforts need to be made for women, single persons, the elderly and retired persons. In conclusion, the SRH of a pacemaker population can be trustworthy established by means of a single-dimensional SRH question.

[Atrial pacing for prevention of atrial fibrillation. Influence of septal atrial pacing, atrial overdrive and AV-delay-optimization on atrial fibrillation burden]

BACKGROUND

Atrial overdrive and optimized interatrial conduction time can reduce atrial fibrillation (AF). Increased ventricular stimulation results in a higher incidence of atrial fibrillation.

PATIENTS AND METHODS

In 25 patients with paroxysmal AF, a dual-chamber pacemaker (Identity DR 5370, St. Jude Medical) was implanted. Atrial leads were placed randomly either septal (n=12) or conventional (n=13). Dynamic atrial overdrive (DAO) was activated and the AV delay was optimized according to Koglek's method. After 3, 6, 9, and 12 months automatic mode switch (AF burden) was analysed.

RESULTS

No difference in implantation parameters were observed between groups. Technical implantation parameters were in the normal range for both groups. After 12 months patients in the septal group had less AF burden (1% vs. 7%, p=0.06), and the total number of AF episodes was reduced.

CONCLUSION

Septal pacing is safe. In combination with DAO and AV delay optimization it may reduce the AF burden, which can be observed after 12 months.

The place of hybrid therapies with drugs to supplement nonpharmacological therapies in atrial fibrillation

Atrial fibrillation (AF) is one of the most common cardiac arrhythmias, and its prevalence continues to rise as the aged population increases. Comparative studies of rhythm control and rate control have been equivocal; however, the benefits of rhythm control may have been offset by the limitations of antiarrhythmic drugs. More recently, nonpharmacological therapies have emerged that provide hope of more effective rhythm control. Catheter ablation techniques have gained favour with high success rates in specialized centers, although these techniques are not without complications and require considerable expertise. Pacing therapies designed to reduce harmful right ventricular pacing and increase physiological pacing have shown benefit in AF patients with bradycardia. Despite this progress, no single modality confers benefit for all patients. Strategies to combine these treatment modalities in a hybrid approach has shown increasing promise for subgroups of AF patients.

The MINERVA study design and rationale: a controlled randomized trial to assess the clinical benefit of minimizing ventricular pacing in pacemaker patients with atrial tachyarrhythmias

BACKGROUND

Dual-chamber (DDD) pacing has generally been regarded as "physiologic pacing" and therefore expected to be superior to ventricular pacing. Major randomized trials have so far failed to demonstrate significant reductions in the incidences of mortality, stroke, and heart failure. It has been shown that unnecessary ventricular pacing in patients with sinus node dysfunction or only intermittent atrioventricular block is associated with ventricular desynchronization and increased risk of atrial tachyarrhythmias (ATA).

METHODS

The MINimizE Right Ventricular pacing to prevent Atrial fibrillation and heart failure (MINERVA) study is a prospective, multi-center, randomized, international, single-blind, controlled trial designed to determine whether physiologic pacing through the managed ventricular pacing (MVP) algorithm combined with preventive atrial pacing (PAP) and atrial antitachycardia pacing (ATP) is superior to standard DDD pacing in terms of 2-year reduction in death, permanent ATA, and cardiovascular hospitalizations. Patients with standard class I or II indications for permanent DDD pacing and history of ATA will receive a Medtronic EnRhythm implantable pacemaker (Medtronic, Minneapolis, MN). After a 1-month run-in period, patients will be randomized in a 1:1:1 manner to the DDD (control group, all OFF), the DDDRP (MVP + PAP + ATP ON), and the MVP group (only MVP ON). Up to 1,300 patients will be included in approximately 70 centers in Europe, the Middle East, and Asia.

CONCLUSIONS

The MINERVA study will make an important contribution to the management of patients with paroxysmal ATA and accepted indications for dual-chamber pacemaker implantation by determining whether physiologic pacing combined with PAP and ATP is superior to standard DDD pacing in terms of reduction of mortality, incidence of permanent ATA, and cardiovascular hospitalizations.

