Fulguration of Accessory Pathways in any Location: Report of Seventy Cases

Ablation of accessory pathways (AP) in any location was performed in 70 consecutive patients using either a right or a left approach. Left free wall pathways were approached via a patent foramen ovale (eight patients) or by transseptal catheter (eight patients). The best ablation site was localized by recording a potential most likely due to Kent bundle activation (33/70 patients), the earliest site of retrograde atrial activation during orthodromic reciprocating tachycardia, earliest ventricular potentials recorded before or synchronous with the delta wave in standard ECG leads, disappearance of preexcitation due to pressure of the catheter on the AP (eight patients), good degree of pacemap concordance with ventricular preexcitation. Two 160 joules cathodal shocks in close succession were delivered and the sequence reeated depending on the results. Preexcitation disappeared in 63 patients and there was no recurrence of arrhythmia in 68 patients without any antiarrhythmic therapy over a follow-up ranging from 1 to 42 months. No serious side effects were observed except for two patients who developed permanent complete AV block. However, one of them occurred after an unsuccessful surgical attempt which had damaged the AV function. Fulguration is effective for APs in diverse locations. These results indicate that appropriate treatment of patient with the Wolff-Parkinson-White syndrome should be reassessed. At present, the therapy of arrhythmias related to the Wolff-Parkinson-White syndrome is no longer a question of either antiarrhythmic drugs or surgery. Fulguration, in our experience, is effective for abolishing accessory pathways in any location.     

Factors Predicting Success in DC Catheter Ablation of Accessory Pathways

In a series of 33 patients with accessory pathways, 26 had successful catheter ablation (fulguration [23 patients] or modification [3 patients]) of their accessory pathway conduction, and could be considered as a clinical success. One hundred thirteen single discharge or double discharge shocks were delivered, and each shock was studied to reveal which parameters were important to predict the success or failure of catheter ablation. Double discharge shocks resulted in successful accessory pathway modification or ablation twice as often as single discharge shocks (32% vs 16%). This effect was more pronounced in left lateral accessory pathways (48% vs 4%). Shocks in the electro physiologically defined ventricular zone were more likely to be successful (33%) than shocks delivered in the atrial zone (14%), irrespective of accessory pathway location. The presence of a probable Kent potential was the parameter most strongly associated with success. The parameter most strongly associated with failure, with a 100% negative predictive value, was the absence of earliest activation recorded on the ablating catheter prior to shock delivery. An AV interval of < 60 msec significantly divided the successful from the unsuccessful shocks (P = 0.01). The VA interval during orthodromic reciprocating tachycardia or right ventricular stimulation did not allow for significant division into successful and unsuccessful attempts in this relatively short series. VA intervals, when longer, were predictive of failure but, when shorter, had low positive predictive value. Mean follow-up in 25 successful patients was 15 ± 6 months. All patients did well in the followup period. Neither those patients with ablation nor modification of the accessory pathway had recurrent episodes of tachycardia or required pharmacological treatment for control of arrhythmias.     

Localization of Left Free-Wall and Posteroseptal Accessory Atrioventricular Pathways by Direct Recording of Accessory Pathway Activation

With the advent of catheter ablation techniques, precise localization of accessory AV pathways (AP) assumes greater importance. In an efort to define the course of AP fibers, we attempted to record activation of 56 left free-wall and 23 posteroseptal APs in 62 patients undergoing eiectrophysiological study. The coronary sinus (CS) and great cardiac vein (GCV) were mapped using orthogonal catheter electrodes, which provide a recording dipole perpendicular to the AV groove. The tricuspid annulus (TA) was mapped using a 2 mm spaced octapolar electrode catheter. Potentials were considered to represent AP activation only if they could be dissociated from both atrial and ventricular activation by programmed stimulation. Orthogonal catheter electrodes in the CS and GCV were advanced heyond the site of earliest retrograde atrial activation and/or earliest antegrade ventricular activation in 45 of the 56 left free-wall APs, and AP potentials were recorded from 42 (93%). An oblique course was identified in 36 APs, with the ventricular insertion being recorded 4–30 mm (median 15 mm) distal or anterior to the atrial insertion. In three patients, antegrade and retrograde conduction proceeded over different (but close) parallel fibers. AP potentials were recorded from 19 of 23 posteroseptal pathways. Ten pathways (left posteroseptal) were recorded from the CS, beginning 5–11 mm (median 9 mm) distal to the os, with potentials extending 8–18 mm (median 11 mm) distally. Four pathways (midseptal) were recorded along the TA, anterior to the CS ostium and posterior to the His bundle catheter. Five pathways (right posteroseptal) were recorded along the TA, directly opposite or immediately posterior to the CS ostium. One of the patients had both midseptal and left posteroseptal pathways and three patients had both right posteroseptal and left posteroseptal pathways. We conclude: 1) left free-wall APs transit the AV groove obliquely and may be comprised of multiple, closely spaced, parallel fihers; 2) the anatomical location of “posteroseptal” pathways is variable and the presence of fibers at multiple sites is common; and 3) direct recordings of AP activation facilitate tracking of the accessory pathway along its course from atrium to ventricle and help identify the presence of multiple fibers.     

