Catheter Ablation of Atrioventricular Nodal Reentrant Tachycardia in Patients With Congenital Heart Disease.

Atrioventricular (AV) nodal reentrant tachycardia represents the most common regular supraventricular arrhythmia in humans, and catheter ablation of the so called slow AV nodal pathway has been effectively performed for decades. In patients with congenital heart disease, a combination of different factors makes catheter ablation of AV nodal reentrant tachycardia substrate particularly challenging, including abnormal venous access to intracardiac structures, abnormal intracardiac anatomy, potentially deviant and often unpredictable sites of the specific conduction system, loss of traditional anatomic landmarks, and congenital cardiac surgery that may complicate the access to the AV nodal area. Published experiences have confirmed the efficacy and the relative safety of such procedures when performed by experts, but the risk of complications, in particular AV block, remains non-negligible. A thorough knowledge and understanding of anatomic and electrical specificities according to underlying phenotype are essential in addressing these complex cases. Considering the major consequences associated with AV block in patients with complex congenital heart disease, particularly those without low risk access for transvenous ventricular pacing (eg, single ventricle physiology or Eisenmenger syndrome), the individual risk-benefit ratio should be carefully evaluated. The decision to defer ablation may be the wisest approach in selected patients with either infrequent or hemodynamically tolerated arrhythmias, or when the location of the AV conduction pathways remains uncertain. This narrative review aims to synthetize existing literature on catheter ablation of AV nodal reentrant tachycardia in congenital heart disease, to present main features of common associated pathologies, and to discuss approaches to mapping and safely ablating the slow AV nodal pathway in challenging cases.

Drug-Induced Arrhythmias: A Scientific Statement From the American Heart Association.

Many widely used medications may cause or exacerbate a variety of arrhythmias. Numerous antiarrhythmic agents, antimicrobial drugs, psychotropic medications, and methadone, as well as a growing list of drugs from other therapeutic classes (neurological drugs, anticancer agents, and many others), can prolong the QT interval and provoke torsades de pointes. Perhaps less familiar to clinicians is the fact that drugs can also trigger other arrhythmias, including bradyarrhythmias, atrial fibrillation/atrial flutter, atrial tachycardia, atrioventricular nodal reentrant tachycardia, monomorphic ventricular tachycardia, and Brugada syndrome. Some drug-induced arrhythmias (bradyarrhythmias, atrial tachycardia, atrioventricular node reentrant tachycardia) are significant predominantly because of their symptoms; others (monomorphic ventricular tachycardia, Brugada syndrome, torsades de pointes) may result in serious consequences, including sudden cardiac death. Mechanisms of arrhythmias are well known for some medications but, in other instances, remain poorly understood. For some drug-induced arrhythmias, particularly torsades de pointes, risk factors are well defined. Modification of risk factors, when possible, is important for prevention and risk reduction. In patients with nonmodifiable risk factors who require a potentially arrhythmia-inducing drug, enhanced electrocardiographic and other monitoring strategies may be beneficial for early detection and treatment. Management of drug-induced arrhythmias includes discontinuation of the offending medication and following treatment guidelines for the specific arrhythmia. In overdose situations, targeted detoxification strategies may be needed. Awareness of drugs that may cause arrhythmias and knowledge of distinct arrhythmias that may be drug-induced are essential for clinicians. Consideration of the possibility that a patient's arrythmia could be drug-induced is important.

Relationship between heart rate on atrioventricular node reentrant tachycardia sustaining and slow path position during procedure of slow path modified ablation using three-dimensional mapping system / 中国介入影像与治疗学

Objective: To observe the relationship between heart rate on atrioventricular node reentrant tachycardia (AVNRT) sustaining and slow path position during procedure of slow path modified ablation using three-dimensional mapping system. Methods: Modified ablation of slow pathway under three-dimensional mapping system was performed in 98 patients with slow-fast (S-F) AVNRT confirmed by invasive electrophysiology examination. The successful target (the site of slow-pathway) and standard His bundle were marked using three-dimensional mapping system, and the distance (Distance A) between the successful target and standard His bundle was measured. The relationship between heart rate in AVNRT and Distance A was analyzed. Results: Distance A was successfully obtained in 96 patients, including 64 tachycardia induced without infusion of isoproterenol, the heart rate was (179.77±29.22)bpm and relevant Distance A was (13.56±5.06)mm, also 32 tachycardia induced with infusion of isoproterenol, the heart rate was (174.91±17.41)bpm and relevant Distance A was (12.43±3.70)mm. No obvious correlation between heart rate and slow path position was found among the above 96 patients (rs=0.048, -0.190; P=0.705, 0.298). Conclusion: There was no obvious correlation between patient's heart rate on AVNRT sustaining and slow path position druing the procedure of slow path modified ablation using three-dimensional mapping system.

