Creation Of Block Research Articles

Success rate of catheter ablation in atrial flutter: Comparison of a 4- or 5-mm tip electrode catheter with an 8-mm tip electrode catheter

Radio frequency (RF) energy is capable of interrupting the reentrant circuit of atrial flutter and curing the arrhythmia. The development of 8-mm tip catheter provides more tissue damage and has offered the promise of improved success. The purpose of our study was to determine if the acute and long-term success with the 8-mm tips were superior to the 4- or 5-mm tips. The outcomes of the first 20 patients in whom an 8-mm tip catheter was used were compared with the previous 20 patients in whom a 4-or 5-mm tip catheter was used. Procedural (acute) ablation success was defined by creation of bi-directional isthmus block. Long-term success was defined as the prevention of clinically evident atrial flutter (AFl) as determined by the absence of symptoms or maintenance of sinus rhythm on electrocardiogram, six months to one year after the procedure. Compared to the 4- or 5-mm tip, the 8-mm catheter tip was associated with a reduced ablation duration {22.3 +/- 16 versus 11.5 +/- 5 min (p = 0.0078)}, a lower mean number of ablations {13.5 +/- 9.9 versus 6.8 +/- 2.9 (p = 0.0065)} and a reduced procedure time {1.8 +/- 0.7 versus 1.1 +/- 0.5 h (p = 0.0032)}. Acute success was 95% in the 4- or 5-mm group versus 80% in the 8-mm group (p = NS), but long-term success was higher in the 8-mm group than the 4- or 5-mm group (87.5 versus 63.2%, p = 0.0436). Eight-millimeter tip catheters for AFl shorten procedure time, reduce the duration and number of ablations and accomplish bi-directional block when compared with smaller tipped catheters. The long-term success rate is better with the 8-mm tips and should be the preferred catheter for RF ablation of AFl.

06/02446 Central Asia: a major emerging energy player in the 21st century: Dorian, J. P. Energy Policy, 2006, 34, (5), 544–555.

The last changes in the energy scene had culminated in an even-growing capacity of influence of the private energy majors on the political and governmental decisions. However, the European Union has at its disposal the necessary elements—the EU-Russia Energy Dialogue and its relationship with Turkey—that could became a useful regional instrument in order to strengthen the EU's position in the International Energy Scene (IES). That is why the purpose of this paper is to propose the creation of a regional energy block, as a new way of understanding energy policies. We shall define this block as a pan-European geo-energy space.To this end, the present work is divided into three parts. Firstly, we will explain the failure of the policies founded on the Market & Institutions approach. Secondly, and within the actual context of the IES, we seek to point out which elements could support the option of a European regional strategy. Finally, in the third part, we will establish that the existence of the EU-Russia Energy Dialogue and the future incorporation of Turkey are the foundations from which a hypothetical pan-European geo-energy space can be built.

Mapping-guided ablation of the cavotricuspid isthmus: A novel simplified approach to radiofrequency catheter ablation of isthmus-dependent atrial flutter

Because the anatomic features of the cavotricuspid isthmus (CTI) are complex, radiofrequency (RF) energy requirements for CTI ablation may vary at each point within the CTI. Conventionally, multiple-site mapping has been required for determining CTI conduction block. The purpose of this study was to develop a more efficacious method for ablation of isthmus-dependent atrial flutter. Forty consecutive patients underwent CTI ablation using a CTI mapping-guided approach (20 patients) or a conventional approach (20 patients). In the CTI mapping-guided approach, an octapolar catheter was positioned on the CTI parallel to, and downstream from, the intended ablation line in order to map and ablate the breakthrough point. Complete CTI block was achieved in all study patients. CTI mapping of incomplete ablation lines revealed that the site with the shortest interval between double potentials did not always coincide with the conduction gap. Disappearance of a breakthrough pattern on the CTI electrograms corresponded to creation of complete CTI block. During ablation, CTI mapping exhibited pseudo-CTI block in 8% of patients in the clockwise direction and 63% of patients in the counterclockwise direction. The number and total time of RF applications were significantly lower with the CTI mapping-guided approach than with the conventional approach (7.7 +/- 3.9 applications vs 13.8 +/- 8.9 applications and 8.9 +/- 4.4 minutes vs 16.3 +/- 11.9 minutes, respectively, P <.05). In the CTI mapping-guided approach, RF applications were not required along the entire CTI in 7 patients (35%). This simplified technique was feasible for creating and determining complete CTI block, with fewer RF applications required.

