R534C mutation in hERG causes a trafficking defect in iPSC-derived cardiomyocytes from patients with type 2 long QT syndrome.

Patient-specific cardiomyocytes obtained from induced pluripotent stem cells (CM-iPSC) offer unprecedented mechanistic insights in the study of inherited cardiac diseases. The objective of this work was to study a type 2 long QT syndrome (LQTS2)-associated mutation (c.1600C > T in KCNH2, p.R534C in hERG) in CM-iPSC. Peripheral blood mononuclear cells were isolated from two patients with the R534C mutation and iPSCs were generated. In addition, the same mutation was inserted in a control iPSC line by genome editing using CRISPR/Cas9. Cells expressed pluripotency markers and showed spontaneous differentiation into the three embryonic germ layers. Electrophysiology demonstrated that action potential duration (APD) of LQTS2 CM-iPSC was significantly longer than that of the control line, as well as the triangulation of the action potentials (AP), implying a longer duration of phase 3. Treatment with the IKr inhibitor E4031 only caused APD prolongation in the control line. Patch clamp showed a reduction of IKr on LQTS2 CM-iPSC compared to control, but channel activation was not significantly affected. Immunofluorescence for hERG demonstrated perinuclear staining in LQTS2 CM-iPSC. In conclusion, CM-iPSC recapitulated the LQTS2 phenotype and our findings suggest that the R534C mutation in KCNH2 leads to a channel trafficking defect to the plasma membrane.

Short QT syndrome in pediatrics.

Short QT syndrome is a malignant cardiac disease characterized by the presence of ventricular tachyarrhythmias leading to syncope and sudden cardiac death. Currently, international guidelines establish diagnostic criteria when QTc is below 340 ms. This entity is one of the main diseases responsible for sudden cardiac death in the pediatric population. In recent years, clinical, genetic and molecular advances in pathophysiological mechanisms related to short QT syndrome have improved diagnosis, risk stratification, and preventive measures. Despite these advances, automatic implantable cardiac defibrillator remains the most effective measure. Currently, six genes have been associated with short QT syndrome, which account for nearly 60% of clinically diagnosed families. Here, we review the main clinical hallmarks of the disease, focusing on the pediatric population.

Catecholaminergic polymorphic ventricular tachycardia: a current overview.

Catecholaminergic polymorphic ventricular tachycardia occurs in healthy children and young adults causing syncope and sudden cardiac death. This is a familial disease, which affect de novo mutation in 50% of the cases. At least two causative genes have been described to be localized in the chromosome 1; mutation of the ryanodine receptor gene and calsequestrin gene. The classical clinical presentation is syncope triggered by exercise and emotion in children and adolescents with no structural heart disease. Polymorphic ventricular tachycardia during treadmill testing, or after isoproterenol infusion, is the most common feature. Therapeutic options include, beta-blockers, calcium-channel blockers and, an implantable cardioverter defibrillator is indicated in high-risk patients. Risk stratification of this disease is very challenging, since some risk factors proved to be useful in some series but not in others. However, family history of sudden cardiac death and symptoms initiated in very young children are important predictors.

Contribution of the electrophysiological and anatomical analysis of the atypical atrioventricular nodal tachycardia circuit.