Slow/Fast Atrioventricular Nodal Reentrant Tachycardia Using the Inferolateral Left Atrial Slow Pathway: Role of the Resetting Response to Select the Ablation Target.

Background We describe a technique to localize the ablation target in patients with an unusual variant of slow/fast atrioventricular nodal reentrant tachycardia (AVNRT) using a slow pathway connecting to the basal inferolateral left atrium. Methods Consecutive patients with slow/fast AVNRT were included. During stable slow/fast AVNRT, a single late atrial extrastimulus (AES) was delivered at the inferolateral left atrium near the mitral annulus. Advancing the next His bundle potential by ≥5 ms, followed by resetting of the tachycardia cycle length, indicated that the AES engaged the anterograde slow pathway. The latest AES resetting AVNRT was considered to be in close proximity to the atrial end of the anterograde slow pathway and was selected as the ablation target. Results In 10 of 843 (1.2%) patients, ablation at the inferolateral left atrium was required. All patients had had failed ablation at the inferior triangle of Koch and roof of the coronary sinus. In all 10 patients, a late AES advanced the His bundle potential by ≥10 ms and reset the tachycardia. Ablation at that site eliminated slow pathway conduction and terminated the tachycardia. Ablation was successful at the site of the latest AES, delivered 49±12 ms after the onset of the His bundle potential. No recurrent tachycardia was noted at 1 year of follow-up. Conclusions The inferolateral left atrium slow pathway is used in a small subset of patients with slow/fast AVNRT. Accurate localization of the ablation target can be achieved by delivering late AES during AVNRT (resetting response).

[3D electronic anatomy mapping guided radiofrequency catheter ablation in 95 children with atrioventricular nodal reentrant tachycardia].

Objective: To investigate the clinical features and evaluate the efficacy of radiofrequency catheter ablation (RFCA) guided by 3D electronic-anatomy mapping system (CARTO3 System) in children with atrioventricular nodal reentrant tachycardia (AVNRT). Methods: This was a retrospective case-controlled study. Data were collected from 95 children with AVNRT who underwent RFCA using CARTO3 System in the first hospital of Tsinghua University from January 2014 to December 2017. The onset age, characteristic of electrophysiology and anatomy feature of Koch triangle were analyzed. The efficacy and safety of ablation and X-ray fluoroscopy were compared with control 135 children with AVNRT who underwent RFCA without using CARTO3 System. The t test or the chi-square test was used for group comparison. Linear regression equation was established for correlation analysis. Results: The onset age of the 95 children (male 55, female 40; the average age (8.0±3.6) years) with AVNRT was (0.2-17.0) years and 23(24.2%) children were less than 3 years old. Electrophysiologic study showed that 84.2% (80 cases) was AVNRT-slow fast (SF), 11.6% (11 cases) AVNRT-slowslow and 4.2%(4 cases) AVNRT-fast slow. The phenomena of atrio-Hisian(AH) jump occurred in 65.3% and the interval of AH jump was (73.0±10.6) ms. The height of Koch triangle (CSo-His) was (22.3±5.8) mm and related with the weight of children (Y=0.171X+ 16.660, r(2)=0.224, P<0.001).The distance between the successful ablation target and the lowest point of His zone (ABL-His) was (11.7±2.6) mm. And there was no relation with the body weight(Y=-0.005X + 11.650, r(2)=0.001, P=0.780) and CSo-His (Y=0.072X+9.914, r(2)=0.030, P=0.171). The acute success rate was 97.9% (93/95) and recurrent rate was 5.4% (5/93) during follow-up. No obvious complication was reported. Compared with control group, the fluoroscopy time ((3.3±2.5) vs. (10.7±5.8) min, t=13.190, P<0.05), radiation dose ((5.4±4.9) vs. (15.5±6.3) mGy, t=13.660, P<0.05), and dose area product (514±445) vs. (2 478±415) mGy·cm(2), t=33.850, P<0.05) were decreased significantly. Conclusions: AVNRT-SF was the most common type of AVNRT. AVNRT incidence in infant and toddlers is lower than that in elder children. CSo-His is correlated with the body weight. ABL-His is relatively fixed. There is no correlation between ABL-His and the body weight and also no correlation between ABL-His and CSo-His. RFCA of AVNRT in children using the CARTO3 system is safe, effective and minimizes X-ray fluoroscopy.

