Dual-site Atrial Pacing Research Articles

Left atrial reverse remodeling and prevention of progression of atrial fibrillation with atrial resynchronization device therapy utilizing dual-site right atrial pacing in patients with atrial fibrillation refractory to antiarrhythmic drugs or catheter ablation

Dual-site right atrial pacing (DAP) produces electrical atrial resynchronization but its long-term effect on the atrial mechanical function in patients with refractory atrial fibrillation (AF) has not been studied. Drug-refractory paroxysmal (PAF) and persistent AF (PRAF) patients previously implanted with a dual-site right atrial pacemaker (DAP) with minimal ventricular pacing modes (AAIR or DDDR mode with long AV delay) were studied. Echocardiographic structural (left atrial diameter [LAD] and left ventricular [LV] end diastolic diameter [EDD], end systolic diameter [ESD]) and functional (ejection fraction [EF]) parameters were serially assessed prior to, after medium-term (n = 39) and long-term (n = 34) exposure to DAP. During medium-term follow-up (n = 4.5months), there was improvement in left atrial function. Mean peak A wave flow velocity increased with DAP as compared to baseline (75 ± 19 vs. 63 ± 23cm/s, p = 0.003). The long-term impact of DAP was studied with baseline findings being compared with last follow-up data with a mean interval of 37 ± 25 (range 7-145) months. Mean LAD declined from 45 ± 5mm at baseline to 42 ± 7mm (p = 0.003). Mean LVEF was unchanged from 52 ± 9% at baseline and 54 ± 6% at last follow-up (p = 0.3). There was no significant change in LV dimensions with mean LVEDD being 51 ± 6mm at baseline and 53 ± 5mm at last follow-up (p = 0.3). Mean LVESD also remained unchanged from 35 ± 6mm at baseline to 33 ± 6mm at last follow-up (p = 0.47). During long-term follow-up, 30 patients (89%) remained in sinus or atrial paced rhythm as assessed by device diagnostics at 3years. DAP can achieve long-term atrial reverse remodeling and preserve LV systolic function. DAP when added to antiarrhythmic drug (AAD) and/or catheter ablation (ABL) maintains long-term rhythm control and prevents AF progression in elderly refractory AF patients. Reverse remodeling with DAP may contribute to long-term rhythm control.

Atrial Fibrillation: Focal or Reentrant or Both?

Ablation for atrial fibrillation (AF) is a genuinely viable and increasingly used option for improving quality of life in patients with symptomatic drug-refractory AF. What is remarkable about the limited success achieved with these procedures is that progress has occurred despite a near complete lack of knowledge about what causes or maintains AF. Focal origins for AF were first demonstrated decades ago1–4 with topical application of acetylcholine to junctional tissues and atrial sites triggering AF. More recently, there has been convincing documentation of rapid tachycardia arising from the pulmonary veins inciting AF, thus supporting the concept of “trigger elimination” contributing to the success of pulmonary vein isolation. However, studies also support the presence of multiple reentrant circuits maintaining and possibly initiating AF.5, 6 The ablation era has taught us7–9 that in persistent and chronic AF, trigger elimination alone is not enough and that substrate modification is probably necessary to decrease the likelihood of reentrant wavelet continuance and thereby increase success rates. Even the most ardent supporter of either hypothesis recognizes the limitations of each. How can a focal source exist in this milieu indefinitely, producing and maintaining chronic AF, and how do multiple reentrant wavelets arise spontaneously? Article see p 384 In this issue of Circulation: Arrhythmia and Electrophysiology , Niu et al10 provide important, interesting, and novel insights into solving this age-old riddle using a previously unexplored angle-autonomic manipulation. Acetylcholine was used to induce AF in 31 canines. In 12 of the animal studies, propafenone was administered. They then ablated the ganglionated plexi (GP). Before ablation, AF could still be induced despite administration of propafenone. After ablation, there was a consistent pattern of electrogram organization and atrial synchronization. In addition, subsequent administration of propafenone resulted in the inability to induce atrial tachyarrhythmia. There are several …

What is the role of the pacing rate in the prevention of atrial tachyarrhythmias?