Human Adult Bone Marrow Mesenchymal Stem Cells Repair Experimental Conduction Block in Rat Cardiomyocyte Cultures

We evaluated whether human adult bone marrow-derived mesenchymal stem cells (hMSCs) could repair an experimentally induced conduction block in cardiomyocyte cultures. Autologous stem cell therapy is a novel treatment option for patients with heart disease. However, detailed electrophysiological characterization of hMSCs is still lacking. Neonatal rat cardiomyocytes were seeded on multi-electrode arrays. After 48 h, abrasion of a 200- to 450-microm-wide channel caused conduction block. Next, we applied adult hMSCs (hMSC group, n = 8), human skeletal myoblasts (myoblast group, n = 7), rat cardiac fibroblasts (fibroblast group, n = 7), or no cells (control group, n = 7) in a channel-crossing pattern. Cross-channel electrical conduction was analyzed after 24 and 48 h. Intracellular action potentials of hMSCs and cardiomyocytes were recorded. Immunostaining for connexins and intercellular dye transfer (calcein) assessed the presence of functional gap junctions. After creation of conduction block, two asynchronously beating fields of cardiomyocytes were present. Application of hMSCs restored synchronization between the two fields in five of eight cultures after 24 h. Conduction velocity across hMSCs (0.9 +/- 0.4 cm/s) was approximately 11-fold slower than across cardiomyocytes (10.4 +/- 5.8 cm/s). No resynchronization occurred in the myoblast, fibroblast, or control group. Intracellular action potential recordings indicated that conduction across the channel presumably occurred by electrotonic impulse propagation. Connexin-43 was present along regions of hMSC-to-cardiomyocyte contact, but not along regions of cardiomyocyte-to-myoblast or cardiomyocyte-to-fibroblast contact. Calcein transfer from cardiomyocytes to hMSCs was observed within 24 h after co-culture initiation. Human mesenchymal stem cells are able to repair conduction block in cardiomyocyte cultures, probably through connexin-mediated coupling.

European energy security: Towards the creation of the geo-energy space

The last changes in the energy scene had culminated in an even-growing capacity of influence of the private energy majors on the political and governmental decisions. However, the European Union has at its disposal the necessary elements—the EU-Russia Energy Dialogue and its relationship with Turkey—that could became a useful regional instrument in order to strengthen the EU's position in the International Energy Scene (IES). That is why the purpose of this paper is to propose the creation of a regional energy block, as a new way of understanding energy policies. We shall define this block as a pan-European geo-energy space. To this end, the present work is divided into three parts. Firstly, we will explain the failure of the policies founded on the Market & Institutions approach. Secondly, and within the actual context of the IES, we seek to point out which elements could support the option of a European regional strategy. Finally, in the third part, we will establish that the existence of the EU-Russia Energy Dialogue and the future incorporation of Turkey are the foundations from which a hypothetical pan-European geo-energy space can be built.

