Atrial Fibrillation During A-V Sequential Pacing

Atrial fibrillation resulted from competition between the P wave and a unipolar cathodal stimulus from the atrial output of an A-V sequential pacemaker Review of 31 patients with recently implanted A-V sequential pacemakers revealed that five, who had not had atrial fibrillation or flutter before implant, developed atrial arrhythmia early after implant As occasional placement of an atrial stimuJus in tlie atrial vulnerable period can occur during normal function, pacer induced atrial fibrillation must be expected Atrial sensing to ensure lack of competition between pacer and spontaneous atrial activity is desirable     

Acute Effects of Different Atrial Pacing Sites in Patients with Atrial Fibrillation: Comparison of Single Site and Biatrial Pacing

It has been reported that a trial single site or biatrial pacing can suppress the occurrence of AF. However, its mechanism remains unclear. The study population included 32 patients with AF (n = 20: AF group), or without paroxysmal AF (n = 12: control group). The mechanism and efficacy of atrial pacing were investigated by electrophysiological studies to determine which was more effective for suppressing AF induction; single site pacing of the right atrial appendage (RAA) or distal coronary sinus (CS-d), or biatrial (simultaneous BAA and CS-d) pacing. In the AF group, AF inducibility was significantly higher with BAA extrastimulus during RAA (12/20; P < 0.0001) or biatrial paced drive (7/20; P < 0.01) than during CS-d paced drive (0/20). In the control group, AF was not induced at any site paced. In the AF group, the conduction delay and other parameters of atrial vulnerability significantly improved during CS-d paced drive. The atrial recovery time (ART) at RAA and CS-d was measured during each basic pacing mode. ART was defined as the sum of the activation time and refractory period, and the difference between ARTs at RAA and CS-d was calculated as the ART difference (ARTD). The ARTD was significantly longer during BAA pacing in the AF group than in control group (155.0 +/- 32.8 vs 128.8 +/- 32.9 ms, P < 0.05). In the AFgroup, ARTDs during biatrial (52.0 +/- 24.2 ms) and CS-d pacing (51.7 +/- 26.0 ms) were significantly shorter than ARTD during RAA pacing. The CS-d paced drive was more effective for suppressing AF induction than biatrial or RAA paced drive by alleviating conduction delay. CS-d and biatrial pacing significantly reduced ARTD compared with RAA pacing.     

Atrial Fibrillation and Embolic Complications in Paced Patients

Atrial fibrillation (AF) and thromboembolism are discussed to he complications of the WI mode. We reinvestigated the spontaneous ECG and the anamnesis of 246 pacemaker patients with the indications second and third degree atrioventricular block (AV block, n = III), sick sinus syndrome (SSS, n - 101) and other indications (n = 34), all had shown sinus rhythm at implantation. The mean implantation time was 63 ± 45 months (203 VVI and 43 dual chamber pacemkers). The results: (1) Atrial fibrillation was found in 63 patients (26%). Only one of them had a DDD pacemaker inserted, the implantation time of dual chamber devices being shorter, however, (2) The incidence of AF in patients with SSS (37%) was significantly higher (P < 0.01) than in patients with AV block (19%). (3) Three patients suffered from strokes or transitory ischemic attacks in the follow-up, only one of them had AF at control. Conclusions: Our results confirm that VVI stimulation favors AF long-term which is most likely due to irritation of the atrial rhythm by retrograde conduction. In our patients the incidence of thromboembolic complications was not higher in the group of patients with AF. However, from this study in surviving patients, we cannot exclude that we Jost some patients due to severe stroke.     