In 1998, Delfaut et al. 1 reported about 30 patients with drug-refractory atrial fibrillation (AF) which recurred in all individuals despite continuation of antiarrhythmic drugs within approximately 1 month, but was suppressed by pacing for a mean of 143 days. Although the main scope of this study was the assessment of dual-site right atrial pacing (which further prolonged the arrhythmia-free interval to 195 days), this observation stimulated interest in atrial overdrive pacing as a potential therapy of AF. Of note, all patients in this study had spontaneous or drug-induced bradycardia, and the investigators carefully adjusted pacing rate and drug dose until a proportion of atrial pacing during sinus rhythm of >80% was achieved. Similarly, Garrigue et al. 2 calculated the mean 24 h heart rate in 22 patients with a dual-chamber pacemaker via the memory of the device and programmed the lower pacing rate just 10 bpm above this value to perform atrial overdrive at an individually optimized rate. Again, overdrive pacing, in this case at a mean of 75 bpm, was associated with a reduction or complete prevention of AF recurrences. These and other observations led to the hypothesis that atrial overdrive pacing, i.e. pacing faster than the sinus rate, for a significant proportion of time may prevent AF. As the PA3 trial showed, atrial pacing in the DDDR mode with 70 bpm achieved atrial pacing for only 67% of the time in patients without sinus bradycardia and was unable to prolong the time to AF recurrence.3 Pacing at higher rates such as 90 bpm can achieve atrial overdrive for >80% of the time but is not tolerated by a number of patients.4 Therefore, pacing algorithms that maintain the atrial pacing rate just above the … *Corresponding author. Tel:+49 69 6301 6512; fax:+49 69 6301 6341. E-mail address: c.w.israel{at}em.uni-frankfurt.de

Dynamic and Dual‐Site Atrial Pacing in the Prevention of Atrial Fibrillation: The STimolazione Atrial DInamica Multisito (STADIM) Study

The impact of new algorithms to consistently pace the atrium on the prevention of atrial fibrillation (AF) remains unclear. Our randomized, crossover study compared the efficacy of single- and dual-site atrial pacing, with versus without dynamic atrial overdrive pacing in preventing AF. We studied 72 patients (mean age = 69.6 +/- 6.5 years, 34 men) with sick sinus syndrome (SSS) and paroxysmal or persistent AF, who received dual-chamber pacemakers (PM) equipped with an AF prevention algorithm and two atrial leads placed in the right atrial appendage (RAA), by passive fixation, and in the coronary sinus ostium (CS), by active fixation, respectively. At implant, the patients were randomly assigned to unipolar CS versus RAA pacing. The PM was programmed in DDDR mode 1 month after implant. Each patient underwent four study phases of equal duration: (1) unipolar, single site (CS or RAA) pacing with the AF algorithm ON (atrial lower rate = 0 ppm); (2) unipolar, single site pacing with the AF algorithm OFF (atrial lower rate = 70 bpm); (3) bipolar, dual-site pacing with AF algorithm ON; (4) bipolar, dual-site pacing with the AF algorithm OFF. Among 40 patients (56%), who completed the follow-up (15 +/- 4 months) no difference was observed in the mean number of automatic mode switch (AMS) corrected for the duration of follow-up, in unipolar (5.6 +/- 22.8 vs 2.6 +/- 5.5) or bipolar mode (3.3 +/- 12.7 vs 2.1 +/- 4.9) with, respectively, the algorithm OFF or ON. With the AF prevention algorithm ON, the percentage of atrial pacing increased significantly from 78.7 +/- 22.1% to 92.4 +/- 4.9% (P < 0.001), while the average ventricular heart rate was significantly lower with the algorithm ON (62.4 +/- 17.5 vs 79.9 +/- 3 bpm (P < 0.001). The AF prevention algorithm increased the percentage of atrial pacing significantly, regardless of the atrial pulse configuration and pacing site, while maintaining a slower ventricular heart rate. It had no impact on the number of AMS in the unipolar and bipolar modes in patients with SSS.

