What is the Relationship of Atrial Flutter and Fibrillation?

Animal models and human studies of atrial activation mapping and entrainment have considerably enhanced our understanding of the anatomical substrate for atrial flutter and created the basis for a definite cure with radiofrequency catheter ablation. As atrial flutter has now become a curable arrhythmia, emphasis is shifting to understand the most common arrhythmia: atrial fibrillation. Furthermore, from clinical observation, it is apparent that there is a relationship between atrial fibrillation and atrial flutter in patients with atrial arrhythmias. Techniques that have informed our understanding of the anatomical basis of atrial flutter may also be useful in understanding the relationship between atrial fibrillation and flutter, including animal models, clinical endocardial mapping, and intracardiac anatomical imaging. Thus, atrial anatomy and its relationship to electrophysiological findings, and the role of partial or complete conduction barriers around which reentry can and cannot occur, may be of importance for atrial fibrillation as well. Ultimately, the relationship between atrial fibrillation and atrial flutter may inform our understanding of the mechanisms of atrial fibrillation itself, and help to develop new approaches to device, catheter-based, and pharmacological therapy for atrial fibrillation.     

Atrial Vulnerability and Electrophysiology Determined in Patients With and Without Paroxysmal Atrial Fibrillation

For elucidation of atrial electrophysiology and vulnerability an electrophysiological study was performed in 45 patients with documented paroxysmal atrial fibrillation and a control group (n = 46). Atrial vulnerability was assessed by programmed atrial stimulation with up to two extrastimuli during sinus rhythm and paced cycle lengths of 600 msec, 430 msec and 330 msec. Sustained atrial fibrillation or flutter was induced in 37/45 patients with paroxysmal atrial fibrillation in contrast to 9/46 patients in the control group (P less than 0.001). Left atrial diameter (M-mode echocardiogram), P wave duration, sinus cycle length, sinus node recovery time, and the effective refractory period of the right atrium were not significantly different between the two study groups. Intraatrial conduction time from the high right atrium (HRA) to the basal right atrium (A) and the functional refractory period of the right atrium were significantly longer in patients with paroxysmal atrial fibrillation.     

Mechanism and Clinical Significance of Atrial Repetitive Responses in Man

We have studied the electrophysiological correlates of atrial repetitive responses, induced by single extrastimuli, in a group of 25 patients undergoing electrophysiologic studies for a variety of supraventricular and ventricular arrhythmias. The incidence of repetitive responses was not related to a previous history of atrial tachyarrhythmias. Repetitive responses were observed only when the extrastimulus elicited a significant intra-atrial conduction delay, as measured from the extrastimulus artifact, to two or three points in the atria. This condition was fulfilled only when the basic atrial rhythm was paced, and it was also facilitated by increasing atrial rate, which shortened the atrial effective refractory period. Atrial pacing thus seemed to facilitate the production of atrial repetitive responses by both promoting intra-atrial conduction delays during extrastimulation, and by shortening the atrial refractory period. Alrial repetitive responses are probably a nonspecific phenomenon, unrelated to a tendency towards atrial tachyarrhythmias; their mechanism is probably local re-entry, related to slow conduction of impulses during incomplete repoiarization, and under favorable conditions they may precipitate atrial flutter or fibrillation in predisposed patients.     

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.     

Active Fixation Atrial Leads: Randomized Comparison of Two Lead Designs

Active fixation leads have reduced the incidence of lead dislodgement in patients with permanent pacemakers. However, theoretic concern that the tissue trauma associated with a myocardial screw-helix may increase the chronic pacing threshold of active compared to passive fixation leads has remained. Whether active fixation leads with a stimulating electrode that is independent of the fixation mechanism are associated with a lower chronic pacing threshold than leads utilizing a screw-helix for both fixation and stimulation is unknown. The present prospective, randomized study compared the acute and chronic atrial pacing and sensing characteristics of two unipolar active fixation leads, one utilizing a screw-helix for both fixation and electrical stimulation, the other with an active porous tip electrode and an electrically inactive helix. Patients were randomized to receive either a Medtronic 6957J lead with an electrically active myocardial screw-helix or a Cordis 329-101P lead with an inactive helix and a porous tip electrode. The baseline characteristics of the groups were comparable. At implantation, the 329-101P lead had a lower mean voltage threshold than the 6957J lead (0.61 +/- 0.16 V vs 1.05 +/- 0.34 V, P = 0.0004). There were no significant differences in atrial electrogram amplitude, slew rate, or lead impedance between the groups. At 6 weeks follow-up, there were no differences in the mean threshold voltage (1.85 +/- 0.36 vs 1.93 +/- 0.69 V), impedance (528 +/- 81 vs 530 +/- 118 ohms), or atrial electrogram amplitude (2.63 +/- 0.50 vs 2.42 +/- 0.95 mV) between the two leads. At long-term follow-up (mean 16.2 +/- 2.8 months, range 13.1-20.0 months) there were no significant differences in voltage threshold (1.65 +/- 0.61 vs 1.97 +/- 0.64 V), impedance (565.5 +/- 81.6 vs 617.7 +/- 146.7 ohms), or atrial electrogram amplitude (2.79 +/- 0.75 vs 3.10 +/- 1.53 mV). Thus, these results suggest that active fixation leads in the atrium with an electrode that is independent of the fixation mechanism do not provide chronic stimulation thresholds or electrogram amplitudes that are superior to those obtained with leads utilizing a myocardial screw-helix as both the active electrode and the fixation device.     