OBJECTIVES: To analyze retrograde conduction during junctional ectopic tachycardia (JET) episodes and investigate the existence of a relationship between the presence of a retrograde block and the risk of atrioventricular block (AVB) development during radiofrequency ablation procedures in patients with nodal atrioventricular tachycardia (NAVT). METHODS: 145 male and female patients aged 16-84 years, with NAVT who had undergone radiofrequency catheter ablation in the posteroseptal region of the right atrium were studied. Evaluation criteria were anatomical location and electrophysiological behavior of retrograde conduction during NAVT, in order to understand the nodal reentrant circuit (classifying the tachycardia as typical or atypical), and monitoring of retrograde conduction during JET episodes for risk-predicting AVB events. RESULTS: Of the 145 patients studied, 132 (91%) met electrophysiological and anatomical criteria of the typical form of NAVT, and 13 (9%) of atypical form. During the ablation, 5.3% with the typical form and 30.8% of the atypical form presented risk events for AVB. After the ablation, complications were a total AVB episode in one patient and a first-degree AVB episode in another in the typical group, and one first-degree AVB in the atypical group. All three episodes were preceded by risk events and resulted in permanent nodal injury. CONCLUSION: Patients with atypical NAVT presented higher percentages of risk events for atrioventricular block than did patients with the typical form (p=0.021).A careful observation of retrograde conduction during JET episodes is vital in order to avoid permanent damage in AV nodal conduction, such as TAVB, after the ablation procedure.

Contribuição da análise eletrofisiológica e anatômica do circuito atípico da taquicardia atrioventricular nodal / Contribution of the electrophysiological and anatomical analysis of the atypical atrioventricular nodal tachycardia circuit

OBJETIVOS: Analisar a condução retrógrada durante os episódios de ritmo juncional ectópico acelerado (JET) e avaliar a existência da relação entre a presença de um bloqueio retrógrado e o risco de desenvolvimento de bloqueio atrioventricular (BAV) durante os procedimentos de ablação por radiofreqüência de pacientes portadores de taquicardia atrioventricular nodal (TAVN). MÉTODOS: Foram 145 pacientes portadores de TAVN, de ambos os sexos, com 16 a 84 anos submetidos à ablação com cateter de radiofreqüência na região póstero-septal do átrio direito. Critérios avaliados: localização anatômica e comportamento eletrofisiológico da condução retrógrada durante TAVN (definindo a taquicardia como típica ou atípica) e monitorização da condução retrógrada durante o JET para eventos de risco para BAV. RESULTADOS: Dos 145 pacientes estudados, 132 (91 por cento) preencheram critérios eletrofisiológicos e anatômicos da forma típica da TAVN e 13 (9 por cento), da atípica. Durante a ablação, 5,3 por cento do grupo das típicas e 30,8 por cento das atípicas apresentaram eventos de risco para BAV. Complicações após ablação foram um episódio de BAV total e outro de BAV de primeiro grau nas típicas e um de BAV de primeiro grau nas atípicas. Os três episódios foram precedidos de eventos de risco que resultaram em uma injúria nodal após procedimento. CONCLUSÃO: Portadores de TAVN atípica apresentaram porcentualmente mais eventos preditores de risco para BAV do que os da típica (p = 0,021), sendo fundamental a observação criteriosa da condução retrógrada durante o JET, afim de se evitar permanente da condução nodal, como o BAVT, após o procedimento ablativo.

OBJECTIVES: To analyze retrograde conduction during junctional ectopic tachycardia (JET) episodes and investigate the existence of a relationship between the presence of a retrograde block and the risk of atrioventricular block (AVB) development during radiofrequency ablation procedures in patients with nodal atrioventricular tachycardia (NAVT). METHODS: 145 male and female patients aged 16-84 years, with NAVT who had undergone radiofrequency catheter ablation in the posteroseptal region of the right atrium were studied. Evaluation criteria were anatomical location and electrophysiological behavior of retrograde conduction during NAVT, in order to understand the nodal reentrant circuit (classifying the tachycardia as typical or atypical), and monitoring of retrograde conduction during JET episodes for risk-predicting AVB events. RESULTS: Of the 145 patients studied, 132 (91 percent) met electrophysiological and anatomical criteria of the typical form of NAVT, and 13 (9 percent) of atypical form. During the ablation, 5.3 percent with the typical form and 30.8 percent of the atypical form presented risk events for AVB. After the ablation, complications were a total AVB episode in one patient and a first-degree AVB episode in another in the typical group, and one first-degree AVB in the atypical group. All three episodes were preceded by risk events and resulted in permanent nodal injury. CONCLUSION: Patients with atypical NAVT presented higher percentages of risk events for atrioventricular block than did patients with the typical form (p=0.021).A careful observation of retrograde conduction during JET episodes is vital in order to avoid permanent damage in AV nodal conduction, such as TAVB, after the ablation procedure.