Efeitos da associação da estimulação atrial dinâmica em duplo sítio atrial com atenolol na prevenção da fibrilação atrial recorrente

Evaluate the effects of optimized atrial stimulation--OAS (dual-site atrial pacing, heart rate above the intrinsic rate, and specific functional algorithm), and the use of atenolol in preventing recurrent atrial fibrillation (AF). Primary endpoint: to quantify the rate of AF episodes. Secondary endpoints: assessment of quality of life, specific cardiovascular symptoms, rate of hospital admissions, rate of electrical and pharmacological cardioversions, and adverse cardiac events. Twenty-five patients with recurrent episodes of paroxysmal AF and sinus node disease had dual-site atrial and ventricular pacemakers implanted, and were started on atenolol, 100 mg/day. Next, they were randomized to two groups: GROUP I: first three months with OAS and the specific pacing algorithm (DAO) turned on, and three more months with the algorithm off. GROUP II: the inverse sequence to GROUP I. The pacing mode chosen was DDDR, and after three months patients underwent clinical and electronic evaluations of the stimulation system by: automatic mode switch (AMS), 24-hour Holter monitoring, Doppler echocardiogram, and SF-36 questionnaire. Following, a crossover comparison took place, and a new assessment was performed six months later. When compared to the group with the algorithm turned off, OAS patients had lower rates of: AF/week (p < 0.001); AMS activations (p < 0.01); hospitalizations (p < 0.001); cardioversions (p < 0.001), and higher scores on the physical and mental components of quality of life. The hybrid therapy adopted, OAS associated with the use of atenolol, reduced the rate of recurrent AF and improved the clinical-functional status of patients with symptomatic bradyarrhythmias.

Dual Site Right Atrial Pacing can Improve the Impact of Standard Dual Chamber Pacing on Atrial and Ventricular Mechanical Function in Patients with Symptomatic Atrial Fibrillation: Further Observations from the Dual Site Atrial Pacing for Prevention of Atrial Fibrillation Trial

The effects of atrial pacing mode on atrial and ventricular function in patients with atrial fibrillation (AF) and bradycardia have not been evaluated. We evaluated atrial and ventricular function during randomization to support pacing (SP), high right atrial pacing (HRA), and dual site right atrial pacing (DAP). Seventy-nine patients (66 +/- 12 yr, 46 male) with standard pacing indications and symptomatic AF were randomized to each of three pacing modes (DAP, HRA, SP) for 6 months in a crossover design. Echocardiographic studies were performed at enrollment and the end of each mode. Paired comparisons of atrial and ventricular function parameters were performed between each pacing mode and baseline. HRA pacing in DDDR mode resulted in increased left ventricular (LV) end systolic volume (78 +/- 42 vs. 60 +/- 31 ml, p = 0.001) and reduced LV ejection fraction (44 +/- 14 vs. 50 +/- 11%, p = 0.007) compared to baseline. These parameters did not change during DAP. DAP resulted in increased peak A wave velocity (75 +/- 19 vs. 63 +/- 23 cm/s, p = 0.003) and atrial filling fraction compared to baseline (0.47 +/- 0.15 vs. 0.38 +/- 0.13, p = 0.005). Atrial and ventricular function were similar between control and SP. DAP, but not HRA or SP, improved left atrial (LA) function in patients with AF and bradycardia. HRA pacing in DDDR mode resulted in LA dilatation and deterioration of LV function which was not observed with DAP.

Atrial fibrillation: profit from cardiac pacing?

