On the role of ventricular conduction time in rate stabilization for atrial fibrillation.

AIM: Ventricular pacing (VP) could stabilize the ventricular rhythm in atrial fibrillation (AF). This study investigates the role of ventricular conduction time (VCT) in rate stabilization for AF. METHODS AND RESULTS: A novel computer model was used to generate various patterns of RR intervals in AF. For each model configuration, the rate stabilization effect of VP was compared with respect to different VCTs. In all tested cases, the ventricular rate in AF could be stabilized at pacing intervals longer than the shortest spontaneous RR intervals. For each model configuration, slightly longer pacing interval (difference <100 ms) was needed to achieve 95% VP when the antegrade/retrograde VCT was increased from 10/10 to 110/110 ms, whereas the VCT had less effect at lower pacing rate. Although longer VCT was associated with increased percentage of ventricular fusion, its role was diminished at higher pacing rate when more retrograde waves could conduct to the atrium. CONCLUSION: Ventricular conduction time has limited effects on rate stabilization, which could be explained by multi-level interactions between antegrade waves induced by AF and retrograde waves induced by VP.     

The role of pacing mode in the development of atrial fibrillation.

Asynchronous ventricular pacing has been shown to increase the risk of development of atrial fibrillation (AF) because of various mechanisms: retrograde atrioventricular (AV) conduction with increase in atrial pressure causing acute atrial stretch and reverse flow in the pulmonary veins, mitral regurgitation, reduced coronary blood flow, adverse neuroendocrine reactions, etc. Dual-chamber pacing preserves atrioventricular synchrony. However, in randomized multicentre trials comparing VVI(R) with DDD(R) pacing, AF is only slightly less frequent in the dual-chamber mode. This is most likely due to unnecessary ventricular pacing, which is frequent in dual-chamber pacing. At nominal values, dual-chamber devices usually do not permit intrinsic AV conduction but promote delivery of the ventricular stimulus at an inappropriate time in an inappropriate place. Programming of long AV delays facilitates spontaneous AV conduction but usually cannot completely avoid unnecessary ventricular pacing and causes other problems in the dual-chamber mode. Atrial septal lead placement can improve left-sided AV synchrony and promote spontaneous AV conduction. Programming of the AAI(R) mode is superior to the dual-chamber mode but cannot be used if AV conduction is impaired intermittently or permanently. Therefore, dedicated algorithms enhancing spontaneous AV conduction in the dual-chamber mode are desirable for a large proportion of pacemaker patients.     

以动态心电图心室率参数指导心房颤动伴长R-R间距者活动时心室率的控制

目的探讨心房颤动(Af)伴长R-R间距活动时的心室率控制情况。方法回顾分析92例住院者的动态心电图(DCG)检查结果,其中:①Af伴长R-R间距62例(A组);②窦性心律、偶发房性早搏及室性早搏30例(B组)。观察两组的心室率分布情况。将A组患者在强心、利尿、抗凝的药物治疗基础上随机分为:常规组(A1组)30例,倍他乐克25毫克2/日;非常规组(A2组)32例,倍他乐克50毫克1/日。采用最高、最低、平均心室率、24h总心室率、每小时平均心率等参数,分析Af伴长R-R间距的心室率控制情况。结果 A组最高心率、平均心率、24h总心率均快于B组,差别有统计学意义(P<0.05,P<0.001)。A组最低心率慢于B组最低心率,差别有统计学意义(P<0.001)。通过适当增加晨起给药量倍他乐克50毫克1/日能达到更好的运动时心室率的控制。患者的最高心率、平均心率、24h总心率均慢于A1组,差别有统计学意义(P<0.05,P<0.001)。其最低心率与B组差别无统计学意义(P>0.05)。结论采用24h DCG对心室率等各项参数进行观察,为临床治疗和疗效的判断提供依据。提示在心室率高峰前用药,即合理增加晨起给药量,可达...     