Catheter Ablation of Accessory Pathways: Technique and Results in 248 Patients

WARIN, J.-F., ET AL.: Catheter Ablation of Accessory Pathways: Technique and Results in 248 Patients. Two hundred and forty-eight patients with refractory arrhythmias related to an accessory pathway underwent catheter ablation. Cathodal shocks (I60 to 240 joules) were delivered through the distal electrode of a standard catheter (usually a quadripolar electrode catheter with 5-mm interelectrode distances). A paddle electrode positioned opposite to the catheter served as the anode. Ablation of 24 right anteroseptal, 16 right parietal, 86 posteroseptal, 120 left parietal and four Mahaim pathways was clinically successful in eliminating symptomatic tachycardia in 236 patients (>96%) over a follow-up of 3 to 64 months. There was no procedure-related death but two patients developed a ventricular fibrillation at the fifth and seventh day, respectively. The latter led to a sudden death since this side effect occurred after discharge. There were no instances of systemic embolus but one pericardial effusion required subxiphoid needle drainage 6 weeks after the procedure. Other complications included: AV block in four patients with posteroseptal and in one with a right anterior septal pathway. In conclusion, a successful clinical outcome may be achieved in most patients. Catheter ablation is an important alternative to cardiac surgery and in our opinion represents first-line treatment when therapy is required.     

Radiofrequency Catheter Ablation of Concealed Atrioventricular Accessory Pathways Using a "Simultaneous Pacing Method"

The retrograde atrial potential at a successful ablation site is usually obscured by the wide and large ventricular potential during atrioventricular reentrant tachycardia or ventricular pacing, which makes it difficult to determine the appropriate ablation site for concealed accessory pathway. A pacing maneuver named the “simultaneous pacing method” is proposed herein to differentiate the retrograde atrial potential from the ventricular potential for a successful ablation of the concealed accessory pathway. Catheter ablation was performed in 12 patients with a single left free-wall concealed accessory pathway. The atrial insertion site was determined by the simultaneous pacing method in six patients (group I) and by ventricular pacing in six patients (group II), In the simultaneous pacing method, electrograms recorded during ventricular pacing in the earliest retrograde atrial activation site are a fusion of the ventricular potential and the following retrograde atrial potential. When atrial and ventricular pacings are performed simultaneously (simultaneous pacing), the end portion of the electrograms recorded at the same site is solely the ventricular component, because atrial is activated earlier. The atrial potential can be confirmed during ventricular pacing in comparison with the electrograms during the “simultaneous pacing.” Radiofrequency catheter ablation was successful in eliminating conduction through the accessory pathway in all 12 patients. The radiofrequency applications in group I were significantly fewer than those in group II (1.7 ± 1.0 in group I, 5.3 ± 3.2 in group II, P < 0.05). The total procedure time in group I was significantly shorter than in group II (57.8± 15.7 vs 106.7 ± 41.6 mins in group II. respectively, P < 0.05). The fluoroscopy time in group I was significantly shorter than in group II (54.0 ± 7.9 vs 81.3± 26.3 mins, respectively, P < O.05). We were able to determine the atrial insertion site of accessory pathways by the simultaneous pacing method. The simultaneous pacing method was useful in eliminating concealed left free-wall accessory pathways.     