Mode Switch Despite Undersensing of Atrial Fibrillation in ODD Pacing

Mode switching algorithms are commonly used to protect the ventricles against high rates induced by atrial tachycardia. In the case of atrial fibrillation (AF), the response of these algorithms depends on the quality of atrial sensing. The Chorum 7234 DDDR pacemaker uses a new mode switching algorithm, based on a statistical analysis of the atrial rhythm. It includes two criteria of diagnosis: "high" if more than 28 of 32 cycles are abnormally accelerated; and "low" if more than 36 of 64 cycles are abnormally accelerated. Methods: From a taped database of electrophysiological studies, episodes of AF lasting more than 2 minutes were selected. A tape recorder replayed the atrial signals into an external Chorum device. Each episode was replayed eight times with a programmed atrial sensitivity increasing from 0.4 –2.0 mV. For each criterion of diagnosis and each programmed sensitivity, the percentage of atrial sensing, the time to switching, and the mean ventricular rate were measured. Ten episodes of AF from 10 patients (9 men and 1 woman; ages 62 ± 16 years) were included: 1.95 ± 0.97 mV and 196 ± 64 ms. The sensitivity of the algorithm to diagnose atrial tachycardia reached 100%, for an atrial sensitivity set between 0.4 and 1.0 mV. The mean percentages of atrial sensed events were 74%± 18% and 46%± 9% for the "high" and "low" criteria, respectively. The mean diagnostic times were 28 ± 26 seconds and 68 ± 27 seconds, respectively. Sensing of < 23% of AF events resulted in failure to diagnose the arrhythmias by both algorithms. In the event of diagnostic failure, the mean ventricular pacing rate was 79 ± 9 ppm. Conclusion: Up to an atrial sensitivity of 1 mV, 100% of AF episodes were diagnosed. The Chorum mode switching algorithms are 100% reliable if > 45% of the AF waves are sensed. In the event of switching failure, the ventricle is protected by an average rate remaining below 80 ppm. (PACE 1996;     

Rate Stabilization by Right Ventricular Pacing in Patients with Atrial Fibrillation

A recent study of de Jongste has demonstrated the lengthening of short R-R intervals in patients with atrial fibrillation by right ventricular pacing. We have further analyzed the data from this study and specifically looked at the effect of right ventricular pacing on the R-R interval instability and heart rate. At the cost of only a slight increase in mean heart rate, a major reduction of the R-R interval instability can be obtained by right ventricular pacing. Based on these findings, we have developed and evaluated an automatic pacing rate algorithm, which continuously varies the stimulation rate in order to stabilize the otherwise irregular rhythm in patients with atrial fibrillation.     

非瓣膜性房颤患者的左心耳特点分析

目的：分析非瓣膜性房颤患者左心耳入口内径、左心耳长度及左心耳射血速率的特点。方法：以我院收治的237例房颤患者为研究对象,回顾性分析阵发性房颤与持续性房颤患者左心耳入口内径、长度及左心耳射血速率的差异,并分析房颤患者左心耳入口内径、长度及射血速率的临床相关因素。结果：与阵发性房颤组相比,持续性房颤组左心耳入口内径显著增大,具有统计学意义（P<0.05）,而两组患者的左心耳长度及左心耳射血速率无统计学差异。Spearman相关分析显示左心耳入口内径与身高、房颤病史长短、左房前后径、左室收缩末内径（left ventricular end-systolic diameter LVESD）、左室舒张末内径（left ventricular end-diastolic diameter LVEDD）呈正相关（P<0.05）,与左室射血分数（left ventricular ejection fraction LVEF)呈负相关（P<0.05）;左心耳长度与左房前后径、LVESD、LVEDD呈正相关（P<0.05）,与LVEF呈负相关(P<0.05);左心耳射血速率与年龄、房颤病史长短、左房前后径、LVESD呈负相关（P<0.05）,与LVEF呈正相关(P<0.05)。结论：持续性房颤患者左心耳入口内径大于阵发性房颤患者,左心耳的入口内径、长度、射血速率与多种因素相关。     