Usefulness of rate regulation through continuous ventricular pacing in patients with drug-controlled slower atrial fibrillation and normal or depressed left ventricular systolic function

We studied 33 clinically stable patients with permanent atrial fibrillation (AF), implanted with a ventricular demand rate-responsive (VVIR) pacemaker or an automatic defibrillator, in order to evaluate whether continuous right ventricular apex pacing (VP) conferring rate regulation may be advantageous when compared with slower drug-controlled AF. Devices were chronically programmed at ventricular backup pacing. Patients were divided in two groups according to their normal (n = 17) or depressed (n = 16) left ventricular systolic function (LVSF). Ventricular function was studied by using tissue Doppler and color M-mode and echocardiography, as well as B-type natriuretic peptide (BNP) measurements. Baseline data during AF were compared to corresponding measurements following a 1-month pacing period after the devices were programmed at a base rate of 70 beats/min. In both groups, VP worsened some indexes of left and right ventricular function (P < 0.05) without significantly affecting cardiac output, left ventricular filling pressures and BNP (P = not significant). We conclude that VP should not be considered advantageous compared to slower AF.     

Conventional and dedicated atrial overdrive pacing for the prevention of paroxysmal atrial fibrillation: the AFTherapy study.

AIMS: This investigation was conducted to determine the effectiveness of several conventional overdrive pacing modalities (single rate and rate responsive pacing at various lower rates) and of four dedicated preventive pacing algorithms in the suppression of paroxysmal atrial fibrillation (AF). METHOD AND RESULTS: In this multi-centre, randomized trial, 372 patients with drug-refractory paroxysmal AF were enrolled. Patients received a dual-chamber pacing device capable of delivering conventional pacing therapy as well as dedicated AF prevention pacing therapies and to record detailed AF-related diagnostics. The primary endpoint was AF burden, whereas secondary endpoints were time to first AF episode and averaged sinus rhythm duration. During a conventional pacing phase, patients were randomized to single rate or rate-responsive pacing with lower rates of either 70 or 85 min(-1) or to a control group with single rate pacing at 40 min(-1). In the subsequent preventive pacing phase, patients underwent pacing at a lower rate of 70 min(-1) with or without concomitant application of four preventive pacing algorithms. A substantial amount of data was excluded from the analysis because of atrial-sensing artefacts, identified in the device-captured diagnostics. In the conventional pacing phase, no significant differences were found between various lower rates and the control group receiving single rate pacing at 40 min(-1) or between single rate and rate-responsive pacing. Patients receiving preventive pacing with all four therapies enabled had a similar AF burden compared with patients treated with conventional pacing at 70 min(-1) (P = 0.47). CONCLUSIONS: The results do not demonstrate a significant effect of conventional atrial overdrive pacing or preventive pacing therapies. However, the observations provided important information for further consideration with respect to the design and conduct of future studies on the effect of atrial pacing therapies for the reduction of AF.     

Increased base rate of atrial pacing for prevention of atrial fibrillation after implantation of a dual-chamber pacemaker: insights from the Atrial Overdrive Pacing Study.

AIMS: Different pacing sites and various algorithms have been utilized to prevent atrial fibrillation (AF) in pacemaker recipients. However, the optimal pacing rate settings have not yet been established. In this randomized, prospective, multicentre, single-blinded, cross over study, rate-adaptive pacing at a high base rate (BR) in patients, age 60 years or above, or a history of paroxysmal AF, who underwent dual-chamber (DDD) pacemaker implantation for standard pacing indications, was evaluated for prevention of AF. METHODS AND RESULTS: In the study cohort of 145 patients implanted with DDD pacemakers with a programmable rest rate (RR) feature, the BR/RR settings were sequentially but randomly adjusted as follows: 60 bpm/Off for the baseline quarter (initial 3 months) and then to either 'A-B-C' or 'C-B-A' settings (A = 70/65 bpm, B = 70/Off, C = 80/65 bpm) for the subsequent quarters each of 3 months duration. Data on automatic mode switch episodes, device diagnostics, and a questionnaire evaluating pacemaker awareness and palpitations were collected. Ninety-nine patients, mean age 77 +/- 10 years, who completed the study protocol and followed for 12 months did not show significant differences in the number of mode switch episodes between any settings used. The percentage of atrial pacing was lower during baseline pacing compared to settings A, B, and C (P < 0.0001). Setting C produced a higher percentage of atrial pacing than A and B (P < 0.01). Although a higher percentage of atrial pacing correlated with a lower incidence of mode switch episodes, there was no statistically significant difference in the number of mode switch episodes between settings A, B, and C. There were no significant differences in the questionnaire scores relating to pacemaker awareness or palpitation. CONCLUSION: Overdrive single-site pacing in the right atrium achieved by programming analysed settings in the present study did not reduce AF as assessed by mode switch episodes. Additionally, no change in the symptoms of arrhythmia or awareness of pacing was seen.     