The impact of cardiac pacing on the prevention of atrial fibrillation is under scientific investigation. Several prospective randomised clinical trials have reported that atrial-based "physiologic" AAI(R)- or DDD(R)-pacing is associated with a lower incidence of paroxysmal and permanent atrial fibrillation than single-chamber ventricular pacing in patients with a conventional pacemaker indication. However, it is still uncertain whether atrial pacing itself has independent antiarrhythmic properties. In contrast, right ventricular pacing is considered to promote atrial fibrillation, even in preserved AV synchrony during dual-chamber pacing. The electrical secondary prevention of atrial fibrillation is mainly based on variations of the atrial pacing site and sophisticated preventive pacing algorithms incorporated in the pacemaker software. Dual-site right atrial and biatrial pacing were reported to exhibit modest to no benefit for the prevention of atrial fibrillation, whereas septal pacing and specific preventive pacing algorithms have been demonstrated to reduce the incidence of atrial fibrillation in a number of clinical trials. However, the role of septal pacing and preventive pacing algorithms still has to be clarified since, overall, study results have been inconsistent so far. One of the main goals of future investigations should be the identification of responder groups of preventive pacing concepts. In clinical practice, the efficacy of pacing algorithms and septal pacing has to be determined in the individual case. These options should be taken into account in patients with symptomatic bradycardia as the indication for cardiac pacing and, in addition, symptomatic atrial fibrillation.

Cardiac pacing device therapy for atrial dysrhythmias: how does it work?

Atrial fibrillation (AF) is the most common dysrhythmia in North America. Paroxysmal or persistent AF affects an estimated 2.8 million individuals, causes significant morbidity, and is associated with 1 billion dollars in healthcare costs each year in the United States. An aging population, the prevalence of hypertension, and the emergence of heart failure as the final common pathway of heart disease finds us in an age where the incidence of AF is ever increasing and the management challenges are indeed an expanding clinical problem. Although guidelines for selection of the appropriate pacing mode have been published, device therapy for the control of AF and paroxysmal AF is an emerging clinical management strategy. In 2001 The American College of Cardiology (ACC)/American Heart Association (AHA) published a document to revise the 1998 guidelines for device therapy, and even now these guidelines require elucidation and inclusion for the use of cardiac pacing device therapy for the control of atrial dysrhythmia. Choosing a complex system, in particular for the patient with persistent and symptomatic atrial dysrhythmia, is a most intricate challenge for the healthcare professional and the healthcare system. Rate dependent effects on refractoriness, reduction of ectopy, remodeling of the substrate, and prevention of pauses have been described as the potential mechanisms responsible for the rhythmic control effect attributed to atrial pacing. However, while permanent cardiac pacing is required for patients with symptomatic bradycardia with atrioventricular block and AF, the concept of pacing for the primary prevention of AF is novel. Pacing algorithms, single site, biatrial, and dual-site atrial pacing and site-specific pacing have all been studied as substrate modulators to prevent recurrent atrial dysrhythmia.A dilemma exists surrounding the primary approach for the control of symptomatic AF with rapid ventricular response. The question remains: should it be to maintain the sinus rhythm or to control the ventricular response rate to the AF and anticoagulate? Variations in the population studied, differences in the pacing algorithms and protocols, and a lack of definitive end points account for the variable results of the studies completed thus far. With the current data available, it appears that for individuals with sinus node dysfunction and paroxysmal AF in combination with a bradyarrhythmia indication for pacing, suppression algorithms may play an additive role with full atrial pacing in the management and reduction of episodes and burden of paroxysmal AF. The goal of these therapies is to reduce the symptoms and hopefully decrease the healthcare costs associated with paroxysmal and persistent AF with uncontrolled ventricular response.

The Role of Multisite Atrial Pacing in Rhythm Control in AF: Insights from Sub‐analyses of the Dual Site Atrial Pacing for Prevention of Atrial Fibrillation Study