The role of pacing in rhythm control and management of atrial fibrillation

Atrial fibrillation is the most common sustained cardiac arrhythmia and is increasing in prevalence with an ageing population. As the arrhythmia is often asymptomatic the true prevalence is likely even higher. Largely because of stroke this arrhythmia places a huge financial burden on the health economy. Despite this, large studies assessing rate versus rhythm control have been equivocal. Because of the ineffectiveness of pharmacological therapy much research effort has been undertaken in device and ablative approaches to rhythm management. Although catheter ablation has gained favour because of the high success rates the technique requires considerable expertise and still has a significant complication profile maintaining interest in pacing therapies for atrial fibrillation. Dual chamber versus single-chamber ventricular pacing has been shown to significantly reduce the incidence of atrial fibrillation. Research is currently underway to see if minimising the deleterious effects of right ventricular apical pacing could further increase the benefits of atrioventricular synchronous pacing. Several studies show some (albeit variable) reduction in AF burden with anti-AF algorithms in the setting of bradycardia. Antitachycardia pacing, on the other hand, has not been shown to treat AF in a randomised trial despite the successful termination of co-existent atrial tachycardias. There is increasing evidence that alternative atrial pacing sites may treat AF by improving atrial function. Furthermore, these strategies coupled with other therapies in a 'hybrid approach' have also showed promising results.

Optimization of pacing algorithms to prevent and treat supraventricular tachyarrhythmias

Preventive atrial pacing and antitachycardia pacing have been proposed for the treatment of atrial fibrillation and associated arrhythmias in patients with indications for device implantation. Preventive algorithms provide overdrive atrial pacing, reduction of atrial premature beats, and prevent short-long atrial cycles with good patient tolerance. However, clinical trials testing preventive algorithms have shown contradictory results, possibly because of different trial designs, end points and patient populations. Factors probably responsible for neutral results include an already high atrial pacing percentage with the conventional DDDR mode, suboptimal atrial pacing site, and the deleterious effects of high percentages of right ventricular apical pacing. Atrial antitachycardia pacing therapies are effective in treating organized atrial tachyarrhythmias (that precede atrial fibrillation), mainly when delivered early after the onset particularly if the tachycardia is relatively slow. Antitachycardia pacing therapies might influence atrial fibrillation burden, but clinical studies have shown conflicting results about this issue. Consistent monitoring of atrial and ventricular rhythm including progression to persistent forms of atrial arrhythmias, variability of atrial arrhythmia recurrence patterns and onset mechanisms as well as antitachycardia pacing efficacy should be recorded in the stored device memory and used for optimal individual programming of these new functions.

Adaptive Bi-Atrial Pacing Improves the Maintenance of Sinus Rhythm

INTRODUCTION

Multiple pacing modalities have been shown to individually decrease atrial fibrillation (AF) burden and relieve symptoms of AF. This investigation retrospectively evaluated whether a combination of bi-atrial pacing with dynamic atrial overdrive (DAO) AF suppression would further decrease AF burden as compared to AF suppression (DAO) alone.

METHODS AND RESULTS

A total of 33 patients were retrospectively evaluated. Patients (n = 16) were identified from the Deborah Heart and Lung Center pacemaker database with DAO programmed on at time of implantation. Patients (n = 17) were identified with bi-atrial pacing leads in right atrium and mid to distal coronary sinus who also had DAO programmed on at the time of implant. Evaluation of interrogated pacing data revealed Percent Time in Mode Switch (18.2%+/- 7.2% vs 0.59%+/- 0.08%) to be significantly lower (P = 0.014) in the bi-atrial paced group. In addition, there were less mode switches per day (MSPD) in the bi-atrial paced group (0.62 +/- 0.43 MSPD) versus control (4.40 +/- 3.24 MSPD) (P = 0.06).

