Posteroseptal Pathway Research Articles

Accuracy of Different Surface Electrocardiogram Algorithms for Localization of Accessory Pathway in Comparison to Invasive Electrophysiological Localization: An Observational Study

Introduction: Detection of accessory pathway (AP) on surface ECG in sinus rhythm helps in the diagnosis of Wolff-Parkinson-White Syndrome (WPW Syndrome), Catheter ablation of AP was indicated in symptomatic patients with preexcitation. Pre-ablation AP localization inferred from the 12-lead surface electrocardiogram (ECG) facilitates a tailored ablation strategy; there by specific risk can be properly assessed. As they are based on pre-excitation in the basal state, available algorithms can lead to complex and ambiguous analysis, mostly due to the variable influence of the AP over QRS morphology. Though various algorithms on surface ECG are available to predict the site of AP on surface ECG, but none of them are accurate. So, we have compared the accuracy of different algorithms in predicting the AP localization in comparison to electrophysiological study (EPS) diagnosis. Methodology: This retrospective observational study cohort consisted of 100 consecutive patients above 15 years of age presented to the tertiary care center with the history of palpitations or for assessment of a manifest AP. Accessory pathways were identified according to the site where successful radiofrequency energy was applied. Arruda algorithm, Milstein algorithm, Fitzpatrick algorithm and Pambrun algorithm were applied on a sinus rhythm manifest preexcited ECG to predict the AP localization by two independent investigators who are unaware of site of successful catheter ablation. Then those were compared with the EPS localization to test the accuracy of individual algorithm. Then Cohen’s Kappa was run to determine if there was agreement between any of the four different algorithms with EPS using SPSS version 20.0. Results: In the study population of 100 patients, male to female ratio of study population was 1.6:1, with a mean age of presentation 43.86 ± 11.4 years with the most common age group of 31 to 45 year. when the AP locations were categorized based on EP Study 56 percent of the AP were found on the left side while 43 percent of the AP were found on right side, 77 percent of the AP were septal pathways. Among the leftsided pathways, left anteroseptal constitutes majority followed by left posteroseptal pathway. On right side majority were in right posteroseptal location in our study. Based on 4 surface ECG algorithms AP was localized and each algorithm was compared with invasive EPS localization for accuracy using Cohen’s Kappa agreement analysis. As per agreement analysis the kappa value for Milstein, Pambrun algorithm, Fitzpatrik and Arruda were 0.188, 0.343, 0.441, and 0.645 respectively. It was found that Arruda algorithm had moderate strength of agreement with the findings of EPS (κ = 0.645). This is the proportion of agreement over and above chance agreement and which was statistically significant and the strongest among all the four algorithms. Conclusion: Our study has compared the accuracy of 4 surface ECG algorithms in predicting the accessory pathway localization with the EPS; it has demonstrated that the Arruda algorithm is more precise and accurate among the available algorithms followed by Fitzpatrik, Pambrun algorithm and Milstein algorithm, Knowing the pathway prior to ablation allows for optimal procedure preparation, mapping pathways that are difficult to find and finally may lessen the catheter-related injury and shortens the procedural time.

Evaluation of T-wave memory after accessory pathway ablation in pediatric patients with Wolff-Parkinson-White syndrome.

T-wave memory (TWM) is a rare cause of T-wave inversion (TWI). Alterations in ventricular activation due to abnormal depolarization may cause repolarization abnormalities on the ECG, even if myocardial conduction returns to normal. These repolarization changes are defined as TWM. In our study, we aimed to determine the frequency of TWM development and the predictors affecting it in the pediatric population who underwent accessory pathway (AP) ablation due to Wolff-Parkinson-White (WPW) syndrome. The data of patients with manifest AP who underwent electrophysiological studies and ablation between 2015 and 2021 were retrospectively analyzed. The study included 180 patients who were under 21 years of age and had at least one year of follow-up after ablation. Patients with structural heart disease, intermittent WPWs, recurrent ablation, other arrhythmia substrates, and those with less than one-year follow-up were excluded from the study. The ECG data of the patients before the procedure, in the first 24h after the procedure, three months, and in the first year were recorded. The standard ablation technique was used in all patients. Postprocedure TWM was observed in 116 (64.4%) patients. Ninety-three patients (51.7%) had a right-sided AP, and 87 patients (48.3%) had a left-sided AP. The presence of posteroseptal AP was found to be significantly higher in the group that developed TWM. Of these patients, 107 (93.1%) patients showed improvement at the end of the first year. Preprocedural absolute QRS-T angle, postprocedural PR interval, and right posteroseptal pathway location were identified as predictors of TWM. The development of TWM is particularly associated with the right-sided pathway location, especially the right posteroseptal pathway location. The predictors of TWM are the preprocedural QRS-T angle, the postprocedural PR interval, and the presence of the right posteroseptal AP.

