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Study objectives: Atrioesophageal fistulas have been reported to be a lethal complication following catheter ablation of atrial fibrillation (AF). The purpose of this study was to investigate the relationship between [...]

Lone atrial fibrillation (AF) is defined as AF occurring in the absence of any other cardiovascular disease. The prognosis of patients with lone AF varies in previous studies, and the clinical and electroanatomical characteristics of lone AF are unclear. The purpose of this study was to investigate the clinical characteristics of lone AF. This study included 203 patients (52±13 years old, 144 males) that underwent circumferential pulmonary vein isolation (CPVI) for paroxysmal AF. The mean voltage and total activation time of the individual atria were obtained by using a NavX mapping system and were compared for patients with lone and non-lone AF. Several parameters, including the age, gender, AF duration, and left atrial (LA) diameter were analyzed. Compared with non-lone AF patients, lone AF patients were significantly younger (49±13 years old vs. 58±11 years old, p<0.001) and had lower body-mass index (BMI, 24.60±2.96 vs. 26.07±3.29, p=0.02), lesser cholesterol level (169.06±31.41 vs. 183.63±31.12, p=0.014), smaller LA diameter (35.89±4.90 vs. 40.86±4.62, p<0.001), and higher LA bipolar voltage (2.10±0.50 vs. 1.83±0.73 mV, p<0.05). Furthermore, a dramatic voltage reduction was observed for 60-year-old patients. Patients with lone AF have unique clinical and electroanatomical characteristics.

Heat shock protein (HSP) 27 is related to the pathogenesis of AF. However, the clinical relationship between HSP27 and AF is unclear. The present study was conducted to determine the clinical relationship between HSP27 and atrial fibrillation (AF).

Sinus node (SN) activity is difficult to assess during atrial fibrillation (AF). The aim of the present study was to investigate SN activity by frequency analysis during AF.

Background: Atrioventricular nodal reentry tachycardia (AVNRT) is based on the concept of dual AV node pathways that are functionally and anatomically distinct. The bigger coronary sinus ostium (CSO) in patients with AVNRT compared to other supraventricular tachycardias (SVTs) may produce separation of atrial inputs into the AV node or create anisotropic conduction, thus giving rise to a different AV nodal physiology. Previous studies measuring the size of the CSO using CS angiography between patients with AVNRT and other SVTs showed conflicting results. Besides, no previous studies have compared the CS morphology of the different forms of AVNRT.

Background: Atrioventricular nodal reentrant tachycardia (AVNRT) can be usually induced by atrial pacing or extrastimulation. However, it is less commonly induced only by ventricular pacing or extrastimulation.

Background:Double atrial potentials recorded in the coronary sinus are not an unusual phenomenon in patients with supraventricular tachyarrhythmias. They have been demonstrated to potentiate the occurrence of atrial tachyarrhythmias. Methods:Two hundred and forty-eight patients were included for investigating the presence of double atrial potentials on the coronary sinus recordings during electrophysiologic study. Group 1 consisted of 136 patients with WPW syndrome and group 2 consisted of 112 patients with atrioventricular nodal reentrant tachycardia (AVNRT). Group 1 patients had a higher incidence of induced atrial fibrillation (AF) (27% vs. 15%, P= 0.045) than group 2 patients. In addition, the incidence of double atrial potentials was significantly higher in group 1 than in group 2 patients (14% vs. 2%, P= 0.001). In group 1, 19 patients with double atrial potentials had a significantly higher incidence of left lateral bypass tracts (79% vs. 39%, P= 0.001) and induced AF (47% vs. 22%, P= 0.01) than 117 patients without double atrial potentials. Conclusions:WPW syndrome, especially with a left lateral bypass tract, had a higher incidence of double atrial potentials and induced AF than AVNRT. WPW patients with double atrial potentials had a higher incidence of induced AF than those without double atrial potentials. These findings may contribute to understanding the mechanism of induced AF in WPW syndrome.

