经食管左房后壁起搏的P波分析

100例无心脏病者经食管左房后壁起搏的 P 波分析表明:Pv_1正双峰(多数为园顶尖峰)型占52%.直立型占46%;P_1.V_(?)平坦型分别占48%与61%;P 电轴右倾占51.5%。这与“左房心律”的诊断标准不完全相符.提示单以 P 波形态确定左房心律仍有探讨的必要。     

Comparison of the acute effects of pacing the atrial septum, right atrial appendage, coronary sinus os, and the latter two sites simultaneously on the duration of atrial activation

OBJECTIVE—To compare the acute effects of right atrial appendage, atrial septal, coronary sinus os, and dual site pacing on the duration of atrial activation.
METHODS—20 patients with a variety of cardiac conditions underwent an intracardiac electrophysiological study. Electrograms were recorded from the right atrial appendage and at multiple sites within the coronary sinus. The duration of atrial activation was measured during pacing at the right atrial appendage, atrial septum, and coronary sinus os, and also during dual site stimulation.
RESULTS—The duration of atrial activation with atrial appendage pacing was notably longer (p < 0.001) than with dual site, septal, or coronary sinus os pacing, but there were no significant differences in atrial activation times between these latter three pacing modes. When stimulating the atria at a cycle length of 500 ms, the mean (SD) duration of atrial activation was 145 (37) ms for right atrial appendage pacing, 93 (26) ms for dual site pacing, 96 (28) ms for septal pacing, and 98 (28) ms for coronary sinus os pacing.
CONCLUSIONS—Assuming that the duration of atrial activation is an important determinant of predisposition to paroxysmal atrial fibrillation, atrial septal pacing or coronary sinus os pacing would appear to offer the same advantage as dual site pacing without the additional complexities associated with the latter pacing mode.


Keywords: atrial septal pacing; dual site pacing; atrial activation; atrial fibrillation     

快速心房刺激对P波时限及离散度的影响

目的分析快速心房刺激对P波时限及离散度的影响.方法在74例射频消融术及82例经食管心房调搏检查中,用180ppm的S1S1刺激心房3min,在刺激前后立刻记录12导联同步心电图,通过心电图测出刺激前后的最大P波时限、最小P波时限及P波离散度,然后进行比较.结果射频消融组最大P波时限在心房刺激后比刺激前有显著性延长（p=0.002）,最小P波时限及P波离散度无显著性差异,食管心房调搏组最大P波时限及P波离散度在心房刺激后比刺激前有显著性增加（p=0.001）,最小P波时限无显著性差异.结论快速心房刺激能引起心房传导时间延长,非均质电活动的离散程度增加.最大P波时限及P波离散度是可以用来评价心房电重构的简便而无创的指标.     

Atrial fibrillatory wave characteristics on surface electrogram: ECG to ECG repeatability over twenty-four hours in clinically stable patients

INTRODUCTION: Fibrillatory waves on the surface ECG have been scrutinized to allow inferences about underlying mechanisms and pathophysiology, based on the premise that fibrillatory waves do not vary "randomly" but provide a consistent reflection of the underlying state of the atria in an individual patient. This premise is untested. METHODS AND RESULTS: Ten standard ECGs were recorded over a 24-hour period in each of 20 clinically stable inpatients with atrial fibrillation. After QRS-T cancellation, the remainder fibrillatory waves were analyzed. Interpatient versus intrapatient differences in fibrillatory wave characteristics were evaluated by analysis of variance (ANOVA). The fibrillatory wave peak-to-peak amplitude of all the patients ranged from 0.06 to 0.35 mV, whereas 1 SD of the amplitude for each patient ranged from 0.004 to 0.053 mV. Short-term peak frequencies of all the patients ranged from 4.6 to 8.0 Hz, whereas 1 SD for each patient varied from 0.2 to 0.5 Hz. For these and all other parameters tested, interpatient differences were significantly greater compared to intrapatient differences (P < 0.0001). CONCLUSION: Fibrillatory wave characteristics are repeatable from ECG to ECG over 24 hours for clinically stable patients, whereas substantial differences are present between patients. Further study of the relationship of such characteristics to pathophysiology and management decisions is valid and warranted.     