Novel pacing modes are being proposed for the prevention or reversion of atrial fibrillation (AF). High right atrial (RA) pacing and septal pacing have not individually reduced arrhythmic events in patients with AF in controlled trials. The DAPPAF trial compared the effectiveness of overdrive high right atrial single and dual site right atrial pacing as compared to demand pacing in prevention of recurrent symptomatic AF in patients with AF &amp; bradyarrhythmias. Methods: From September 1996 to November 2000, 120 patients with documented symptomatic AF were enrolled and followed in a prospective randomized single blind crossover multicenter trial. 73 males &amp; 45 females, mean age 66 ± 11 yrs with recurrent symptomatic AF (paroxysmal in 82 pts, persistent &gt;72 hrs in 30 pts &amp; persistent &gt;30 days in 6 pts) were enrolled. Baseline AF event frequency was ≥1/day in 40 pts, 1/week in 43 pts, &lt;1/week in 30 pts, &amp; unknown in 5 pts. Patients were implanted with dual site right atrial pacing systems and randomly assigned to six‐month treatment periods in overdrive dual, overdrive single or demand pacing. Three primary endpoints (time to first AF recurrence, patient quality of life &amp; tolerance/safety) and several secondary endpoints (device detected sustained AF, atrial &amp; ventricular function indices, &amp; composite endpoints) were examined. Results: Only DAP was significantly effective in preventing recurrent AF and prolonging time to first symptomatic AF recurrence in the presence of class 1 &amp; 3 antiarrhythmic drug therapy; it was more effective than H.A. pacing in reducing asymptomatic AF event frequency; DAY alone prevented left ventricular and left atrial dilatation seen with D'ETRE pacing in this population due to improved left atrial transport; in patients with persistent AF or after Sawtell therapy, DAY maintained efficacy while H.A. pacing showed attrition in effectiveness. DAY was better tolerated than H.A. pacing, with fewer crossovers and comparable safety to H.A. pacing. Conclusions: DAY is an important therapeutic tool in an “hybrid” strategy for management of drug‐refractory AF. It offers antiarrhythmic and hemodynamic benefits and can have therapeutic effects on symptomatic and asymptomatic paroxysmal and persistent AF. It can facilitate efficacy of other antiarrhythmic therapies in AF. Further study of its antiarrhythmic effects with hybrid drug and ablation therapies is now in progress, and long‐term use in an “hybrid” strategy has been reported in large pilot studies.

Improved suppression of recurrent atrial fibrillation with dual-site right atrial pacing and antiarrhythmic drug therapy

Improved suppression of recurrent atrial fibrillation with dual-site right atrial pacing and antiarrhythmic drug therapy

Global P wave duration on the 65-lead ECG: single-site and dual-site pacing in the structurally normal human atrium.

Pacing is believed to prevent atrial fibrillation by reducing atrial activation time. Exact correlation between P wave duration (PWD) on surface ECG and endocardial atrial activation time is still unexplored. In 15 patients without structural heart disease (9 women, age 45 +/- 14 years), single site [high right atrium (HRA), coronary sinus ostium (CSos), distal CS (CSd), high RA septum (Bachmann's bundle, BB)] and dual-site pacing (various combinations) was performed after ablation of supraventricular tachycardia. A 65-lead surface ECG was recorded simultaneously. Endocardial atrial activation time was measured off-line (stimulus - last bipolar recording), and the respective PWD was assessed using the root mean square and 65-channel summary plots. PWD during pacing from BB was significantly shorter (96 +/- 12 msec) than during HRA (121 +/- 15 msec), CSos (108 +/- 9 msec), and CSd pacing (126 +/- 14 msec; P < 0,01, respectively). PWD during dual-site pacing (HRA+BB, 91 +/- 14 msec; HRA+CSos, 96 +/- 7 msec; HRA+CSd, 90 +/- 7 msec; BB+CSd, 96 +/- 12 msec) was not significantly shorter than during pacing from BB. Correlation between endocardial atrial activation time and PWD was 0.83. PWD during single-site and dual-site atrial pacing represents endocardial atrial activation time and can be measured precisely using the 65-lead surface ECG. The fact that high septal pacing results in the shortest PWD may have implications for preventive pacing in patients with atrial fibrillation.

Clinical Experience of Contrast Venography Guided Axillary Vein Puncture for Placement of Pacemaker and Defibrillator Leads in Chinese Patients

Background and Objectives: Subclavian crush phenomenon is associated with lead placement using subclavian puncture (SP). Cephalic venous cutdown (CV), free of this complication, may be too small for use or just not big enough for multiple leads placement as in biventricular pacing or dual site atrial pacing. Contrast venography guided axillary vein puncture (AP) has been described to solve this problem. This study reports on clinical experience of this technique in Chinese patients.

