Immediate Reinitiation of Atrial Fibrillation Following Internal Atrial Defibrillation

Immediate Reinitiation of AF. Introduction: Although the recurrence rate of atrial fibrillation has been reported to be similar to that after external and internal cardioversion, little is known about immediate reinitiation of atrial fibrillation (IRAF) following internal cardioversion. Methods and Results: Thirty-eight patients (24 men; mean age 63 ± 13 years) underwent internal atrial defibrillation. Catheter-based defibrillation electrodes were positioned in the anterolateral right atrium and the coronary sinus. All patients were cardioverted at a mean threshold of 4.6 ± 3.4 J. Five of 38 patients (13%) had 1 to 4 episodes of IRAF. No difference in clinical and echocardiographic characteristics were observed when patients with and without IRAF were compared. Atrial fibrillation was always reinitiated by an atrial premature beat. When the earliest atrial endocardial activation time on the defibrillation catheters was analyzed, these atrial premature heats did not seem to originate from the defibrillation catheters. Twenty-one patients had atrial premature heats without IRAF. When the coupling intervals of the first atrial premature heat in patients without and with IRAF after conversion were compared, a significant difference was found (661 ± 229 vs 418 ± 79 msec, P < 0.05). IRAF was successfully treated with repeated shock delivery after the administration of atropine in 1 patient and intravenous flecainide in 2. Only repeated shock delivery was sufficient to treat IRAF in another 2 patients. Late recurrences of atrial fibrillation occurred in 3 of 5 with IRAK and in 19 of 33 patients without IRAF (P = NS). Conclusion: IRAF after internal atrial defibrillation occurred in 13% of patients, was always initiated by an atrial premature heat having a short coupling interval not originating from the defibrillation catheters, and was prevented by repeated shock delivery with or without preceding administration of pharmacologic agents. IRAF did not predict early recurrences of the arrhythmia after discharge from the hospital, emphasizing the necessity to treat immediate reinitiation promptly to achieve a successful cardioversion.     

Optimization of Shocking Lead Configuration for Transvenous Atrial Defibrillation

Optimum Electrodes for Atrial Defibrillation. Introduction : High atrial defibrillation energy requirements (ADER) in patients with chronic atrial fibrillation (AF) may limit the acceptance of transvenous atrial defibrillation. We evaluated an optimized defibrillation electrode configuration that could help to reduce the ADKR in patients with AF.
Methods and Results : We tested ten different configurations in nine dogs with AF (3.33 ± 2.92 days) induced by rapid atrial pacing. The configurations were: right atrial (RA) appendage as anode und coronary sinus (CS) as cathode; RA and innominate vein (I) as anode to CS (cathode); RA-CS (anode) to I (cathode); I-CS (anode) to RA (cathode); RA and left lateral subcutaneous patch (P) as anode to CS (cathode); RA-CS (anode) to P (cathode); P-CS (anode) to RA (cathode); superior vena cava (SVC) and CS (anode) to RA (cathode); RA-CS (anode) to SVC (cathode); and RA-SVC (anode) to CS (cathode). ADER was defined as the voltage needed to defibrillate the atria in 10% to 90% of 20 consecutive shocks. Three lead systems had ADER lower than the RA (anode) to CS (cathode) configuration, which required a mean of 143 ± 58 volts. These three were: RA-SVC (anode) to CS (cathode) 103 ± 29 V; I-CS (anode) to RA (cathode) 129 ± 39 V; and P-CS (anode) to RA (cathode) 130 ± 38 V. The remaining configurations had ADER higher than the RA (anode) to CS (cathode) configuration.
Conclusion : Adding an additional shocking electrode may reduce ADER when compared with the RA (anode) to CS (cathode) configuration. This concept could he incorporated into future implantable atrial defibrillators or used for refractory patients undergoing temporary transvenous cardioversion.     