Clinical Observations with Long-term Atrial Pacing

Atrial pacing (AP), despite its beneficial hemodynamic and antiarrhythmic effect, is still an underused mode of stimulation. The main purpose of this study was to evaluate the long-term results of AP. Sixty four patients (pts) with sinus node disease (28 male and 36 female: mean age 54,2; range:44–88 years), 3,2% of the total implantation at our clinic were treated with AP between 1982–96. Criteria for atrial pacing were: no AV block in the history, no AV-block during carotid sinus massage, Wenckebach point > 130/min, left atrium <50mm, left ventricular EF >40%. The indication for pacing was predominant sinus bradycardia (SB) in 34 pts and tachycardia-bradycardia syndrome (TBS) in 30 pts. Pts with TBS were on antiarrhythmic treatment, while most pts with SB received no antiarrhythmic drugs. All the pts were checked up at every 3–6 month. Sixty-two pts were followed for 3–154 (mean: 67) months, two pts were lost for follow-up. Repeated lead dislodgment occurred in two pts, which made a pacing mode change necessary. Four pts died during the follow-up period for non-cardiac reasons. At the end of the follow-up period the data of 60 pts were available for evaluation (33 pts with SB, 27 pts with TBS). All the pts with SB were in sinus rhythm, and no patient developed AV block by the end of the follow-up period Seven out of 27 pts with TBS developed chronic atrial fibrillation, 3 out of them suffered a cerebral embolism; the remaining 20 pts were in sinus rhythm, and the number of paroxysmal attacks decreased significantly, which improved their quality of life significantly. Three pts in this group developed a temporary complete AV block, which regressed with decreasing the dosage of antiarrhythmic drugs. Atrial pacing is proved to be a safe and reliable treatment for sick sinus syndrome. Proper patient selection is crucial in preventing the development of AV conduction disturbance. Atrial stimulation had a satisfactory long-term antiarrhythmic effect in pts with sick sinus syndrome (SSS).     

Incidence and Predictive Factors of Atrial Fibrillation in Paced Patients

We have designed a prospective observational study to analyze the incidence and predictive factors of atrial fibrillation (AF) during a long follow-up, in a large population. Atrial fibrillation episodes were documented by the fallback mode switch (FMS) provided by implanted pacemakers. We have included 377 patients (61% men). The pacing indications were atrioventricular (AV) block (49%), sinus node disease (SND, 16%), bradycardia-tachycardia syndrome (BTS, 5%), AV block + SND (19%), AV block + BTS (6%), and BTS + SND (5%). The mean age at implant was 75 ± 12 (range 28–95). Atrial fibrillation before inclusion was documented in 10% of patients. Drug therapy at first follow-up included beta-adrenergic blockers (17% of the patients), amiodarone (13%), and others (16%). The mean follow-up was 30 ± 24 weeks. At least one AF episode was stored during follow-up in the memory of 169 pacemakers (45%). Among patients without history of AF at implant, 46% had documented FMS during follow-up. Patients with AF received more antiplatelet medications than patients without AF (P = 0.03). In patients with AF, New York Heart Association functional class was slightly higher, amiodarone and sotalol were more often prescribed, and the proportion of hypertension was higher than in patients without AF. However, these trends were not statistically significant. A significant higher incidence of premature atrial beats was observed in patients with AF than patients without AF (P < 0.0002). Patients with AF had a lower atrial percentage of paced events (55%) than patients without AF (63%, P < 0.02). These preliminary results confirm the high incidence of AF in paced patients and suggest a preventive effect of atrial pacing. The effects of other clinical variables may be confirmed with a longer follow-up in a larger population.     

Temporary Atrial Pacing in the Prevention of Postoperative Atrial Fibrillation

Background: Atrial fibrillation (AF) is a common complication after coronary artery bypass grafting (CABG). Since its prevention with prophylactic drug therapy has limited success, alternative approaches are desirable. This study examined the efficacy of atrial or biatrial pacing, compared with no pacing, on the incidence of AF after isolated CABG.
Methods: From August 2002 to September 2004, 240 patients underwent CABG. After surgery, right and left atrial epicardial pacing wires were implanted for 72 hours of temporary pacing. Patients were randomly assigned to one of three groups: no pacing (control group), right atrial (RA), and biatrial (BiA) pacing. Cardiac rhythm was monitored continuously during intensive care, or daily on the ward. The primary endpoints of this study were an episode of AF occurring up to 72 hours after CABG and the risk factors correlated with this event.
Results: Atrial and BiA pacing significantly lowered the incidence (1.25% vs 25%, P = 0.001) of AF episodes, and were both correlated (odd ratio 0.038; 95% confidence interval 0.005–0.29) with a decrease in rates of postoperative AF. Multivariable analysis identified older age (odd ratio 1.074; 95% confidence interval 1.024–1.12) and no pacing as independent risk factors of postoperative AF.
Conclusions: Temporary right atrial or biatrial pacing after CABG significantly decreased the postoperative incidence of AF. Multivariable analysis identified older age and no pacing as predictors of AF occurrence .     