Dual site right atrial pacing in the prevention of symptomatic atrial fibrillation refractory to drug therapy and unrelated to sinus bradycardia.

Dual-site right atrial pacing has been shown recently to prevent atrial fibrillation relapses in patients affected by drug-refractory, highly-recurring tachyarrhythmia, associated to sinus bradycardia. The aim of our study was to verify whether this stimulation modality could be useful in patients affected by refractory atrial fibrillation unassociated to sinus bradycardia. Fifteen patients (6 males) affected by refractory, symptomatic atrial fibrillation, and potential candidates to AV node ablation, were prospectively enrolled. Mean age was 65 +/- 5 years (range 62-78). Associated pathology was arterial hypertension in 12, and dilated cardiomyopathy in 3. Eight patients were affected by persistent atrial fibrillation, and seven by paroxysmal atrial fibrillation. The duration of the arrhythmia was 61 +/- 63 months (range 3-216). Left atrial diameter was 39.4 +/- 4.2 mm (range 33-46), left ventricular end-diastolic diameter was 52.4 +/- 12.2 mm (range 41-90), and left ventricular ejection fraction was 55 +/- 16 (range 18-81). Single chamber atrial pacing was used in 10 patients, dual chamber in 5 patients. The mean duration of follow up was 24 +/- 12 months (range 3-41). During this period the number of episodes of atrial fibrillation decreased from a mean of 13 +/- 38 (range 1-150) to 0.4 +/- 0.7 (range 0-2.3) per month (p < 0.001). In the subgroup of patients with persistent atrial fibrillation the number of episodes decreased from a mean of 20.4 +/- 52.4 (range 1-150) to 0.6 +/- 0.9 (range 0-2.3) (p < 0.001). In patients with paroxysmal atrial fibrillation the number of episodes decreased from 4.6 +/- 3.5 (range 2-12) to 0.2 +/- 0.5 (range 0-1.4) (p < 0.001). One patient (6.7%) developed chronic atrial fibrillation 16 months after the implant, 2 remaining patients (13%) had their arrhythmia unaltered. After the implant the number of Class 1 antiarrhythmic drugs fell from 18 to 6 (p < 0.001) and that of Class 2 changed from 0 to 7 p < 0.001). The use of Class 3 and 4 did not change significantly. No complications related to implant were observed. Permanent dual-site right atrial pacing can prevent atrial fibrillation recurrences in patients affected by highly symptomatic episodes unassociated to sinus bradycardia.

Dual-site atrial pacing for atrial fibrillation in patients without bradycardia

Atrial pacing has been shown to delay the onset of atrial fibrillation (AF) when compared with ventricular pacing in patients with sick sinus syndrome. The role for pacing in the control of AF in patients without bradycardia is uncertain. We performed a randomized, crossover, single-blinded study in 22 patients (14 women, aged 63 ± 10 years) with paroxysmal AF refractory to treatment with oral sotalol (202 ± 68 mg/day) and no bradycardic indication for pacing. All patients received a dual-chamber pacemaker with 2 atrial pacing leads positioned at the high right atrium and coronary sinus ostium, respectively. Patients were randomized in a crossover fashion to be paced for 12 weeks, either with high right atrial (RA) pacing at 30 beats/min (“Off”) or dual-site RA pacing with an overdrive algorithm that maintained atrial pacing at a rate slightly above the sinus rate (“On”). Treatment on resulted in a significantly higher percentage of atrial pacing and a reduction in atrial ectopic frequency than the treatment off period. The time to the first clinical AF recurrence was prolonged (15 ± 17 to 50 ± 35 days, p = 0.006), and total AF burden was reduced (45 ± 34% vs 22 ± 29%, p = 0.04) in the on-treatment phase. However, there was no difference in AF checklist symptom scores or overall quality-of-life measures. Dual-site RA pacing with continued sinus overdrive prolonged the time to AF recurrence and decreased AF burden in patients with paroxysmal AF. The absence of a major impact on symptom control suggests that pacing should be used as an adjunctive therapy with other treatment modalities for AF.