Successful catheter ablation of the accessory pathway in an unusual location in a 13-year-old girl with a coronary sinus diverticulum and Wolff-Parkinson-White syndrome.

Wolff-Parkinson-White syndrome is a congenital cardiac pre-excitation syndrome that is effectively treated by ablating the accessory pathway. However, accessory pathways located in the posteroseptal region can sometimes be challenging. In this paper, we present the successful ablation of the epicardial posteroseptal accessory pathway through the middle cardiac vein in a 13-year-old girl with a coronary sinus diverticulum and Wolff-Parkinson-White syndrome, after unsuccessful ablation attempts at different locations. If the ablation procedure fails, the possibility of the posteroseptal pathway should be kept in mind, and coronary sinus angiography should be performed. In cases with a coronary sinus diverticulum where ablation is not successful, other coronary sinus structures, for example, the middle cardiac vein should be considered as potential accessory pathways.

Clinical Course and Electrophysiological Characteristics of Permanent Junctional Reciprocating Tachycardia in Children.

In this study, we aimed to evaluate the clinical aspects, electrophysiological studies, and ablation results of permanent junctional reciprocating tachycardia in children. The study comprised 29 pediatric patients diagnosed with permanent junctional reciprocating tachycardia between 2011 and 2021 in 2 pediatric electrophysiology centers. From the file records, the basic demographic characteristics of the patients, as well as electrocardiographic and echocardiographic findings, were acquired retrospectively. The medical treatment and responses of the patients throughout follow-up, as well as the electrophysiological study and ablation data of the patients who had electrophysiological study, were assessed. The mean age at diagnosis of the patients was 3.13 ± 4.43 (0-18) years and the mean weight was 18.22 ± 19.68 (3.8-94) kg. Eighteen patients (62.1%) were girls. Eleven patients (38%) developed tachycardia-induced cardiomyopathy. Tachycardia was incessant in 15 patients (51.7%). In total, 22 patients required 26 ablation procedures. Tachycardia-induced cardiomyopathy and multidrug-resistant tachycardia were the most prevalent indications for ablation. The right posteroseptal pathway was detected in 18 patients (81.8%). The acute procedure success rate was 100% (22/22). The recurrence rate was 18% (4/22) and 3 of them underwent successful ablation again. The overall success percentage was 95.4% (21/22). None of the patients had any complications. The mean follow-up period was 4.39 ± 3.05 years. Although permanent junctional reciprocating tachycardia is uncommon, it is often persistent, resistant to medical treatment, and associated with a substantial risk of tachycardia-induced cardiomyopathy. Catheter ablation can be performed on these patients at any age, with minimal risk of complications and a high success rate. It is crucial to keep monitor of the patients' recurrence.

Pediatric T-wave memory after accessory pathway ablation in Wolff-Parkinson-White syndrome.

Altered ventricular depolarization due to manifest accessory pathway conduction (ie, Wolff-Parkinson-White syndrome) leads to repolarization abnormalities that persist after pathway ablation. The term T-wave memory (TWM) has been applied to these changes, as the postablation T-wave vector "remembers" the pre-excited QRS vector. In adults, these abnormalities can be misinterpreted as ischemia leading to unnecessary interventions. To date, no comprehensive studies have evaluated this phenomenon in the pediatric population. The purpose of this study was to define TWM in the pediatric population, identify preablation risk factors, and delineate the timeline of recovery. Pre- and postablation electrocardiograms (ECGs) in patients ≤25 years were analyzed over a 5-year period. Frontal plane QTc interval, T-wave axis, QRST angle, and T-wave inversions were used to identify patients with TWM. Univariate analysis was performed to determine the association of preablation ECG features with the outcome of TWM. TWM was present in 42% of pediatric patients, with resolution occurring within 3 months of ablation. Preablation QRS axis <0° was a strong predictor of TWM (odds ratio [OR] 15.2; 95% confidence interval [CI] 5.7-40), followed by posteroseptal pathway location (right posteroseptal-OR 8.9; 95% CI 4.2-18.8; left posteroseptal-OR 6.1; 95% CI 1.7-22.3). The degree of pre-excitation had a modest association with the development of TWM. No adverse events were observed. TWM is less common in children compared to adults, and normalization occurred within 3 months postablation. The most predictive features for the development of TWM include a leftward pre-excited QRS axis and posteroseptal pathway location.