CONCLUSION

Bi-atrial pacing while used in conjunction with an adaptive pacing suppression algorithm (DAO) may successfully be used to inhibit PAF.

Temporal variability of atrial fibrillation in pacemaker recipients for bradycardia: implications for crossover designed trials, study sample size, and identification of responder patients by means of arrhythmia burden

BACKGROUND

Most clinical trials that have tested pacing therapies to prevent and treat atrial tachyarrhythmias (AT) have chosen endpoints such as AT frequency or burden (defined as percentage of time a patient is in AT), but failed to show unequivocal evidence of a clinical impact.

AIM

The aim of our multicenter prospective observational study was to measure the variability of AT burden and estimate its impact on study outcomes.

METHODS AND RESULTS

Two hundred and fifty patients indicated for permanent pacing and suffering from AT (age 71 +/- 9 years; 47.2% male) received a dual-chamber pacemaker. AT burden was measured in two consecutive, 2-month observation periods; the Monte Carlo method was then applied to simulate findings of a crossover design study. We simulated several models of therapy impact, each model being characterized by the percentage of responder patients and the percentage reduction in AT burden. To show a significant impact of AT therapies in a sample of 250 patients in whom 100, 75, or 50% would be theoretical responders to therapies, AT burden reduction should be at least 27, 32, or 57%, respectively. Temporal fluctuations in AT burden were so high that about 60% of patients would falsely appear as responders or nonresponders in a crossover study, regardless of AT burden reduction.

CONCLUSIONS

In patients paced for bradycardia and suffering from AT, high intrapatient variability in AT burden was measured. Various models of therapy impact showed that, in crossover trials of AT therapies, time-related fluctuations in AT burden negatively impact on sample sizes and impair the ability to identify patients as responders or nonresponders.

First multi-centre evaluation of a knowledge-based implant-assistant for implantable cardioverter-defibrillators

AIMS

Modern implantable cardioverter-defibrillators (ICDs) place increasing demands on the physician, as their complexity requires more and more knowledge and effort in handling them. To overcome this problem an implant-assistant has been developed, which transfers clinical data entered by the physician into a complete set of parameters for programming a dual-chamber ICD (Tachos-DR, Biotronik, Berlin, Germany) at DFT testing (DFT-Prog) and first permanent programming (Perm-Prog) after implant.

METHODS AND RESULTS

Routine ICD implantations were initially evaluated by clinical experts at 19 centres in USA and Europe from 178 patient files. The rating of parameters was related to the number of parameters available in each patient. For DFT-Prog, 98.4% of parameter suggestions were identical to experts' expectations, an additional 1.0% were accepted, 0.5% were rejected, and none was considered harmful. This resulted in an overall acceptance of 94.4% of the DFT-Prog. For Perm-Prog, 96.1% of parameters were identical to those advised by experts, an additional 2.4% were accepted, 1.5% rejected, and seven parameters (0.04%) were considered potentially harmful by experts with an overall acceptance of 86.5%. Adaptation of the implant-assistant increased the overall acceptance to 100% for DFT-Prog and 90.6% for first Perm-Prog without any potentially harmful suggestions.

CONCLUSION

The ICD implant-assistant, which allows the physician to programme ICDs directly from clinical data, is a promising method to simplify the programming of modern ICDs.