Catheter inversion to achieve complete isthmus block in patients with typical atrial flutter

Endocardial catheter ablation is now considered as the therapy of first choice in highly symptomatic patients with recurrent atrial flutter. Despite of primary success rates between 90 and 100% complete isthmus block is sometimes hard to achieve. We present ablation results of 100 consecutive patients suffering from typical right atrial flutter. After a mean of 18 energy applications persistent bidirectional isthmus block could not be achieved in 16 patients and right atrial angiography was performed in all of them. In 9 patients a large Eustachian valve was detected and considered responsible for failure of endocardial catheter ablation of atrial flutter. Catheter manipulation targeting the anterior region of the Eustachian ridge was successful in all patients after looping the ablation catheter within the right atrium. With a mean of 3 additional RF applications, 6 of the 9 affected patients could be successfully ablated. Large Eustachian ridges are not a rare finding in patients undergoing ablation of typical right atrial flutter. Inversion of the ablation catheter within the right atrium is a simple technique providing excellent tissue contact of the ablation electrode with the anterior region of the Eustachian Ridge. Using this approach, the creation of bidirectional isthmus block is possible in the majority of the respective patients.

Where to draw the mitral isthmus line in catheter ablation of atrial fibrillation: histological analysis

A linear lesion between the left inferior pulmonary vein orifice and mitral annulus, the so-called mitral isthmus, may improve the success of catheter ablation for atrial fibrillation. Gaps in the lesion line, however, may facilitate left atrial flutter. The aim of the study was to determine the optimal location of the lesion line by serial sectioning of the isthmus area. In a post-mortem study of 16 patients with normal left atria, serial sections of the isthmus area from 10 mm superior to and 30 mm inferior to the isthmus were studied by light microscopy. The length of the isthmus was 35+/-7 mm. On average, the muscle sleeve around the coronary sinus ended 10 mm inferior to the isthmus. The prevalence of a ramus circumflexus <5 mm from the endocardial surface, decreased from 60% in the most superior section to 0% in the most inferior section. Atrial arteries were frequently present in all sections. The thickness of atrial myocardium, the ramus circumflexus sometimes very close to the endocardium, a myocardial sleeve around the coronary sinus, and local cooling by atrial arteries and veins may complicate the creation of conduction block in the mitral isthmus.

Beating-heart epicardial radiofrequency ablation: optimal temperature setting

PurposePulmonary vein isolation is a simple procedure, which has recently been reported as an effective treatment for the termination of atrial fibrillation. Although there are several clinical reports of beating-heart epicardial ablation, the optimal temperature has not been experimentally investigated. We evaluated the effective temperature for the placement of circular lesions around the pulmonary vein–left atrial junction. DescriptionTwelve swine underwent epicardial ablation to create linear conduction block lesions around the pulmonary vein–left atrial junction by a seven-electrode ablation catheter. The ablation was performed at 60°C (group I), 70°C (group II), 80°C (group III), and 90°C (group IV) for 120 seconds. The creation of a firm conduction block across the ablated lesion under pacing was compared. EvaluationComplete conduction block was observed in all groups except group I. However, heat injury to adjacent structures in group IV and transient discoloration of the tissue surrounding coronary arteries in groups III and IV were observed. ConclusionsThe effective temperature for epicardial radiofrequency pulmonary vein isolation was 120 minutes and above 70°C.

Catheter inversion: a technique to complete isthmus ablation and cure atrial flutter.

Cure of typical atrial flutter (AFL) by catheter ablation to produce bidirectional block across the tricuspid annulus-inferior vena cava isthmus (IS) is highly effective, but failures may occur. We describe a technique that may allow creation of bidirectional block where a conventional strategy has failed. AFL ablation was performed using the conventional approach with a mapping/ablation (ablation) catheter introduced via the right femoral vein (RFV) to create a line of bidirectional block across the IS. If this was not achieved after five passes of the ablation catheter from the tricuspid annulus to the inferior vena cava (IVC) a catheter inversion technique was used. This allowed stable positioning of the ablation catheter at the IVC end of the isthmus. In 11 patients, a mean of 17 (range 3 to 45) radiofrequency (RF) applications was given before the catheter inversion technique was applied. Following catheter inversion a mean of 4 (1 to 14) further RF applications achieved bidirectional isthmus block in every patient. No complications occurred. Catheter inversion provides a simple, safe, and effective means of achieving bidirectional isthmus conduction block in cases where a conventional ablation strategy might have failed.