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.     

经心内和食管快速心房刺激对P波时限及离散度的影响

目的分析快速心房刺激对P波时限及离散度的影响。方法在74例射频消融术经电极导管起搏高位右房及82例经食管心房调搏检查者中,用180次/分的S1S1刺激心房3min,在刺激前后立刻记录12导同步心电图,通过心电图测出刺激前后的最大P波时限(Pmax)、最小P波时限(Pmin)及P波离散度(Pd),然后进行比较。结果:射频消融组Pmax在心房刺激后比刺激前有显著性延长(P<0.01),Pmin及Pd无显著性差异。食管心房调搏组Pmax及Pd在心房刺激后显著性增加(P<0.01),Pmin无显著性差异。结论:快速心房刺激能引起心房传导时间延长,非均质电活动的离散程度增加。     

Effect of Bachmann's bundle pacing on atrial fibrillation: electrophysiologic assessment

BACKGROUND: It has recently been reported that simultaneous multisite atrial pacing, Bachmann's bundle (BB) pacing, and coronary sinus (CS) pacing are useful for preventing the induction of atrial fibrillation (AF). HYPOTHESIS: We investigated whether a simple pacing approach via BB could reduce the induction of AF by extrastimuli (S2) from the right atrial appendage (RAA). METHODS: Programmed electrical stimulation was performed from the RAA and the area of BB at the superior aspect of the atrial septum, and bipolar recordings were obtained from the RAA, BB, and CS in 14 patients. RESULTS: In five patients, AF was induced with critically timed RAA-S2 delivered during RAA pacing. However, AF was not induced in any patient when RAA-S2 was delivered during BB pacing. The duration of the P wave during BB pacing was significantly shorter than that during RAA pacing and sinus rhythm (BB 80 +/- 16 ms vs. RAA 106 +/- 36 ms vs. sinus rhythm 100 +/- 24 ms, p < 0.05). The intra-atrial conduction time to the distal coronary sinus (CSd) caused by early S2 at the RAA was significantly reduced by BB pacing (BB 114 +/- 22 ms vs. RAA 157 +/- 35 ms, p < 0.001). CONCLUSION: Bachmann's bundle pacing reduces atrial conduction time caused by RAA-S2 and may be useful for preventing the induction of AF.     

P wave signal-averaged ECG in normal population and in patients with converted atrial fibrillation

Background: Signal‐averaged electrocardiography of the P wave (P wave SAECG) is a noninvasive method for evaluating the risk of atrial fibrillation (AF). We aimed to study P wave SAECG parameters in a large number of apparently healthy subjects and to compare them with patients with converted AF. Methods: We examined 591 individuals; P wave SAECG were recorded in 330 normal subjects, 31 patients with converted persistent AF and 57 patients with converted paroxysmal AF immediately after conversion, at 12 and 24 hours after conversion, then after 3 and 6 months. P wave SAECG were recorded using a commercially available machine aiming to obtain a noise level <1 μV. Results: In the normal population the duration of the filtered P wave (PWD) was higher in men. P wave duration, RMS₄₀ and RMS₃₀ were significantly correlated with age. By comparing the normal population with patients with persistent AF converted to sinus rhythm we demonstrated significant differences in PWD and P wave integral. Patients with recurrent persistent AF had significantly higher PWD. The study of patients with paroxysmal AF, compared to the control group, showed significant increase of the same parameters: PWD and integral of the P wave. Patients with recurrent paroxysmal AF had higher PWD and lower RMS₄₀, RMS₃₀, RMS₂₀. Conclusions: Filtered P wave duration was higher in men; PWD was weakly but significantly correlated with age. Patients with paroxysmal or persistent AF converted to sinus rhythm had significantly higher P wave duration and P wave integral. Ann Noninvasive Electrocardiol 2011;16(4):351–356     