Introduction:The outcome of patients with early recurrence of atrial fibrillation (AF) (within one month) after ablation procedure is controversial. Furthermore, the predictors of early and late (up to mean follow-up 30 months) recurrence of AF are not investigated in depth. Aims of the Study:The aim of the present study was to investigate the predictors of early and late recurrence of AF after catheter ablation of arrhythmogenic foci initiating AF in patients with paroxysmal AF. Methods and Results:The study included 207 patients (155 men; mean age 62 ± 13 years) who received catheter ablation of paroxysmal AF. Eighty-one (39%) patients had early recurrence of AF. Five clinical variables were related to the early recurrence of AF: (1) old age (≥65 years) (P= 0.004); (2) presence of associated cardiovascular disease (P= 0.01); (3) presence of multiple AF foci (P= 0.004); (4) presence of AF foci from left atrial free wall (P= 0.039); (5) left atrial enlargement (P= 0.038). Multivariate analysis demonstrated that presence of multiple AF foci could predict early recurrence of AF (P= 0.013; ratio = 2.24; 95% CI 1.18 to 4.25). During the follow-up period (30 ± 11 months), 70 (34%) patients had late recurrence of AF, and two clinical variables were related to the late recurrence of AF: (1) presence of early recurrence of AF (P= 0.025); (2) presence of multiple AF foci (P= 0.034). Multivariate analysis found that presence of early recurrence of AF could predict late recurrence of AF (P= 0.046; hazard ratio = 1.62; 95% CI 1.01 to 2.59). Late recurrence of AF happened in 35 (43%) of the 81 patients with early recurrence of AF, and in 35 (28%) of the 126 patients without early recurrence of AF. Conclusions:Early AF recurrence could predict late AF recurrence.

Introduction:Recently, several studies showed that focal atrial fibrillation (AF) can be initiated by ectopic beats from the vein of Marshall (VOM). However, the incidence and best fluoroscopic views of VOM have never been reported. Methods and Results:106 patients (Non-AF = 52, AF = 54) underwent balloon-occluded coronary sinus angiography using seven fluoroscopic views (PA, Lateral, RAO 30°, RA 30° + Caudal 20°, LAO 30°, LAO 60°, LAO 60° + Cranial 20°). The total incidence of VOM was 74.5% (79/106), without significant difference in age (81.1 vs. 71.0%, >65 vs. ≤65 yrs, p= 0.257) and sex (male vs. female = 72.7 vs. 77.5%, p= 0.585). Furthermore, similar incidence of VOM was noted in patients with Non-AF (71.2%) and AF group (77.8%, p= 0.434). The RAO 30° fluoroscopic view can demonstrate all the left atrial veins and VOM. However, only the LAO 30° fluoroscopic view could confirm VOM and differentiate it from left atrial veins (after vs. before junction of coronary sinus and great cardiac vein, respectively). Conclusion:VOM was equally distributed in patients with different arrhythmias, and the appropriate fluoroscopic view was important for the differential diagnosis of VOM and left atrial veins.

The coherence mapping was used in frequency analysis of atrial fibrillation (AF). Unipolar electrograms were recorded at AF and during infusion of antiarrhythmic drug, using a 120-electrode array (electrode spacing is 3 mm) placed on the right atrial free wall of canine. We used magnitude-squared coherence in frequency (MSCF) maps to show the frequency distribution during AF. The spectra were limited to 2-15 Hz for AF signals. We chose each site as a reference and established its MSC spectra with other sites in the array. Dominant frequency (DF) was defined by maximum power of spectrum from reference. MSC spectrum was calculated for every point in the array relative to the reference site. If the MSC value of DF is greater than or equal to 0.5, the frequency at this site is set to DF, otherwise it is set to zero. The majority of these values was assigned as the DF of that position. The spatial distribution of DFs was presented as a map, MSCF map. The dominant area (DA) was chosen from the isochronal maps. We developed the MSCF maps for four episodes: (1) normal sinus rhythm: (2) AF without drug infusion: (3) just before AF termination by drug infusion: (4) sinus rhythm following termination. The results show that MSCF map in DA just before AF termination has a uniform pattern. The signals in DA have lower frequencies and longer cycle lengths compared with those in other areas (P< 0.05). In conclusion, this mapping study of the epicardial surface during induced atrial fibrillation in canine right atrial wall has demonstrated that a dominant area near SA node may have an important role for drug-induced AF termination.