Cytogenetic analysis in lymphocytes from workers occupationally exposed to low levels of ionizing radiation.

The aim of the present study was to perform a cytogenetic analysis in peripheral lymphocytes of 36 individuals occupationally exposed to low levels of ionizing radiation, and compare the results with 36 controls, using the chromosomal aberrations test (CA), sensitivity to bleomycin and cytokinesis-blocked micronucleus assay (MN). The frequencies of CA/100 cells observed for the exposed workers were not significantly higher than in controls (P>0.05). The mean break/cell (b/c) for the controls and exposed workers was 0.59±0.39 and 0.57±0.29, respectively (P>0.01). The MN frequencies were significantly increased (P<0.01) in exposed workers (6.13±3.18) in comparison with controls (5.11±3.85). The mean MN was also statistically higher in the non-smoker exposed when compared with non-smoker controls, 5.80±3.09 and 5.15±4.08, respectively (P<0.01). The cytogenetic analysis of MN proved to be the most sensitive biological marker to assess the cellular response to low levels of irradiation.

Effects of right bundle branch block on the antidromic circus movement tachycardia in patients with presumed atriofascicular pathways.

BACKGROUND: The typical and most common tachycardia in patients with atriofascicular pathways is a macro reentrant tachycardia, with anterograde conduction over the decrementally conducting bypass tract and retrograde conduction over the right bundle branch-His-AV node axis resulting in a short V-right bundle branch and short V-H interval. OBJECTIVES: To report on changes in rate and QRS configuration when right bundle branch block (RBBB) develops spontaneously during antidromic tachycardia using an atriofascicular fiber. METHODS: Three of 25 patients with an antidromic circus movement tachycardia using a right-sided atriofascicular pathway showed episodes of right bundle branch block (RBBB) during ventriculo-atrial conduction. Effect of retrograde RBBB on tachycardia rate and QRS configuration was studied using intracardiac and extracardiac recordings. RESULTS: All 3 patients showed prolongation of their V-A interval when retrograde RBBB occurred during tachycardia, resulting in a longer tachycardia cycle length. The VA time increase ranged from 85 to 100 msec, with a mean 346 +/- 5 msec. Two of the 3 patients also showed a change in QRS configuration due to a more leftward shift of the frontal plane QRS axis. CONCLUSION: Rate changes in antidromic tachycardia in patients with atriofascicular fibers can be based on a shift in VA conduction from one bundle branch to the other. This may be accompanied by changes in the frontal plane QRS axis because of a change in ventricular activation sequence.

Inaccurate electrocardiographic interpretation of long QT: the majority of physicians cannot recognize a long QT when they see one.

BACKGROUND: Physicians in all fields of medicine may encounter patients with long QT syndrome (LQTS). It is important to define the percentage of physicians capable of distinguishing QT intervals that are long from those that are normal because LQTS can be lethal when left untreated. OBJECTIVES: The purpose of this study was to define the percentage of physicians in the different disciplines of medicine who can recognize a long QT when they see one. METHODS: We presented the ECGs of two patients with LQTS and two healthy females to 902 physicians (25 world-renowned QT experts, 106 arrhythmia specialists, 329 cardiologists, and 442 noncardiologists) from 12 countries. They were asked to measure the QT, calculate the QTc (the QT interval corrected for the heart rate), and determine whether the QT is normal or prolonged. RESULTS: For patients with LQTS, >80% of arrhythmia experts but <50% of cardiologists and <40% of noncardiologists calculated the QTc correctly. Underestimation of the QTc of patients with LQTS and overestimation of the QTc of healthy patients were common. Interobserver agreement was excellent among QT experts, moderate among arrhythmia experts, and low among cardiologists and noncardiologists (kappa coefficient = 0.82, 0.44, and < 0.3, respectively). Correct classification of all QT intervals as either "long" or "normal" was achieved by 96% of QT experts and 62% of arrhythmia experts, but by only <25% of cardiologists and noncardiologists. CONCLUSIONS: Most physicians, including many cardiologists, cannot accurately calculate a QTc and cannot correctly identify a long QT.

