Efficacy of consistent atrial pacing algorithm for suppression of atrial arrhythmias in patients with sick sinus syndrome and atrial fibrillation

Atrial overdrive provides the best opportunity to suppress atrial arrhythmias. Atrial preference pacing (APP) algorithm has been designed to achieve a high percentage of atrial pacing. The aim of this study was to assess the efficacy of APP algorithm in patients with implanted pacemakers and tachycardia-bradycardia syndrome. The subjects were 17 patients (mean age, 71.7+/-9.0 years old, 4 males) implanted with a DDDR pacemaker Thera DR (Medtronic, Minneapolis, MN, USA). All patients had sick sinus syndrome and paroxysmal atrial fibrillation before pacemaker implantation. Informed consent was obtained from each participant before enrollment. DDDR and mode switch or APP were randomly programmed. After two weeks, the pacing mode was switched to another mode. The percentage of atrial pacing was significantly higher in APP than in DDDR (97.7+/-1.4 versus 52.3+/-30.8, P<0.0001). Atrial premature beat counts were significantly greater in DDDR than in APP (30689+/-42534 versus 7717+/-10700, P<0.005). There was no significant difference in mode switch episode counts between DDIR and APP (2.6+/-5.5 versus 8.4+/-19.2, NS). Although there was no significant difference in mode switch episode counts between DDDR and APP, APP algorithm can successfully prevent atrial premature beats in patients with tachycardia-bradycardia syndrome.     

Impact of Consistent Atrial Pacing Algorithm on Premature Atrial Complexe Number and Paroxysmal Atrial Fibrillation Recurrences in Brady-Tachy Syndrome: A Randomized Prospective Cross Over Study

Aim of the study: The Consistent Atrial Pacing (CAP) algorithm has been designed to achieve a high percentage of atrial pacing to suppress paroxysmal atrial fibrillation. The aim of our study was to compare the impact of DDDR+CAP versus DDDR pacing on paroxysmal atrial fibrillation recurrences and triggers in patients with Brady-Tachy Syndrome. Methods: 61 patients, 23 M and 38 F, mean age 75±9 y, affected by Brady-Tachy Syndrome, implanted with a DDDR pacemaker, were randomized to DDDR or DDDR+CAP pacing with cross over of pacing modality after 1 month. Results: 78 % of patients in DDDR pacing and 73 % in DDDR+CAP pacing (p=n.s.) were free from symptomatic paroxysmal atrial fibrillation recurrences. During DDDR+CAP pacing, the atrial pacing percentage increased from 77±29 % to 96±7 % (p<0.0001). Automatic mode switch episodes/day were 0.73±1.09 in DDDR and 0.79±1.14 (p=n.s.) in DDDR+CAP. In patients with less than 50 % of atrial pacing during DDDR, automaticmode switch episodes/day decreased during DDDR+CAP from 1.13±1.59 to 0.23±0.32 (p<0.05) and in patients with less than 90 % from 1.23±1.27 to 0.75±1.10 (p<0.001). The number of premature atrial complexes per day decreased during DDDR+CAP from 2665±4468 to 556±704 (p<0.02). Conclusion: CAP algorithm allowed continuous overdrive atrial pacing without major side effects. Triggers of paroxysmal atrial fibrillation induction, such as premature atrial complexes, were critically decreased. Paroxysmal atrial fibrillation episodes were reduced in patients with atrial pacing percentage lower than 90 % during DDDR pacing.     

Electrophysiological determinants of atrial fibrillation in sinus node dysfunction despite atrial pacing.