Predictors of Zero X-Ray Ablation for Supraventricular Tachycardias in a Nationwide Multicenter Experience.

BACKGROUND: This multicenter, prospective study evaluated the determinants of zero-fluoroscopy (ZFL) ablation of supraventricular tachycardias. METHODS AND RESULTS: Four hundred thirty patients (215 male, 55.4±22.1 years) with indication to electrophysiological study or ablation of supraventricular tachycardias were enrolled. All participating physicians agreed to follow the as low as reasonably achievable policy. A procedure was defined as ZFL when no fluoroscopy was used. The total fluoroscopy time inversely correlated to the number of procedures previously performed by each operator since study start (r=-0.112; P=0.02). Two hundred eighty-nine procedures (67.2%) were ZFL; multivariable analysis identified as predictors of ZFL: procedure after the 30th for each operator, compared with procedures up to the ninth (P=0.011; hazard ratio, 3.49; 95% confidence interval [CI], 1.79-6.80); the type of arrhythmia (P=0.031; electrophysiological study and atrioventricular nodal reentry tachycardia ablation having the highest probability of ZFL; hazard ratio, 6.87; 95% CI, 2.08-22.7 and hazard ratio, 2.02; 95% CI, 1.04-3.91, respectively); the operator's (P=0.002) and patient's age (P=0.009). Among operators, achievement of ZFL varied from 0% to 100%; 8 (22.8%) operators achieved ZFL in <25% of their procedures; 17 (48.6%) operators achieved ZFL in >75% of their procedures. The probability of ZFL increased by 2.8% (hazard ratio, 0.98; 95% CI, 0.97-0.99) as patient's age decreased by 1 year. Acute procedural success was obtained in all cases. CONCLUSIONS: The use of 3-dimensional mapping system completely avoided the use of fluoroscopy in most cases, with very low fluoroscopy time in the remaining and high safety and effectiveness profiles. Achievement of ZFL was predicted by the type of arrhythmia, operator's experience, and patient's age.

3D electronic anatomy mapping guided radiofrequency catheter ablation in 95 children with atrioventricular nodal reentrant tachycardia / 中华儿科杂志

Objective@#To investigate the clinical features and evaluate the efficacy of radiofrequency catheter ablation (RFCA) guided by 3D electronic-anatomy mapping system (CARTO3 System) in children with atrioventricular nodal reentrant tachycardia (AVNRT).@*Methods@#This was a retrospective case-controlled study. Data were collected from 95 children with AVNRT who underwent RFCA using CARTO3 System in the first hospital of Tsinghua University from January 2014 to December 2017. The onset age, characteristic of electrophysiology and anatomy feature of Koch triangle were analyzed. The efficacy and safety of ablation and X-ray fluoroscopy were compared with control 135 children with AVNRT who underwent RFCA without using CARTO3 System. The t test or the chi-square test was used for group comparison. Linear regression equation was established for correlation analysis.@*Results@#The onset age of the 95 children (male 55, female 40; the average age (8.0±3.6) years) with AVNRT was (0.2-17.0) years and 23(24.2%) children were less than 3 years old. Electrophysiologic study showed that 84.2% (80 cases) was AVNRT-slow fast (SF), 11.6% (11 cases) AVNRT-slowslow and 4.2%(4 cases) AVNRT-fast slow. The phenomena of atrio-Hisian(AH) jump occurred in 65.3% and the interval of AH jump was (73.0±10.6) ms. The height of Koch triangle (CSo-His) was (22.3±5.8) mm and related with the weight of children (Y=0.171X+ 16.660, r2=0.224, P<0.001).The distance between the successful ablation target and the lowest point of His zone (ABL-His) was (11.7±2.6) mm. And there was no relation with the body weight(Y=-0.005X + 11.650, r2=0.001, P=0.780) and CSo-His (Y=0.072X+9.914, r2=0.030, P=0.171). The acute success rate was 97.9% (93/95) and recurrent rate was 5.4% (5/93) during follow-up. No obvious complication was reported. Compared with control group, the fluoroscopy time ((3.3±2.5) vs. (10.7±5.8) min, t=13.190, P<0.05), radiation dose ((5.4±4.9) vs. (15.5±6.3) mGy, t=13.660, P<0.05), and dose area product (514±445) vs. (2 478±415) mGy·cm2, t=33.850, P<0.05) were decreased significantly.@*Conclusions@#AVNRT-SF was the most common type of AVNRT. AVNRT incidence in infant and toddlers is lower than that in elder children. CSo-His is correlated with the body weight. ABL-His is relatively fixed. There is no correlation between ABL-His and the body weight and also no correlation between ABL-His and CSo-His. RFCA of AVNRT in children using the CARTO3 system is safe, effective and minimizes X-ray fluoroscopy.