The usefulness of surface 12-lead electrocardiogram to predict intra-atrial conduction block after successful atrial flutter ablation

Intraatrial conduction block at the inferior vena cava-tricuspid annulus isthmus was shown to predict successful atrial flutter ablation. However, its demonstration requires the use of several electrode catheters. Thus, a simple approach using surface 12-lead ECG to prove the conduction block would be valuable. Twenty-two patients were prospectively studied during low septal and low lateral atrial pacing before and after successful atrial flutter ablation. Creation of the conduction block was confirmed by comparing the sequence of atrial activation using 3 multipolar catheters during atrial pacing before and after ablation. During low septal pacing, there was no significant difference before and after ablation in P-wave width, axis, or morphology. During low lateral atrial pacing, there was a significant P-wave axis rotation towards the right (from −67 ± 27° to +13 ± 35°, P < .001), and P-wave polarity in limb lead II changed from predominantly negative to predominantly positive in 21 of 22 patients. There was also an increase in P-wave width (from 136 ± 32 to 169 ± 36 ms, P < .001) and stimulus-to-QRS interval (from 268 ± 61 ms to 343 ± 95 ms, P < .001) during low lateral pacing that was not observed during low septal pacing. We conclude that creation of a conduction block in the inferior vena cava-tricuspid annulus isthmus modifies surface 12-lead ECG during low lateral atrial pacing only. We also suggest that P-wave polarity in limb lead II during low lateral pacing could be used as a noninvasive marker of unidirectional counter-clockwise conduction block during atrial flutter ablation.

The protectionist bias of duty drawbacks: evidence from Mercosur

In a political-economy setting where tariffs and duty drawbacks are endogenously chosen through industry lobbying, it is shown that full duty-drawbacks are granted to exporters who use imported intermediates in their production. This in turn decreases their incentives to counter-lobby against high tariffs on their inputs. In equilibrium, higher tariffs will be observed on these goods. The creation of a regional block will change the political equilibrium. Duty-drawbacks will be eliminated on intra-regional exports, which in turn will lead to lower tariffs for goods used as inputs by intra-regional exporters. Evidence from Mercosur suggests that the elimination of duty-drawbacks for intra-regional exports led to increased counter-lobbying by users of intermediate products. In its absence the common external tariff would have been on average 3.5 percentage points (25 percent) higher.

Progressive isthmus delay during atrial flutter ablation: the critical importance of isthmus spanning electrodes for distinguishing pseudoblock from block.

Bidirectional isthmus block is associated with successful atrial flutter ablation, whereas creation of increased isthmus conduction delay without block can be proarrhythmic. Often, halo catheter electrodes fail to provide adequate sub-Eustachian isthmus recordings. The aim of this study was to determine if progressive isthmus conduction delay results in the false appearance of block during atrialflutter ablation. A 20-pole deflectable catheter was prospectively positioned across the sub-Eustachian isthmus (from the coronary sinus os [CSO] to 7:00 on the tricuspid valve annulus [TVA] clock face in the left anterior oblique [LAO] projection) in nine patients undergoing atrial flutter ablation. During sinus rhythm, conduction time was measured from the CSO to the 7:00 position while pacing the CSO. Measurements were repeated after each linear lesion and after conduction block was achieved. Transisthmus conduction time at baseline, just prior to success, and after the presence of complete block was 54 +/- 9, 123 +/- 39, and 155 +/- 30 ms, respectively (P < or = 0.01). The marked delay prior to complete block resulted in reversal of the activation sequence in electrodes at TVA 7:00, creating the false appearance of isthmus block; the isthmus electrodes clearly distinguished delay from block. Catheter ablation results in progressive isthmus conduction delay prior to the creation of complete block. Electrodes spanning the isthmus and line of block are critical for distinguishing conduction delay (and pseudoisthmus block) from block.