Short atrioventricular Mahaim fibers: observations on their clinical, electrocardiographic, and electrophysiologic profile.

UNLABELLED: Short A-V manheim fiber. INTRODUCTION: A short atrioventricular decrementally conducting accessory pathway is an uncommon variant of preexcitation. Available data from small series suggest that their decremental properties might not be caused by A-V nodal-like tissue. METHODS: We compared clinical, electrocardiographic and electrophysiologic parameters in two groups of patients: 8 patients with a short A-V Mahaim pathway (Group A), and 33 patients with atriofascicular pathways (Group B). Radiofrequency catheter ablation was carried out guided by activation mapping at the annulus in Group A patients and targeting the "M" potential in Group B patients. RESULTS: After ablation of all associated rapidly conducting bypass tracts, 7 of the 8 Group A patients showed clear preexcitation. In only 1 of 8 patients the short A-V Mahaim fiber was actively engaged in a reentrant tachycardia circuit. During radiofrequency catheter ablation an automatic rhythm occurred in 4 of 8 patients. Intravenous adenosine caused conduction a block in the Mahaim fiber in 3 of the 5 patients tested. In group B, no patient showed clear preexcitation (P<00001) while 72% had a minimal preexcitation pattern. Twenty-nine of the 33 patients had a circus movement tachycardia with AV conduction over the atriofascicular fiber. During radiofrequency catheter ablation 30 of 33 patients showed accessory pathway automaticity. Adenosine caused transient block at the atriofascicular pathway in 11 (92%) of the 12 patients tested. CONCLUSIONS: While short decrementally conducting right-sided accessory pathways show a typical ECG pattern different from atriofascicular pathways, their electrophysiologic properties do not seem to be uniform. Those pathways can be successfully interrupted by catheter ablation.

The electrocardiogram during sinus rhythm and tachycardia in patients with Mahaim fibers: the importance of an "rS" pattern in lead III.

OBJECTIVES: The purpose of the study was to identify the electrocardiographic (ECG) characteristics of the Mahaim fiber. BACKGROUND: Mahaim fibers are slowly conducting accessory pathways reaching into the right ventricle. They often play a role in tachycardias. METHODS: We retrospectively analyzed 40 patients with Mahaim fibers. Five patients had associated Wolff-Parkinson-White syndrome and were excluded from the study. Two patients had a short atrioventricular decremental accessory pathway and were also excluded. The remaining 33 patients had a tachycardia with anterograde conduction over a Mahaim fiber. Twenty were female. Their mean age was 24 +/- 10 years. RESULTS: The most common pattern of minimal preexcitation during sinus rhythm was an rS pattern in lead III. This was found in 20 patients. There was a match between the presence of rS in lead III during sinus rhythm and left axis deviation during tachycardia with anterograde conduction over the Mahaim fiber. After ablation, a different QRS pattern emerged in lead III, indicating the absence of conduction over the Mahaim fiber. To obtain information on the prevalence of an rS pattern in lead III in age-matched controls with palpitations and without structural heart disease, the 12-lead ECG of 200 young individuals were examined. An rS pattern in lead III was found in 6%. CONCLUSIONS: A narrow QRS with an rS pattern in lead III during sinus rhythm in a patient with a history of palpitations should alert the physician to the possibility of a Mahaim fiber. During tachycardia, these patients typically show a left bundle branch block-like QRS complex with left axis deviation.