Device-based therapies for atrial fibrillation

Ablation of the atrioventricular conduction system and pacemaker implantation is the preferred procedure for patients with atrial fibrillation (AF) in whom a rate control strategy has been selected but in whom rate-controlling medications are intolerable or ineffective. Selection of standard right ventricular (RV) pacing versus biventricular pacing is individualized, based on the degree and etiology of left ventricular dysfunction. Atrial-based pacing is clearly preferable to ventricular-based pacing in patients with sick sinus syndrome, because it leads to a reduction in the development of AF. Emerging evidence indicates that excess RV pacing is deleterious, increasing AF, heart failure, and possibly mortality. Therefore, physiologic pacing with minimization of RV pacing is desirable. Atrial pacing algorithms that increase the frequency of atrial pacing have shown modest efficacy in the prevention of AF. Use of atrial pacing algorithms is reasonable for patients with a history of AF and standard bradycardia indications for permanent pacing in whom maintenance of sinus rhythm is desirable. Studies assessing novel and multiple site atrial pacing therapies have mixed results, without compelling evidence of clinically important benefit. The exceptions are biatrial and right atrial overdrive pacing immediately after cardiac surgery. Several studies have shown effective suppression of postoperative AF with their use. Device therapy (eg, atrial antitachycardia pacing and defibrillation) for the termination of AF is effective in reducing arrhythmia burden. However, improvement in clinically relevant end points is not established and indications are not clearly defined. If a patient lacks an indication for an implantable cardioverter-defibrillator, we do not offer atrial defibrillation as a treatment option. Atrial arrhythmias may be better prevented by programming to avoid ventricular pacing than by specific atrial interventions.

Device therapy for atrial fibrillation

Currently, there are more therapeutic options available for AF patients with recurrent symptomatic AF episodes. The studies on the role of device therapy for AF have been promising thus far, but they have not achieved any of the goals of AF management. Based on large randomized clinical trials, patients with SSS should receive atrial-based pacing devices. Moderate sized randomized studies have shown minimal benefit of multi-site pacing in AF prevention, even when combined with antiarrhythmic agents. Alternative site pacing such as septal pacing (high or low), however, may be more advantageous, as it achieves similar results in terms of AF reduction with less hardware. The role of ATP in AF prevention is still in its infancy and will need further studies to determine its role in conjunction with antiarrhythmic agents. Furthermore, the role of radiofrequency ablation of pulmonary veins and other sites of AF initiation has been evolving and may be offered to more patients in the future. This approach may be more acceptable to patients and may gain wider acceptance for some groups of AF patients rather than device therapy. In any event, there is still a large role for pacemaker therapy in the management of AF, especially in patients who cannot benefit from curative ablation or surgery procedures, or patients who have failed these procedures, and particularly elderly patients who typically do not undergo these procedures. Based on current understanding, careful selection of pacing sites and pacing algorithms may help in reducing AF episodes in patients receiving devices.

Hybrid therapy of atrial fibrillation: algorithms and outcome

Rhythm control methods have not shown superior outcomes to rate control strategies in atrial fibrillation. Newer approaches to rhythm control employ "hybrid" therapies combining pharmacologic and non pharmacologic interventions. Pathophysiologic insights into mechanisms of atrial fibrillation (AF) suggest that arrhythmogenesis is due to interactions of multiple triggering rhythms and a complex electrophysiologic substrate resulting in the emergence of multiple tachyarrhythmias, often in disparate locations that may coexist in time. Thus, an "hybrid" therapy prescription is more likely to address several of the etiologic factors culminating in clinical AF. Results of pilot clinical studies of hybrid therapy are encouraging and involve drugs, devices and ablation techniques in varying permutations. Hybrid therapy algorithms using right heart procedures can improve efficacy with potentially lower risk. Considerations in implementation of these algorithms include staged or simultaneous interventions and a right versus left heart strategy. The parallel with the current coronary disease management paradigm is obvious and relevant.

Atrial Tachyarrhythmia Recurrence Temporal Patterns in Bradycardia Patients Implanted with Antitachycardia Pacemakers

INTRODUCTION

New-generation pacemakers allow continuous atrial tachyarrhythmia (AT) monitoring that provides accurate information about AT type, frequency, burden, and temporary evolution.