Time course of structural adaptations in chronic AV block dogs: evidence for differential ventricular remodeling.

To determine the nature and time course of biventricular hypertrophy and concomitant electrical and mechanical changes after creation of complete atrioventricular block (CAVB), six adult dogs (22-30 kg) were subjected to serial magnetic resonance imaging (MRI) and electrocardiography. After 6 days of CAVB, left ventricular (LV) mass, ejection fraction (EF), and Q-T time at a paced rhythm of 60 beats/min were already significantly increased. Maximal values were reached within 14-21 days of CAVB: LV mass, from 116 +/- 11 to 143 +/- 12 g; right ventricular (RV) mass, from 40 +/- 3 to 55 +/- 6 g; EF, from 68 +/- 6% to 86 +/- 5%; and Q-T time, from 285 +/- 25 to 330 +/- 35 ms, all P < 0.05. Cardiac output returned to baseline at day 14. End-diastolic wall thickness increased only in the RV, in which angiotensin type 1 (AT1) receptor mRNA expression was significantly greater. The autopsy correlated well with the MRI results (r = 0.98, P< or = 0.01). In conclusion, electrophysiological, mechanical, and structural adaptation processes after bradycardia-induced volume overload develop rapidly and are completed within 3 wk. The degree of hypertrophy was greater in the RV, which was associated with an increase in AT1 receptor mRNA.

Response to flecainide infusion predicts long-term success of hybrid pharmacologic and ablation therapy in patients with atrial fibrillation

OBJECTIVESWe tested the hypothesis that the response to flecainide infusion can identify patients with atrial fibrillation (AF) in whom the hybrid pharmacologic and ablation therapy reduces the recurrences of AF.BACKGROUNDInfusion of class IC anti-arrhythmic drugs may promote transformation of AF into atrial flutter. Catheter ablation of atrial flutter has been demonstrated to be highly effective in preventing recurrences of atrial flutter.METHODSSeventy-one consecutive patients with paroxysmal or chronic AF, in whom flecainide infusion (2 mg/kg body weight, intravenously) determined the transformation of AF into common atrial flutter (positive response), were randomized to receive one of the following treatments: oral pharmacologic treatment with flecainide (group A, n = 23); the hybrid treatment (catheter ablation of the inferior vena cava-tricuspid annulus isthmus, plus oral flecainide) (group B, n = 24); or catheter ablation of the isthmus only (group C, n = 24). Thirty-seven patients with a negative response to flecainide, who chose to be submitted to the hybrid treatment, were selected as the control group (group D).RESULTSDuring a mean follow-up period of 24 ± 7.2 months, the recurrences of AF and atrial flutter in group B (42%) were significantly lower than those in group A (78%, p < 0.001), group C (92%, p < 0.001) and group D (92%, p < 0.001).CONCLUSIONSThe creation of a complete bi-directional conduction block at the inferior vena cava-tricuspid annulus isthmus, plus flecainide administration, reduces the recurrences of both AF and atrial flutter in patients with class IC atrial flutter. Moreover, the early response to flecainide is safe and reliable in identifying patients who may benefit from this therapy.

Kinematic and block theory analyses for shiplock slopes of the three Gorges dam site in China