AIMS: The effectiveness of atrial pacing in reducing the incidence of atrial fibrillation in patients with sinus node dysfunction is incomplete, and the correlation between electrophysiological atrial properties and the effect of permanent atrial pacing has been poorly investigated. Accordingly, the aim of the present study was to correlate electrophysiological data, in terms of atrial refractoriness, conduction parameters, and propensity to atrial fibrillation induction, and the likelihood of atrial fibrillation after DDD device implantation. METHODS AND RESULTS: The authors reviewed electrophysiological data of 41 patients with sinus node dysfunction (mean age 70 +/- 8 years, who were investigated free of anti-arrhythmic treatments before pacemaker implantation. At a drive cycle length of 600 ms, effective and functional refractory periods, S1-A1 and S2-A2 latency, A1 and A2 width, and latent vulnerability index (effective refractory period [ERP] A2), were measured. Atrial fibrillation induction was tested with up to three extrastimuli in 34 patients. Induction of sustained atrial fibrillation (> 1 min) was considered as the end-point. P-wave duration on the surface ECG in lead II/V1 was also measured. Minimal atrial rate was programmed between 60 and 75 bpm (mean: 64 +/- 4 bpm). After implantation, the patients were followed-up for 28 +/- 17 months, and ECG-documented occurrence of atrial fibrillation was determined. Electrophysiological characteristics of patients with (n = 12) or without (n = 29) paroxysmal atrial fibrillation before implantation were similar. When comparing patients with (n = 11) or without (n = 30) post-pacing atrial fibrillation occurrence, no differences were found in age, underlying heart disease, left atrial size, minimal pacing rate, and follow-up duration. Additionally, between the two former groups, there was no significant difference in terms of effective refractory periods (233 +/- 47 ms vs 239 +/- 25 ms), functional refractory periods (280 +/- 48 ms vs 272 +/- 21 ms), S1-A1 (44 +/- 20 ms vs 37 +/- 13 ms) and S2-A2 latency (77 +/- 28 ms vs 66 +/- 22 ms), and A1 duration (60 +/- 23 ms vs 53 +/- 16 ms). In contrast, in patients with post-pacing atrial fibrillation occurrence, the P wave was more prolonged (116 +/- 22 ms vs 98 +/- 13 ms; P < 0.01), A2 was longer (116 +/- 41 ms vs 87 +/- 27 ms; P < 0.01), effective refractory periods/A2 was lower (2.1 +/- 0.4 cm vs 3.1 +/- 1.4 cm; P < 0.05), and rate of atrial fibrillation induction was higher (8/11 patients vs 8/23 patients; P < 0.05). Electrophysiological characteristics of patients free of post-pacing atrial fibrillation with associated (n = 6) or unassociated (n = 24) paroxysmal atrial fibrillation history before implantation were quite similar. In patients with post-pacing atrial fibrillation with associated (n = 6) or unassociated atrial fibrillation history (n = 5) before implantation, effective refractory periods was statistically different (207 +/- 23 ms vs 264 +/- 46 ms; P < 0.05). Values of effective refractory periods < 220 ms were significantly more frequent in patients with post-pacing atrial fibrillation than in patients without (4/11 patients vs 2/30 patients; P < 0.05). When comparing patients with post-pacing atrial fibrillation with effective refractory periods > or = 220 ms (n = 7) and < 220 ms (n = 4), A2 duration was remarkably prolonged (145 +/- 42 ms vs 90 +/- 11 ms; P < 0.05) in those with effective refractory periods > or = 220 ms. By contrast, between the two groups, effective refractory periods/A2 were identical (2.08 +/- 0.6 cm vs 2.15 +/- 0.3 cm; P = n.s.). CONCLUSION: Prolonged atrial refractoriness, lesser degrees of conduction disturbance and a lower rate of atrial fibrillation induction seem to be predictive of stable sinus rhythm. In contrast, patients with persistence of atrial fibrillation despite pacing have a more abnormal and inhomogeneous atrial substrate, as well as a higher rate of atrial fibrillation induction. Prolonged P wave, shortened refractoriness, or remarkably abnormal conduction disturbances in the presence of prolonged refractoriness limit the effectiveness of standard atrial pacing in atrial fibrillation prevention. Identification of predictive criteria of failure of single-site atrial pacing may be used to consider dual-site atrial pacing in such patients with sinus node dysfunction.     

Haemodynamics of induced atrial fibrillation: a comparative assessment with sinus rhythm, atrial and ventricular pacing

The haemodynamics and myocardial lactate consumption during induced atrial fibrillation (AF) were studied in 10 patients with paroxysmal AF. Their mean age (+/- SD) was 61 +/- 5 years and none had clinical evidence of ischaemic or rheumatic heart disease. Compared with sinus rhythm, the onset of AF was associated with a reduction in systolic blood pressure (152 +/- 13 mmHg) in AF vs 169 +/- 23 mmHg in sinus rhythm, P less than 0.01). There was no consistent change in cardiac output at the onset of AF compared with sinus rhythm, but the cardiac output was lower compared with regular atrial pacing at rates similar to those of induced AF (3.85 +/- 0.76 vs 4.38 +/- 0.89 l min-1, P less than 0.02). Compared with sinus rhythm or rate-matched atrial pacing, AF was associated with an elevated pulmonary arterial pressure (24.2 +/- 5.6 mmHg in AF vs 17.9 +/- 14.4 mmHg in sinus rhythm, P less than 0.01) and pulmonary arterial wedge pressure (18.6 +/- 5.6 vs 9.7 +/- 3.9 mmHg, P less than 0.01). The haemodynamic changes during AF were similar to those seen during regular ventricular pacing at an equivalent rate, although the latter was associated with a lower systolic blood pressure (152 +/- 13 mmHg in AF vs 136 +/- 25 mmHg in ventricular pacing, P less than 0.05) and higher right atrial pressure (8.2 +/- 4.4 vs 11.5 +/- 7.5 mmHg respectively, P less than 0.05), presumably due to the deleterious effects of cannon 'a' waves.(ABSTRACT TRUNCATED AT 250 WORDS)     

Bipolar atrial sensing thresholds in sinus rhythm and atrial tachyarrhythmias. A comparative analysis in patients with DDDR pacemakers.