Background:Patient-activated event re- corders are useful for the diagnosis of arrhythmia in patients with palpitation and presyncope. However, the utility of event recorders in patients suspected of arrhythmia but presenting with other symptoms is not clear. Furthermore, the factors influencing their utility have not been evaluated. Methods:Event recorder reports of six hundred and sixty consecutive patients referred due to clinical suspicion of cardiac arrhythmia were reviewed. We divided symptoms into four groups: palpitation, presyncope, chest tightness, and dyspnea. We calculated the diagnostic yield according to patients' symptoms reported on the record, and analyzed the factors affecting the utility of event recorders. Results:The overall diagnostic yield was 64%, and those of palpitation, presyncope, chest tightness, and dyspnea were 66%, 57%, 51% and 60%, respectively. The most common five findings in our patients were sinus rhythm (36%), sinus tachycardia (30%), atrial premature complex (14%), ventricular premature complex (12%), and atrial fibrillation/atrial flutter (7%). The recording duration (8 ± 4 days) was short in the present study, but the overall diagnostic yield was similar to those of previous ones. Women had lower diagnostic yields than men, especially in atrial flutter-fibrillation. The diagnostic yield was not influenced by age, ordered doctors, or history of cardiovascular disease. Conclusions:Patient-activated event recorders provided a good diagnostic yield in patients with different presentations of cardiac arrhythmia, and women had lower diagnostic yield in atrial flutter-fibrillation.

Monophasic action potential-like electrocardiogram simulating acute myocardial infarction has been reported in patients with hyperkalemia. We report two cases presenting marked diffuse RS-T elevation resembling monophasic action potential. They had abnormal electrolyte levels, including hyperkalemia and hypocalcemia in case 1 and hypokalemia and hypocalcemia in case 2. The ECG abnormality returned to baseline after correction of potassium and calcium. We conclude that monophasic action potential-like electrocardiogram is caused by electrolyte disturbance other than acute myocardial infarction.

Several investigators have identified the pulmonary vein as the most common initiator of atrial fibrillation, and isolation of the pulmonary vein from atrial tissue can cure approximately 70 of patients with paroxysmal atrial fibrillation. Ongoing trials of a new device may increase the success rate and decrease the complication rate during the pulmonary vein isolation procedure.

Introduction:Radiofrequency catheter ablation of the cavotricuspid isthmus is an effective therapy for typical atrial flutter (AFL), however, the long-term recurrence of AFL and early or late occurrence of atrial fibrillation (AF) are not well defined. This study investigated the long-term (up to 68 months) outcome of patients with typical AFL after catheter ablation of the cavotricuspid isthmus. Methods:This study included 380 patients with typical AFL, who received linear ablation of the cavotricuspid isthmus. They were followed up at the outpatient clinic. A questionnaire was used to evaluate the symptoms suggestive of tachyarrhythmias, and 12-lead ECG, Holter monitoring and event recorders were used to confirm the diagnosis of tachyarrhythmias. Results:At the end of study, 47 patients lost follow-up, so that 333 patients were enrolled into final analysis. Ten (3%) patients had failed ablation of typical AFL. Univariate analysis showed that left atrial dimension was the only factor related to failed ablation. During the long-term follow-up period of 29 ± 17 months (range 7 to 68 months), 29 (9%) patients had recurrent AFL, including 15 with typical and 14 with atypical AFL. Univariate and multivariate analyses showed that incomplete isthmus block and inducible atypical AFL were the independent predictors of recurrent typical and atypical AFL, respectively. One hundred and two (31%) patients developed AF, including 48 with early occurrence of AF (within 3 months after ablation), and 54 with late occurrence of AF (greater than 3 months). Univariate and multivariate analyses showed that prior history of AF and inducible AF were independent predictors of early occurrence of AF, and prior history of AF was the only independent predictor of late occurrence of AF. Conclusions:Linear ablation of the cavotricuspid isthmus is an effective therapy with low recurrence rate for patients with typical AFL. However, one-third patients had early or late occurrence of AF.