Atrial Fibrillatory Electrogram Measurement Allows Atrial Lead Placement in Patients Who Develop Atrial Fibrillation During Permanent Dual Chamber Pacemaker Implantation

The benefit of DDD(R) pacing is proven even in patients with intermittent atrial fibrillation. Atrial fibrillation developing during dual chamber pacemaker implantation creates a difficult problem. Maneuvers to reestablish a stable atrial rhythm often are required if atrial fibrillation sets in. This study was performed to determine if atrial lead placement can be performed with acceptable long-term results in the presence of atrial fibrillation. Twenty-one patients in whom atrial fibrillation developed during permanent pacemaker implantation were included in this study. In 12 patients, episodes of intermittent atrial fibrillation had been documented before the procedure. Screw-in leads were used in 15 patients and J-shaped passive fixation leads in 6 patients. AH leads were bipolar. The intraoperative atrial fibrillation electrogram amplitudes ranged from 0.9 to 3.2 mV (mean 1.8 ± 0.6 mV). One patient required lead revision due to a high atrial pacing threshold after conversion to SR. One patient remained in atrial fibrillation at 3-month follow-up. The other 20 patients converted to SR, 11 of whom had intermittent atrial fibrillation with successful mode switch activation. P wave amplitudes were 2.8 ± 6 mV (range 1.4 to 4.0 mV) after conversion to SR. The mean atrial pacing threshold was 1.1 ± 0.5 V (range 0.5 to 3.5 V). Placement of atrial leads in patients who develop atrial fibrillation during pacemaker implantation is feasible; fibrillatory electrogram amplitudes showed a good correlation with the atrial signal after conversion to an organized atrial rhythm (r = 0.698). Acceptable atrial pacing thresholds can be expected as well.     

Atrial Refractory Periods after Atrial Premature Beats in Patients with Paroxysmal Atrial Fibrillation

To study the effects of an atrial premature beat on atrial refractory periods, we investigated 11 patients (group A) who were the control group, 12 patients suffering from paroxysmal atrial fibrillation (group B), and 10 patients (group C) without arrhythmias but with cardiopathy or cardiomyopathy. At every eighth complex of a constant atrial electrostimulated rhythm a fixed premature extrastimulus was introduced, and effective and functional refractory periods (ERP and FRP) were measured in three different sites of the right atrium, before and after introduction of this extrastimulus. Average ERP and FRP shortened respectively in group A, from 220.28 ± 25.68 msec and 281.17 ± 28.15 msec before extrastimulation, to 190.58 ± 22.74 msec and 245.88 ± 19.86 msec after; in group B, from 219.44 ± 27.38 msec and 284 ± 30.06 msec to 191.66 ± 28.72 msec and 253.23 ± 34.01 msec; and in group C from 229.03 ± 29.65 msec and 289.67 ± 51.62 msec to 194.19 ± 24.6 msec and 237.74 ± 39.59 msec. The average dispersions of ERP and FRP in group A were, respectively: 41.81 ± 21.36 msec and 36.36 ± 18.04 msec before extrastimulation, 28.18 ± 18.14 msec and 35.45 ± 15.72 msec after. In group B: 26.66 ± 19.46 msec and 41.66 ± 16.96 msec versus 45.83 ± 23.91 msec and 45 ± 34.77 msec and in group C: 27 ±11.59 msec and 45 ± 29.15 msec versus 29 ± 18.52 and 27 ± 18.88. It is concluded that an atrial premature beat tends to shorten the dispersion of atrial refractory periods when patients are free of arrhythmias, and to lengthen them when paroxysmal atrial fibrillation are documented.     