Morphological study of middle cardiac vein in human hearts of north western UP and its application for interventional procedure

The aim of present study was to study morphology of middle cardiac vein in human hearts. The study was conducted on middle cardiac vein of thirty human hearts with due clearance from ethical committee. The mean diameter of middle cardiac vein was 2.57 1.16 mm and the mean length was 74.69 ± 21.10 mm. There was also statistically significant relationship between length of middle cardiac vein and weight of cadaver. In some hearts middle cardiac vein and small cardiac vein together form common trunk and then drain into coronary sinus. Middle cardiac vein can be used for radio frequency ablation of a posteroseptal pathway. It can also be used for newer interventional technique such as selective catheterization. It may be one of the choices of implantation of pacing leads.

Incidence, clinical, electrophysiological characteristics and outcomes of patients with Wolff-Parkinson-White syndrome and atrial fibrillation

Aims and objectivesAtrial fibrillation (AF) with preexcitation can be life threatening. Our study evaluated the incidence, clinical features, electrophysiologic characteristics and outcomes of patients presenting with AF and fast ventricular rates associated with an antegrade conducting accessory pathway. MethodsHospital data of patients who had undergone electrophysiology study and radiofrequency ablation for AF and Wolff-Parkinson-White (WPW) syndrome was retrospectively evaluated over 10 years and prospective data was further collected over 1 year. Out of 2876 patients undergoing electrophysiology study, 320 patients had manifest preexcitation on ECG. Forty one patients who had presented with AF and fast ventricular rates were included in the study. ResultsForty one (12.8%) patients out of 320 patients of WPW syndrome patients presented with AF and fast ventricular rates. Mean age of presentation was 38.5 ± 12.3 yrs. Twenty nine (72.5%) were male. Most common presenting features were palpitations, presyncope and syncope. Twenty eight (71.1%) patients were electrically cardioverted on presentation, of which two patients having narrow complex tachycardia, when given adenosine, developed AF and fast ventricular rates and had to be electrically cardioverted. Intravenous amiodarone converted AF to sinus rhythm in 11 (28.9%) patients. Right postero-septal pathway (33.3%) followed by coronary sinus epicardial pathway (22.9%) were the most commonly located pathways associated with AF. Five (12.2%) patients had multiple pathways. CS diverticulum was seen in 6 (14.7%) patients. Ablation was done during AF in 6 (14.7%) patients. All except one had immediate successful ablation. One patient had a recurrence of preexcitation on follow up and successfully ablated during redo procedure. ConclusionAF with WPW syndrome is not uncommon. AF is commonly associated with posteriorly located accessory pathways, CS diverticulum and multiple pathways. Radiofrequency ablation has good outcomes.

Occurrence of atrioventricular block during supraventricular tachycardia: What is its possible mechanism?

A female patient was admitted to our hospital for catheter ablation arising from paroxysmal supraventricular tachycardia (PSVT). In the laboratory, PSVT (the earliest retrograde atrial activation at the coronary sinus ostium) with intermittent atrioventricular (AV) block could be induced repeatedly. The tachycardia could be terminated during ventricular pacing without retrograde conduction to the atria. Therefore, orthodromic AV reciprocating tachycardia (AVRT) and atrial tachycardia (AT) could be ruled out and AV nodal re-entrant tachycardia (AVNRT) was subsequently considered. Initial attempts using slow or intermediate AV nodal ablation failed to cure the tachycardia. We considered the possibility of orthodromic AV reciprocating tachycardia (AVRT) with AV block occurring during the tachycardia. The tachycardia was successfully terminated during the ablation of the right posteroseptal pathway at the coronary sinus ostium. We hypothesized about the possible explanation that might help to clarify the phenomenon of AV block during SVT in order to provide some guidance to other clinicians confronted with similar patient challenges in the future.