心房按需起搏的临床应用

AAI起搏是治疗房室传导正常的病态窦房结综合征(SSS)的理想方法,它可保持正常的房室收缩顺序及防止VVI起搏时心房压力上升,对预防心房纤颤(Af)有一定作用。本组17例AAI起搏主要用于房室传导正常的SSS,其中4例合并间断发作的Af,1例合并阵发性室上性心动过速(PSVT)。在随诊观察1～15个月之间,Af未再发作,PSVT也得到控制。本组17例全都采用螺旋形主动电极。我们体会其优点为电极可固定在心房之任何部位,操作简单,不易移位,采用可程控多参数的SSI型起搏器,便于定期进行心房调搏,观察房室传导功能的变化及处理可能发生的感知障碍及输出阻滞。     

The Impact of the Distance between the Atrial Electrode and the Atrial Wall on Atrial Undersensing in Patients with VDD Pacemakers: Long‐Term Follow‐Up

Aim: Atrial undersensing (AUS) in single‐lead VDD pacemakers may be due to diminished P‐wave amplitude secondary to local inflammation beneath the electrodes closer to atrial wall. The aim of this study was to assess the potential effect of distance between atrial electrode and atrial wall on immediate and long‐term atrial sensing stability in VDD systems. Methods: A total of 275 patients with normal sinus node function who received VDD pacemakers were enrolled into the study and were followed up for a median duration of 33 months. During each control visit, a standard 12‐lead electrocardiogram (ECG) was obtained and standard pacemaker function assessment was performed including testing for pacing threshold and atrioventricular synchrony. The distance between atrial electrode and atrial wall was measured from chest X‐ray. Results: Of the 275 patients, AUS was detected in 59 patients. Univariate predictors of AUS were use of closely spaced bipolar ring atrial electrode (CSBR) (P = 0.01), wider atrial ring‐spacing (P = 0.03), and atrial sensitivity programmed to a higher level (P = 0.001). Use of CSBR (P = 0.04) and atrial sensitivity ≥0.3 mV (P = 0.02) were observed to be the independent predictors for AUS. When the distance between atrial electrode and atrial wall was <7 mm, AUS was less with diagonally arranged bipolar ring electrodes (DABR) than it was with CSBRs (P = 0.02). Conclusions: The distance between atrial electrode and atrial wall does not appear to affect AUS incidence in VDD pacemakers. For VDD electrodes closer to atrial wall, AUS was significantly less likely in DABR‐type electrodes.     

Regional Entrainment of Atrial Fibrillation in Man

Entrainment of Atrial Fibrillation. Introduction : The feasibility of entrainment of macroreentrant atrial arrhythmias such as atrial flutter is well documented. Recently, it has been shown that regional entrainment of atrial fibrillation is feasible in dogs.
Methods and Results : Three patients with chronic atrial fibrillation underwent electrophysiologic evaluation with attempted entrainment of atrial fibrillation prior to successful endocardial atrial defibrillation. A 16-pole catheter was positioned in the trabeculated right atrium, and in two patients a multipolar catheter was positioned along the septum. In addition, two large surface area defibrillation catheters were placed, one in the lateral right atrium and one in the coronary sinus. Regional entrainment was attempted in the right atrium and from the catheter in the coronary sinus. Entrainment was achieved in the right atrium in all three patients over a cycle length range of 28, 17, and 13 msec, respectively, and over a radius of atrial tissue of at least 2.8 cm. Regional entrainment was demonstrated from the coronary sinus in one patient during simultaneous right atrial entrainment. Termination of atrial fibrillation during entrainment was not observed.
Conclusion : Regional entrainment of chronic atrial fibrillation is feasible in humans.     

Clinical Shock Tolerability and Effect of Different Right Atrial Electrode Locations on Efficacy of Low Energy Human Transvenous Atrial Defibrillation Using an Implantable Lead System