Reliability of Atrial Screw-in Leads

The aim of this study was to investigate long-term performance of a carbon coated atrial screw-in lead. During implantation of 247 leads of this type we measured an average stimulation threshold of 0.74 V(range: 0.2–1.6 V) at 1 ms pulse width. Mean lead impedance came to 446 ohms (range: 263–1000 ohms) resulting in an arithmetical energy consumption of 1.51 μJ(range: 0.1–7.21 μJ). Average P wave amplitude was 3.9 mV (range: 1.3–11 mV). After a mean follow-up of 16.4 months (range; 3–60 months) we found excellent threshold results in 76% of the patients permitting a safety programming al half of nominal value. An additional 14% nominal settings could be retained. With regard to chronic lead impedance of 488 ohms (range: 315–1327 ohms) we calculated an average chronic energy consumption of 10.83 μJ (range: 1.62–22.78 μJ) during safety programming. This made up 34.6% of the corresponding energy consumption during nominal programming. Eighty percent of the patients showed chronic P waves above 2 mV; nearly half of them (n - 94 = 38%) showed a proper sensing function even when programmed to minimal sensitivity settings or above 4 mV. In 19 leads (8%) we observed unsatisfying threshold results requiring high output programmings. All threshold increases occurred within the first year, 84% (n = 16/19) within the first 3 postoperative months. An additional five leads (2%) were found to have a loss of capture, and one (0.5%) a loss of sensing. These complications required reoperation as well as one dislocation (0.5%) resulting in a low complication rate of 3% as compared to the total complication rate of all implanted atrial leads which was substantially higher (n = 48/652 = 7.5%). With regard to our results we consider the carbon coated atrial screw-in lead to have proven long-term reliability.     

Characterization of atrial fibrillation in man: studies following open heart surgery.

The nature of localized atrial activation during atrial fibrillation was characterized in 34 patients following open heart surgery. Bipolar atrial electrograms (AEG) recorded in each patient with atrial fibrillation exhibited a myriad of sizes, shapes, polarities, amplitudes, and beat-to-beat intervals. On the basis of the AEG morphology and the nature of its baseline, we have classified the recordings into four Types. Type I was characterized by discrete AEG complexes separated by an isoelectric baseline free of perturbation, Type II by discrete AEG complexes but with perturbations of the baseline between complexes, Type III by AEGs which failed to demonstrate either discrete complexes or isoelectric intervals, and Type IV in which AEGs of Type III alternated with periods characteristic of Type I and/or Type II. In 22 patients, the AEGs were recorded a second time, and in 11 of these patients the type of atrial fibrillation changed between the first and second recording period. An atrial flutter-fibrillation pattern in the ECG was associated with a relatively ordered atrial activation pattern and a relatively slow atrial rate. Human atrial fibrillation is not an electrophysiologically homogeneous process when compared among different patients or ad seriatim in the same patient.     