Editor’s Perspective: The Interatrial Septum

In this installment of our journal’s teaching rounds, Debruyne et al1 provide an outstanding learning experience constructed on simple and logical teaching steps of what at first glance seems to be a complex and partially random observation. Their case and the findings they discuss highlight the difficulties in specifically targeting 1 of 2 structures living together on the true interatrial septum Article see p e73 A true septum is a partitioning wall shared between 2 structures. The true interatrial septum is a relatively limited structure, which in the periannular region is referred to as the midseptum. The fossa ovalis and this midseptal region are the only places where one can penetrate and can create an intraconnection between the 2 atria. More superiorly, the right and the left atria separate from each other with intervening fibrous tissue and pericardiac fat. This is why transseptal puncture across the superior limbus (above the fossa) necessarily exits the heart before reentering the left atrium. More caudally, the coronary sinus and the pyramidal space constitute the so-called posterior septum. This region, however, is not a partition between the right and the left atria but a separate posterior pyramid-shaped space. The midseptum is the place of residence for the compact AV node. Although accessory …

Mitral Valve Injury After Radiofrequency Ablation for Wolff-Parkinson-White Syndrome

A 39-year-old athletic female with symptomatic Wolff-Parkinson-White syndrome underwent an electrophysiological study and subsequent ablation of orthodromic reentrant tachycardias using left lateral, posterolateral, and posteroseptal accessory pathways. Ablation was performed with 7F medium- and large-curl Safire catheters using the retrograde aortic approach. Eighteen radiofrequency lesions were delivered at the mitral valve annulus (50 W, 60°, 10–60 seconds), and 8 were delivered in the coronary sinus, with weak persistence of antegrade conduction through the posteroseptal pathway. Two weeks later, she presented to the emergency room with a new episode of supraventricular tachycardia, She had been having dyspnea since the ablation procedure. A transthoracic echocardiogram revealed severe mitral regurgitation with a regurgitant volume of 66 ml and estimated regurgitant orifice of 39 mm2 (Figure [C, F, and G]); the left atrium was enlarged with a volume index of 36 ml/m2. Transesophageal echocardiogram revealed a ruptured chord to the anterior leaflet adjacent to the posteromedial commissure (Figure [E]). Given the symptoms and severity of the mitral valve regurgitation, the decision …

Intermittently "Pre-Excited" ECG after Accessory Pathway Ablation: Unsuccessful Procedure or a Complication?

A 52-year-old woman with previously unsuccessful posteroseptal pathway ablation using radiofrequency energy presented with intermittently occurring short PR followed by a wide QRS complex, and complaining of palpitations with characteristics different from previous history. During a second electrophysiological procedure no signs of preexcitation were found. Ventricular discharges with fusion with sinus beats were revealed, and catheter ablation of premature contractions originating from the proximity to previous accessory pathway was carried out.

Coronary sinus diverticulum as a cause of resistant posteroseptal pathway ablation

Coronary sinus (CS) anomalies such as diverticulum, persistent left superior vena cava or CS ostium dilatation are predominantly found in patients with accessory pathway-related tachycardias. Diverticulum of the proximal CS found in 7–11% of patients with postero-septal or left posterior manifests accessory pathways. We reported a 28 year old gentleman with manifested postero-septal accessory pathway, who underwent repeat electrophysiological study (EPS) and radiofrequency ablation for previously failed ablation. Huge CS diverticulum was identified by angiography as a reason for resistant accessory pathway. Successful RF ablation was achieved at the neck of the diverticulum without complications. Other associated anomalies were ruled out by cardiac computerized tomography (CT) and trans-esophageal echocardiography.

Atrioventricular Nodal Reentrant Tachycardia

Atrioventricular nodal reentrant tachycardia (AVNRT) represents the most common regular supraventricular arrhythmia in humans.1 The precise anatomic site and nature of the pathways involved have not yet been established, and several attempts to provide a reasonable hypothesis based on anatomic or anisotropic models have been made.2 There has been considerable evidence that the right and left inferior extensions of the human atrioventricular (AV) node and the atrionodal inputs they facilitate may provide the anatomic substrate of the slow pathway, and a comprehensive model of the tachycardia circuit for all forms of AVNRT based on the concept of atrionodal inputs has been proposed.2 Still, however, the circuit of AVNRT remains elusive. Recently, time-honored conventional schemes for the diagnosis and classification of the various forms of the arrhythmia have been refuted in part by evolving evidence. Recognition of the various types of AVNRT is important, however, to expedite diagnosis and allow implementation of appropriate ablation therapy without complications. We present an update on AVNRT with a particular emphasis on electrophysiological criteria used for the differential diagnosis of regular, supraventricular tachycardias. Typically, AVNRT is a narrow-complex tachycardia, ie, QRS duration <120 ms, unless aberrant conduction, which is usually of the right bundle-branch type, or a previous conduction defect exists. Tachycardia-related ST depression and RR-interval variation may be seen. RR alternans in AVNRT has been attributed to the proposed model of a figure of 8 reentry with continuous crossing over of antegrade activation through an inferior input to the contralateral superior input via the node.2 In the typical form of AVNRT (slow-fast), abnormal (retrograde) P′ waves are constantly related to the QRS and in the majority of cases are indiscernible or very close to the QRS complex (RP′/RR <0.5). Thus, P′ waves are either masked by the QRS complex or …

Incessant Tachycardia Following Posteroseptal Pathway Ablation: A Pseudo-r′ or Pseudo-Pseudo-r′ Wave in V1?