Objectives. The objectives of this study were 1) to evaluate the effect of different right atrial electrode locations on the efficacy of low energy transvenous defibrillation with an implantable lead system; and 2) to qualitate and quantify the discomfort from atrial defibrillation shocks delivered by a clinically relevant method.Background. Biatrial shocks result in the lowest thresholds for transvenous atrial defibrillation, but the optimal right atrial and coronary sinus electrode locations for defibrillation efficacy in humans have not been defined.Methods. Twenty-eight patients (17 men, 11 women) with chronic atrial fibrillation (AF) (lasting ≥1 month) were studied. Transvenous atrial defibrillation was performed by delivering R wave-synchronized biphasic shocks with incremental shock levels (from 180 to 400 V in steps of 40 V). Different electrode location combinations were used and tested randomly: the anterolateral, inferomedial right atrium or high right atrial appendage to the distal coronary sinus. Defibrillation thresholds were defined in duplicate by using the step-up protocol. Pain perception of shock delivery was assessed by using a purpose-designed questionnaire; sedation was given when the shock level was unacceptable (tolerability threshold).Results. Sinus rhythm was restored in 26 of 28 patients by using at least one of the right atrial electrode locations tested. The conversion rate with the anterolateral right atrial location (21 [81%] of 26) was higher than that with the inferomedial right atrial location (8 [50%] of 16, p < 0.05) but similar to that with the high right atrial appendage location (16 [89%] of 18, p > 0.05). The mean defibrillation thresholds for the high right atrial appendage, anterolateral right atrium and inferomedial right atrium were all significantly different with respect to energy (3.9 ± 1.8 J vs. 4.6 ± 1.8 J vs. 6.0 ± 1.7 J, respectively, p < 0.05) and voltage (317 ± 77 V vs. 348 ± 70 V vs. 396 ± 66 V, respectively, p < 0.05). Patients tolerated a mean of 3.4 ± 2 shocks with a tolerability threshold of 255 ± 60 V, 2.5 ± 1.3 J.Conclusions. Low energy transvenous defibrillation with an implantable defibrillation lead system is an effective treatment for AF. Most patients can tolerate two to three shocks, and, when the starting shock level (180 V) is close to the defibrillation threshold, they can tolerate on average a shock level of 260 V without sedation. Electrodes should be positioned in the distal coronary sinus and in the high right atrial appendage to achieve the lowest defibrillation threshold, although other locations may be suitable for certain patients.     

Clinical Validation of New Pacing-Sensing Configurations for Atrial Automatic Capture Verification in Pacemakers

INTRODUCTION: This study evaluated an atrial automatic capture verification scheme based on atrial evoked response (AER). Atrial pacing was between Atip and Can (Atip-Can) using different coupling capacitances (CCs). Independent pairs of sensing electrodes between Aring and Vtip (Aring-Vtip) or between Aring and a separate indifferent electrode (Aring-Indiff) were used to reduce pacing-induced afterpotentials. METHODS AND RESULTS: A custom-made external pacing system was used to perform automatic step-up and step-down pacing (0.1 to 7.1 V at 0.5 msec, step size of 0.1 V) using different CCs (2 or 15 microF). Intracardiac signals from Aring-Indiff and Aring-Vtip were independently recorded and analyzed both in real time and off-line to detect AER. Every paced beat also was visually inspected and compared with surface ECG to verify the captures. With the intracardiac signals properly filtered, AER detection was based on the signal within a window of 12 to 65 msec after the stimulus. Data from 27 patients (4 chronic and 23 acute implantations; age 65.6+/-13.9 years) were analyzed. Bipolar atrial lead measurements using a standard pacing system analyzer were as follows (mean +/- SD): impedance 695+/-227 ohms, P wave amplitude 4.2+/-2.3 mV, slew rate 1.1+/-0.9 V/sec, and pacing threshold at 0.5 msec 1.0+/-0.5 V. The results with CC = 2 microF showed that of 9,500 atrial paced beats, correct capture verification rates were 99.8% (Aring-Indiff) and 99.4% (Aring-Vtip). Similar results were achieved with CC = 15 microF (99.7% and 99.5%, respectively). CONCLUSION: AER can be reliably detected using independent pacing (Atip-Can) and sensing (Aring-Vtip or Aring-Indiff) electrodes. Therefore, atrial automatic capture verification by AER detection is feasible.     

普通心室电极经冠状窦行永久左房起搏的初步探讨(附四例报告)

报道普通心室电极经冠状静脉窦行永久左房起搏的最初应用。普通心室电极在置入前均剪去电极头端的一侧翼。 4例患者均顺利置入冠状窦 ,并定位于冠状窦中、远端。术中测试参数 (单极 ) :电压 0 .5～ 1.2 (平均 0 .90 )V ,阻抗 380～ 75 0 (平均 5 0 7.5 )Ω ,P波振幅 2 .6～ 6 .0 (平均 4.40 )mV。术后 (2～ 3个月后 )参数 (单极 ) :电压 1.2～ 2 .0(平均 1.6 5 )V ,P波振幅 2 .0～ 5 .0 (平均 3.6 0 )mV。在最后一次随访 (9～ 16月 ,平均 12月 ) ,4例患者冠状窦电极起搏和感知均良好 ,没有与导线有关的并发症。结论 :从最初应用经验看 ,普通心室电极置入冠状窦中、远端可行 ,安全 ,且价格便宜 ,适用于临床应用     