Radiofrequency Catheter Ablation of Atriofascicular Accessory Pathways Guided by Discrete Electrical Potentials Recorded at the Tricuspid Annulus

Background: The purpose of this study was to test the feasibility of using the recording of discrete electrical potentials to guide radiofrequency catheter ablation of atriofascicular accessory pathways with Mahaim-like properties. Methods and Results: Four patients (3 females, 1 male) who fulfilled criteria for having atriofascicular accessory pathways with Mahaim-like properties and preexcited reciprocating tachycardia underwent radiofrequency catheter ablation. The mean age was 35 years (range 27–47). Symptoms were present for a mean of 10.5 years (range 6–18). Recording of discrete electrical potentials of the atriofascicular pathway was attempted by mapping the tricuspid annulus in sinus rhythm, during atrial pacing, and during reciprocating tachycardia. During atrial pacing, a mean of seven radiofrequency pulses (range 1–14), delivered to the tricuspid annulua at the area where electrical potentials were recorded, eliminated conduction through the atriofascicular accessory pathway in all patients. No complications occurred. Tachycardia did not reoccur during a mean follow-up of 5 months (range 3–9). Conclusions: Recording of discrete electrical potentials at the tricuspid annulus identifies an optimal ablation site where radiofrequency current can safely eliminate conduction through atriofascicular accessory pathways with Mahaim-like properties.     

Radiofrequency Ablation of Accessory Pathways: Characteristics of Transiently and Permanently Effective Pulses

The purpose of this study was to characterize and compare the radiofrequency current applications that produced permanent or transient accessory pathway conduction block. One hundred fifty-two radiofrequency energy applications that induced permanent (permanently effective pulses, n = 48) or transient (transiently effective pulses, n = 104) accessory pathway block in 57 patients with 60 accessory pathways were analyzed. The time from the onset of current application to disappearance of preexcitation or termination of supraventricular tachycardia by permanently effective pulses was 1-15 seconds (mean 3.6 +/- 3.8 sec) compared to 2-29 seconds (mean 11.5 +/- 7.5 sec) by transiently effective pulses (P less than 0.01). After transiently effective pulses that induced block in accessory pathway, conduction resumed within 5 minutes while induced block by permanently effective pulses persisted in 44 of 48 patients (92%) during follow-up of 11 +/- 12 months. The accessory pathway conduction returned in the remaining four patients after ablation 2 weeks to 7 months. After transiently effective pulses, 41 impulses were delivered to the same site using a higher power output (n = 32) and/or longer energy delivery duration (n = 20) without new mapping of accessory pathway location. Thirty-six of these impulses again resulted in transient accessory pathway block, four had no effect, only one impulse induced a permanent block in the accessory pathway. Pulses with higher power outputs tended to induce transient effects more frequently than pulses with lower energy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thermistor Guided Radiofrequency Ablation of Atrial Insertion Sites in Patients with Accessory Pathways

Radiofrequency ablation has gained acceptance in the treatment of patients with symptomatic Wolff-Parkinson-White syndrome. The purpose of this study was to characterize the relation between temperature and other electroconductive parameters in patients undergoing atrial insertion accessory pathway ablation utilizing a thermistor equipped catheter. The mean temperature and power at sites of atrial insertion ablation are lower than has been previously associated with creation of radiofrequency lesions in the ventricle. While high cavitary blood flow in the atrium may result in cooling, the thinner atrial tissue may require less energy to achieve adequate heating than ventricular myocardium.     

Unipolar Electrogram Models for Prediction of Outcome in Radiofrequency Ablation of Accessory Pathways

Meticulous catheter positioning dose to the accessory pathway is essential for successful radiofrequency ablation. The aim of this study was to identify local unipolar electrogram characteristics predictive of radiofrequency ablation outcome, enabling more accurate accessory pathway localization and catheter positioning. So far mainly bipolar electrogram parameters have been evaluated, stressing the importance of the presence of an accessory pathway potential. However, especially in the absence of this parameter, the unipolar recording mode can be expected to hold severol advantages. Nine local unipolar electrogram characteristics were analyzed in preexcited sinus rhythm directly preceding radiofrequency pulses in 35 consecutive patients with a manifest occessory atrioventricular pathway. A total of 1,230 unipolar electrogram complexes were analyzed and recorded at 138 ablation sites. Ablation was successful in 30/35 patients (86%). Multivariate analysis provided two unipolar models for prediction of ablation outcome: in Model I, sites with a suspected accessory pathway potential, local AV interval ≤ 30 msec and catheter stability had 76% probability of success, but no more than 1% in their absence. In contrast, using the bipolar recording mode, presence of a suspected accessory pathway potential was the only one of these parameters shown to differentiate between successful and unsuccessful sites, with a predicted chance of success of 48%. Model II, not requiring assessment of possible accessory pathway potentials, showed a 63% probability of success for the combination of initial positivity of the local ventricular signal ≤ 0.1 mV, AV interval ≤ 30 msec, and catheter stability, but no more than 7% in their absence. Moreover, gradual decrease of initial ventricular positivity and AV interval while approaching a subsequently successful site allows the use of these parameters as dynamic mapping tools. Local unipolar electrogram parameters may thus facilitate precise accessory pathway localization and catheter positioning while offering important information supplementary to the bipolar mode, and enable accurate prediction of ablation outcome at a given site also in the absence of accessory pathway potential recording.     