Dual site atrial pacing is effective for atrial fibrillation prevention in patients with and without atrial conduction delay Atul Prakash, Sanjeev Saksena, Ryszard Krol. CV Institute, Atlantic Health System, Passaic, NJ

Dual site atrial pacing is effective for atrial fibrillation prevention in patients with and without atrial conduction delay Atul Prakash, Sanjeev Saksena, Ryszard Krol. CV Institute, Atlantic Health System, Passaic, NJ

Dual-site atrial pacing and overdriving in the pipaf study: ongoing status

Dual-site atrial pacing and overdriving in the pipaf study: ongoing status

Dual-site atrial pacing and overdriving in the pipaf study: ongoing status

Dual-site atrial pacing and overdriving in the pipaf study: ongoing status

Multisite atrial pacing: an option for atrial fibrillation prevention? preliminary results of the Dutch dual-site right atrial pacing for prevention of atrial fibrillation study

Multisite pacing is a novel concept for the prevention of recurrent drug-refractory atrial fibrillation (AF). Two different pacing methods have been described, biatrial pacing and dual-site right atrial stimulation. The use of multisite pacing as preventive therapy for recurrences of atrial fibrillation is still under investigation. We conducted a prospective, randomized, crossover study in patients with recurrent drug-refractory AF without or with minimal structural heart disease. After implantation of a DDD pacemaker, patients were randomized to either dual-site pacing first (Group I) or single-site (high right atrium) pacing first (Group II) and, after 6 months of treatment, the device was reprogrammed to the other pacing mode. Preliminary results of 13 patients in each group are presented. Clinical characteristics of patients in both groups with respect to age, sex, left atrial dimension, left ventricular function, and New York Heart Association (NYHA) functional class were comparable. Pacing therapy was combined with antiarrhythmic drug treatment. After completion of the study protocol, the arrhythmia-free interval was not remarkably different in either group. However, the endpoint free interval (i.e., the need for electrical cardioversion because of recurrent AF lasting >24 hours, was less during dual-site pacing in Group II. Within 6 months, 43 patients enrolled in this study will have completed the protocol.

Emerging indications for permanent pacing.

New indications for pacing are being investigated in the areas of vasovagal syncope, hypertrophic obstructive cardiomyopathy, dilated cardiomyopathy, and atrial fibrillation. It is hoped that pacing will offer an alternative therapy to patients who are refractory to medical therapy. Although pacing for vasovagal syncope continues to be controversial, it appears that a highly symptomatic group with a predominately cardioinhibitory component can benefit. Current data indicate that dual-chamber pacing should not be considered therapeutically equal to septal myectomy in patients with hypertrophic obstructive cardiomyopathy, but may be considered in those more than 65 years of age, or in others who are not good surgical candidates. Biventricular or left ventricular pacing appears promising in heart failure patients and may be combined with implantable cardioverter-defibrillator therapy. Lead technology for coronary vein placement needs further improvement. Dual-site atrial pacing appears to help prevent recurrences of atrial fibrillation and may become a useful adjunct to drug, ablative, and implantable cardioverter-defibrillator therapies.

Atrial fibrillation: nonpharmacologic approaches

Various nonpharmacologic interventions are available for patients with atrial fibrillation (AF) who are refractory to standard drug therapy. Atrioventricular junctional ablation and permanent pacing is a very effective therapy for patients with AF and a poorly controlled ventricular response. The surgical MAZE procedure has been performed on small numbers of patients but is remarkably successful in restoring and maintaining sinus rhythm. The role of permanent pacing as treatment for paroxysmal AF is undergoing evaluation and dual-site atrial pacing appears particularly promising in reducing the number of episodes of paroxysmal AF. Certainly the most exciting frontier in the treatment of AF is radiofrequency catheter ablation procedures. Our understanding of the mechanisms of paroxysmal AF and chronic AF has expanded enormously in the past 5 years. Radiofrequency lesions in pulmonary veins using standard technology will cure many cases of paroxysmal AF. However, catheter systems under development offer a great promise of treating most paroxysmal and chronic AF within the next few years. These developments will revolutionize our approach to this ever more prevalent clinical problem.