Atrial signal analysis and defibrillation threshold assessment in chronic persistent and reinduced atrial fibrillation

INTRODUCTION: Induced versus spontaneous atrial fibrillation (AF) is of interest for assessing atrial defibrillation threshold reproducibility. METHODS AND RESULTS: Twenty-one patients with chronic AF underwent internal cardioversion with assessment of atrial defibrillation threshold at baseline and at reinduced AF. High right atrial (HRA) and coronary sinus (CS) bipolar recordings were analyzed to measure the mean local atrial period, its coefficient of variation, the 5th (P5) and 95th (P95) percentiles of atrial intervals, and the percentage of points lying at the baseline (number of occurrences), and to quantify AF organization. Atrial defibrillation threshold was comparable in baseline and reinduced AF in terms of leading-edge voltage and delivered energy. Baseline and reinduced AF were comparable with regard to overall signal parameters (both in HRA and CS) and the presence of an organized arrhythmia pattern. As for individual variables, P5 increased while P95 and coefficient of variation decreased in reinduced AF compared with spontaneous AF (statistical significance was achieved for all these parameters in HRA, but only for coefficient of variation and P95 in CS). CONCLUSION: Sustained AF reinduced after cardioversion of chronic AF is comparable with baseline AF in terms of atrial defibrillation threshold, atrial cycle length, and pattern of organization. Therefore, a clinical model based on reinduction of sustained AF after cardioversion is suitable for studying the effects of a series of interventions on atrial defibrillation threshold. However, because this model does not yield a form of AF with comparable indices of local refractoriness (e.g., P5), it is not recommended when analyzing local electrophysiologic properties.     

Atrial defibrillation with a transvenous lead: a randomized comparison of active can shocking pathways.

OBJECTIVES: The purpose of this study was to compare transvenous atrial defibrillation thresholds with lead configurations consisting of an active left pectoral electrode and either single or dual transvenous coils. BACKGROUND: Low atrial defibrillation thresholds are achieved using complex lead systems including coils in the coronary sinus. However, the efficacy of more simple ventricular defibrillation leads with active pectoral pulse generators to defibrillate atrial fibrillation (AF) is unknown. METHODS: This study was a prospective, randomized assessment of shock configuration on atrial defibrillation thresholds in 32 patients. The lead system was a dual coil Endotak DSP lead with a left pectoral pulse generator emulator. Shocks were delivered either between the right ventricular coil and an active can in common with the proximal atrial coil (triad) or between the atrial coil and active can (transatrial). RESULTS: Delivered energy at defibrillation threshold was 7.1 +/- 6.0 J in the transatrial configuration and 4.0 +/- 4.2 J in the triad configuration (p < 0.005). Moreover, a low threshold (< or = 3 J) was observed in 69% of subjects in the triad configuration but only 47% in the transatrial configuration. Peak voltage and shock impedance were also lowered significantly in the triad configuration. Left atrial size was the only clinical predictor of the defibrillation threshold (r = 0.57, p < 0.002). CONCLUSIONS: These results indicate that low atrial defibrillation thresholds can be achieved using a single-pass transvenous ventricular defibrillation lead with a conventional ventricular defibrillation pathway. These data support the development of the combined atrial and ventricular defibrillator system.     