The granitic rock mass that exists in the shiplock region of the Three Gorges dam site contains a number of major discontinuities and about four sets of minor discontinuities. One hundred and thirty three major discontinuities have been mapped around the shiplock covering an area of 1740×600 m. These major discontinuities were used to perform rock slope kinematic and block theory analyses. Kinematic analyses were performed under the following two cases: (1) assuming all the mapped discontinuities cross the shiplock; (2) using only discontinuities that actually intersect the shiplock. Under case (1) and case (2) the shiplock faces in the proposed permanent shiplock region in fresh rock were found to be stable up to a cut slope of about 45° and 58°, respectively. Block theory was applied to identify different block types that exist on the shiplock faces and to estimate the maximum safe slope angles on the shiplock faces. The orientations of the major discontinuities that actually intersect the shiplocks were considered in this analysis. The total length of the shiplock (1750 m) was divided into 50 m segments. From the stereo-plots, the key blocks (Type I) and/or potential key blocks (Type II) were found for only five segments of the shiplock slopes. It was found that the dip of the cut slope should be less than about 60° to avoid creation of a key block on the proposed shiplock slopes. However, it is important to keep in mind that these conclusions are based on the kinematic analyses performed using only the major discontinuities. Further kinematic as well as kinetic analyses are recommended incorporating minor discontinuities, water forces, earthquake forces etc. before making the final conclusions about the maximum safe slope angle for the shiplock region.

Microstructure of ethylene-1-hexene and ethylene-1-octene copolymers obtained over Ziegler–Natta catalysts supported on MgCl2(THF)2

The ethylene copolymerizations with 1-hexene or 1-octene in the presence of hydrogen using three catalysts, MgCl2(THF)2/VOCl3/Et2AlCl, MgCl2(THF)2/VCl4/Et2AlCl, MgCl2(THF)2/TiCl4/Et2AlCl, were investigated. It was found that the addition of hydrogen into the copolymerization feed reduces the molecular weight of the copolymers produced and decreases the activity of all the studied catalysts. The microstructure of the copolymers obtained was determined on the basis of 13C NMR investigations and the reactivity ratios of the comonomers were calculated. The lack of tendency of the olefin comonomers to the creation of the polymer block was confirmed. It was found that the products of the comonomers reactivity ratios are close to the value of 1 and they are independent of both the catalyst and comonomer type. This means that the structure of all the copolymers obtained is random.

Persistent atrial flutter in patients treated for atrial fibrillation with amiodarone and propafenone: electrophysiologic characteristics, radiofrequency catheter ablation, and risk prediction.

Antiarrhythmic drugs have been reported to promote the conversion of atrial fibrillation to atrial flutter in patients with paroxysmal atrial fibrillation. However, information about the electrophysiologic mechanism and response to radiofrequency ablation of these drug-induced atrial flutters is limited. Furthermore, the determinants of the development of persistent atrial flutter in patients treated for atrial fibrillation with antiarrhythmic drugs are still unknown. Among the 136 patients treated for atrial fibrillation with amiodarone (n = 96) or propafenone (n = 40), 15 (11%, mean age 65.5 +/- 12.3 years) were identified to have subsequent development of persistent atrial flutter based on surface ECG characteristics during antiarrhythmic drug treatment. The mean interval between the beginning of drug treatment and the onset of atrial flutter was 5.0 +/- 5.5 months. Intracardiac mapping and entrainment studies revealed that 11 patients had counterclockwise typical atrial flutter, and 4 had clockwise typical atrial flutter. All 15 patients underwent successful ablation with creation of complete bidirectional isthmus conduction block. After a mean follow-up of 12.3 +/- 4.2 months, 14 (93%) of 15 patients who underwent successful ablation and continued taking antiarrhythmic drugs have remained in sinus rhythm. Univariate analysis of clinical variables demonstrated that only atrial enlargement was significantly related to the occurrence of persistent atrial flutter. In patients with atrial fibrillation, persistent typical atrial flutter might occur during antiarrhythmic drug treatment, and atrial enlargement was a risk factor for the development of such an arrhythmia. Radiofrequency ablation and continuation of pharmacologic therapy offered a safe and effective means of achieving and maintaining sinus rhythm.

Radiofrequency catheter ablation of atrial flutter after orthotopic heart transplantation: insights into the redefined critical isthmus

We report a case of successful radiofrequency catheter ablation of recurrent atrial flutter in a heart transplant recipient and discuss technical aspects of the procedure. A counterclockwise flutter circuit was defined during endocardial mapping of the donor atrium. Termination of atrial flutter was achieved by creating lines of radiofrequency lesions from the tricuspid ring to the suture line between donor and recipient atria. Creation of bidirectional conduction block in the tricuspid ring-suture line isthmus resulted in abolition of atrial flutter.