Electrocardiogram during tachycardia in patients with anterograde conduction over a Mahaim fiber: old criteria revisited.

OBJECTIVES: The aim of this study was to prospectively evaluate the sensitivity, specificity, and positive and negative predictive values of previously described ECG criteria to identify preexcited tachycardia due to decrementally conducting accessory pathways (QRS axis between 0 and -75 degrees , QRS width < or = 0.15 seconds, an R wave in lead I, an rS pattern in lead V(1), RS > 1 QRS transition > V(4), and cycle length between 220 and 450 ms). BACKGROUND: Preexcited tachycardia associated with decrementally conducting right-sided accessory pathways usually shows a rather "narrow" QRS complex and can be difficult to differentiate from supraventricular tachycardia (SVT) with left bundle branch block (LBBB) aberrant conduction. METHODS: We analyzed three groups of patients: 32 patients with an atriofascicular pathway (group I); 8 patients with long (n = 3) or short (n = 5) decrementally conducting right-sided AV pathway (group II); and a control group that consisted of 35 patients with SVT and LBBB (group III). RESULTS: Presence of all six criteria had 87.5% sensitivity in group I and a 0% sensitivity in group II. There were four false negatives in group I. The negative predictive value was 82.5%, with six false positives in group III (five patients with an aberrant LBBB-shaped tachycardia with ventriculoatrial conduction over an accessory AV pathway). The criterion cycle length was not helpful. CONCLUSIONS: Criteria for identifying a tachycardia with anterograde conduction over a Mahaim fiber are helpful only in atriofascicular pathways, with a sensitivity of 87.5% and a negative predictive value of 82.5%. The major cause of false positives was a tachycardia with aberrant LBBB conduction and ventriculoatrial conduction over an accessory AV pathway.

Clinical and molecular characterization of patients with catecholaminergic polymorphic ventricular tachycardia.

BACKGROUND: Mutations in the cardiac ryanodine receptor gene (RyR2) underlie catecholaminergic polymorphic ventricular tachycardia (CPVT), an inherited arrhythmogenic disease occurring in the structurally intact heart. The proportion of patients with CPVT carrying RyR2 mutations is unknown, and the clinical features of RyR2-CPVT as compared with nongenotyped CPVT are undefined. METHODS AND RESULTS: Patients with documented polymorphic ventricular arrhythmias occurring during physical or emotional stress with a normal heart entered the study. The clinical phenotype of the 30 probands and of 118 family members was evaluated, and mutation screening on the RyR2 gene was performed. Arrhythmias documented in probands were: 14 of 30 bidirectional ventricular tachycardia, 12 of 30 polymorphic ventricular tachycardia, and 4 of 30 catecholaminergic idiopathic ventricular fibrillation; RyR2 mutations were identified in 14 of 30 probands (36% bidirectional ventricular tachycardia, 58% polymorphic ventricular tachycardia, 50% catecholaminergic idiopathic ventricular fibrillation) and in 9 family members (4 silent gene carriers). Genotype-phenotype analysis showed that patients with RyR2 CPVT have events at a younger age than do patients with nongenotyped CPVT and that male sex is a risk factor for syncope in RyR2-CPVT (relative risk=4.2). CONCLUSIONS: CPVT is a clinically and genetically heterogeneous disease manifesting beyond pediatric age with a spectrum of polymorphic arrhythmias. beta-Blockers reduce arrhythmias, but in 30% of patients an implantable defibrillator may be required. Genetic analysis identifies two groups of patients: Patients with nongenotyped CPVT are predominantly women and become symptomatic later in life; patients with RyR2 CPVT become symptomatic earlier, and men are at higher risk of cardiac events. These data provide a rationale for prompt evaluation and treatment of young men with RyR2 mutations.