Incessant Tachycardia Following Posteroseptal Pathway Ablation: A Pseudo-r′ or Pseudo-Pseudo-r′ Wave in V1?

Incidence of coronary artery injury immediately after catheter ablation for supraventricular tachycardias in infants and children

Several case reports have documented coronary artery stenosis or even occlusion after radiofrequency energy ablation (RFA) in children and adults. Coronary involvement early and late after RFA has also been described in animal models. The purpose of this study was to assess prospectively the incidence of coronary artery injury early after catheter ablation for supraventricular tachycardias (SVT) in children. From October 2002 to January 2008, 212 consecutive patients younger than 21 years with SVT underwent selective coronary angiography before and 30 minutes after RFA or cryoablation. Median patient age was 12 years (range 0.3-20.4 years), and median body weight was 47 kg (range 5.5-130 kg). An accessory pathway was diagnosed in 112 patients, AV nodal reentrant tachycardia (AVNRT) in 84 patients, and both an accessory pathway and AVNRT in 16 patients. Congenital heart disease was present in 31 patients. In 2 of 117 patients who had RFA for an accessory pathway, an acute reduction in luminal diameter of the coronary artery adjacent to the ablation site was observed. These two patients with a structurally normal heart showed ST-segment changes with normalization of the ECG within 1 week. Both were clinically asymptomatic, and two-dimensional echocardiography documented normal ventricular function. Noninvasive testing did not reveal any evidence of persistent myocardial ischemia. No coronary artery damage was noted after ablation for AVNRT or after ablation with cryoenergy. Coronary artery narrowing adjacent to the RFA site was noted in 2 of 117 patients with an accessory pathway and occurred only in patients with a posteroseptal pathway. Coronary angiography could be helpful in avoiding coronary lesions in these settings.

Ablation of incessant orthodromic reciprocating tachycardia in a child with congenitally corrected transposition of great arteries and ebsteinoid malformation of left atrioventricular valve

We report about a patient with congenitally corrected transposition of the great arteries and ebsteinoid malformation of left atrioventricular (AV) valve who presented with incessant orthodromic atrioventricular reciprocating tachycardia due to a left posteroseptal accessory pathway. Radiofrequency catheter ablation using trans-septal approach successfully eliminated the posteroseptal pathway across the morphologic tricuspid valve. This report highlights the importance of delineating the anatomy of the interatrial septum in complex congenital heart diseases for performing safe trans-septal puncture during ablation of accessory pathways.

Markers of Coronary Sinus Accessory Pathways in Pediatrics

Coronary sinus accessory pathways (CSAPs), atrioventricular connections formed by the coronary sinus myocardial coat, have been described in adult patients, but not systematically described in pediatric patients. Patients who underwent CSAP ablation were compared to patients with right posteroseptal (RPS) pathway ablation (control group) from November 2004 to June 2007. Retrospective reviews of preablation 12-lead electrocardiogram (EKG), fluoroscopic, and intracardiac electrogram data were then performed to identify electrophysiologic markers of CSAP. A total of 23 patients were identified: 13 with CSAP and 10 with RPS pathways. Preablation EKGs demonstrated preexcitation in 8/10 (80%) patients with RPS pathways versus 9/13 (69%) patients with CSAP (P = 0.66). Preexcitation with a negative delta wave in lead II was seen in 5/9 (56%) patients with CSAP versus 0/8 in RPS (P = 0.029), and preexcitation with a positive delta wave in augmented vector right (aVR) was seen in 9/9 (100%) patients with CSAP versus 3/8 (37.5%) with RPS (P = 0.009). Accessory pathway (AP) potentials were seen on the coronary sinus (CS) catheter in 6/13 (46%) of CSAP and in 0 RPS ablations (P = 0.019). Recurrence of tachycardia occurred in 5/13 (38%) of patients with CSAP and 1/10 (10%) of patients with RPS pathways (P = 0.18). CSAPs should be considered when preablation EKG demonstrates preexcitation with a negative delta wave in lead II and a positive delta wave in aVR, and if an AP potential is seen on the CS catheter. Recurrence of tachycardia postablation or the need for multiple ablations should raise suspicion for a CSAP.