METHODS AND RESULTS

We performed a prospective multicenter study to describe AT temporal patterns in patients with sinus bradycardia and AT. Two hundred forty patients (123 men; age 71 +/- 8 years) were implanted with a DDDRP pacemaker (model AT500, Medtronic Inc.). All patients were followed for 13 months. The first-month stabilization period of all patients was discarded from analysis. Seventy percent of patients had AT recurrences. Mean time to first AT recurrence (48.2 days, 95% confidence interval [CI] 37.0-59.5 days) was significantly longer than the time between first and second AT episode (10.3 days, 95% CI 6.7-13.9 days, P < 0.01). A minority of patients had a uniform time distribution of AT recurrences: <25% of patients had AT episodes in more than 6 of the 12 months considered in the study. The probability density function of consecutive sinus rhythm days between AT episodes was calculated for each of 40 patients who experienced >25 AT episodes and fitted by power law and exponential functions. The best fit was obtained by power law function in 60% of patients, by exponential function in 10%, and the two models gave comparable results in 30% of patients.

CONCLUSION

In our population of patients with a history of sinus bradycardia and AT who were implanted with a new device equipped with atrial pacing therapies, 30% did not experience AT recurrences in the 12-month study period. Analysis of interevent time showed that in 60% of patients AT recurrences do not follow a uniform or random distribution. These findings bring into question the use of cross-over design and time to first AT recurrence as a clinical outcome in trials for AT therapy in this patient population.

Pacing to prevent atrial fibrillation

INTRODUCTION

Pacing has been proposed as a nonpharmacologic treatment option to prevent atrial tachyarrhythmias (ATs) in drug-refractory patients. This article reviews the current state of pacing to prevent ATs.

METHODS AND RESULTS

Different pacing modalities have been assessed with regard to their ability to prevent AT: conventional DDDR pacing with elevated lower rate limit, biatrial pacing, dual-site right atrial pacing, atrial septal pacing, and pacing with the use of dedicated pacing algorithms. Small studies suggest a benefit of conventional pacing for AT prevention in patients with bradycardia, but a randomized trial did not reveal any AT reduction by conventional pacing in patients without bradycardia. AT prevention by biatrial or dual-site right atrial pacing has been reported in small studies, but randomized trials did not show a clear benefit of these pacing techniques. Small studies showed a reduced AT recurrence rate in patients with septal pacing at the triangle of Koch or at Bachmann's bundle. Two large randomized trials with preventive pacing algorithms showed a significant AT reduction compared to conventional pacing, but this was not confirmed in four trials.

CONCLUSION

Pacing seems to be able to suppress ATs in a minority of patients; however, prospective identification of responders to different pacing modalities does not appear to be feasible at the present time.

A new pacemaker algorithm for the treatment of atrial fibrillation: results of the Atrial Dynamic Overdrive Pacing Trial (ADOPT)

OBJECTIVES

The Atrial Dynamic Overdrive Pacing Trial (ADOPT) was a single blind, randomized, controlled study to evaluate the efficacy and safety of the atrial fibrillation (AF) Suppression Algorithm (St. Jude Medical Cardiac Rhythm Management Division, Sylmar, California) in patients with sick sinus syndrome and AF.

BACKGROUND

This algorithm increases the pacing rate when the native rhythm emerges and periodically reduces the rate to search for intrinsic atrial activity.

METHODS

Symptomatic AF burden (percentage of days during which symptomatic AF occurred) was the primary end point. Patients underwent pacemaker implantation, were randomized to DDDR with the algorithm on (treatment) or off (control), and were followed for six months.

RESULTS

Baseline characteristics and antiarrhythmic drugs used were similar in both groups. The percentage of atrial pacing was higher in the treatment group (92.9% vs. 67.9%, p < 0.0001). The AF Suppression Algorithm reduced symptomatic AF burden by 25% (2.50% control vs. 1.87% treatment). Atrial fibrillation burden decreased progressively in both groups but was lower in the treatment group at each follow-up visit (one, three, and six months) (p = 0.005). Quality of life scores improved in both groups. The mean number of AF episodes (4.3 +/- 11.5 control vs. 3.2 +/- 8.6 treatment); total hospitalizations (17 control vs. 15 treatment); and incidence of complications, adverse events, and deaths were not statistically different between groups.