房间隔起搏对阵发性心房颤动患者最大P波时限和P波离散度的影响

观察房间隔起搏对阵发性心房颤动 (AF)患者最大P波时限 (Pmax)及P波离散度 (Pd)的影响 ,探悉房间隔起搏防治AF发作的电生理机制。对 2 1例阵发性AF患者和 2 6例室上性心动过速行射频消融术无阵发性AF患者 ,分别进行右心耳和房间隔起搏 ,比较不同部位起搏对阵发性AF和无阵发性AF患者的Pmax和Pd影响。结果 :阵发性AF患者较无阵发性AF患者Pmax和Pd值明显大 (分别为 1 35± 1 5vs 1 1 9± 1 4ms ,P <0 .0 5 ;36 .5± 9.2vs 1 9.7± 7.1ms ,P <0 .0 1 ) ;房间隔起搏使阵发性AF患者Pd、Pmax显著下降 (分别为 2 3 .4± 8vs 36 .5± 9.2ms ,1 2 0± 1 1vs1 35± 1 5ms,P均 <0 .0 5) ;右心耳起搏使无阵发性AF患者Pmax和Pd明显增加 (分别为 1 32± 1 2vs 1 1 9± 1 4ms,2 5 .5± 8.5vs 1 9.7± 7.1ms ,P均 <0 .0 5)。结论 :右心耳起搏能够使无阵发性AF患者Pmax和Pd值增加。房间隔起搏能够明显降低阵发性AF患者Pmax、Pd ,纠正房内或房间传导延缓 ,改善心房内电活动的各向异性 ,防治AF发作     

Acute atrial dilatation slows conduction and increases AF vulnerability in the human atrium

Stretch Slows Conduction in the Human Atrium . Introduction: The mechanisms by which atrial stretch favors the development of a substrate for atrial fibrillation (AF) are not fully understood. In this study, the role of stretch‐induced conduction changes in the creation of a proarrhythmic substrate has been investigated by quantifying the spatial distribution of local conduction velocities (CVs) in the human atrium during acute atrial dilatation. Methods and Results: Electroanatomic mapping of right atrial activation was performed in 10 patients during coronary sinus pacing under control condition and during acute atrial dilatation. Atrial stretch was obtained by simultaneous atrioventricular (AV) pacing at a cycle length of 450–500 ms. Local CVs were accurately estimated by applying the principle of triangulation and spatially mapped over the whole right atrial endocardial surface. Simultaneous AV pacing significantly increased right atrial volume from 72.0 ± 29.0 to 86.3 ± 31.3 mL (P < 0.001). The 23% increase in atrial volume resulted in an overall decrease in atrial CV from 65.8 ± 5.9 to 55.2 ± 7.2 cm/s (P < 0.001) and an increased incidence of slow conduction sites or local conduction blocks from 10.3 ± 4.2% to 15.9 ± 7.7% (P < 0.01). Acute atrial dilatation concurrently increased AF vulnerability, with 6 of 10 patients developing AF episodes under stretch condition. Conclusion: Quantification of stretch‐induced conduction changes in the human atrium is feasible by combining simultaneous AV pacing and CV map construction. Acute atrial dilatation results in conduction slowing and significant increase in AF vulnerability, suggesting the role of stretch‐induced conduction disturbances in the creation of a substrate for AF. (J Cardiovasc Electrophysiol, Vol. 22, pp. 394‐401)     

Implantable Atrial Defibrillators

Implantable Atrial Defibrillators. Due to the limited efficacy of antiarrhythmic drugs for atrial fibrillation, several nonpharmacologic therapeutic options have evolved. One of these is an implantable atrial defibrillator. Recent studies have shown that internal atrial defibrillation is feasible with relatively low energies. To date, the optimal electrode configuration involves large surface area catheters in the right atrium and coronary sinus. In humans, atrial defibrillation can generally be achieved with < 2 J using this electrode configuration and a biphasic shock waveform. For shocks < 5 J, there is no significant pathological damage to the atria or coronary sinus. Further investigation is needed to guarantee that atrial defibrillation shocks do not provoke ventricular arrhythmias. Preliminary data suggest that atrial defibrillation shocks synchronized to R waves that are not closely coupled are safe. In addition, the shocks are well tolerated if the shock energy is < 1.5 J. With additional studies to confirm the safety of implantable atrial defibrillators, further reduce shock energy, and improve patient tolerance, an implantable atrial defibrillator can become an acceptable therapy for patients with symptomatic, paroxysmal atrial fibrillation.     