Influence of pacing modalities on the incidence of atrial fibrillation in patients without prior atrial fibrillation. A prospective study

Aim Many studies suggest that patients who receive a physiologicalpacemaker have a reduced incidence of atrial fibrillation comparedto patients receiving a ventricular pacemaker. Methods In order to evaluate the impact of different pacing modalitieson the incidence of atrial fibrillation, we prospectively analysed210 patients. Patients with previous episodes of atrial fibrillationwere excluded from the study. The patient population included110 patients paced for sick sinus syndrome and 100 patientspaced for total atrio-ventricular block or second degree typeatrioventricular block. Results Patients were followed for 5 years; the incidence of atrialfibrillation was 10% at 1 year, 23% at 3 years and 31% at 5years. There was an increase in the incidence of atrial fibrillationin patients receiving a ventricular pacemaker compared to patientsreceiving a physiological pacemaker. Conclusion The pacing modality appeared to influence the incidence of atrialfibrillation in paced patients; patients with ventricular pacinghad a significantly higher incidence of arrhythmias than didpatients with physiological pacing.     

Septal atrial pacing for the prevention of atrial fibrillation.

AIMS: Atrial fibrillation (AF) produces significant morbidity and mortality. The current method of permanent pacing of the right atrium (RA) may cause delayed interatrial conduction and predispose to AF. We hypothesized that atrial septal pacing would reduce AF compared with high RA pacing. METHODS AND RESULTS: The patients were randomized into two groups. After randomization, patients received a dual-chamber rate-responsive device capable of mode-switching with advanced telemetry features. Devices were programmed in a standardized manner. To be eligible, the patients were required to have a conventional indication for a permanent pacemaker and recurrent paroxysmal AF. Group 1 was paced from high RA and Group 2 was paced from the atrial septum. Analysis of 43 patients who have completed 6 months of follow-up and 22 patients who completed 12 months of follow-up showed no significant differences in the number of mode-switching episodes or in AF burden between groups (P = NS by Mann-Whitney) although there was a trend for less AF with septal pacing. There were no differences in thresholds, sensing, or lead impedance. Lead parameters remained stable over time and there were no displacements of the electrodes after implantation. No patient experienced lead-related complications. A significant variability in AF burden was noted in this patient population. CONCLUSIONS: Implantation of an atrial-active fixation lead on the atrial septum is safe and feasible. However, this study showed no significant difference between septal pacing and high atrial pacing, using the endpoints of AF duration and number of AF episodes.     

快速心室率心房纤颤的房室传导改良

对１３例药物难以控制的快室率心房纤颤（房颤）病人进行经射频消融房室传导改良，射频消融靶点选择右房内房间隔之后、中或前部。射频能量为２０～３０Ｗ，平均发放射频８±３次。结果：９例房室改良成功，３例失败，１例于术后３天发生Ⅲ°房室传导阻滞。９例术后２天及２个月休息时心率、活动时心率、最高心率及最低心率较术前有明显下降（Ｐ＜０．０５）．１例于术后１１个月复发，其机理与部分或全部损伤后结间束或部分损伤房室结有关。认为射频消融房室传导改良为治疗药物难以控制的快室率房颤的一种相对安全有效的方法。     

Right atrial preventive and antitachycardia pacing for prevention of paroxysmal atrial fibrillation in patients without bradycardia: a randomized study.