Wavelength Index at Three Atrial Sites in Patients with Paroxysmal Atrial Fibrillation

PADELETTI, L., et.al .: Wavelength Index at Three Atrial Sites in Patients with Paroxysmal Atrial Fibrillation . The purpose of this study was to evaluate the wavelength index (WLI) at three atrial sites in a group of 23 patients with recurrent episodes of lone paroxysmal atrial fibrillation (LPAF) and a control group (n = 20). All patients underwent programmed atrial stimulation (paced cycle length = 600 ms) at high, medium, and low lateral right atrial wall. P wave duration, sinus cycle length, and corrected sinus node recovery time were not significantly different between the two study groups. WLI was calculated according to the following formulas: atrial effective refractory period (AERP)/duration of atrial extrastimulus electrogram (A₂) or AERP/A₂+ atrial latency; and atrial functional refractory period (AFRP)/A₂. WLI was significantly shorter in LPAF than in the control group at each of the paced atrial sites independently of the formula used. Duration of premature atrial electrogram appeared to play the major role in determining the difference in WLI between patients with paroxysmal atrial fibrillation and the control group.     

A New Pacing Algorithm for Overdrive Suppression of Atrial Fibrillation

Constant rapid pacing may suppress arrhythmias, but it is usually poorly tolerated in the long term. We report a pilot study of a new pacing algorithm for overdrive suppression of atrial premature complexes (APCs) and atrial fibrillation (AF), which prevents postextrasystolic pauses and varies the pacing rate in response to the frequency of APCs. The algorithm was tested in a multiple crossover study for 24 hours in dual chamber pacemakers implanted in 70 patients. Comparison was made on ambulatory recordings between the number of atrial arrhythmias commencing with the algorithm active and inactive. In all cases, the algorithm functioned as designed. No patient was aware of its operation, and no malignant arrhythmias were induced. The 36 recordings that showed atrial arrhythmia were included for analysis. The effects of the algorithm were: APCs (estimated from pacemaker statistics) reduced in 18 patients, increased in 8 (P = 0.02); atrial salvos reduced in 12, increased in 4 (P = 0.041); and AF reduced in 11, increased in 8 (P = NS). In all patients with frequent AF (> 5 episodes in total), fewer episodes occurred when the algorithm was active. We conclude that the algorithm is safe and well tolerated, reduces atrial ectopic activity, and may reduce the frequency of sustained atrial fibrillation.     

Detection of Atrial Fibrillation During Sinus Tachycardia Induced by Exercise in Patients with Implantable Atrial Defibrillators

Accurate detection of atrial fibrillation (AF) is essential for appropriate operation of an implantable atrial defibrillator (IAD). However, during episodes of sinus tachycardia, distinction between AF and sinus rhythm (SR) using the quiet interval and baseline crossing analysis in the detection algorithm of the IAD may be difficult. The efficacy of this AF detection algorithm was tested in five patients implanted with an IAD (MFTRIX, Model 3000 or 3020, InControl Inc.) during treadmill exercise testing. The IADs were programmed to Monitor Mode with a wake up cycle of 1 minute for AF detection using the device nominal parameters or modified parameters, and to mark rhythms appropriate for shock delivery. A mean peak heart rate of 137 ± 26 beats/min was reached during maximum exercise, and one patient developed transient AF. Seventy-eight (75 in SR, 3 in AF) and 91 (89 in SR, 2 in AF) runs of AF detection were performed using the nominal and modified parameters, respectively. The IAD detected AF and SR accurately, except for one episode of false-positive AF detection during sinus tachycardia at the nominal settings, but inappropriate shocks were prevented by minimum RR interval criteria that limited discharge at high heart rate. These results indicate that the AF detection algorithm in the IAD may become more vulnerable to false-positive AF detection during sinus tachycardia, which were avoided by reprogramming the Quiet Interval and minimum RR interval criteria for AF detection. Exercise testing appeared useful to program optimal settings of the IAD in preparation for daily activities.     