老年阵发性房颤患者体表心电图f-f间期变化与房颤持续时间及心房电重构的关系

目的 :研究老年阵发性房颤 （PAF）患者体表心电图 f- f间期变化与房颤持续时间及心房电重构的关系。方法 :选择无心房扩大 ,患有初发或新近发生的 PAF的老年人 ,于随访期前后分别进行 2 4 h Holter监测 ,同意者行心脏电生理检查测右房有效不应期 （ERP） ,随访半年。结果 :入选 32例 ,有 9例于随访期前后行心电生理检查 ,5例失访。采集到以下数据 :2 4 h房颤发作次数 （N）较基线没有显著变化 （2 4± 4 vs 2 4± 4 ,P>0 .0 5 ） ;2 4 h房颤发作累计时间 （TT）显著延长 （2 36± 32 m in vs 2 89± 31min,P<0 .0 1） ;最长一次发作持续时间 （L T）无显著差异 （4 2± 12min vs 4 5± 12 min,P>0 .0 5 ） ;2 4 h平均持续时间 （MT）显著延长 （8.1± 1.2 m in vs 10 .2± 1.6 min,P<0 .0 1） ;平均 f- f间期 （Mf- f）显著缩短 （0 .15± 0 .0 2 s vs0 .11± 0 .0 1s,P<0 .0 5 ）。ERP与对照相比显著缩短 （2 0 8± 11ms vs191± 8ms,P<0 .0 1）。Δ ERP与 Δf- f呈直线正相关 :r=0 .8839,P<0 .0 1,Δ TT与 Δ f- f直线正相关 :r=0 .76 0 4 ,P<0 .0 1,ΔMT与 Δ f- f直线正相关 :r=0 .76 0 ,P<0 .0 1。结论 :老年 PAF患者体表心电图 f- f间期缩短可作为预测老年人 PAF持续时间延长和反映心房发生电重构的有效指标。     

The Results of Pacing Trials for the Prevention and Termination of Atrial Tachyarrhythmias: Is There Any Evidence of Therapeutic Breakthrough?

Atrial fibrillation (AF) is now recognized as the most prevalent sustained cardiac arrhythmia and it is associated with considerable mortality and morbidity. The demand for effective therapeutic strategies for AF has always been high and is anticipated to further increase. Anticoagulation and pharmacologic antiarrhythmic therapy or radiofrequency catheter ablation remain the mainstay of treatment for AF. Among the wide range of nonpharmacologic options which are presently being investigated, only ablation in or around the pulmonary veins and the surgical maze procedure have been shown to accomplish the aim of the curative treatment of the arrhythmia.Preventative atrial pacing and antitachycardia pacing may offer an attractive alternative option for the management of AF by either eliminating the triggers and/or by modifying the substrate of the arrhythmia. The results of several recent trials have shown a significant increase in the time to first AF recurrence, a decrease in atrial conduction time, and a trend towards reduction in AF burden, suggesting that atrial pacing may prevent AF due to improved synchronization of atrial depolarization.The recognition of potential triggers of AF, such as atrial premature complexes, short-long sequence, and bradycardia, has encouraged the development of novel atrial pacing algorithms designed to prevent the initiation of the arrhythmia on an individual basis. Observations of AF often starting with regular atrial activity consistent with atrial tachycardia have supported the hypothesis that early antitachycardia pacing may prevent progression to AF.The concept of 'hybrid therapy' based on the combination of several different therapeutic strategies suggests that antitachycardia pacing therapy, integrated with an atrial defibrillator and preventative atrial pacing modes, may act synergistically to prevent AF. Dual chamber cardioverter-defibrillators with capacity to prevent and interrupt AF may offer more comprehensive and successful treatment for patients with advanced heart disease, frequent paroxysms of AF, and the risk of proarrhythmia.     