AIMS: To investigate the efficacy of preventive and antitachycardia pacing (ATP) in patients with symptomatic paroxysmal atrial fibrillation (AF) without bradyarrhythmias. METHODS AND RESULTS: In this randomized cross-over pilot study, we randomized 38 symptomatic paroxysmal AF patients 'without' bradyarrhythmias to atrial pacing lower rate 70 ppm and prevention and ATP therapies ON or to atrial pacing lower rate 34 ppm and prevention and ATP therapies OFF during 12 weeks with a 4 week washout period in between. The atrial lead was preferably placed in the inter-atrial septum. Antiarrhythmic drugs were continued during the study. Primary endpoint was AF burden. Mean age was 62 +/- 9 years and 27 (71%) patients had lone AF. Septal lead placement was accomplished in 26 (68%) patients. During the treatment ON, there was a trend for AF burden reduction [from median 3.3% (1.0-15.2) to 2.4% (0.2-12.2), P = 0.06, reduction 27%]. If septal lead placement was accomplished, AF burden reduction was statistically significant [44% reduction, from median 2.5% (1.0-8.0) to 1.4% (0.2-8.4), P = 0.03]. Quality of life and symptoms did not change, also not in the septal group. CONCLUSION: A hybrid therapy of preventive and ATP pacing and antiarrhythmic drugs may significantly reduce but not abolish AF burden if septal pacing is realized.     

Clinical predictors of atrial fibrillation in Brugada syndrome.

AIMS: Atrial arrhythmias have been reported in patients with Brugada syndrome. The aim of this study was to evaluate clinical predictors of atrial fibrillation (AF) in Brugada syndrome. METHODS AND RESULTS: Patients diagnosed with Brugada ECG pattern were enrolled in the study. Type 1, 2, and 3 Brugada ECG pattern was found in 28, 56, and 31 patients, respectively. A total of 85 healthy age and gender-matched subjects were selected as a control group. Mean age, maximum P-wave duration (P(max)), P-wave dispersion (P(disp)), and left atrial dimension were not significantly different between patients and controls. There were no differences between P(max), P(disp), and left atrial dimension of the type 1, 2, and 3 Brugada patients. Spontaneous paroxysmal AF was detected in 15 of 28 type 1 Brugada patients (53%) and none of the type 2 and 3 Brugada patients. All 15 patients with AF had at least one episode of paroxysmal AF and none of the patients showed persistent or chronic AF. All 15 patients who had paroxysmal AF had previous life threatening cardiac events. In contrast, paroxysmal AF did not occur in type 1 Brugada patients without previous life threatening cardiac events. In multiple regression analysis, only the occurrence of previous life threatening cardiac events was a risk factor for paroxysmal AF (P = 0.0001). CONCLUSION: It is concluded that the most important predictor of AF in Brugada syndrome is the occurrence of previous life threatening cardiac events.     

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.     

动态心电图对心房颤动合并长R—R间歇的临床分析

目的探讨动态心电图对分析心房颤动合并长R，R间歇（≥1．5秒）、逸搏及逸搏心律出现的时间是否与睡眠有关。方法将人选病例分为睡眠相关组和睡眠无关组进行观察。采用动态心电图连续监测24小时心电图，据患者记录的生活日志，分析长R—R间歇、逸搏及逸搏心律出现的时间。结果睡眠相关组85例患者中发生长R—R间歇1．5～2．0秒，〉2．0秒逸搏及逸搏心律人平均数分别为：（25．72±7．90）次／分钟、（7．30±0．99）次／分钟和（6．83±1．25）次／分钟；睡眠无关组35例患者分别为：（203．20±40．84）次／分钟、（35．14±7．59）次／分钟、（27．80±6．19）次／分钟。睡眠无关组明显高于睡眠相关组（P〈0．01），风心病患者R—R间歇〉2．0秒，逸搏及逸搏心律频度明显高于其它病种（P〈0．01）。结论心房颤动伴长R—R间歇，逸搏及逸搏心律与睡眠相关时，多与迷走神经张力增高有关；而与睡眠无关时，应考虑病理性房室阻滞。风心病持续房颤由于使用洋地黄及β-受体阻滞剂易于出现长间歇。     