CONCLUSIONS

The ADOPT demonstrated that overdrive atrial pacing with the AF Suppression Algorithm decreased symptomatic AF burden significantly in patients with sick sinus syndrome and AF. The decrease in relative AF burden was substantial (25%), although the absolute difference was small (2.50% control vs. 1.87% treatment).

New approaches to atrial fibrillation management: a critical review of a rapidly evolving field

Atrial fibrillation (AF) is the most common cardiac arrhythmia, the prevalence of which is increasing with the aging of the population. Because of its clinical importance and the lack of highly satisfactory management approaches, AF is the subject of active clinical and research efforts. This paper reviews recent and on-going developments in pharmacological and non-drug management of AF. The ideal therapeutic goal for AF is the production and maintenance of sinus rhythm. Comparative studies suggest that available class I and III drugs have comparable and modest efficacy for sinus rhythm maintenance. Amiodarone, with actions of all antiarrhythmic classes, has recently been shown to have clearly superior efficacy compared with other available drugs. Newer agents are in development, but their advantages are as yet unclear and appear limited. A potentially interesting approach is the prescription of drugs upon the occurrence of an attack, rather than on a continuous basis. Recent insights into AF mechanisms may permit therapy to prevent development of the AF substrate. An alternative to sinus rhythm maintenance is a rate control approach, with no attempt to prevent AF. Drugs to effect rate control include digitalis, beta-blockers and calcium channel antagonists. Digitalis has limited value for control of exercise heart rate and for paroxysmal AF, but is particularly well suited for patients with concomitant AF and congestive heart failure. AV-nodal ablation and pacing is an effective alternative for rate control but leaves the patient pacemaker dependent. The relative merits of rate versus rhythm control are being evaluated in ongoing trials, preliminary results of which indicate no statistically significant differences in primary endpoints but highlight the risks of rhythm control therapy. In patients requiring pacemakers, physiological pacing (dual chamber devices or atrial pacing) has an advantage over purely ventricular pacemakers in AF prevention. Newer pacing modalities that produce more synchronised atrial activation, as well as pacemakers that prevent excessive atrial rate swings, show promise in AF prevention and may soon see wider use. The usefulness of automatic atrial defibrillators is presently limited by discomfort during shocks. Targeted destruction of pulmonary vein foci by radiofrequency catheter ablation suppresses paroxysmal AF. Efficacy in persistent AF is lower and still under study. Problems include potential recurrence in other veins and a small but nontrivial risk of pulmonary vein stenosis. Surgical division of the atria into zones with limited electrical connection, the MAZE procedure, is highly effective in AF prevention but is a major intervention that is not applicable to most patients. In conclusion, significant advances are being made in the management of patients with AF but much more work remains to be done.

The results of pacing trials for the prevention and termination of atrial tachyarrhythmias: is there any evidence of therapeutic breakthrough?

Atrial fibrillation (AF) is now recognized as the most prevalent sustained cardiac arrhythmia and it is associated with considerable mortality and morbidity. The demand for effective therapeutic strategies for AF has always been high and is anticipated to further increase. Anticoagulation and pharmacologic antiarrhythmic therapy or radiofrequency catheter ablation remain the mainstay of treatment for AF. Among the wide range of nonpharmacologic options which are presently being investigated, only ablation in or around the pulmonary veins and the surgical maze procedure have been shown to accomplish the aim of the curative treatment of the arrhythmia. Preventative atrial pacing and antitachycardia pacing may offer an attractive alternative option for the management of AF by either eliminating the triggers and/or by modifying the substrate of the arrhythmia. The results of several recent trials have shown a significant increase in the time to first AF recurrence, a decrease in atrial conduction time, and a trend towards reduction in AF burden, suggesting that atrial pacing may prevent AF due to improved synchronization of atrial depolarization. The recognition of potential triggers of AF, such as atrial premature complexes, short-long sequence, and bradycardia, has encouraged the development of novel atrial pacing algorithms designed to prevent the initiation of the arrhythmia on an individual basis. Observations of AF often starting with regular atrial activity consistent with atrial tachycardia have supported the hypothesis that early antitachycardia pacing may prevent progression to AF. The concept of "hybrid therapy" based on the combination of several different therapeutic strategies suggests that antitachycardia pacing therapy, integrated with an atrial defibrillator and preventative atrial pacing modes, may act synergistically to prevent AF. Dual chamber cardioverter-defibrillators with capacity to prevent and interrupt AF may offer more comprehensive and successful treatment for patients with advanced heart disease, frequent paroxysms of AF, and the risk of proarrhythmia.