[Study on the three-dimensional mapping to reduce the X-ray exposure dose of interventional doctors in radiofrequency catheter ablation of atrioventricular nodal reentry tachycardia].

Objective: To explore the advantage of radiofrequency catheter ablation under the three-dimensional mapping in the treatment of atrioventricular nodal reentrant tachycardia (AVNRT) in reducing the X-ray exposure dose of interventional doctors. Methods: 79 patients with AVNRT, in the first hospital of Shanxi Medical University from January 2015 to June 2016, performed to do radiofrequency catheter ablation treatment were selected, and according to the random number method were divided into two-dimensional mapping group and three-dimensional mapping group. The two-dimensional mapping group was mapped the ablation target at the X-ray, while the ablation target was mapped by CARTO 3 system in the three-dimensional mapping group. Compare the X-ray fluoroscopy time, success rate, complications rate and doctor's X-ray exposure dose between the two groups. Results: Compared with the two-dimensional mapping group, acute success rate and complication rate of the three dimensional mapping group were not statistically significant (P>0.05) , while the X-ray fluoroscopy time and the X-ray dose of the three-dimensional mapping group decreased significantly, the difference was statistically significant (P<0.05) . Conclusion: Three-dimensional mapping can significantly reduce the X-ray irradiation time and interventional doctor's X-ray exposure dose in radiofrequency catheter ablation of AVNRT patients and the potential hazards of ionizing radiation on the human body.

Atrioventricular Nodal Reentrant Tachycardia in Patients With Congenital Heart Disease: Outcome After Catheter Ablation.

BACKGROUND: The relationship of atrioventricular nodal reentrant tachycardia to congenital heart disease (CHD) and the outcome of catheter ablation in this population have not been studied adequately. METHODS AND RESULTS: A multicenter retrospective study was performed on patients with CHD who had atrioventricular nodal reentrant tachycardia and were treated with catheter ablation. There were 109 patients (61 women), aged 22.1±13.4 years. The majority, 86 of 109 (79%), had CHD resulting in right heart pressure or volume overload. Patients were divided into 2 groups: group A (n=51) with complex CHD and group B (n=58) with simple CHD. There were no significant differences between groups in patients' growth parameters, use of 3-dimensional imaging, and type of ablation (radiofrequency versus cryoablation). Procedure times (251±117 versus 174±94 minutes; P=0.0006) and fluoroscopy times (median 20.8 versus 16.6 minutes; P=0.037) were longer in group A versus group B. There were significant differences between groups in the acute success of ablation (82% versus 97%; P=0.04), risk of atrioventricular block (14 versus 0%; P=0.004), and need for chronic pacing (10% versus 0%; P=0.008). There was no permanent atrioventricular block in patients who underwent cryoablation. After 3.2±2.7 years of follow-up, long-term success was 86% in group A and 100% in group B (P=0.004). CONCLUSIONS: Atrioventricular nodal reentrant tachycardia can complicate the course of patients with CHD. This study demonstrates that the outcome of catheter ablation is favorable in patients with simple CHD. Patients with complex CHD have increased risk of procedural failure and atrioventricular block.

Nonfluoroscopic Imaging as Guidance for Radiofrequency Ablation of Atrioventricular Nodal Reentrant Tachycardia after Mustard Repair.