Wave similarity mapping shows the spatiotemporal distribution of fibrillatory wave complexity in the human right atrium during paroxysmal and chronic atrial fibrillation

INTRODUCTION: The complexity of waveforms during atrial fibrillation may reflect critical activation patterns for the arrhythmia perpetuation. In this study, we introduce a novel concept of map, based on the analysis of the wave morphology, which gives a direct evidence in the human right atrium on the spatiotemporal distribution of fibrillatory wave complexity in paroxysmal (PAF) and chronic (CAF) atrial fibrillation. METHODS AND RESULTS: Electrograms were recorded from a 64-electrode catheter in the right atrium of 15 patients during PAF (n = 8) and CAF (n = 7). Wave similarity maps were constructed by calculating the degree of morphological similarity of activation waves (S) at each atrial site and by following its temporal evolution. During PAF the spatiotemporal distribution of the waveforms was highly consistent across the subjects and was determined by the anatomic location. Wave similarity maps showed the existence of an extended area with low similarity index, which covered the low posteroseptal atrium (S = 0.28 +/- 0.09) and the septal region (S = 0.22 +/- 0.04), and the presence of a large tongue with high similarity index, which penetrated the lateral wall (S = 0.55 +/- 0.08) starting from the high anterolateral atrium (S = 0.54 +/- 0.06). A completely different spatiotemporal pattern was seen during CAF. No distinct regions with different similarity indexes were recognized, but a uniformly distributed low similarity index (S = 0.27 +/- 0.07) was found. The spatial pattern was highly stable in time with fluctuations of S < 0.04. CONCLUSION: Quantification of the spatiotemporal distribution of fibrillatory wave complexity is feasible in humans by wave similarity mapping. Anatomic anchoring of waveforms during PAF and pattern destruction during CAF was determined.     

Atrial pacing in the management of sick sinus syndrome: Long-term observation for conduction disturbances and supraventricular tachyarrhythmias

Atrial pacing (AAI) in sick sinus syndrome (SSS) has been questionedbecause of the risk of distal conduction disturbances (DCD)and atrial tachyarrhythmias. The authors studied the incidenceof clinically relevant DCD and arrhythmias in 52 SSS patientswith AAI. The observation time was 25–67 (mean 48) months. Invasive electrophysiologic investigation was performed preoperativelyin 29 cases and preoperative atrial pacing to Wenckebach blockor to 150 ppm in 23. The preoperative investigation showed prolongedHV-time in three cases and Wenckebach block at 110ppm in onecase, while six patients had LAH-block, five RBB-block and twofirst degree A V-block. No further DCD developed in any of thesepatients. Second-degree type IA V-block developed in two patientsafter 2 and 19 months, respectively. One had been treated withdigitalis and verapamil and was asymptomatic. The other patient,who had a low ventricular rate, experienced near-syncope. Thesetwo blocks could not be predicted from the preoperative andperoperative investigations. In five patients (10%) permanent atrial fibrillation developedduring the follow-up period. The incidence of concomitant supraventriculartachyarrhythmias in the patients with the bradycardia-tachycardiasyndrome appeared to be unaffected by the pacemaker treatment.     

Dual Site Right Atrial Pacing can Improve the Impact of Standard Dual Chamber Pacing on Atrial and Ventricular Mechanical Function in Patients with Symptomatic Atrial Fibrillation: Further Observations from the Dual Site Atrial Pacing for Prevention of Atrial Fibrillation Trial