Atrial pacing for the prevention and termination of atrial fibrillation

Atrial fibrillation (AF) affects about 2% of the general population and 8%-11% of those older than 65 years. The demand for effective therapeutic strategies for AF is anticipated to increase substantially as the proportion of the elderly population increases. Atrioventricular nodal ablation accompanied by permanent pacemaker implantation is an established option in elderly patients with intractable arrhythmia and poor ventricular rate control. However, it renders most patients pacemaker dependent and does not eliminate symptoms associated with loss of atrial transport or reduce the risk of stroke. The considerable limitations of rhythm or rate control strategies prompted interest in preventative atrial pacing, which may reduce the incidence of AF by either eliminating the triggers and/or by modifying the substrate of AF. Atrial or dual-chamber pacing has been proven to prevent or delay progression to permanent AF in elderly patients with sinus node dysfunction as compared with ventricular pacing. Patients with advanced atrial conduction delay may benefit from atrial resynchronization pacing. There may be additional benefits associated with the use of particular sites of pacing, specific pacing algorithms designed to target potential triggers of AF, and pace-termination of atrial tachycardia. Preventive and antitachycardia pacing algorithms incorporated in implantable cardioverter-defibrillators and pacemakers are currently under investigation and may offer a valuable alternative to antiarrhythmic drug therapy in elderly patients with left ventricular dysfunction at high risk of proarrhythmia or worsening heart failure. The evolution of hybrid therapy, in which two or more different strategies are employed in the same patient, may be the most effective approach to management of AF.

Suppression of atrial tachyarrhythmias by pacing

INTRODUCTION

Treatment of atrial tachyarrhythmias (ATs) remains difficult in many patients. Accordingly, new therapeutic approaches for AT suppression are evaluated. Atrial pacing may prevent ATs by modifying the electrophysiologic conditions required for sustained ATs.

METHODS AND RESULTS

New pacing algorithms for prevention of AT are aimed at permanent overdrive suppression of arrhythmic activity, reduction of dispersion of atrial refractoriness produced by short-long cycles, more aggressive overdrive pacing after spontaneous sinus conversion to prevent early reinitiation of ATs, and prevention of inadequate rate decay in patients with vagally induced ATs. AT prevention may be achieved by dedicated atrial pacing sites, e.g., pacing at the insertion of Bachmann's bundle or biatrial pacing, which compensates for interatrial conduction delay. Preexciting regions of critical conduction delay, pacing at the triangle of Koch or coronary sinus os, and dual-site right atrial pacing have shown antiarrhythmic effects. Atrial preventive pacing and pharmacologic treatment may work synergistically in the concept of hybrid therapy. To prevent atrial electrical remodeling, early termination of AT seems desirable. This may be achieved by implanted devices that automatically detect ATs and provide atrial antitachycardia pacing for organized ATs. Initial studies showed that regular AT can automatically be terminated in approximately 50% of treated episodes.

CONCLUSION

Pacing for prevention of AT and termination of organized AT episodes may become important steps within the concept of hybrid therapy of AT. However, their clinical efficacy and optimal patient selection remain to be evaluated in prospective, well-designed clinical trials.