Catheter Induced Mechanical Stunning of Accessory Pathway Conduction: Useful Guide to Successful Transcatheter Ablation of Accessory Pathways

Established electrophysiological criteria indicating anatomical proximity to an accessory pathway include early ventricular or atrial activation during antegrade or retrograde accessory pathway conduction, recording of accessory pathway potentials, and pace map concordance. This article describes two cases of RF catheter ablation of accessory pathways, during which positioning of the mapping catheter at specific sites on the endocardial aspect of the atrioventricular annulus led to prolongation of accessory pathway refractoriness and/or slowing of conduction. HF energy application at these sites successfully abolished accessory pathway conduction. When observed on an "intentional" basis during catheter mapping, catheter induced stunning of accessory pathway conduction provides evidence of satisfactory electrode-tissue contact in addition to anatomical proximity, and may give additional predictive value to successful transcatheter accessory pathway ablation.     

Analysis of Local Electrogram Characteristics Correlated with Successful Radiofrequency Catheter Ablation of Accessory Atrioventricular Pathways

Due to the limited myocardial lesions produced by radiofrequency current, the ablation of accessory pathways (AP) requires precise localization of such connections. The purpose of this study was to ascertain which characteristic(s) of the local bipolar electrogram, recorded from the ablation and adjacent electrode immediately prior to the application of radiofrequency current, correlated with precision in localization adequate to permit AP ablation. Signal analysis was performed for 326 sets of electrograms preceding the attempted ablation of 107 APs in 100 consecutive patients. For 80 antegrade APs, the following variables were evaluated: (1) the presence or absence of an AP potential; (2) the local atrial-AP interval; (3) the local atrioventricular (AV) interval; and (4) the relationship between the onset of local ventricular depolarization and onset of delta wave of the surface electrocardiogram. For the 27 concealed APs, the following characteristics were evaluated: (1) the presence or absence of an AP potential; and (2) the local VA interval during reciprocating tachycardia or ventricular pacing. RESULTS: Antegrade APs: By statistical analysis, the best correlate of successful ablation of an antegrade AP was a local AV interval less than or equal to 40 msec (positive predictive value = 94%; 95% confidence intervals [CI] = 81%-100%). Local AV intervals less than or equal to 50 msec preceded 88% of successful AP ablations, compared to only 8% of failed radiofrequency current applications. The positive predictive value of the other variables were: presence of an AP potential: 35% (95% CI = 27%-40%); local atrial-AP intervals less than or equal to 40 msec: 54% (95% CI = 43%-66%); and local ventricular depolarization preceding onset of the delta wave 43% (95% CI = 34%-52%). For concealed APs, the positive predictive value of a VA interval less than 60 msec was 71% (95% CI = 48%-88%); the positive predictive value for the presence of an AP potential was 58% (95% CI = 32%-81%). CONCLUSIONS: No single electrogram characteristic had a positive predictive value and a sensitivity greater than 90% for AP localization adequate for radiofrequency current ablation. For antegrade APs, the best correlate of adequate localization was a local AV interval less than or equal to 40 msec; as a corollary, radiofrequency current applications at sites where the local AV was greater than 60 msec, were unlikely to be effective. Objective criteria for the localization of concealed APs were less certain. Electrogram analysis, as a guide to AP localization and ablation, requires careful analysis of multiple variables, with analysis of the local AV interval a salient objective factor.     