Effect of Electrode Length on Atrial Defibrillation Thresholds

Electrode Length for Atrial Defibrillation. Introduction: Catheter-based electrodes have been used previously to terminate episodes of atrial fibrillation in animals and man. Typically, these electrodes span 6 to 7 cm, and lowest energy requirements are achieved when these electrodes are positioned in the distal coronary sinus and in the right atrium. The purpose of this study was to evaluate the use of longer electrode lengths for atrial defibrillation. Methods and Results: In 15 patients, two decapolar catheters were inserted, one into the distal coronary sinus and one in the right atrium. To provide longer electrodes lengths, a third catheter was inserted and alternated positioned in the right atrium or coronary sinus. A 6-cm electrode span was obtained by using the distal 8 rings on the coronary sinus catheter or 8 consecutive electrodes on the right atrial catheter and increased from 6 to 11 cm by connecting consecutive, nonoverlapping rings of the third catheter with the 10 rings of the initial right atrial or coronary sinus catheter. Atrial defibrillation thresholds were determined twice, in a randomized order, in each patient for each of the three combinations of electrode lengths. All 15 patients could he successfully converted to sinus rhythm without complications; however, one patient could be converted reproducibly with only 2 of the 3 electrode combinations. Mean thresholds were 306 ± 102 V, 5.9 ± 4.0 J for the 6 cm/6 cm electrode length combination with an impedance of 72 ± 18 ω. For the electrode combination using the 11-cm electrode in the right atrium, the defibrillation threshold was 296 ± 107 V, 5.8 ± 3.9 J with an impedance of 61 ± 17 ω and was 294 ± 91 V, 5.6 ± 3.6 J with an impedance of 55 ± 11 ω for the 11-cm electrode in the coronary sinus. There were no significant differences in defibrillation voltage or energy (P > 0.05) associated with the longer electrode lengths; however, the longer electrode lengths did significantly lower shock impedance (P < 0.05). Conclusion: The use of longer electrodes, when using the right atrium to coronary sinus shock vector, does not lower the defibrillation requirements for restoration of sinus rhythm.     

Feasibility of Atrial Sensing Via a Free-Floating Single-Pass Defibrillation Lead for Dual-Chamber Defibrillators

Background: Detection and misclassification of rapidly conducted atrial fibrillation (AF) and marked sinus tachycardia by implantable cardioverter defibrillators (ICD) can result in the delivery of inappropriate therapies. Continuous atrial sensing may improve the differentiation between supraventricular and ventricular tachycardia. The present approach is to implant a separate atrial pacing lead connected to a dual-chamber defibrillator. We hypothesized that a free-floating single-pass defibrillation lead reliably senses the atrial electrical activity. The aim of the study was to assess during implantation the efficacy of a custom-built free-floating single-pass defibrillation lead and to record sinus rhythm (SR), induced AF, and atrial flutter (Afl). Methods: The free-floating single-pass defibrillation lead (Biotronik, Berlin, Germany) had an atrial bipole with 10 mm spacing and a distance between the atrial bipole and the electrode tip of 13.5, 15 or 17-cm. The lead was temporarily implanted in 15 patients during an ICD implantation. Fifteen seconds recordings were made during SR and after the induction of AF and Afl as well as during induced ventricular fibrillation. The amplitude and the time that the amplitude was less than 0.3 mV were assessed. Results: The amplitude during SR (2.1 ± 1.4 mV) was significantly higher compared with the amplitudes for Afl (1.3 ± 0.5 mV; p < 0.02) and AF (0.7 ± 0.5 mV; p < 0.001). Low amplitudes were not observed during SR and rarely during Afl (1.6 ± 3.1%), but they were observed 19.9 ± 15.9% of the time during AF (p < 0.05). The correlation coefficients between SR and AF amplitudes were r = 0.25, between SR and Afl amplitudes r = 0.31, and between AF and Afl amplitudes r = 0.41. During the ventricular fibrillation conversion test 9 patients were in continuous SR. The P-wave amplitude before the induction of ventricular fibrillation was 2.1 ± 1.4 mV. The signal during ventricular fibrillation decreased to 1.1 ± 0.7 mV and increased immediately after the termination of ventricular fibrillation to 1.6 ± 0.8 mV. Conclusions: The recorded unfiltered signals indicate that SR as well as AF and Afl can immediately be detected after the implantation of the new free-floating single-pass defibrillation lead. High signal amplitude during SR did not predict high amplitude during AF or Afl. During induced ventricular fibrillation the P-wave amplitude decreased intermittently.     