Background:Complete bi-directional isthmus block is the endpoint of typical atrial flutter ablation. The purpose of this study was to investigate the feasibility of the local double potential (DP) interval and the change in transisthmus conduction time for predicting complete isthmus block after ablation of the cavotricuspid isthmus. Methods:The study population consisted of 32 patients with typical atrial flutter after a procedure of radiofrequency (RF) ablation of the cavotricuspid isthmus (16 had incomplete block and 16 had complete block). The transisthmus conduction time was determined during pacing from the proximal coronary sinus and low lateral right atrium before and after RF ablation. The DP interval close to the ablation line was evaluated after final RF energy application. Results:In the counterclockwise direction, transisthmus conduction time had an increase of 37 ± 25.4% and 127.3 ± 35.5% (P< 0.001), and the DP interval was 63.3 ± 8.7 ms and 120 ± 17.4 ms (P< 0.001) after achievement of incomplete and complete block, respectively. The sensitivity, specificity, positive and negative predictive values of an increase in the transisthmus conduction time ≥50% were 100%, 81%, 84% and 100%, respectively; those of DP interval ≥100 ms were 100%. In the clockwise direction, transisthmus conduction time had an increase of 38.8 ± 28.6% and 135.7 ± 63.6% (P< 0.001), and the DP interval was 63.6 ± 13.8 ms and 127.7 ± 27.1 ms (P< 0.001) after achievement of incomplete and complete block, respectively. The sensitivity, specificity, positive and negative predictive values of an increase in the transisthmus conduction time ≥50% were 100%, 67%, 83% and 100%, respectively; those of the DP interval ≥100 ms were 100%. Conclusions:The transisthmus conduction time ≥50% increase or DP interval ≥100 ms was feasible to predict complete bi-directional isthmus block.

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The presence of ectopic rhythm has been considered to be the most important marker for successful slow pathway ablation, but the details of different ectopic rhythms have not been well described. This study included 83 consecutive patients with typical AV node reentrant tachycardia who underwent slow pathway ablation. The interval between the atrial signals of the His bundle electrogram and the distal ablation catheter [A(H)-A(Ab)], and the interval between the atrial components of the distal ablation catheter and the ostium of coronary sinus catheter [A(Ab)-A(CSos)] were measured. One hundred episodes of ectopic rhythm occurred with 81 (81%) successful applications. There are two different origins and three activation sequences of ectopic rhythms, including HIS rhythm (78 applications, the earliest atrial activation in the His bundle electrogram), CSos rhythm (6 applications, the earliest atrial signal in the coronary sinus ostium electrogram) and CSos preceding HIS (CSos→HIS) rhythm (16 applications, the atrial activation sequences changing from CSos to HIS rhythm). The CSos rhythm had a shorter mean cycle length (445 ± 81 vs. 511 ± 132 vs. 579 ± 140 ms, p < 0.05), a shorter [A(Ab)-A(CSos)] interval (−2.5 ± 9.8 vs. 14.1 ± 11.2 vs. 12.8 ± 8.4 ms, p < 0.05) and a lower success rate (33% vs. 84% vs. 94% p < 0.05) than HIS rhythm and CSos→HIS rhythm. Otherwise, the mean cycle length of ectopic rhythm was significant shorter in successful than in failed ablation (506 ± 135 vs. 559 ± 118 ms, p = 0.04). In conclusion, we found two different origins and three activation sequences of ectopic rhythms. CSos rhythm had a lower success rate in ablation of slow pathway, thus it was a poor marker for successful ablation.

This study investigated the difference of atrial electrophysiologic characteristics between a normal and dilated atrium and compared them among patients with paroxysmal atrial fibrillation and flutter. Twenty-seven patients with paroxysmal atrial fibrillation and 28 patients with paroxysmal atrial flutter were divided into four subgroups, according to the presence of a normal atrium or bilateral atrial enlargement. Thirty patients without atrial arrhythmia (20 patients with normal atrium and 10 patients with bilateral atrial enlargement) were included in control group. The atrial refractoriness in patients with a dilated atrium was longer than those with normal atrial size. In patients with paroxysmal atrial fibrillation and patients of control group, the P-wave duration and interatrial conduction velocity with or without atrial enlargement were similar. However, in patients with paroxysmal atrial flutter, P-APCS(86 ± 10 ms vs. 73 ± 9 ms, p < 0.05) and P-ADCS(109 ± 9 ms vs. 95 ± 9 ms, p < 0.05) in patients with a dilated atrium were longer than in patients with a normal atrium. The patients with paroxysmal atrial fibrillation or atrial flutter all demonstrated longer P-wave duration and interatrial conduction time than control group. Among the groups with a normal atrium or a dilated atrium, atrial refractoriness in patients with paroxysmal atrial flutter was shorter than that in control group. Moreover, in the patients with a normal atrium, the potential minimal wavelength in control group (6.6 ± 1.7) was longer than that of paroxysmal atrial fibrillation (5.3 ± 1.1), or atrial flutter (5.0 ± 1.2). These findings suggest that atrial electrophysiologic characteristics of a dilated atrium were different from those of normal atrium, and these changes were different between paroxysmal atrial fibrillation and flutter. Multiple factors are considered to be related to the genesis of atrial tachyarrhythmias.