Transesophageal Echocardiographic Evaluation for Mural Thrombus Following Radiofrequency Catheter Ablation of Accessory Pathways

Background: Catheter ablation of accessory pathways (APs) provides a definitive therapy for patients with Wolff-Parkinson-White Syndrome. The reported incidence of thrombus formation on ablation-induced injuries with direct current shock varies from 0%-20% in animal studies. The purpose of this study was to determine the prevalence of mural thrombus following catheter ablation with radiofrequency current of accessory pathways in humans. Methods and Results: Radiofrequency current (30–35 warts) was applied through a catheter electrode placed against the mitral or tricuspid annulus guided by catheter recordings of AP potentials. Transthoracic (TTE) and transesophageal echocardiography (TEE) were performed in 95 of 111 patients, at 18 ± 6 hours following catheter ablation. After ablation. no thrombus was identified at or near the ablation site in any patient. Two out of 95 patients had a mural thrombus at a remote site that was detected by TEE but not by TTE. No new wall motion abnormality was detected in any patient. No significant regurgitant valvular lesion was found in any patient. Conclusion: Intracardiac thrombus was not identified at the site of catheter ablation, possibly owing to the small lesions produced by radiofrequency energy and high blood flow normally present in those areas. However, patients may be at small risk for mural thrombus at a remote site from prolonged placement of catheters.     

Radiofrequency Catheter Ablation of a Concealed Accessory Atrioventricular Pathway After Heart Transplantation

Three months after orthotopic cardiac transplantation, a 46-year-old man developed paroxysmal supraventricular tachycardia. Electrophysiological investigation of the arrhythmia led to the diagnosis of an atrioventricular reentrant tachycardia involving a left lateral concealed accessory pathway. When antiarrhythmic drugs failed to suppress the arrhythmia, radiofrequency catheter ablation of the accessory pathway was performed without complication.     

Histopathological Changes Following Laser Ablation of a Left-Sided Accessory Pathway in a Human

Laser ablation was performed intraoperatively in a patient with coronary artery disease and Wolff-Parkinson-White syndrome. Histopathological evaluation of the laser ablation site revealed a transverse laser incision in the left atrial septum and mitral valve annulus. There was hemorrhage in the atrioventricular (AV) groove with interruption of a posterolateral AV connection. The laser lesion was confined largely to the atrial aspect of the AV annulus. We conclude that laser catheter ablation of accessory pathways is feasible in humans.     

Perioperative Mapping of Parahisian Accessory Pathways

VERBEET, T.W., ET AL.: Perioperative Mapping of Parahisian Accessory Pathways. In 1989, two patients were operated for deep septal "parahisian" pathways in our institution. Three different mapping techniques were used. (1) Epicardial activation mapping with a belt of 21 bipolar electrodes positioned around the heart. This belt was positioned either on the atrial or on the ventricular side of the atrio-ventricular annulus in order to localize both the atrial and the ventricular insertion of the bypass tract. (2) Right intra-atrial activation mapping on the normothermic beating heart with a bipolar hand-held probe. (3) Right intra-atrial cryomapping at 0°C. The "parahisian" pathways are remote from the epicardium and the pattern of epicardial activation is different from that of the free-wall pathways. Case 1: The electrophysiological study showed a concealed anteroseptal bypass tract. The peroperative atrial epicardial mapping during orthodromic tachycardia (OT) showed simultaneous activation of the posteroseptal area and of the basis of the right appendage. Right intra-atrial mapping during OT showed an anteroseptal "parahisian" pathway. Case 2: The ECG and electrophysiological study showed a right posterior pathway. The first site of epicardial ventricular activation during atrial stimulation was the right posterior area, 30 ms after the onset of the delta wave. The first site of epicardial atrial activation during OT was the posteroseptal area. The right intra-atrial mapping showed a posteroseptal "parahisian" bypass tract. This localization was confirmed with cryomapping. Conclusions: Some patterns of epicardial mapping may suggest the presence of a deep septal "parahisian" bypass tract: retrograde atrial activation at different sites (mimicking activation among multiple pathways); delay between the delta wave and the first epicardial electrogram. Right intra-atrial activation and cryomapping are useful to confirm the diagnosis.     

Permanent Mechanical Catheter Ablation of an Accessory Pathway in a Child

Permanent mechanical ablation of an accessory atrioventricular pathway was observed in an infant during intracavitary electrophysiological mapping. The persistent lack of preexcitation was confirmed during a 15-month follow-up period.     