Clinical Utility of Intraatrial Pacemaker Stored Electrograms to Diagnose Atrial Fibrillation and Flutter

POLLAK, W.M., et al. : Clinical Utility of Intraatrial Pacemaker Stored Electrograms to Diagnose Atrial Fibrillation and Flutter. The purpose of this study was to determine if intraatrial electrograms (EGMs) are required to diagnose specific types of atrial tachyarrhythmias detected by pacemaker diagnostics. DDD pacemakers in 56 patients were programmed to store episodes of atrial tachyarrhythmias. Some episodes had a stored atrial EGM snapshot of the atrial tachyarrhythmia. The EGMs were analyzed to confirm whether the stored episodes were true atrial tachyarrhythmias or other pacemaker-sensed events. EGM confirmation of atrial tachyarrhythmias correlated with increasing duration and rate of episodes. In particular, using EGMs, 8 (18%) of 44 episodes < 10 seconds in duration confirmed atrial tachyarrhythmias compared to 16 (89%) of 18 episodes > 5 minutes in duration (  P < 0.001  ). Only 10 (18%) of 56 detected atrial arrhythmia episodes at rates < 250 complexes per minute were confirmed by the atrial EGM as true arrhythmias compared to 33 (57%) of 58 detected episodes at rates > 250/min (  P < 0.001  ) Twenty-nine (91%) of 32 EGM confirmed episodes of atrial fibrillation/flutter had an atrial rate > 250 complexes per minute and were a minimum of 10 seconds in duration. Fifteen (88%) of 17 episodes meeting the combined stored data criteria of > 250 complexes per minute and duration > 5 minutes were confirmed as atrial fibrillation or flutter by stored EGMs. Atrial EGMs identified that 71 (62%) of 114 stored high atrial rate (HAR) episodes were events other than true atrial tachyarrhythmias. Pacemaker diagnostic data with intraatrial EGMs can diagnose specific atrial tachyarrhythmias and identify other pacemaker-sensed events. Stored episodes > 250 complexes per minute and > 5 minutes in duration had a high correlation with atrial fibrillation and flutter.     

Left atrial tachycardia after right atrial separation for chronic atrial fibrillation with atrial septal defects

A right atrial separation procedure was performed for the ablation of chronic atrial fibrillation in four cases, concomitant with the repair of the atrial septal defect. After the operation, chronic atrial fibrillation disappeared in three of them and left atrial tachycardia occurred in the other one. Left atrial tachycardia is an arrhythmia encountered after a right atrial separation procedure.     

Long-term outcome following ablation of atrial flutter occurring late after atrial septal defect repair

Aims: In patients with surgical atrial septal defect (ASD) repair, late atrial flutters (AFLs), including cavotricuspid isthmus (CTI)‐dependent and non‐CTI‐dependent scar‐related flutter (AFL), are common. Radiofrequency ablation (RFA) of these arrhythmias has a high acute success rate. We aimed to characterize the long‐term freedom from atrial arrhythmias in this population. Methods: Twenty consecutive patients undergoing RFA for AFL late after ASD repair were included. Electrophysiological assessment included multipolar activation, entrainment, and electroanatomic mapping. Clinical, electrocardiograph, and Holter monitoring follow‐up was conducted every 6 months. Results: Mean age was 53 ± 13 years. Time from surgical repair to RFA was 29 ± 15 years. All patients had CTI‐dependent AFL (20/20). There were 1.6 ± 0.7 arrhythmias per patient; other arrhythmias included non‐CTI‐dependent AFL (14), focal atrial tachycardia (two), and atrioventricular nodal reentry tachycardia (two) . Acute success was obtained in 100%. Five patients with recurrent AFL (three CTI dependent, two non‐CTI dependent) at 13 ± 8 months had successful repeat RFA. At 3.2 ± 1.6 years follow‐up since the last procedure, 90% of patients with successful RFA for AFL remained free of their clinical arrhythmia. However, 30% of the original 20 patients had documented atrial fibrillation (AF) 2.1 ± 1.6 years after the last procedure; five (25%) required AF intervention. One stroke (5%) occurred in the context of late AF. Conclusion: RFA of AFL occurring late after surgical ASD repair has a low long‐term risk of recurrence, although 25% of patients required two procedures. However, there is a high late incidence of AF (30%), with an additional 25% of patients requiring intervention for AF. (PACE 2011; 34:431–435)     

Can Early Timed Internal Atrial Defibrillation Shocks Reduce the Atrial Defibrillation Threshold?