Automatic mode switching (AMS) function in dual chamber pacemakers depends on adequate detection of atrial tachyarrhythmias. There are few data on showing how intra-operative atrial signal amplititude during sinus rhythm can predict atrial tachyarrhythmias after pacemaker implantation. In 43 patients undergoing DDDR pacemaker implantation and atrioventricular nodal ablation for the treatment of drug-refractory paroxysmal atrial fibrillation, atrial sensing thresholds during sinus rhythm and during induced atrial tachyarrhythmias (24-48 h after device implantation) were analysed. Five different DDDR pacemaker systems were implanted (Chorus 7034, Ela Medical n = 13; Meta DDDR 1254, Telectronics Pacing Systems n = 12; Vigor DR 1230, Guidant n = 6; Trilogy DR 2364, Pacesetter, n = 2; Kappa DR 401, Medtronic USA n = 10). Every patient received a steroid-eluting, screwing, bipolar atrial lead (Medtronic, Capsure-Fix 4068). The mean P wave amplitude during implantation was 3.91 +/- 1.14 mV. The mean atrial sensing threshold during sinus rhythm and during all modes of induced atrial tachyarrhythmias was 3.35 +/- 1.0 mV, and 1.52 +/- 0.92 mV, respectively (P < 0.001). Atrial fibrillation was induced in 36 patients. The mean sensing threshold during sinus rhythm in this patient group was 3.39 +/- 1.01 mV, the mean sensing threshold during atrial fibrillation was 1.27 +/- 0.56 mV, reflecting a 63% reduction of sensing threshold compared with sinus rhythm (P < 0.001). Atrial flutter was induced in seven patients. The mean sensing threshold during sinus rhythm was 2.92 +/- 1.19 mV, the mean sensing threshold during atrial flutter was 2.79 +/- 1.26 mV, reflecting a reduction of 5% (ns) compared with sinus rhythm. Atrial sensing thresholds during sinus rhythm were significantly correlated with sensing thresholds during atrial tachyarrhythmias (r = 0.44; P < 0.002), but there were significant variations in intra-individual results. The reduction of atrial sensing thresholds between sinus rhythm and induced atrial tachyarrhythmias ranged from 30% to 82%. CONCLUSION: Bipolar atrial sensing thresholds during sinus rhythm are correlated with sensing thresholds during atrial tachyarrhythmias, but there is a large degree of variance in individual patients. A 4:1 to 5:1 atrial sensing safety margin based on sensing threshold during sinus rhythm is a predictor for adequate postoperative detection of atrial tachyarrhythmias and the function of AMS devices.     

Effects of right atrial pacing preference in prevention of paroxysmal atrial fibrillation: Atrial Pacing Preference study (APP study).

BACKGROUND: Several preliminary studies have indicated that atrial pacing can prevent atrial tachyarrhythmias. The suggested mechanisms by which pacing may be effective include suppression of premature atrial beats. METHODS AND RESULTS: The Atrial Pacing Preference (APP; Guidant, St Paul, MN, USA) algorithm allows the pacemaker to maintain a pacing rate slightly higher than the sinus rate. The preventive effects of APP on paroxysmal atrial fibrillation (AF) were studied in 51 patients (70+/-11 years). Nine patients did not complete the protocol. The pacemaker was programmed in random order to APP off and APP on at 3 different settings (ie, 8, 16 and 32 cycles) for 4 weeks each, using a cross-over design. Percentage atrial pacing was lower in APP off than at the other settings. Premature beat counts were greater in APP off than at the other settings. There was a significant difference in mode switch episode counts between APP off and the most effective setting (3,818+/-15,356 vs 596+/-1,719; p<0.01). CONCLUSIONS: The APP algorithm is a promising method for preventing atrial tachyarrhythmia in patients with an implanted pacemaker and AF. Optimizing the setting of the APP algorithm is an important issue in the prevention of AF.     

Atrial pacing for suppression of early reinitiation of atrial fibrillation after successful internal cardioversion.