心房颤动患者RR长间期的分布规律及其临床意义

目的观察心房颤动(简称房颤)时RR长间期的发作规律及射频消融术后的变化,探讨房颤RR长间期的临床意义。方法记录并分析持续性/永久性房颤患者动态心电图中RR长间期发生时间及次数,对因永久性房颤行环肺静脉电隔离(CPVA)术治疗者,观察其转复窦性心律后房室传导阻滞发生情况。结果205例患者中203例(99.02%)出现≥1.5s长间期,24:00时至凌晨04:00时出现次数最多,10:00时至12:00时次之。62例接受CPVA术的永久性房颤患者均伴长RR间期,全部成功终止房颤转复窦性心律,术后心电图示6例Ⅰ度房室传导阻滞(AVB)(9.7%),未发现Ⅱ度AVB,3例因窦房结功能障碍置入永久起搏器。结论持续性/永久性房颤患者常见≥1.5s的RR长间期,绝大多数并非病理性房室传导阻滞所致。     

艾司洛尔与毛花苷控制快速心房颤动患者心室率的短时疗效比较

目的比较静脉应用艾司洛尔与毛花苷控制快速心房颤动患者心室率的短时疗效和安全性。方法60例快速心房颤动患者，心室率≥120次／min，随机分为艾司洛尔组、毛花苷组各30例。艾司洛尔组首次剂量给予0．5mg／kg，1min静注，观察5min，若心室率〉100次／min或下降〈20％，则追加0．5mg／kg，同时以0．05mg·kg-1·min-1微量泵起始维持，维持量最大可加至0.3mg·kg-1·min-1，若血压〈90／60mmHg，则停止试验。毛花苷组首次剂量给予毛花苷0．4mg或0．2mg缓慢静注，若心室率〉100次／min或下降〈20％，可追加0．2mg。观察两组用药后5min、10min、30min、60min、90min和120min心率、血压及临床表现；同时记录用药后药物起效时间及不良反应。结果两组患者用药后不同时刻的心室率均明显降低，与用药前比较差异均有统计学意义，用药2h后艾司洛尔组心室率下降幅度大于毛花苷组（P〈0．05）；艾司洛尔和毛花苷组平均起效时间分别为（6．4±3．8）min和（43．1±12．6）min，两者差异具有统计学意义（P〈0．01）。艾司洛尔和毛花苷组总有效率分别为86．3％和83．3％（P〉0．05），无统计学意义；两组不良反应发生率无统计学意义。结论静脉应用艾司洛尔控制快速心房颤动患者心室率的短时疗效显著，安全性好。     

Dronedarone for prevention of atrial fibrillation: a dose-ranging study.

AIMS: Dronedarone, a benzofurane derivative without iodine substituents, shares the electrophysiologic properties of amiodarone. This study was designed to determine the most appropriate dose of dronedarone for prevention of atrial fibrillation (AF) after cardioversion. METHODS AND RESULTS: Patients with persistent AF were randomly allocated to 800, 1200, 1600 mg daily doses of dronedarone or placebo. The main analysis was conducted on 199/270 patients, who entered the maintenance phase following pharmacological cardioversion or, if unsuccessful, DC cardioversion. Within 6-month follow-up, the time to AF relapse increased on dronedarone 800 mg, with a median of 60 days vs 5.3 days in the placebo group (relative risk reduction 55% [95% CI, 28 to 72%] P=0.001). No significant effect was seen at higher doses. Spontaneous conversion to sinus rhythm on dronedarone occurred in 5.8 to 14.8% of patients (P=0.026). There were no proarrhythmic reactions. Drug-induced QT prolongation was only noticed in the 1600 mg group. Premature drug discontinuations affected 22.6% of subjects given 1600 mg dronedarone versus 3.9% on 800 mg and were mainly due to gastrointestinal side effects. No evidence of thyroid, ocular or pulmonary toxicity was found. CONCLUSION: Dronedarone, at a 800 mg daily dose, appears to be effective and safe for the prevention of AF relapses after cardioversion. The absence of thyroid side effects and of proarrhythmia are important features of the drug. Further studies are needed to better delineate the antiarrhythmic profile of the drug.     