Cardiomiopatia arritimogênica do ventrículo direito. Valor preditivo da dispersäo do intervalo QT para avaliaçäo de risco arritmogênico e de morte súbita / Arrhythmogenic cardiomyopathy of the right ventricle. Predictive value of QT interval dispersion to assess arrhythmogenic risk and sudden death

OBJECTIVE: To determine in arrhythmogenic right ventricular cardiomyopathy the value of QT interval dispersion for identifying the induction of sustained ventricular tachycardia in the electrophysiological study or the risk of sudden cardiac death. METHODS: We assessed QT interval dispersion in the 12-lead electrocardiogram of 26 patients with arrhythmogenic right ventricular cardiomyopathy. We analyzed its association with sustained ventricular tachycardia and sudden cardiac death, and in 16 controls similar in age and sex. RESULTS: (mean +/- SD). QT interval dispersion: patients = 53.8+/-14.1ms; control group = 35.0+/-10.6ms, p=0.001. Patients with induction of ventricular tachycardia: 52.5+/-13.8ms; without induction of ventricular tachycardia: 57.5+/-12.8ms, p=0.420. In a mean follow-up period of 41+/-11 months, five sudden cardiac deaths occurred. QT interval dispersion in this group was 62.0+/-17.8, and in the others it was 51.9+/-12.8ms, p=0.852. Using a cutoff > or = 60ms to define an increase in the degree of the QT interval dispersion, we were able to identify patients at risk of sudden cardiac death with a sensitivity of 60 percent, a specificity of 57 percent, and positive and negative predictive values of 25 percent and 85 percent, respectively. CONCLUSION: Patients with arrhythmogenic right ventricular cardiomyopathy have a significant increase in the degree of QT interval dispersion when compared with the healthy population. However it, did not identify patients with induction of ventricular tachycardia in the electrophysiological study, showing a very low predictive value for defining the risk of sudden cardiac death in the population studied.

O desfibrilador externo semi-automático na parada cardiorrespiratória fora do hospital, quando cada segundo conta na sobrevivência / Automated external defibrilation, when every minute counts

Desde o final da década de 1960, os desfibriladores têm sido efetivos e apresentam sensibilidade de mais de 70 'por cento' a 80 'por cento' a reversäo de taquicardia ventricular ou fibrilaçäo ventricular. A falha na desfibrilaçäo sempre foi mais frequente na fibrilaçäo ventricular fixa, a qual é também chamada de assistolia grosseira. Entretanto, todas as modificaçöes técnicas presentes nos desfibriladores externos semi-automáticos têm permitido maior eficiência na desfibrilaçäo. Adicionalmente, com a diminuiçäo do peso, do tamanho e do custo, tais unidades podem ser disseminadas em ambientes públicos, permitindo acesso mais precosse à desfibrilaçäo. Näo devemos impedir que profissionais näo-médicos possam estar aptos a utilizar um dos desfibriladores externos semi-automático e liberar um choque terapêutico a tempo, tanto no ambiente intra como extra-hospitalar pois cada minuto é importante e preditror de sucesso ou recuperaçäo do paciente com parada cardiorrespiratória.

Modificaçäo do nódulo sinusal via cateter por energia de radiofreqüência em pacientes com taquicardia sinusal inapropriada. Avaliaçäo dos resultados imediatos e tardios / Sinus node modification by catheter using radiofrequency current in a patient with inappropriate sinus tachycardia. Evaluation of early and late results

Säo apresentados os resultados imediatos e tardios, observados com a modificaçäo do nódulo sinusial via cateter, usando-se energia de radiofreqüência, em portadora de taquicardia sinusal inapropriada. O procedimento normalizou os níveis de freqüência cardíaca nas 24h seguintes e após seis seis meses, mostrando-se, portanto,efetivo e seguro. Apesar da reduçäo da freqüência cardíaca a níveis normais, houve manutençäo dos sintomas apresentados pela paciente, sugerindo que näo säo decorridos, exclusivamente, do processo taquicárdico.