AIMS: To evaluate the efficacy of atrial pacing in the suppression of early reinitiation of atrial fibrillation after successful internal cardioversion. METHODS AND RESULTS: The efficacy of atrial pacing in suppressing early reinitiation of atrial fibrillation was studied in 12 of 45 (29%) patients with early reinitiation of atrial fibrillation after successful cardioversion. These patients were randomized to undergo either repeated defibrillation alone or repeated defibrillation followed by high right atrial pacing at 500 ms in a crossover fashion. In patients with persistent early reinitiation of atrial fibrillation despite atrial pacing at 500 ms and repeated defibrillation, atrial pacing at 300 ms was tested. Lastly, if early reinitiation of atrial fibrillation persisted, administration of intravenous sotalol (1.5 mg. kg(-1)) was tested. Atrial pacing at 500 ms after defibrillation prevented early reinitiation of atrial fibrillation in five of 12 (42%) patients, and was significantly more effective than repeated defibrillation (0/9 patients, 0%, P<0.05). During atrial pacing at 500 ms, the density of atrial premature depolarizations (APDs) was significantly decreased (2.4+/-2.4 APDs. min(-1)vs 16.4+/-9.8 APDs. min(-1), P<0. 05) and the coupling interval of atrial premature depolarization was significantly increased (420+/-32 ms vs 398+/-19 ms, P<0.05) as compared to no pacing. In the remaining seven (58%) patients, atrial pacing at 500 ms failed to prevent early reinitiation of atrial fibrillation, but significantly decreased the density of atrial premature depolarization (3.4+/-2.4 APDs. min(-1)vs 14.2+/-4.8 APDs. min(-1), P<0.05) and delayed the onset of early reinitiation of atrial fibrillation (33+/-17s vs 11+/-11 s, P<0.05). Atrial pacing at 300 ms decreased the coupling interval of atrial premature depolarization as compared to no pacing and during atrial pacing at 500 ms (P<0.05), but without early reinitiation of atrial fibrillation suppression. Administration of intravenous sotalol was effective in preventing early reinitiation of atrial fibrillation in five of seven (71%) patients where pacing failed to suppress early reinitiation of atrial fibrillation. CONCLUSION: The results of this study suggest that atrial pacing can be useful when combined with transvenous defibrillation in patients with early reinitiation of atrial fibrillation.     

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.     

Combined efficacy of atrial septal lead placement and atrial pacing algorithms for prevention of paroxysmal atrial tachyarrhythmia

INTRODUCTION: The combined role of atrial septal lead location and atrial pacing algorithms in the prevention of atrial tachyarrhythmias (AT/AF), including both atrial fibrillation and flutter, is unknown. We tested the hypothesis that atrial prevention pacing algorithms could decrease AT/AF frequency in patients with atrial septal leads, bradycardia, and paroxysmal AT/AF. METHODS AND RESULTS: A total of 298 patients (age 70 +/- 10 years; 61% male) from 35 centers were implanted with a DDDRP pacing system including three AT/AF prevention pacing algorithms. Lead site was randomized at implant to right atrial septal or nonseptal. Patients were randomized 1 month postimplant to AT/AF prevention ON or OFF for 3 months and then crossed over for 3 months. Patients logged symptomatic AT/AF episodes via a manual activator. Prevention efficacy was evaluated based on intention-to-treat in 277 patients (138 septal) with complete follow-up. No changes in device-recorded AT/AF frequency or burden were observed with algorithms OFF versus ON or between patients randomized to septal versus nonseptal lead location. Analysis of other secondary outcomes revealed that AT/AF prevention pacing resulted in decreased atrial premature contractions in both the septal (1.9 [0.2-8.7] vs 3.3 [0.3-10.6]x 103/day; P < 0.01) and nonseptal groups (0.9 [0.2-3.3] vs 1.3 [0.3-5.5]x 103/day; P < 0.001). Patients with septal leads had fewer symptomatic AT/AF episodes ON versus OFF (1.4 +/- 3.0 vs 2.5 +/- 5.2/month, P = 0.01). CONCLUSION: The combination of three atrial prevention pacing algorithms did not decrease device classified atrial tachyarrhythmia frequency or burden during a 3-month cross-over period in bradycardic patients and septal or nonseptal atrial pacing leads. Prevention pacing was associated with decreased frequency of premature atrial contractions and with decreased symptomatic atrial tachyarrhythmia frequency in patients with atrial septal leads.     

The use of atrial overdrive and ventricular rate stabilization pacing algorithms for the prevention and treatment of paroxysmal atrial fibrillation: the Pacemaker Atrial Fibrillation Suppression (PAFS) study.