Most tachycardias in the pulmonary venous atrium are inaccessible by direct means and require either a retrograde approach or a transseptal approach for ablation. We present a case in which successful radiofrequency ablation of common atrioventricular nodal reentrant tachycardia was accomplished via a retrograde transaortic approach guided by nonfluoroscopic mapping with use of the NavX™ mapping system. The patient was a 49-year-old woman who at the age of 4 years had undergone Mustard repair for complete dextrotransposition of the great arteries. Three-dimensional reconstructions of the ascending aorta, right ventricle, systemic venous atrium, left ventricle, and superior vena cava-inferior vena cava baffle complex were created, and the left-sided His bundle was marked. After a failed attempt at ablation from the systemic venous side, we eliminated the atrioventricular nodal reentrant tachycardia by ablation from the pulmonary venous side. This case is, to our knowledge, the first report of successful radiofrequency ablation of common atrioventricular nodal reentrant tachycardia after Mustard repair for this congenital cardiac malformation in which ablation was guided by 3-dimensional nonfluoroscopic imaging. This imaging technique enabled accurate anatomic location of the ablation catheters in relation to the His bundle marked from the systemic venous side.

Study on the three-dimensional mapping to reduce the X-ray exposure dose of interventional doctors in radiofrequency catheter ablation of atrioventricular nodal reentry tachycardia / 中华劳动卫生职业病杂志

Objective@#To explore the advantage of radiofrequency catheter ablation under the three-dimensional mapping in the treatment of atrioventricular nodal reentrant tachycardia (AVNRT) in reducing the X-ray exposure dose of interventional doctors.@*Methods@#79 patients with AVNRT, in the first hospital of Shanxi Medical University from January 2015 to June 2016, performed to do radiofrequency catheter ablation treatment were selected, and according to the random number method were divided into two-dimensional mapping group and three-dimensional mapping group. The two-dimensional mapping group was mapped the ablation target at the X-ray, while the ablation target was mapped by CARTO 3 system in the three-dimensional mapping group. Compare the X-ray fluoroscopy time, success rate, complications rate and doctor’s X-ray exposure dose between the two groups.@*Results@#Compared with the two-dimensional mapping group, acute success rate and complication rate of the three dimensional mapping group were not statistically significant (P>0.05) , while the X-ray fluoroscopy time and the X-ray dose of the three-dimensional mapping group decreased significantly, the difference was statistically significant (P<0.05) .@*Conclusion@#Three-dimensional mapping can significantly reduce the X-ray irradiation time and interventional doctor’s X-ray exposure dose in radiofrequency catheter ablation of AVNRT patients and the potential hazards of ionizing radiation on the human body.

Catheter Ablation of Atypical Atrioventricular Nodal Reentrant Tachycardia.

BACKGROUND: Because of its low prevalence, data on atypical atrioventricular nodal reentrant tachycardia (AVNRT) are scarce, and the optimal ablation method has not been established. Our study aimed at assessing the efficacy and safety of conventional slow pathway ablation, as applied for typical cases, in atypical AVNRT. METHODS: We studied 2079 patients with AVNRT subjected to slow pathway ablation. In 113 patients, mean age 48.5±18.1 years, 68 female, atypical AVNRT or coexistent atypical and typical AVNRT without other concomitant arrhythmia was diagnosed. Ablation data and outcomes were compared with a group of age- and sex-matched control patients with typical AVNRT. RESULTS: Fluoroscopy and radiofrequency current delivery times were not different in the atypical and typical groups, 20.3±12.2 versus 20.8±12.9 minutes (P=0.730) and 5.9±5.0 versus 5.5±4.5 minutes (P=0.650), respectively. Slow pathway ablation was accomplished from the right septum in 110 patients, and from the left septum in 3 patients, in the atypical group. There was no need for additional ablation lesions at other anatomic sites, and no cases of atrioventricular block were encountered. Recurrence rates of the arrhythmia were 5.6% in the atypical (6/108 patients) and 1.8% in the typical (2/111 patients) groups in the next 3 months following ablation (P=0.167). CONCLUSIONS: Conventional ablation at the anatomic area of the slow pathway is the therapy of choice for symptomatic AVNRT, regardless of whether the typical or atypical form is present.

Spontaneous Transition of Double Tachycardias with Atrial Fusion in a Patient with Wolff-Parkinson-White Syndrome.