Mecanismos e dinâmica da progressão dos episódios de bloqueio atrioventricular 2: 1 para bloqueio atrioventricular de alto grau / Mechanisms and dynamics of episades of progression of 2:1 A-V block to high degree A-V

PURPOSE--To evaluate the mechanisms and dynamics of episodes of progression to high degree (HD) atrioventricular (AV) block (B) analyzed during incremental atrial pacing (St), in patients with previous 2:1 His-Purkinje (HP) AVB. METHODS--Data from 4 patients were analyzed. All of them with history of syncope and ECG exhibiting 2:1 AVB with wide QRS pattern. The AVB was in the HP system (HPS) in all. Every patient was submitted to electrophysiologic study with incremental atrial pacing, by which the conduction sequences and the AV conduction ratios (AVR) were analyzed. The basal (B) cycle length (CL) was defined as the shortest interval between two conducted beats (spontaneous or pacing-induced). The incremental atrial stimulation was performed beginning with CL 10 msec shorter than BCL until reaching 250 msec. RESULTS--Nineteen episodes of progression to HD-AVB were seen. A) With StCL between 31 and 26 of BCL, AVR were 3:1, 4:1 and 5:1, with only one blocking zone (BZ) in the HPS; B) with StCL between 24 and 22 of BCL, AVR were 5:1, 7:2, 9:2e11:3. In this situation a 2nd BZ ensues-on proximal, site of a decremental conduction, situated in the AV node (AVN) or in the HPS, and the other (distal level) always in HPS; C) with StCL between 24 and 16 of BCL, AVR were 5:1, 6:1, 10:2, 11:2 and 12:3. Here, these AVR were explained by postulating 3 BZ where 2 were in AVN and 1 in HPS, or inversely with 1 in AVN and 2 in HPS. The decremental conduction occurred in 1 or 2 out 3 BZ and an integral conduction (like 2:1 or 3:1) in the others. CONCLUSION--The BCL is the determinant of the AVR observed. As the StCL is shortened (< 26 BCL) a 2nd or 3rd BZ in the AVN or in the HPS ensues. These observations suggest that the mechanisms and dynamics of progression to HD-AVB apply only during incremental atrial pacing and there is a clear difference with what has been observed with the progression occurring exclusively at AV node.

Terapia ablativa do flutter atrial tipo I com radiofreqüência / Type I Atrial Flutter Ablation Therapy with Radiofrequency

PURPOSE--To present initial experience on radiofrequency (RF) ablation of atrial flutter (AFL) guided by anatomic and electrophysiologic parameters. METHODS--Eight patients (six males), mean-age of 42 +/- 17.5 years with chronic type I AFL (mean cycle length of 251 +/- 14.3 msec, range 240 to 280 msec) were undergone to RF catheter ablation applied between inferior vena cava (IVC) and tricuspid annulus (TA). Two had persistent and two the paroxysmal form. Two had surgical corrected congenital heart disease (atrial septal defect in 2 and ventricular septal defect in 1). Four had systolic dysfunction and 2, an atrial tachycardia associated with the AFL. RESULTS--Areas of slow conduction represented by fractionated potentials were recorded between IVC and TA in all patients. RF ablation was successful in 8/8 patients (100). The mean number of RF applications was 9.2 +/- 6.2 (4-24). The successful ablation site was located in the isthmus between IVC and TA in seven patients and in the lateral wall in the patient with ASD. Successful sites had an early atrial activation preceding the atrial electrogram (range from -65 to -82 ms). In one patient the RF energy was successfully delivered between the atriotomy scar (AS) and IVC. After three months follow-up six remained free of recurrent AFL. One pt had type 1 AFL recurrence and one with ASD had a type II AFL. The Type II AFL was successfully ablated between AS and IVC. CONCLUSION--Fractionated potentials were commonly observed between IVC and T; AFL ablation can be guided by anatomic landmarks or electrophysiologic parameters; electrograms recorded at successful sites were early and never fractionated; the long-term evaluation must be analyzed prospectively.