Atrial defibrillator

Atrial fibrillation (AF) is a frequent and costly health care problem representing the most common arrhythmia resulting in hospital admission. Total mortality and cardiovascular mortality are significantly increased in patients with AF compared to controls. In addition to symptoms of palpitations, patients with AF have an increased risk of stroke and may also develop decreased exercise tolerance and left ventricular dysfunction. All of these problems may be reversed with restoration and maintenance of sinus rhythm. External electrical cardioversion has been a remarkably effective and safe method for termination of this arrhythmia. Originally described by Lown et al. in 1963, it has been a well accepted mode of acute therapy. However, this technique requires general anesthesia or heavy sedation. Internal atrial defibrillation has been evaluated as an alternative approach to the external technique for over 2 decades. Recent studies have shown that low-energy internal atrial defibrillation using biphasic shocks is an effective and safe means in restoring sinus rhythm in patients with AF and should be considered especially in patients in whom external cardioversion attempts have failed. Implantable Atrial Defibrillator: Recently, a stand alone IAD, the Metrix System (models 3000 and 3020), has entered clinical investigation. Atrial defibrillation is accomplished by a shock delivered between electrodes in the right atrium and the coronary sinus. The right atrium lead has an active fixation in the right atrium. The coronary sinus lead has a natural spiral configuration for retention in the coronary sinus, and can be straightened with a stylet. Both leads are 7 French in diameter and the defibrillation coils are each 6 cm in length. The electrodes may be placed using separate leads, or very soon by using a single bipolar lead. A separate bipolar right ventricular lead is used for R wave synchronization and post shock pacing. The Metrix defibrillator can be used to induce AF by using R wave synchronous shocks and can store intracardiac electrograms (EGMs) for up to 2 minutes from the most recent 6 AF episodes. The device can be programmed into one of the following operating modes: fully automatic, patient activated, monitor mode, bradycardia pacing only, and off. As AF is not life-threatening, in the automatic mode the device is only intermittently active in detecting and treating AF, and this "sleep wake-up" cycle interval is programmable. The device employs extensive processing both for detection and R wave synchronization. In April 1996, the phase I Metrix multicenter clinical trial was started. As of May 1997, a total of 51 Metrix systems had been implanted as part of the phase I multicenter clinical trial. Preliminary data suggest that both defibrillation thresholds and electrograms are stable over time (implant to 3 months). Detection accuracy has been excellent (100% specificity, 92.3% sensitivity) and there have been no errors of R wave selection for synchronization. No proarrhythmias have resulted from over 3700 shocks delivered. The device is effective in electrically converting 96% of the spontaneous episodes of AF. In 27% of episodes several shocks were required because of early recurrence of AF. In 5 patients, the atrial defibrillator was removed: 2 infections, 1 cardiac tamponade, 1 permanent loss of telemetry, 1 patient required His-Bundle ablation because of frequent episodes of drug refractory AF with rapid ventricular response. Initial clinical experience under controlled conditions with the Metrix system suggests that the implantable atrial defibrillator may offer a therapeutic alternative for a subgroup of patients with drug refractory, symptomatic, long lasting, and infrequent episodes of AF. Further efforts must be undertaken to reduce the patient discomfort associated with internal atrial defibrillation in an attempt to make this new therapy acceptable to a larger patient population with AF. (ABSTRACT TRUNCATED)     

Placement of atrial pacing leads during atrial fibrillation. Feasibility and subsequent lead performance.

AIMS: To assess the feasibility of placing permanent atrial pacing leads during atrial fibrillation (AF) and whether such leads function satisfactorily. METHODS AND RESULTS: Prospective study of 17 consecutive patients in whom permanent atrial leads were positioned during an episode of paroxysmal AF. Fluoroscopic position ('figure of 8' or side-to-side movement and anterior position in RAO projection), lead impedance (> 300 but < 1000 ohms) and intracardiac electrogram (average peak to peak amplitude > 1 mV) were used to define an acceptable lead position. At 8 weeks post implant we measured: pulse duration pacing threshold at 5 V; lead impedance at 5 V and 0.5 ms; intracardiac electrogram (EGM) signal amplitude. At the end of the study we reviewed patients to establish whether AF had become permanent. In all patients, follow-up demonstrated satisfactory lead function. All leads had impedances between 300 and 1000 ohms. Pacing thresholds were all < 0.1 ms at 5 V. Mean atrial EGM amplitude seen in sinus rhythm was 3.3 mV (range 1.2-8.4); in patients where all follow-up was in AF in was 2.1 mV (range 1.5-2.5). Nine patients (53%) developed permanent AF. CONCLUSION: Placing atrial leads during AF is feasible using the technique described. However, some patients progress to chronic AF, eliminating the benefits of atrial pacing.     