Pacemaker prevention therapies for the control of drug-refractory paroxysmal atrial fibrillation.

AIMS: Atrial septal pacing has been shown to prevent paroxysmal atrial fibrillation (PAF) refractory to drugs in patients without inappropriate bradycardia. This study assesses the effects of atrial septal pacing using new pacing algorithms designed to prevent the initiation or maintenance of PAF. METHODS AND RESULTS: Eleven Medtronic AT500 and 6 Guidant Pulsar Max pacemakers were implanted. The incremental benefit of prevention pacing therapies was compared with DDDR pacing by analysis of pacemaker-stored electrograms, ambulatory electrocardiography, symptoms and quality of life questionnaires. RESULTS: Atrial septal pacing reduced AF burden by >50% in 13/17 patients (76.5%). Activation of a combined pacing algorithm (atrial pacing preference; atrial rate stabilization; and post mode-switch overdrive pacing) in patients with AT500 pacemakers produced a marginal reduction in AF burden (mean %AF 0.61 ON, 0.73 OFF, P=0.53 ns). Conversely in the Pulsar Max group when atrial pacing preference was activated, AF burden was slightly increased (mean %AF 5.84 ON, 3.73 OFF,P =0.13). Symptoms improved with atrial septal pacing but did not change when prevention algorithms were activated. CONCLUSION: Atrial septal pacing resulted in a marked improvement in AF burden and symptoms. Activation of specific prevention pacing algorithms provided more continuous atrial pacing but had limited and heterogeneous effects on AF burden.     

心率与心房颤动关系的研究进展

心房颤动（简称“房颤”）是临床上最常见的心律失常,其发病率随年龄增长而增加。心房重构是房颤的核心机制,包括电重构、结构重构及自主神经重构。自主神经功能障碍在房颤的发生、发展中起着重要的作用,而心率可以间接反映自主神经功能。心率与房颤发生的关系以及房颤射频消融术后心率变化与房颤复发关系复杂,且一直在研究中。     

Atrial fibrillatory rate and irregularity of ventricular response as predictors of clinical outcome in patients with atrial fibrillation

Atrial fibrillation (AF) remains the most common arrhythmia encountered in clinical practice. Electrocardiogram (ECG)-based predictors of clinical outcome, however, have mostly been studied during sinus rhythm, whereas noninvasive risk stratification of patients with AF remains largely unexplored. Advances in ECG signal processing have led to the development of noninvasive methods of atrial fibrillatory rate (AFR) assessment using spatiotemporal QRST cancellation and time frequency analysis that demonstrated its predictive value for the outcome of pharmacologic and catheter-based interventions for AF. Recently, the prognostic value of AFR was evaluated in patients with congestive heart failure and indicated that reduced AFR may be an independent predictor of total and congestive heart failure–related mortality. A high degree of irregularity of the RR intervals during AF and its dependence on the modulation of the atrioventricular conduction rather than sinus node automaticity hampers the use of conventional heart rate variability approach in patients with AF. However, RR irregularity measures that can be applied to short-time ECG recordings appear to be promising predictors of clinical outcome.     

风湿性心脏病心房颤动伴长RR间期的心内电生理研究

目的 评价心房颤动（房颤）伴长ＲＲ间期患者电复律后房室结功能,探讨房颤伴二度房室阻滞的诊断标准。方法 ２０例房颤伴长ＲＲ间期的患者,均在电复律后行心内电生理检查,测定房室结功能。结果 除１例为一度房室阻滞外,其余１９例房室结功能均正常。结论 房颤伴长ＲＲ间期不应作为临床诊断二度房室阻滞的标准。