Objectives. The purposes of this study were to evaluate the atrial electrophysiology and autonomic nervous system in patients who had paroxysmal supraventricular tachycardia (PSVT) associated with paroxysmal atrial fibrillation (PAF).

Objectives. This study compared the long-term effects of complete atrioventricular junction (AVJ) ablation with those of AVJ modification in patients with medically refractory atrial fibrillation (AF).

Objectives. This study sought to study the change in autonomic tone that precedes the initiation of paroxysmal atrial flutter.

To investigate the ECG characteristics, the electrophysiologic properties, and an effective radiofrequency catheter ablation technique in patients with septal accessory pathways.

Among a consecutive series of 600 patients who underwent radiofrequency catheter ablation for AV node reentrant tachycardia, 14 patients (age 29-76 years) had a prolonged AH interval during sinus rhythm (172±18 ms, range 140 to 200). Seven of them had unsuccessful ablation during the previous ablation sessions. Eight patients with anterograde dual AV node pathway physiology received anterograde slow pathway ablation, and the other 6 patients without dual-pathway physiology received retrograde fast pathway ablation. All patients had successful elimination of AV nodal reentrant tachycardia after a mean of 4±4 radiofrequency applications, power level 36±6 watts and a pulse duration of 42±4 seconds. The postablation AH interval remained unchanged. During a follow-up period of 25±13 months, one patient who received slow pathway ablation developed 2:1 AV block with syncope. As compared with the other 586 patients without a prolonged AH interval, these 14 patients had significantly poorer anterograde AV nodal function and lower incidence of anterograde dual AV node physiology (P<0.01). We concluded that slow pathway ablation in patients with dual pathway physiology, and retrograde fast pathway ablation in patients without dual pathway physiology were effective and safe in patients with a prolonged AH interval. However, delayed onset of symptomatic AV block is possible and careful follow-up is necessary.

Previous reports on the anatomic discordance between atrial andventricular insertion sites of left free-wall accessory pathways werelimited and their findings were controversial. The purpose of this studywas to explore the fiber orientation and related electrophysiologiccharacteristics of left free-wall accessory pathways. The study populationcomprised 96 consecutive patients with a single left free-wall accessorypathway (33 manifest and 63 concealed pathways), who underwentelectrophysiologic study and radiofrequency catheter ablation using theretrograde ventricular approach. The atrial insertion site of the accessorypathway was defined from the cinefilms as the site with the earliestretrograde atrial activation bracketed on the coronary sinus catheterduring tachycardia, and the ventricular insertion site was defined as thesite where successful ablation of the pathway was achieved. Forty-twopatients (44%) had their atrial insertion sites 5-20 mm (10 ±3 mm) distal to the ventricular insertion sites (proximal excursion), 30(31%) patients had their atrial insertion sites 5-20 mm (12 ±3 mm) proximal to the ventricular insertion sites (distal excursion), and24 (25%) patients had directly aligned atrial and ventricular insertion sites. Retrograde conduction properties, including 1:1 VA conduction and effective refractory period, were significantly poorer inthe pathways with proximal excursion (302 ± 67, 285 ± 61 msrespectively) than in those with distal excursion (264 ± 56, 250± 48 ms respectively) or direct alignment (272 ± 61, 258± 73 ms respectively). Accessory pathways at the more posteriorlocation had a significantly higher incidence of proximal excursion (P= 0.006), and those at the more anterior location had a higherincidence of distal excursion (P = 0.012). In conclusion, a widevariation in fiber orientations and related electrophysiologic characteristics was found in left free-wall accessory pathways. This mayhave important clinical implications for radiofrequency ablation.

Objectives. The purpose of this study was to study electrophysiologic characteristics and compare the electrophysiologically guided focal ablation technique and linear ablation technique in patients with common atrial flutter in a prospective randomized fashion.

Objectives. This study sought to characterize the functional properties of decremental accessory atrioventricular (AV) pathways and to investigate their pharmacologic responses.

Objectives. This study sought to investigate electrophysiologic characteristics and possible anatomic sites of multiple anterograde slow atrioventricular (AV) node pathways and to compare these findings with those in dual anterograde AV node pathways.

Objectives. This study evaluated the effect of high intensity drive train (S1) stimulation on the atrial effective refractory period (ERP) and its relation to the autonomic nervous system.