Adverse effects of Wolff-Parkinson-White syndrome with right septal or posteroseptal accessory pathways on cardiac function

Wolff-Parkinson-White syndrome with right septal or posteroseptal accessory pathways causes eccentric septal mechanical activation and may provoke left ventricular (LV) dyssynchrony and dysfunction. The aim of the study was to evaluate the effect of radiofrequency catheter ablation (RFA) of the accessory pathways on LV function. Retrospectively, transthoracic echocardiography and electrocardiogram recordings were analysed in 34 patients (age: 14.2 +/- 2.5 years) with right septal or posteroseptal accessory pathways prior and after (median: 1 day) successful RFA. Results prior to RFA, LV ejection fraction was decreased (<55%) in 19/34 patients (56%). After RFA, QRS duration was normalized (129 +/- 23 vs. 90 +/- 11, P < 0.0001), LV function improved (ejection fraction: 50 +/- 10 vs. 56 +/- 4%, P = 0.0005) and septal-to-posterior wall motion delay as a global measure for LV dyssynchrony decreased (110 +/- 94 vs. 66 +/- 53, P = 0.012). Longitudinal two-dimensional strain evaluated in five patients demonstrated a decrease of left intraventricular mechanical delay from 292 +/- 125 to 118 +/- 37 ms after RFA. Wolff-Parkinson-White syndrome with right septal or posteroseptal accessory pathways may cause LV dyssynchrony and jeopardize global LV function. Radiofrequency catheter ablation resulted in normalized QRS duration, mechanical resynchronization, and improved LV function. Even in the absence of arrhythmias, RFA of right septal or posteroseptal pathways may be considered in patients with significantly decreased LV function.

Radiofrequency catheter ablation of accessory pathway-mediated tachycardia is a safe and effective long-term therapy

Background The primary purpose of the study was to evaluate long-term clinical results of radiofrequency catheter ablation of accessory pathway-mediated tachycardia. Methods Catheter ablation was performed in 321 patients who were subsequently followed up for an average of 36 months. Results Accessory pathway-mediated tachycardia was abolished by catheter ablation in 308 patients (96%). Right free wall (10.6%) and right posteroseptal (14.9%) accessory pathway was associated with higher failure rate than left-sided pathways (2.3%, p<0.01). Atrioventricular block occurred in two patients during ablation of anteroseptal pathway. Recurrence of accessory pathway conduction occurred in 13 (4.1%) patients, principally within the first 4 weeks after ablation procedure. Recurrence in right free wall (12.8%) or right posteroseptal (14.2%) pathways was higher than in left-sided pathways (1.8%, p<0.01). Conclusions Radiofrequency catheter ablation has high immediate success rate and long-term recurrence of accessory pathway conduction or tachycardia. Right free wall or right posteroseptal pathways are associated with higher incidence of initial ablation failure and short- to medium-term recurrence.

Single chamber atrial fibrillation involving only the left atrium: implications for maintenance and radiofrequency ablation therapy.

Due to the anatomic and the functional interatrial relationship, AF is a biatrial process. Whether one of the atria could sustain AF is not known. This study included 11 patients (mean age 57 +/- 10 years, 7 men) with AF who showed a distinct activation pattern, characterized by regular activity in the right atrium (RA) and irregular fibrillatory activity confined to the left atrium (LA) throughout the AF episodes. Each of the atria was mapped with 64-electrode basket catheters. AF was monitored for 74 +/- 26 minutes. Complex and irregular activity with a cycle length of 138 +/- 43 ms was observed in the LA throughout the monitoring time. The posterior and the roof of the LA showed the highest degree of disorganization. RA was activated by regular wavefronts with a cycle length of 194 +/- 22 ms (P < 0.001, compared with LA). No fibrillatory activity was observed in the RA. All wavefronts that activated the RA were of septal origin: high anteroseptal 52%, low posteroseptal 22%, mid-septal 18, and dual wavefronts (from the high anteroseptal and low posteroseptal pathways) 8%. The lateral wall of the RA was activated in a superoinferior direction in 82% of all activations. A left-to-right conduction block during AF and a rotor of fibrillatory activity located in the posterior wall of the LA were observed in two patients. Isolated AF in the LA showed various surface electrocardiographic patterns. It is concluded that LA alone without participation of the RA can sustain AF. These data have implications for mechanisms and the ablative therapy of AF.