Background: The effects of atrial pacing mode on atrial and ventricular function in patients with atrial fibrillation (AF) and bradycardia have not been evaluated. We evaluated atrial and ventricular function during randomization to support pacing (SP), high right atrial pacing (HRA), and dual site right atrial pacing (DAP).Methods: Seventy-nine patients (66 ± 12 yr, 46 male) with standard pacing indications and symptomatic AF were randomized to each of three pacing modes (DAP, HRA, SP) for 6 months in a crossover design. Echocardiographic studies were performed at enrollment and the end of each mode. Paired comparisons of atrial and ventricular function parameters were performed between each pacing mode and baseline.Results: HRA pacing in DDDR mode resulted in increased left ventricular (LV) end systolic volume (78 ± 42 vs. 60 ± 31 ml, p = 0.001) and reduced LV ejection fraction (44 ± 14 vs. 50 ± 11%, p = 0.007) compared to baseline. These parameters did not change during DAP. DAP resulted in increased peak A wave velocity (75 ± 19 vs. 63 ± 23 cm/s, p = 0.003) and atrial filling fraction compared to baseline (0.47 ± 0.15 vs. 0.38 ± 0.13, p = 0.005). Atrial and ventricular function were similar between control and SP.Conclusion: DAP, but not HRA or SP, improved left atrial (LA) function in patients with AF and bradycardia. HRA pacing in DDDR mode resulted in LA dilatation and deterioration of LV function which was not observed with DAP.This study was supported by a grant from the Electrophysiology Research Foundation, Warren, NJ and Medtronic Inc., Minneapolis, MN. Drs. Delfaut and Prakash were supported by grants from the Electrophysiology Research Foundation during the term of this study. Drs. Saksena and Nanda were consultants to Medtronic during this study. Dr. Hettrick and Mr. Ziegler are employees of Medtronic.     

Incremental programming of atrial anti-tachycardia pacing therapies in bradycardia-indicated patients: effects on therapy efficacy and atrial tachyarrhythmia burden.

AIMS: Efficacy of pace-termination of atrial arrhythmias (ATP) may depend on atrial cycle length and regularity. Whether device programming of ATP therapies can improve ATP efficacy and alter atrial tachyarrhythmia burden is unknown. METHODS AND RESULTS: ATP efficacy was evaluated in 61 patients (39 males; 66 +/- 10 years) with a standard indication for pacing, 95% with a history of AT/AF. Each patient was implanted with a novel DDDRP pacemaker capable of delivering ATP therapy. ATP efficacy and AT/AF frequency and burden were compared within each patient during a period of nominal ATP programming (NP) followed by a period of aggressive incremental programming (IP). Adjusted ATP-termination efficacy was higher during IP than during NP (54.8% vs 37.9%, P < 0.05). No differences in AT/AF frequency (3.3 +/- 5.9 vs 3.2 +/- 6.9 day(-1)) or burden (18 +/- 28% vs 18 +/- 29%) were observed comparing NP with IP. The majority of episodes during both the NP (81%) and IP (77%) periods terminated within 10 min. Episodes lasting 24 h or more accounted for only 0.4% of the episodes in both groups. but accounted for 38% of the average burden during NP and 51% during IP. CONCLUSIONS: Device programming of ATP therapies can influence the number of treated episodes and the efficacy of ATP therapies although arrhythmic frequency and burden may not change. Total atrial arrhythmia burden is disproportionately influenced by long (>24 h) episodes.     

胺碘酮与缬沙坦对阵发性心房颤动患者P波离散度的影响的研究

目的 评价胺碘酮与缬沙坦对阵发性心房颤动（PAF）患者P波离散度和最大P波时限（Pmax）的影响。方法 96例阵发性心房颤动的患者被随机分成胺碘酮加缬沙坦组32例，胺碘酮组31例，缬沙坦组33例。对照组34例为正常健康人，观察药物治疗3个月前后心电图Pmax和Pdis的变化。结果 阵发性心房颤动患者Pmax、Pdis治疗前均与对照组比有显著性差异（P〈0．01），药物治疗3个月后，胺碘酮治疗能改善Pmax和Pdis，但胺碘酮加缬沙坦组改善Pmax和Pdis更显著（P〈0．05），缬沙坦组则与治疗前相比无显著性差异（P〉0．05）。结论 PAF患者的Pmax和Pdis与对照组相比有显著性差异，胺碘酮加缬沙坦治疗能显著改善PAF患者的Pmax和Pdis。     

Deterioration of organization in the first minutes of atrial fibrillation: a beat-to-beat analysis of cycle length and wave similarity