特发性房颤患者心房电生理特点的临床观察

【目的】分析特发性房颤（idiopathic atrial fibrillation,IAF）患者与正常对照在基础状态及不同联律间期早搏刺激后心房有效不应期（effective refractory period,ERP）,不应期离散度（ERPdispersion,ER—PD）的差别,探讨IAF的发病机制。【方法】2005年4～7月住院的21例无器质性心脏痛室上性心动过速患者,其中6例伴有阵发性房颤。所有患者室上速射频消融成功后,程控刺激高右房（high right atrium,HRA）,冠状窦远端（coronary sinus distal,CSD）,测出上述两个部位基础刺激时（S1S1 500ms）心房ERP。保持基础刺激不变,分别给予不同联律间期的S2早搏刺激（S1S1不应期＋20ms,＋70ms,＋120ms,＋170ms）,通过发放S3测出不同S2早搏刺激后心房ERP。以基础及早搏刺激后HRA与CSD不应期的差值作为ERPD。【结果】6例IAF患者在HRA予S2早搏刺激（S1S1不应期＋20ms）时诱发房颤,HRA的ERP在基础及各种联律早搏刺激时明显短于对照组（P〈0．05）,CSD刺激时ERP两组无差别（P〉0．05）,IAF组ERPD较对照明显增大（P＜0．05）。（S1S1不应期＋20ms）的S2刺激较其他S2刺激使心房ERP缩短最为明显（P＜0．05）。【结论】HRA短ERP,增大的ERPD是IAF患者发病的电生理基础。短联律间期早搏刺激使ERP缩短更为明显,是房颤发作的始动因素。     

Atrial Vulnerability in Patients with Paroxysmal "Lone" Atrial Fibrillation

Little is known about the electrophysiological properties of the atrium predisposing to paroxysmal atrial fibrillation (AF), especially in patients without structural heart disease. This study was conducted to analyze intraatrial conduction, atrial refractoriness, and arrhythmia inducibility in patients with lone paroxysmal AF. An electrophysiological study was performed in 24 patients with a documented history of lone paroxysmal AF but in sinus rhythm at the time of the electrophysiological study. Twelve patients without any history of atrial arrhythmias served as controls. The patients with lone paroxysmal AF showed a significant prolonged local conduction time S1A1 (70 ± 21 ms vs 36 ± 12 ms, P < 0.0001), a lack of rate adaptation of the functional refractory period (FRP changes/cycle length changes < 10% in 15 of 24 patients with lone paroxysmal AF vs 1/12 controls, P = 0.002) and a higher incidence of inducible AF with only one extrastimulus (13/24 vs 0/12, P = 0.0014). The total P wave duration in the surface ECG (89 ± 14 ms vs 83 ± 8 ms, P = 0.15), the intraatrial conduction time (36 ± 14 ms vs 28 ± 8 ms, P = 0.07), the presence of a fragmented atrial electrogram (16/24 vs 7/12, P = 0.62), the absolute value of the effective refractory period (204 ± 28 ms vs 212 ± 23 ms, P = 0.42), and the vulnerability index (3.0 ± 1.5 vs 3.6 ± 1.5, P = 0.26) were not statistically different between the two groups. The presence of a prolonged (> 50 ms) S1A1 and/or the presence of a lack of rate adaptation of the FRP and/or the presence of inducible AF identified patients with spontaneous lone paroxysmal AF with a sensitivity of 96%, a specificity of 67%, a positive predictive value of 85%, and a negative predictive value of 89%. In patients with lone paroxysmal AF. the electrophysiological study using conventional techniques allows not only to detect AF inducibility using a nonaggressive protocol, but also to reveal several electrophysiological abnormalities related to the atrial substrate itself. This atrial vulnerability may explain the high incidence of recurrences in patients with lone paroxysmal AF.