AIMS: The PAFS study is a randomized, multicentre investigation of the effects of third generation anti-atrial fibrillation pacemaker algorithms in patients with paroxysmal atrial fibrillation (PAF). METHODS AND RESULTS: 182 patients (72 +/- 9 years, 55% male) with at least three symptomatic episodes of PAF within prior 3 months resistant to two anti-arrhythmics were enrolled. A pacemaker-derived atrial fibrillation (AF) burden of 1-50% was required in the initial induction phase. Seventy-nine patients fulfilled these criteria and were randomized to four, month-long phases in a crossover design. Algorithm phases were 'rate soothing' on, 'ventricular rate stabilization' on, and 'All on', which included these two algorithms plus post-AF response. The algorithm phases were compared to 'All off' dual chamber universal mode (DDD 60) for the analysis. Forty-two percent of patients enrolled in the monitoring phase had no AF. The percentage of AF induced by premature atrial contractions (PACs) was significantly reduced by rate soothing from 25 to 17% (P < 0.05). There was no significant change in AF burden, AF episode number, quality of life, or symptoms with any algorithm (P = ns). CONCLUSION: The rate-soothing algorithm by atrial overdrive pacing reduced PAC-initiated PAF. However, there was no overall change in AF burden, PAF episodes, patient symptoms, or quality of life. Forty-two percent of PAF patients did not show any AF after enrollment, suggesting that bradycardia pacing alone eliminates AF.     

Ablate and pace for drug refractory paroxysmal atrial fibrillation. Is ablation necessary?

BACKGROUND: Atrio-ventricular junctional ablation with pacemaker insertion has been shown to improve quality of life in patients with drug refractory paroxysmal atrial fibrillation. It is unknown whether this improvement is secondary to the ablation procedure or to the pacemaker mode utilised. To investigate this we reviewed our experience of implanting a dual chamber rate responsive pacemaker with mode switching (DDDR/MS) alone on quality of life in this patient group. METHODS AND RESULTS: Over a 1-year period, 19 patients (mean age 62+/-9 years, 13 female) with drug refractory paroxysmal atrial fibrillation (mean duration of symptoms 8.7+/-7 years, failed 3.1+/-0.9 anti-arrhythmic drugs, amiodarone in 15) were recruited. Quality of life was assessed at baseline and after 1 month using a cardiac specific questionnaire, the modified Karolinska questionnaire. The mean score for all patients significantly improved by 39% at follow up (baseline 59+/-24, 1 month 36+/-24, P=0.001). Individually 15 patients (79%) had an improvement in their score, whilst for 13 patients (68%) their symptoms were sufficiently improved after pacing that ablation was not required. The benefit was maintained to a mean follow up of 12+/-5 months (score 31+/-20, P<0.001). Six patients remained symptomatic after pacing and requested further treatment. Benefit was unrelated to symptoms at baseline or the number and total duration of paroxysmal atrial fibrillation episodes recorded on pacemaker Holter. CONCLUSIONS: Patients with drug refractory paroxysmal atrial fibrillation, DDDR/MS pacing alone can improve quality of life without concurrent atrio-ventricular junctional ablation in a significant proportion of patients.     

Effect of gender on atrial electrophysiologic changes induced by rapid atrial pacing and elevation of atrial pressure

INTRODUCTION: The incidence of atrial fibrillation is greater in men than in women, but the reasons for this gender difference are unclear. The purpose of this study was to evaluate the effects of gender on the atrial electrophysiologic effects of rapid atrial pacing and an increase in atrial pressure. METHODS AND RESULTS: Right atrial pressure and effective refractory period (ERP) were measured during sinus rhythm and during atrial and simultaneous AV pacing at a cycle length of 300 msec in 10 premenopausal women, 11 postmenopausal women, and 24 men. The postmenopausal women were significantly older than the premenopausal women (61 +/- 8 years vs 34 +/- 10 years; P < 0.01). During sinus rhythm, mean atrial ERP in premenopausal women was shorter (211 +/- 19 msec) than in postmenopausal women and age-matched men (242 +/- 18 msec and 246 +/- 34 msec, respectively; P < 0.05). Atrial ERPs in all patients shortened significantly during atrial and simultaneous AV pacing. However, the degree of shortening during atrial pacing (43 +/- 8 msec vs 70 +/- 20 msec and 74 +/- 21 msec; P < 0.05) and during simultaneous AV pacing (48 +/- 16 msec vs 91 +/- 27 msec and 84 +/- 26 msec; P < 0.05) was significantly less in premenopausal women than in postmenopausal women or age-matched men. CONCLUSION: The results of this study demonstrate a significant gender difference in atrial electrophysiologic changes in response to rapid atrial pacing and an increase in atrial pressure. The effect of menopause on the observed changes suggests that the gender differences may be mediated by the effects of estrogen on atrial electrophysiologic properties.     