Among patients with Wolff-Parkinson-White syndrome, atrioventricular reciprocating tachycardia (AVRT) and atrioventricular nodal reentrant tachycardia (AVNRT) can coexist in a single patient. Direct transition of both tachycardias is rare; however, it can occur after premature atrial or ventricular activity if the cycle lengths of the two tachycardias are similar. Furthermore, persistent atrial activation by an accessory pathway (AP) located outside of the AV node during ongoing AVNRT is also rare. This article describes a case of uncommon atrial activation by an AP during AVNRT and gradual transition of the two supraventricular tachycardias without any preceding atrial or ventricular activity in a patient with preexcitation syndrome.

Pitfalls of Atrial Advancement Using a Ventricular Extra-stimulus During Supraventricular Tachycardia

The delivery of single His-refractory ventricular extra-stimulus during supraventricular tachycardia is useful to identify the mechanism of the tachycardia. We present the different responses based on the ventricular extra-stimulus site. Our findings demonstrate that the atrial activation via an accessory pathway was not advanced based on the ventricular pacing site. Therefore, atrioventricular tachycardia could masquerade as atrioventricular nodal reentrant tachycardia.

Spontaneous Transition of Double Tachycardias with Atrial Fusion in a Patient with Wolff-Parkinson-White Syndrome

Among patients with Wolff-Parkinson-White syndrome, atrioventricular reciprocating tachycardia (AVRT) and atrioventricular nodal reentrant tachycardia (AVNRT) can coexist in a single patient. Direct transition of both tachycardias is rare; however, it can occur after premature atrial or ventricular activity if the cycle lengths of the two tachycardias are similar. Furthermore, persistent atrial activation by an accessory pathway (AP) located outside of the AV node during ongoing AVNRT is also rare. This article describes a case of uncommon atrial activation by an AP during AVNRT and gradual transition of the two supraventricular tachycardias without any preceding atrial or ventricular activity in a patient with preexcitation syndrome.

Fibrilação atrial durante taquicardia por reentrada nodal atrioventricular: achado sugestivo da presença de via superiorcomum nodal / Atrial fibrillation during atrioventricular nodal reentry tachycardia: a suggestive finding favoring the presence of the upper common nodal pathway

Na taquicardia por reentrada nodal atrioventricular, a necessidade do átrio para a manutenção da taquicardia é controverso. Descrevemos um caso de fibrilação atrial ocorrendo durante taquicardia por reentrada nodal atrioventricular sem afetar o ciclo da arritmia, e discutimos as evidências favorecendo a presença de umavia comum superior.

In Atrioventricular Nodal Reentry Tachycardia the requirement of the atrium for the maintenance oftachycardia is controversial. We describe a case of atrial fibrillation that occurred during Atrioventricular Nodal Reentry Tachycardia without affecting the arrhythmia cycle, and discuss the evidences favoring the presence ofan upper common pathway.

Coexistent Types of Atrioventricular Nodal Re-Entrant Tachycardia: Implications for the Tachycardia Circuit.

BACKGROUND: There is evidence that atypical fast-slow and typical atrioventricular nodal re-entrant tachycardia (AVNRT) do not use the same limb for fast conduction, but no data exist on patients who have presented with both typical and atypical forms of this tachycardia. We compared conduction intervals during typical and atypical AVNRT that occurred in the same patient. METHODS AND RESULTS: In 20 of 1299 patients with AVNRT, both typical and atypical AVNRT were induced at electrophysiology study by pacing maneuvers and autonomic stimulation or occurred spontaneously. The mean age of the patients was 47.6±10.9 years (range, 32-75 years), and 11 patients (55%) were women. Tachycardia cycle lengths were 368.0±43.1 and 365.8±41.1 ms, and earliest retrograde activation was recorded at the coronary sinus ostium in 60% and 65% of patients with typical and atypical AVNRT, respectively. Thirteen patients (65%) displayed atypical AVNRT with fast-slow characteristics. By comparing conduction intervals during slow-fast and fast-slow AVNRT in the same patient, fast pathway conduction times during the 2 types of AVNRT were calculated. The mean difference between retrograde fast pathway conduction during slow-fast AVNRT and anterograde fast pathway conduction during fast-slow AVNRT was 41.8±39.7 ms and was significantly different when compared with the estimated between-measurement error (P=0.0055). CONCLUSIONS: Our data provide further evidence that typical slow-fast and atypical fast-slow AVNRT use different anatomic pathways for fast conduction.