The defibrillation threshold is markedly reduced very early following the initiation of ventricular fibrillation. The purpose of this study was to determine if the same finding holds true for atrial defibrillation. Sustained, reproducible AF was induced with programmed atrial pacing using acetyl-beta-methylcholine chloride (40-640 microL/min) in six adult sheep (heart weight 245-300 g). Seven timing intervals (125 ms, 200 ms, 1 s, 3 s, 10 s, 30 s, and 5 min after AF induction) and two lead configurations: (1) RA as cathode and CS as anode; and (2) RA as cathode and RV apex as anode were tested. Single capacitor biphasic waveforms (3/1 ms) were delivered and atrial defibrillation thresholds (ADFTs) were determined in random order. No significant differences in leading edge voltage and total energy were detected for the RA-CS configuration for the seven timing intervals. For the RA-RV configuration, a significant difference was detected comparing the voltage for 125 ms to the 5-minute timing interval. For all times except 125 ms, the RA-RV threshold was significantly higher than the RA-CS level. In contrast to ventricular defibrillation, the ADFT does not change significantly within the first 5 minutes after the initiation of AF for the RA-CS configuration. However, if the shock is given very early (125 ms after AF induction) with the RA-RV configuration, the ADFT is lowered almost to the RA-CS level.     

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。     

Right Atrial Separation Procedure for Eliminating Chronic Atrial Fibrillation Associated with Atrial Septal Defect

Chronic atrial fibrillation (AF) had been documented in a patient with atrial septal defect for 7 years. A right atrial separation procedure was performed for ablation of chronic AF, concomitant with repair of the atrial septal defect, and followed by atrial electrophysiological mapping. A horizontal transectional incision extending to the borders of the atrial septum and the tricuspid annulus was made. Cryolesions of the atrial isthmus between the margin of the upper incision and the tricuspid valve annulus were created at -60†C for 2 minutes at a time. After the operation, the patient had restored normal sinus rhythm during a subsequent follow-up period of 48 months.     

Effect of coexisting cardiovascular disease on the long-term efficacy and safety of the implantable atrial defibrillator

The long-term efficacy and safety of implantable atrial defibrillator (IAD) therapy in patients with AF and cardiovascular disease is unclear. The aim of this study was to evaluate the efficacy and safety of IAD therapy in patients with and without coexisting cardiovascular disease. In 115 patients implanted with an IAD, 85 patients had cardiovascular disease: 41 (48%) patients had 1 cardiovascular abnormality, 29 (35%) patients had 2, 13 (15%) patients had 3, and 2 (2%) patients had 4 different cardiovascular abnormalities. The device was programmed into a rhythm monitoring mode for the first 3-month postimplant period. All defibrillation therapy was performed under physician supervision to monitor safety and efficacy. After this initial monitoring period, patients were allowed to activate their device away from the hospital or clinic. A total of 357 spontaneous AF episodes occurred in 83 (72%) patients during observed operation and the mean shock efficacy was 93.5+/-20.3% (lower 95% confidence interval [CI] 89.8%). As of the lastfollow-up, 58 (55%) patients had transition to receive nonphysician observed therapy. Forty-two (72%) patients had experienced 332 episodes of AF for which theyhad received device therapy away from the hospital/clinic (mean shock efficacy 90.5+/-39.7%). The presence of hypertension, valvular heart disease, and ischemic heart disease did not affect the shock efficacy of the IAD during physician observed and nonobserved therapy (P > 0.05). However, the presence of congestive heart failure was associated with a lower clinical efficacy during observed and nonobserved therapy (P < 0.05). Overall, 5,262 shocks have been delivered with the IAD without any episode of proarrhythmia. The observed proarrhythmic risk was 0%, with an estimated maximum proarrhythmic risk of 0.06% per shock (95% upper CI). A stand-alone IAD appears to be safe in the presence of cardiovascular disease. The lower clinical efficacy for AF associated with congestive heart failure might be related to a higher rate of early reinitiation of AF after defibrillation.     

Atrial Septal Pacing: A Method for Pacing Both Atria Simuhaneously

By pacing both atria simultaneously, one could reliably predict and optimize left-sided AV timing without concern for IACT. With synchronous depolarization of the atria, reentrant arrhythmias might be suppressed. We studied four male patients (73 ± 3 years) with paroxysmal atrial fibrillation and symptomatic bradyarrhythmias using TEE and fluoroscopy as guides; a standard active fixation screw-in lead (Medtronic model #4058) was attached to the interatrial septum and a standard tined lead was placed in the ventricle. The generators were Medtronic model 7960. The baseline ECG was compared to the paced ECG and the conduction time were measured to the high right atrium, distal coronary sinus and atrial septum in normal sinus rhytbm, atrial septal pacing, and AAT pacing. On the surface ECG, no acceleration or delay in A V conduction was noted during AAI pacing from the interatrial septum as compared with normal sinus rhythm. The mean interatrial conduction time for all 4 patients was 106 ± 2 ms; the interatrial conduction time measured during AAT pacing utilizing the atrial septal pacing lead was 97 ± 4 ms (P = NS). During atrial septal pacing, the mean conduction time to the high right atrium was 53 ± 2 ms. The mean conduction time to the lateral left atrium during atrial septal pacing, was likewise 53 ± 2 ms. We conclude that it is possible to pace both atria simultaneously from a single site using a standard active fixation lead guided by TEE and fluoroscopy. Such a pacing system allows accurate timing of the left-sided AV delay.     