Implantable atrial defibrillator with a single-pass dual-electrode lead

OBJECTIVES

We examined the feasibility and efficacy of using a single-pass, dual-electrode (Solo) lead for atrial fibrillation (AF) detection and defibrillation.

BACKGROUND

The efficacy and safety of an implantable atrial defibrillator (IAD) has been extensively studied; however, separate right atrial (RA) and coronary sinus (CS) defibrillation leads are used for the present system.

METHODS

We studied the use of the Solo lead for AF detection and defibrillation in 17 patients who underwent cardioversion of chronic AF. The Solo lead with a proximal 6-cm RA electrode and a distal 6-cm spiral-shaped CS electrode were positioned into the CS with the RA electrode against the anterolateral RA wall. The RA-CS electrogram signal amplitudes were measured and the efficacy of the Solo lead for AF detection and defibrillation was assessed by using an external version of the IAD.

RESULTS

The leads were inserted in all patients without complication (mean fluoroscopy time: 13.3 ± 6.8 min). The mean RA-CS signal amplitude was 484 ± 229 μV during sinus rhythm and 274 ± 88 μV during AF (p < 0.05). All patients had satisfactory atrial signal amplitude to allow accurate detection of sinus rhythm. Successful cardioversion was achieved in 16/17 (94%) patients with an atrial defibrillation threshold of 320 ± 70 V (5.5 ± 2.7 J). Insufficient interelectrode spacing resulted in suboptimal electrode locations, associated with a lower atrial signal amplitude, a higher atrial defibrillation threshold and diaphragmatic stimulation.

CONCLUSIONS

These results suggest a simplified lead configuration with optimal interelectrode spacing can be used with an IAD for AF detection and defibrillation.     

A Prospective Randomized Study to Assess the Efficacy of Rate and Site of Atrial Pacing on Long-Term Development of Atrial Fibrillation

The Septal Pacing for Atrial Fibrillation Suppression Evaluation (SAFE) study is a single-blinded, parallel randomized designed multicenter study in pacemaker indicated patients with paroxysmal atrial fibrillation (AF). The objective is to evaluate whether the site of atrial pacing–-conventional right atrial appendage versus low atrial septal—with or without atrial overdrive pacing will influence the development of persistent AF. The study will provide a definitive answer to whether a different atrial pacing site or the use of AF suppression pacing or both can give incremental antiarrhythmic benefit when one is implanting a device for a patient with a history of paroxysmal AF.     

Design and Implementation of the Dual Site Atrial Pacing to Prevent Atrial Fibrillation (DAPPAF) Clinical Trial

The Dual Site Atrial Pacing to Prevent Atrial Fibrillation (DAPPAF) study compares dual site, single site and support pacing modalities in the prevention of atrial fibrillation (AF) in patients with a history of paroxysmal AF (PAF) and a bradyarrhythmic indication for pacing. The trial is a randomized crossover comparison of dual site atrial pacing, single site atrial pacing, and a support pacing control period (DDI at 50 ppm or VDI) done in six month intervals. Patient inclusion requires at least 2 documented AF episodes in the three months prior to enrollment. The patients can be on concurrent antiarrhythmic drug regimens but this regimen must remain constant throughout the protocol. Patients with AV nodal ablation are excluded from this study. The primary endpoints of the study compare the time to first recurrence of clinically significant symptomatic AF with ECG verification, and quality of life among the three treatment modes. Secondary endpoints include time to first recurrence of all AF episodes as monitored by the pacemaker, the measurement of echocardiographic parameters, and symptoms logged by the patients. This trial was designed after pilot studies showed dual site pacing to be safe, feasible and preliminary results suggested increased maintenance of sinus rhythm with atrial pacing.