Introduction: It has been recently suggested that many episodes of atrial fibrillation (AF) may be partially organized at the onset and thus more suitable for antitachycardia pacing therapy. Nevertheless, the time course of organization in the first minutes of AF has not been quantified yet.
Methods and Results: Twenty episodes of paroxysmal AF were studied. Electrograms were recorded from the right atrium (RA), distal (CSd), and proximal coronary sinus (CSp). The time course of AF cycle length (AFCL) and the regularity of wave morphology (similarity index S) were beat-to-beat measured at each recording site during the first 7 minutes of AF. AFCL and S showed a decreasing trend after the onset of AF. AFCL decreased from 208 ± 31 to 171 ± 21 msec (P < 0.001), from 206 ± 40 to 169 ± 23 msec (P < 0.001) and from 190 ± 42 to 152 ± 18 msec (P < 0.05), respectively, in RA, CSd, and CSp. Similarly, the similarity index decreased in CSd from 0.37 ± 0.27 to 0.12 ± 0.09 (P < 0.01) and in RA from 0.40 ± 0.18 to 0.17 ± 0.16 (P < 0.001). The 80% of the decrease occurred during the first 3 minutes of the arrhythmia, while after this time both cycle length and similarity index did not change significantly anymore. Conversely, the electrical activity in CSp was highly disorganized (S = 0.05 ± 0.03) even in the first minute of AF, and no decreasing temporal trend was observed.
Conclusion: Higher levels of organization and longer fibrillation intervals exist at the onset of AF. The degree of organization of the electrical activity decays within less than 3 minutes. Since antitachycardia pacing success rate increases with high levels of organization, these results suggest an early delivery of pacing treatment.     

Dependence of electrogram duration in right posteroseptal atrium and atrium-pulmonary vein junction on pacing site: mechanism and implications regarding atrioventricular nodal reentrant tachycardia and paroxysmal atrial fibrillation

INTRODUCTION: The fractionated atrial electrogram, a signal helpful in identifying the target site for radiofrequency catheter ablation of the slow AV nodal pathway, is considered to arise from nonuniform anisotropic electrical activity. However, the effects of pacing sites and radiofrequency ablation on these electrograms are not clear. Similarly, the nature of the fractionated atrial electrogram in the atrium-pulmonary vein junction has yet to be determined. METHODS AND RESULTS: Two experiments were performed in this study. Experiment 1 evaluated the fractionated atrial electrogram at target sites before and after slow AV nodal pathway ablation during sinus rhythm or during pacing from different sites. Group 1A consisted of 16 patients with dual AV nodal pathway physiology and AV nodal reentrant tachycardia who underwent successful ablation without residual slow AV nodal pathway. Group 1B consisted of 7 patients who underwent successful elimination of AV nodal reentry but with residual dual AV nodal pathway physiology. Group 1C consisted of 6 patients who still had AV nodal reentrant tachycardia after two applications of radiofrequency energy. In group 1D, there were 16 patients with dual AV nodal pathway physiology, but without inducible AV nodal reentrant tachycardia. In group 1E, there were 15 patients without dual AV nodal pathway physiology. Experiment 2 investigated the fractionated atrial electrogram in the ostium of the left and right superior pulmonary veins in 18 patients with paroxysmal atrial fibrillation (2A) and in 8 patients without paroxysmal atrial fibrillation (2B). Before radiofrequency ablation, electrogram duration in the right posteroseptal atrium during pacing from the middle coronary sinus or the right posterolateral atrium was shorter than that during pacing from the high right atrium (HRA) in all group 1 patients. After the successful elimination of the slow AV nodal pathway conduction in group 1A, atrial electrogram duration during HRA pacing was shorter than that before ablation. In experiment 2 patients, electrogram duration during pacing from the proximal or distal coronary sinus was shorter than that during pacing from HRA or sinus rhythm. CONCLUSION: These findings suggest that the fractionated atrial electrograms in the right posteroseptal atrium and ostium of left or right superior pulmonary veins are potentially consistent with nonuniform anisotropic propagation. Alternations of electrogram characteristics after successful radiofrequency ablation of the slow AV nodal pathway may arise from the changes of nonuniform anisotropic activity in the right posteroseptal atrium.