Prediction of Permanent Atrial Sensing by Preoperative Esophageal Atrial Wave Evaluation

Atrial undersensing is a common problem in permanent atrial and dual chamber pacing. The purpose of this study was to evaluate the relationship between transesophageal atrial wave (EsAW) and right atrial endocavitary (RA). Forty-seven patients 72 ± 9.7 years of age, with symptomatic bradyar-rhythmias were studied. The EsAW was filtered with a high pass filter of 10 Hz (Arzco preamplifier-filter), using 1, 2, and 3 cm bipolar transesophageai catheters. Atrial bipolar floating 1, 2, and 3 cm electrograms from the high RA (HRA) and from the mid RA (MRA), as well as unipolar electrograms from the right auricle (RAUR) were recorded 1 day later. Comparison by paired t-test showed no significant differences between EsAW and bipolar sensing in RA, but significant differences between EsAW and RAUR (P = 0.0001). The results of the Spearman correlation coefficient for sensing (mV) for EsAW, HRA, and MRA, respectively, were: 1 cm, 1.8 ± 0,9, 1.7 ± 0,9, and 1.9 ± 0.9 (z > 3.5; P < 0.0003); 2 cm, 2.2 ± 0.9, 1.9 ± 0.8, and 2.1 ± 0.9 (z > 2.3; P < 0.03); 3 cm, 2.1 ± 1, 2 ± 0.9, and 2.2 ± 1.0 (z > 2.9; P < 0.003); and the result for the monopolar RAUR was 3.0 ± 1.0 (z < 1.4; P > 0.17). These findings, if confirmed in more patients, indicate that preoperative EsAW recording could be useful in estimating the quality of bipolar floating electrograms from the RA but not of unipolar RAUR.     

动态心房超速起搏治疗阵发性心房颤动

目的：评价动态心房超速起搏（dynamic atrial overdrive,DAO)方式治疗阵发性心房颤动的疗效。方法：3例均为女性，58－69岁，均为病态窦房结综合征合并阵发性心房颤动患者，植入Pacesetter公司Trilogy DR DAO 2364L型双腔起搏器。随机单盲将患者分为A组：DAO on和B组：DAO off；4个月后交换，即改为A组DAO off及B组DAO on再4个月，随访8－12个月。随访内容包括症状、抗心律失常药物增减及用程控仪观察自动模式转换（auto mode switch,AMS)的次数。结果：1）症状：3例心悸、胸闷症状无论在DAO off或on时均有好转。2）AMS：A组1例在DAO on及off各4个月的随访中，AMS分别为1次或0次，后继续off 4个月，AMS仍为0次，随继续关闭DAO。程控结果显示99％为心房起搏。该患者植入起搏器前后均未服用过抗心律失常药物。A组另1例在DAO on时AMS为764次，off时AMS为6232次，on较off则AMS发生率下降88％。该患者一直服用莫雷西嗪和肠溶阿司匹林。B组患者BAO off时AMS为16441次，on时AMSo 8081次，on较off时AMS下降51％。该患者因无明显心房颤动引起的症状而在DAO on期间自行停服抗心律失常药物。结论：动态心房超速起搏方式具有一定的预防阵发性心房颤动的作用。     

阿托伐他汀联合胺碘酮治疗原发性高血压伴阵发性房颤的研究

目的 探讨阿托伐他汀治疗原发性高血压伴阵发性心房颤动的疗效及对左心房内径、C反应蛋白(CRP)的影响.方法 入选原发性高血压伴阵发性心房颤动患者80例,随机分成两组:对照组40例;阿托伐他汀组40例.均服药1年.观察两组治疗前后疗效及左心房内径、C反应蛋白的变化.结果 ①两组治疗后,对照组有效率38.4%,阿托伐他汀组有效率62.5%(x2=4.56 P<0.05);②两组治疗后比较,阿托伐他汀组左心房内径增大程度低于对照组(P<0.05),血CRP浓度比对照组降低明显(P<0.05).结论 阿托伐他汀能通过抗炎、抑制左心房重构作用预防阵发性心房颤动复发.