Limited benefit of septal pre-excitation in pace prevention of atrial fibrillation

BACKGROUND: Pre-excitation of the intra-atrial septum (IAS) by pacing at the ostium of the coronary sinus (CSO) can prevent atrial fibrillation (AF) in case of single atrial premature beats (APBs). We investigated whether pre-excitation of IAS, either by pacing at CSO or at the right ventricle in the presence of retrograde conduction (RV), can prevent atrial tachyarrhythmia triggered by single and multiple APBs. AF vulnerability was compared to pacing at the right atrium (RA) and sinus rhythm (SR). METHODS: Seventeen patients, age 52 +/- 21 years, who exhibited retrograde VA conduction and reproducible induction of atrial tachyarrhythmia during an electrophysiological procedure, were studied. Both during SR and pacing (S1-S1:600 ms) at RA, CSO, and right ventricle (RV), single (A1-S2:200 ms) and multiple premature stimuli (A1-S2-S3-S4:200-180-180 ms) were delivered at RA (4 x diastolic threshold). RESULTS: During pacing at RA, single and multiple APBs invariably induced runs of atrial tachyarrhythmia (mean duration 34 +/- 67 sec and 37 +/- 69 sec, range 1 sec to 20 min). During preventive pacing at CSO and RV, single APBs (A1-S2:200 ms) did not induce atrial arrhythmia (0 +/- 0 sec, 0 +/- 0 sec, P < 0.05 vs pacing at RA). In contrast, when multiple APBs were applied, pacing at CSO or RV failed to prevent initiation of AF (mean duration 36 +/- 63 sec, 38 +/- 65 sec, NS). Also during SR, single APBs did not induce AF (0 +/- 0 sec, P < 0.05 vs pacing at RA) whereas multiple APBs invariably induced AF (39 +/- 74 sec, NS). CONCLUSIONS: Compared to pacing at RA, pre-excitation of IAS either by pacing at CSO or at RV with retrograde conduction can prevent initiation of paroxysms of atrial tachyarrhythmia triggered by single but not by multiple right APBs. These findings imply that the potential benefit of choosing an optimal pacing site in patients requiring atrial-based pacing is limited. Moreover, in the absence of bradycardia, no specific pacing site offers incremental benefit over the natural "protective" effect of sinus rhythm.     

Electrocardiographic analysis of ectopic atrial activity obscured by ventricular repolarization: P wave isolation using an automatic 62-lead QRST subtraction algorithm

INTRODUCTION: Atrial activity on the surface ECG during premature beats and supraventricular arrhythmias frequently is obscured by the superimposed QRST complex of the previous cardiac cycle. This study examines the performance of a newly developed automatic QRST subtraction algorithm to isolate ectopic P waves from the preceding T-U wave. METHODS AND RESULTS: The 62-lead ECG recordings were obtained during (1) sinus rhythm and programmed right atrial stimulation in 12 patients (group A); and (2) sinus rhythm and atrial premature beats, atrial tachycardia, or paroxysmal atrial fibrillation in 5 patients (group B). Pacing in group A patients was conducted at a slow drive cycle length to generate an ectopic P wave not obscured by the previous QRST complex and by delivering single premature extrastimuli at progressively shorter coupling intervals to produce an ectopic P wave obscured by the upsloping (early T-U wave), peak (middle T-U wave), and downsloping component of the T-U wave (late T-U wave). All ectopic P waves in group B patients were concealed by the preceding T-U wave. Automatic QRST subtraction was attained using an adaptive template constructed from averaged QRST complexes (mean 83 +/- 25 complexes) obtained during sinus rhythm (groups A and B) or atrial overdrive pacing (group A). P wave integral maps subsequently were computed, visually compared, and mathematically correlated. A high correspondence in spatial map pattern was observed between integral maps of "nonobscured" and previously "obscured" paced P waves obtained in group A patients (mean r = 0.88 +/- 0.07) as well as between integral maps of two to three previously obscured P waves with the same atrial arrhythmia morphology obtained in group B patients (mean r = 0.94 +/- 0.05). Improved morphologic P wave replication in group A patients was acquired when concealment occurred in the early (mean r = 0.90 +/- 0.08) or late part of the T-U wave (mean r = 0.90 +/- 0.06) as opposed to the middle T-U wave (mean r = 0.85 +/- 0.07) (P = NS and P < 0.05 for early vs middle and late vs middle T-U wave, respectively). CONCLUSION: This novel automatic 62-lead QRST subtraction algorithm enables discrete isolation of T-U wave obscured ectopic atrial activity on the surface ECG while retaining the intricate spatial detail in P wave morphology. Future clinical application of the algorithm may enable improved ECG localization of focal triggers of paroxysmal atrial fibrillation, atrial tachycardia, and the atrial insertion of accessory pathways.     