Radiofrequency Ablation of Bilateral Quadruple Accessory Pathways in a Patient with Wolff-Parkinson-White Syndrome

A patient with drug refractory supraventricular tachycardia showed electrophysiological evidence of bilateral quadruple accessory pathways. The conduction was bidirectional in the left posteroseptal and left posterolateral accessory pathways, antegrade in the right lateral accessory pathway, and retrograde in the right anterior accessory pathway. The four pathways participated in seven types of reciprocating tachycardias. Radiofrequency ablation eliminated the four pathways successfully. The patient was asymptomatic and free of any drug during a 10-month follow-up.     

Electrophysiological Demonstration of Anterograde Concealed Conduction in Accessory Atrioventricular Pathways Capable Only of Retrograde Conduction

Anterograde concealed conduction into the concealed accessory atrioventricular (AV) pathway has been postulated to be one of the factors preventing the reciprocating process via the accessory pathway in patients with the concealed Wolff-Parkinson-White(WPW) syndrome but its presence has not been documented. To demonstrate the occurrence of anterograde concealment, 12 patients with the concealed WPW syndrome were selected for study. A pacing protocol was designed in which the retrograde conduction of the ventricular extrastimulus over the accessory pathway was assessed during ventricular pacing aione (conventional method) and during the AV simultaneous pacing (simultaneous method); the results were then compared. When the high right atrium was simultaneously paced, the effective refractory period of the concealed accessory pathway shortened as compared with the conventional method in five of 12 patients (from 341.7 ± 110.8 to 312.5 ± 108.2 msec, n = 12), whereas, it decreased in all patients studied when the coronary sinus near the accessory pathway was simultaneously paced (from 375.7 ± 135.0 to 287. ± 116.1 msec, n = 7). These results demonstrate that the AV simultaneous pacing frequently shortens the refractoriness of the concealed accessory AV pathway and such facilitation seems to he well explained by the probable anterograde concealment in it and peeling back of the refractory barrier.     

Right Atrial Appendage to Right Ventricle Accessory Atrioventricular Connection: A Case Report

Atrial and ventricular attachments of accessory atrioventricular connections have classically been localized to adjacent atrial and ventricular tissues, and this principle is responsible for the widespread success of radiofrequency catheter ablation. We present anatomical evidence of an unusually located accessory atrioventricular connection, which bridged the atrioventricular ring epicardially, directly from the base of the right atrial appendage to the right ventricle. This observation might offer a new insight into unusual accessory atrioventricular connection locations and may explain why some endocardial radiofrequency catheter ablation procedures might fail.     

Transesophageal Echocardiographic Guidance of Transseptal Left Heart Catheterization During Radiofrequency Ablation of Left-Sided Accessory Pathways in Humans

Radiofrequency ablation (RFA) of left-sided accessory pathways can be achieved using catheters introduced by a retrograde or transseptal approach. Transesophageal echocardiography (TEE) has previously been demonstrated to be safe and efficacious in guiding transseptal puncture in patients during mitral valvuloplasty (MV). This study was undertaken to assess the feasibility, safety, and clinical utility of TEE during transsepta! puncture and RFA of left-sided accessory pathways. Methods: TEE was performed during transseptal puncture in 30 patients (41 ± 12 years, 19 females), 15 patients during attempted RFA of a left-sided accessory pathway and 15 patients during attempted balloon MV. Results: There was no difference in age, sex distribution, or procedural complications when MV patients were compared to RFA patients. At baseline, left atrial dimension was increased and congestive heart failure was more common when MV patients were compared to RFA patients (P < 0.05) Adequate baseline two-dimensional and Doppler TEE images were obtained in all patients. One patient sustained mild esophageal bleeding during the TEE, Positioning of the transseptal catheter in the fossa ovalis was facilitated and confirmed by TEE in 29 of 30 cases. One case of cardiac perforation occurred and was associated with inadequate TEE localization of the fossa ovalis. Thrombus was detected on the transseptal catheter by TEE in two cases prior to systemic heparinization. In both cases, thrombus was removed without embolic event. Conclusions: TEE safely guides transseptal puncture in patients undergoing RFA of left-sided accessory pathways. TEE markers of the fossa ovalis facilitate puncture and may reduce the risk of cardiac perforation particularly in patients with a normal size left atrium. TEE may be especially valuable for identifying thrombus during transseptal puncture.