Radiofrequency catheter ablation of common atrial flutter: significance of palpitations and quality-of-life evaluation in patients with proven isthmus block.

Creation of a complete bidirectional inferior vena cava-tricuspid annulus isthmus block (CBIB) by radiofrequency catheter ablation is now a well-accepted criterion for prevention of common atrial flutter (AFl) recurrences. However, some patients still complain of palpitations after ablation, and it is not known whether these are related to AFl recurrences or to other arrhythmias. Among 100 consecutive patients referred to our institution for AFl ablation, CBIB was created in 83. There were 54 patients (group A) in whom AFl was the only documented arrhythmia before ablation and 29 patients (group B) in whom atrial fibrillation (AFib) had been documented in addition to AFl. An electrophysiological control study was performed in 40 patients 1 to 3 months after ablation. Arrhythmic events, medications, and functional status were evaluated at midterm follow-up (n=77; 14. 7+/-8.4 months; range, 4 to 34 months). The SF-36 questionnaire and the Symptom Checklist--Frequency and Severity Scale specific for cardiac arrhythmia were used to assess quality of life in 63 patients at long-term follow-up (27.1+/-8.5 months). Recurrence of AFl was documented in only 1 patient 6 months after ablation. AFib was recorded in 28 patients (36.4%), and atypical AFl was found in 3 patients. Thirty-two group A patients (66.7%) and 17 group B patients (58.6%) were still arrhythmia free at midterm follow-up. Even at long-term follow-up and in group B patients, AFl ablation was followed by a clear improvement in quality of life. Palpitations after creation of CBIB are due mostly to AFib but not to AFl recurrence. This technique provides a significant and persistent clinical benefit and may suppress all atrial arrhythmia in a subset of patients suffering from both AFl and AFib.

Radiofrequency catheter ablation of the atria eliminates pacing-induced sustained atrial fibrillation and reduces connexin 43 in dogs.

We assessed the effects of radiofrequency catheter ablation (RFCA) of the atrial epicardium on pacing-induced sustained atrial fibrillation (AF) and the expression and distribution of the intercellular gap junction protein connexin 43 (Cx43) in dogs. In 12 mongrel dogs, after creation of complete AV block and implantation of a ventricular inhibited pacemaker, a high-rate pulse generator (20 to 30 Hz to induce AF) was implanted in the neck, connected to a right atrial endocardial pacing lead, and used to pace the atrium for 10 to 14 weeks. In group 1 (n=9 dogs), corrected sinus node recovery time (CSNRT), P-wave duration, 24-hour Holter ECG, maximal heart rate (MHR) in response to isoproterenol, and intrinsic heart rate (IHR) after atropine (0.04 mg/kg) and propranolol were measured before and after atrial pacing and RFCA. Group 2 dogs were used to assess the effect of chronic AF alone on Cx43 expression and distribution. All group 1 dogs developed sustained (>24 hours) AF. Right-sided RFCA of the atria eliminated the sustained AF in 5 dogs, but both right and left atrial RFCA was required to abolish sustained AF in the other 4 dogs. After RFCA restored sinus rhythm, CSNRT and P-wave duration were prolonged and MHR and IHR were decreased. Chronic rapid atrial pacing (group 2) increased the expression of Cx43, which was absent in ablated areas and markedly depressed in viable atrial myocytes near the ablation zones (group 1). Rapid atrial pacing for long time periods induced sustained AF that can be eliminated by linear right and left atrial lesions created with RFCA, with preservation of sinus rhythm and atrial contractile function. Chronic AF increased the expression and distribution of gap junction protein Cx43, which became reduced in ablated and nearby nonablated areas.