A new pacemaker algorithm for the treatment of atrial fibrillation: results of the Atrial Dynamic Overdrive Pacing Trial (ADOPT)

OBJECTIVES: The Atrial Dynamic Overdrive Pacing Trial (ADOPT) was a single blind, randomized, controlled study to evaluate the efficacy and safety of the atrial fibrillation (AF) Suppression Algorithm (St. Jude Medical Cardiac Rhythm Management Division, Sylmar, California) in patients with sick sinus syndrome and AF. BACKGROUND: This algorithm increases the pacing rate when the native rhythm emerges and periodically reduces the rate to search for intrinsic atrial activity. METHODS: Symptomatic AF burden (percentage of days during which symptomatic AF occurred) was the primary end point. Patients underwent pacemaker implantation, were randomized to DDDR with the algorithm on (treatment) or off (control), and were followed for six months. RESULTS: Baseline characteristics and antiarrhythmic drugs used were similar in both groups. The percentage of atrial pacing was higher in the treatment group (92.9% vs. 67.9%, p < 0.0001). The AF Suppression Algorithm reduced symptomatic AF burden by 25% (2.50% control vs. 1.87% treatment). Atrial fibrillation burden decreased progressively in both groups but was lower in the treatment group at each follow-up visit (one, three, and six months) (p = 0.005). Quality of life scores improved in both groups. The mean number of AF episodes (4.3 +/- 11.5 control vs. 3.2 +/- 8.6 treatment); total hospitalizations (17 control vs. 15 treatment); and incidence of complications, adverse events, and deaths were not statistically different between groups. CONCLUSIONS: The ADOPT demonstrated that overdrive atrial pacing with the AF Suppression Algorithm decreased symptomatic AF burden significantly in patients with sick sinus syndrome and AF. The decrease in relative AF burden was substantial (25%), although the absolute difference was small (2.50% control vs. 1.87% treatment).     

Does atrial overdrive pacing prevent paroxysmal atrial fibrillation in paced patients?

The role of atrial overdrive pacing for the suppression of paroxysmal atrial fibrillation remains unclear. To investigate this we have performed a randomised study evaluating the role of an increased atrial base rate in suppressing this arrhythmia in patients implanted with a permanent pacemaker (Chorum ELA) for sick sinus syndrome with previous documented paroxysmal atrial fibrillation. Twenty-seven patients (mean age, 69; 15 female) were randomised to two 3-month single-blinded crossover periods of DDDR pacing. The pacemaker was set with a base rate of 60 bpm (normal) during one period and at 10 bpm (overdrive) above the average heart rate during the other, mean (S.D.) 75+/-7 beats/min (range, 70-96). The fallback algorithm of the pacemaker was activated to record the number and duration of paroxysmal atrial fibrillation episodes. During the overdrive period there was a significant increase in the total duration of atrial pacing (normal 60+/-26% vs. overdrive 72+/-28%, P<0.001). However there was no significant difference in the number of paroxysmal atrial fibrillation episodes (normal 43+/-109 vs. overdrive 43+/-106, P=ns), or their total duration (normal 42+/-108 h vs. overdrive 99+/-254 h, P=ns). In conclusion, atrial overdrive pacing, achieved by increasing the atrial base rate, has no incremental benefit in the suppression of paroxysmal atrial fibrillation when compared to rate responsive pacing with a base rate of 60 bpm.     

抗心房颤动起搏器临床应用的初步结果

目的初步评价德国百多力公司生产的PhilosDDDR型起搏器抗心房颤动（房颤）功能的效果。方法38例病态窦房结综合征合并阵发性房颤的患者置入了PhilosDDDR型起搏器,术后打开模式转换功能（Auto-Mode-Switch,AMS）,关闭抗房颤功能。记录1个月AMS次数、心房及心室起搏百分比、心率、房性早搏（房早）次数及临床症状等。之后打开抗房颤功能,并将此功能设置在“中档”,1个月后使用程控仪调出以上数据,并比较开启此功能前后1个月二者的差异。结果与起搏器置入术前比较,不论抗房颤功能开启与否,绝大多数患者头晕、气短、乏力、心悸等症状明显减轻或消失,运动耐受量改善。在打开抗房颤功能后,多数患者诉临床症状与开启此功能前差异无统计学意义,5例（13．2％）患者诉心悸及气短;在使用程控仪将抗房颤功能由“中档”降到“低档”后症状明显减轻。打开抗房颤功能后,房早发生率显著性降低（P〈0．05）,心房起搏的比率及心率明显增加（P〈0．05）。然而,AMS次数无显著性减少（P〉0．05）,说明房性快速性心律失常无明显减少。结论将PhilosDDDR型起搏器的抗房颤功能设置在“中档或低档”,虽然房早显著性减少,心房起搏比率增加,但房颤或房性心动过速并无显著性降低。     

Prevention of chronic atrial fibrillation by pacing in the region of Bachmann's bundle: results of a multicenter randomized trial