Objectives. The purpose of this study was to use an electrocardiographic (ECG) algorithm, derived from the results of radiofrequency ablation, to discriminate atrioventricular node reentrant tachycardia (AVNRT) from atrioventricular reciprocating tachycardia (AVRT) and to localize a concealed accessory pathway, prospectively.

Prediction of accessory pathway location before radio-frequency ablation has become increasingly important for patients with Wolf-Paridnson-White syndrome. However, existing electrocardiographic (ECG) criteria for localization of accessory pathways have several limitations, and the polarity of delta waves has not been well defined. In the present study, 369 patients with a single anterogradety conducting accessory pathway who underwent successful radiofrequency ablation were included. The polarity of delta waves was defined and categorized in detail, and various ECG characteristics of the most preexcited QRS complexes were examined and compared with QRS complexes after successful ablation in the initial 182 patients, which included morphology and polarity of delta waves, initial 20, 40, and 60ms segments of the preexcited QRS complex, R/S ratio in the precordial leads, R/S ratio in the frontal leads, delta wave axis in the frontal plane, polarity of delta waves in the frontal leads, and polarity of delta waves in the precordial leads. The polarity of the initial 40ms segment of the most preexcited QRS complexes in each of the frontal leads, and the polarity of the initial 60ms segment of the most preexcited QRS complex in each of the precordial leads proved to be the best representatives of delta wave polarity in the respective leads. The most discriminative characteristics were combined to form the following algorithm: step 1, analysis of R/S ratio in V2; step 2, existence of positive delta wave in lead III (initial 40ms); step 3, existence of positive or negative delta waves in V1, (initial 60ms); and step 4, delta wave polarity in aVF or analysis of R/S ratio in V1. The new algorithm is featured by its easiness to be applied because only 4 ECG leads and 4 steps are required, and the same ECG characteristic is used in the same step in both arms of the algorithm. Together with 3 other criteria (those of Arruda, Filzpatrick, and Xie), it was prospectively evaluated in 187 subsequent patients, and it turned out to be more accurate (93%) than other algorithms (86%, 86%, 85%, respectively; all p values <0.05). We conclude that this new algorithm, through a comprehensive analysis of delta waves and an R/S ratio in a large group of patients, offers an accurate criterion for predicting accessory pathway location.

A 71-year-old male patient was admitted for catheter ablation of the pulmonary veins to treat paroxysmal atrial fibrillation. Atrial fibrillation originating from the left superior pulmonary vein was induced after a pause of atrial pacing under isoproterenol infusion and became sustained. Spontaneous transition from atrial fibrillation to typical atrial flutter was noted after complete isolation of the pulmonary vein focus from the left atrium. Subsequently linear ablation of the cavotricuspid isthmus was created with completely bi-directional isthmus conduction block. We hypothesized that ectopic pulmonary vein focus played an important role in the spontaneous conversion of atrial fibrillation to typical atrial flutter, and complete isolation of the pulmonary vein could stop the spontaneous transition between the two atrial tachyarrhythmias.

Background: In animal studies, atrial fibrillation has been shown to shorten the atrial refractory period and impair its rate adaptation. However, little is known about the effects of chronic atrial fibrillation on atrial electrophysiology and its recovery course in humans. Methods and results: Nineteen patients, mean age 64±14 years, with chronic atrial fibrillation of more than six months duration were included in this study. All of them were successfully converted to sinus rhythm with an external defibrillator. Atrial effective refractory periods at right atrial appendage and distal coronary sinus were determined with five pacing cycle lengths (300, 400, 500, 600 and 700 ms) at 30 min after cardioversion and once a day for four days. The atrial conduction properties, including P wave duration of surface ECG, and right and left atrial conduction times, were also measured at the same time interval. Twenty age-matched patients without a history of atrial tachyarrhythmia were evaluated as controls. In comparison with controls, chronic atrial fibrillation significantly shortened the atrial effective refractory period, impaired its rate adaptation response, especially at distal coronary sinus, and depressed the conduction properties of atria. The atrial conduction properties did not change during the four-day follow-up period; however, the atrial effective refractory period was gradually prolonged and its rate adaptation response improved after restoration of sinus rhythm. Conclusions: In humans, chronic atrial fibrillation significantly shortened the atrial effective refractory period, and impaired its rate adaptation response. Restoration and maintenance of sinus rhythm could reverse these electrophysiological changes.