INTRODUCTION: Atrial pacing locations that decrease atrial activation and recovery time may be preferable in patients with a history of atrial arrhythmias. This multicenter prospective randomized study compared the efficacy of Bachmann's bundle (BB) region pacing to right atrial appendage (RAA) pacing in patients with recurrent paroxysmal atrial fibrillation (AF). METHODS AND RESULTS: Patients with standard pacing indications (n = 120, 70+/-11 years) were randomized to atrial pacing in either the RAA (n = 57) or BB region (n = 63). Implantation time was similar between groups (88+/-36 min [n = 38] for BB vs 83+/-34 min [n = 34] for RAA). No differences in pacing threshold, impedance, or sensing between BB and RAA groups were observed at implantation or after the 6-week, 6-month, and 1-year follow-up periods. Average length of follow-up was 12.6+/-7.4 months for the BB group and 11.8+/-8.0 months for the RAA pacing group. The percentage of atrial pacing was similar between groups (61%+/-34% RAA vs 65%+/-31% BB at 2 weeks after implant). BB atrial pacing significantly (P < 0.05) shortened p wave duration compared with sinus rhythm (123+/-21 msec vs 132+/-21 msec, n = 50) 2 weeks after implant. In contrast, p wave duration was longer during atrial pacing from the RAA position compared with sinus rhythm (148+/-23 msec vs 123+/-23 msec, n = 37). Additionally, p wave duration was shorter during BB pacing than during RAA pacing. Patients with BB pacing had a higher (P < 0.05) rate of survival free from chronic AF (75%) compared with patients with RAA pacing (47%) at 1 year. CONCLUSION: BB region pacing is safe and effective for attenuating the progression of AF.     

Improved cardiac function and quality of life following upgrade to dual chamber pacing after long-term ventricular stimulation.

AIMS: Many patients with sinus node disease or atrioventricular block have previously received pacemakers with only ventricular stimulation (VVI or VVIR). This study aimed to investigate whether quality of life and cardiac function were affected by an upgrade to dual chamber pacing (DDDR or DDIR) following long-term ventricular stimulation. METHODS: After implantation of an atrial lead and a DDDR pulse generator, a randomized, double-blind crossover study was performed in 19 patients, previously treated with ventricular pacing for a median time of 6 X 8 years. Patients were randomized to 8 weeks with either VVIR or DDDR/DDIR pacing; after this time, the other mode was programmed for 8 weeks. At the end of each period, the patients' quality of life was evaluated and echocardiography was performed together with Holter monitoring and blood samples for brain natriuretic peptide. RESULTS: Sixteen of the patients preferred DDDR and two VVIR pacing (P=0 X 001); one was undecided. Seven patients demanded an early crossover while paced in the VVIR mode, vs none in the DDDR mode (P=0 X 008). Quality of life was higher in the DDDR mode in 11 of 17 modalities, reaching statistical significance for dyspnoea (P<0 X 05) and general activity (P<0 X 05). Echocardiography showed significantly larger left ventricular end-diastolic dimensions in the DDDR mode (P=0 X 01), whereas end-systolic dimensions did not differ. Left ventricular systolic function was significantly superior in the DDDR mode (mean aortic velocity-time integral: P<0 X 001) and left atrial diameter was significantly smaller in the DDDR mode (P=0 X 01). The plasma level of brain natriuretic peptide was significantly lower in DDDR mode (P=0 X 002). CONCLUSION: An upgrade to dual chamber rate adaptive pacing results in significantly improved quality of life and cardiac function as compared to continued VVIR stimulation and should thus be considered in patients with ventricular pacemakers who have not developed permanent atrial fibrillation or flutter.     

特殊心房起搏程序预防和治疗阵发性心房颤动的临床效果

目的评价特殊心房起搏程序预防和治疗阵发性心房颤动(PAF)的临床效果。方法12例病窦综合征合并PAF患者植入Vitatron Selection 900E(AF2.0、DDDR)型双腔起搏器,比较患者术后不同阶段PAF的发作总数、持续时间、AF负荷和心房起搏比率。结果除1例外,其余11例术后第2个月和第6个月(起搏预防阶段)比术后第1个月(监测阶段)的PAF事件数[80(25;215),57(12;102)vs 203(86;425)],房颤总持续时间[1.9 d(0.6d;5.3 d),1.5 d(0.3 d;6.1 d)vs 2.9 d(0.8 d;9.8 d)],AF负荷[6.3%(2.0%;17.7%),5.0%(1.0%;20.6%)vs 9.6%(2.7%;32.8%)]均减低(P均<0.05),心房起搏比率增加[60%(40%;80%),54%(42%;84%)vs46%(26%;54%),P<0.05]。结论预防性心房起搏程序可以减少PAF事件的发生,降低AF负荷,改善患者的症状,具有短期的疗效。